On 4/9/2011 2:21 PM Steve Turner spake thus:

On 4/9/2011 3:43 PM, Smarty wrote:

On 4/8/2011 8:52 PM, Steve Turner wrote:

A continuation of the "Why does the 115V-24V transformer keep
blowing on my Trane XB80?" discussion I started on 04/02/2011.

Yep, My A/C unit blew another transformer. Pictures (and wiring
diagram) he

http://www.flickr.com/photos/bbqboye...7626457562742/

Trane's manual for the unit is here (for perhaps better viewing
of the wiring diagrams that I also copied to my above flickr site
as jpg images):

http://www.trane.com/webcache/un/fur...7_04012009.pdf

As you can probably see in the pictures, there is visible charring of the
115V leads going into the transformer, and of course the 115V circuit is open
(again). If you didn't see my first thread, this is the third transformer the
unit has blown. In the previous discussion, it was discussed that perhaps the
first one just blew because of old age (6 years), and the second blew because
it wasn't a proper replacement (poor quality, made in China, etc.). This
third unit is most certainly a proper replacement, and it's most certainly
indicative of a real problem I have somewhere else in the unit. I didn't see
any such charring on the previous two units, at least not like this.

I never got a real chance to test out the system after installing this third
transformer. We had cool weather for several days, and I never tried to force
the system to come on so I could monitor it; that was probably a mistake.
Unfortunately, I was also absent from the premises during the extended times
when the unit was most likely operational, so that didn't help either.
However, my family tells me that it WAS working and cooling the house rather
nicely, for at least a day, perhaps two. I'm getting 115V in all the right
places, so it doesn't look like an over-voltage condition to me. Perhaps it's
an overheating condition? It looks to me like the only real load on this
circuit is the blower motor; could the motor be causing this? The blower
spins freely when I turn it by hand. Start capacitor on the motor maybe?
Relay on the control board perhaps?

If you are not comfortable with taking current measurements, or do not have an
ammeter, or do not wish to sit there waiting for some unusual condition which
is drawing too much current, you could temporarily install an in-line fuse
holder and automotive cartridge fuse rated at or above the secondary side
amperage which the transformer is rated. With this fuse installed on the
secondary side, in series with the load, you could then determine if the load
is indeed drawing too much current from the secondary and burning out the
transformer, versus primary side excess voltage being the problem.

A rough guess would be that the contactor coil should maybe be drawing about a
quarter to a half an amp of current at 24V. The transformer secondary should
not need to source a lot more than that amount of current to provide adequate
power to the coil of the contactor.

Fuses are a lot cheaper than transformers......

There may be an intermittent short in the wiring to the coil, a short in the
coil itself, a breakdown of the coil insulation allowing a short to ground when
the coil heats up or cools or vibrates, etc.

Yes Smarty, I would very much like to try this approach because I don't want to
zap any more transformers. Lots of people have suggested it, but there appear
to be more types of fuses than there are insects, and I have no idea what
*exact* type to look for.

Well, it's not exactly rocket science. And you can't hurt anything,
unless you get a fuse that's too big (i.e., rated at too many amps).

First thing you gotta figure out is how much current your transformer is
rated at. Since your wiring diagrams don't say, we have to take an
educated guess.

The only thing connected to the transformer is a thingamajig called the
"integrated furnace control" (IFC). Even without seeing this thing, I
can guess with confidence that it's an electronic circuit board which
controls the operation of the furnace. Since it undoubtedly does so
through relays (either mechanical or electronic), it's safe to assume
that it doesn't draw much current.

Let's say 1 amp to start. We could be wrong, but that's a good starting
point. So what we need is a fuse rated at *at least* 24 volts (could be
much more, up to 120 or 240 volts), and *exactly* 1 amp. To be on the
safe side, let's get a "fast blow" fuse. Hey, fuses are cheaper than
transformers, right?

So install such a fuse, run the unit and see what happens.

If the fuse blows right away, it's probably too small, so use the next
bigger fuse; let's say 1.5 A.

Now you want to stop at some point, let's say 2-3 amps, because now
you're getting up to where you may be exposing whatever fault there is
with the unit and risking blowing the transformer again. If this
happens, you're going to have to bite the bullet and find out what's
wrong with the damn thing. But at least your 3rd transformer will still
be intact.


--
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wassup
nuttin
wan2 hang
k
where
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On Sat, 9 Apr 2011 06:53:25 -0700, "Bill"
wrote:

"Steve Turner" wrote in message
...
On 4/8/2011 10:16 PM, Tony Miklos wrote:
On 4/8/2011 8:52 PM, Steve Turner wrote:
A continuation of the "Why does the 115V-24V transformer keep
blowing
on my Trane XB80?" discussion I started on 04/02/2011.

Yep, My A/C unit blew another transformer. Pictures (and wiring
diagram)
he

http://www.flickr.com/photos/bbqboye...7626457562742/

Trane's manual for the unit is here (for perhaps better viewing of
the
wiring diagrams that I also copied to my above flickr site as jpg
images):


http://www.trane.com/webcache/un/fur...7_04012009.pdf



As you can probably see in the pictures, there is visible charring
of
the 115V leads going into the transformer, and of course the 115V
circuit is open (again).

Three times it fried the primary? I'd guess it's getting 240vac at
times. It's
very unusual for the primary to go bad from a short on the
secondary side, and
the picture shows that the secondary wasn't overheated like the
primary was.
Where's all those electricians talking about an open neutrals when
you need
them? If it measures 120vac tie a light bulb into the primary side
and leave it
where it can be seen. Have the family let you know if it ever gets
brighter
than normal. Or better yet, call a pro.

That very thought crossed my mind, but I'm not sure how that could
happen. The unit is on a dedicated 115V circuit tied to a
single-pole breaker. Where would the possibility exist for the
neutral to become hot? In the breaker box?


A neutral in a breaker box could have a loose connection. These
connections can heat up and cool down as more/less electricity is used
on the panel in question. And there may be a point where the
connection fails momentarily or arcs. Then if you lose the neutral
connection, 120 volt circuits become 240 volt circuits via other
circuits turned on in the panel on the other leg.

The solution to that problem is usually to have the electric company
or electrician retorque the main panel lug nuts to the panel
manufacturers tightness specifications in inch lbs. Note POWER IS
ALWAYS HOT TO THESE CONNECTIONS and this is NOT a DIY thing!

A similar problem can be with what is called a MWBC or Multi-Wire
Branch Circuit. These are 2 separate 120 V circuits run to the same
area that share one neutral wire. So 2 hots and 1 neutral coming from
the breaker panel. A loose neutral connection with that one wire and
same problem.


MWBC is not legal for a furnace and never has been (at least in
Canada) and a main panel neutral problem should have manifested
iteself with light bulbs flaring/dimming or other indications of
"wonky" voltage elsewhere in the house.

When the entire panel is having this problem, you would see lights get
brighter as the problem occurs.

If just a problem with one MWBC, then only those circuits would have
the problem.

On 4/9/2011 2:30 PM A. Baum spake thus:

An amp meter goes in series with the secondary (or primary) of the
transformer. You can convert amps to volt-amps by multiplying volts times
amps. 24 volts times 1 amp = 24 volt-amps. I don't remember if
transformers are rated differently for the primary or secondary or which
one is usually used. It might be in the technical data usually packed
with the transformer or stamped on the transformer somewhere.

Using the primary side would be more conservative (= a bit safer), since
it will include any losses between primary and secondary sides. But it
really doesn't matter. And I'd much prefer to measure current on the
secondary side, rather than deal with 120-volt juice.

He still has the problem of finding an AC ammeter, since a DMM won't
handle AC current.


--
The current state of literacy in our advanced civilization:

yo
wassup
nuttin
wan2 hang
k
where
here
k
l8tr
by

- from Usenet (what's *that*?)

Well, the way I see it. If he FUSES the SECONDARY side, and
the transformer BLOWS, it might still be a BAD NEUTRAL. At
this point, MY best GUESS is some kind of problem with the
SECONDARY wiring. But, I'm NOT THERE to check.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


wrote in message
...
On Fri, 08 Apr 2011 19:52:06 -0500, Steve Turner

You NEED to fuse the secondary - then IF it is an overload
problem you
will just pop the fuse, and not the transformer. 24 volt, 35
VA = 1,5
amp FAST BLOW fuse.

If the fuse does not blow and the transformer does, it
PROVES, almost
beyond a doubt, that you have bad luck getting a good
transformer.

The other option is to closely monitor the primary current
and see
what you have.

On 4/9/2011 11:13 AM Stormin Mormon spake thus:

Agree, sounds like electrical problem, and the OP isn't
quite skilled enough to find it.

.... and you're certainly not competent to even comment on it.


--
The current state of literacy in our advanced civilization:

yo
wassup
nuttin
wan2 hang
k
where
here
k
l8tr
by

- from Usenet (what's *that*?)

On 4/9/2011 2:42 PM spake thus:

On Sat, 9 Apr 2011 06:53:25 -0700, "Bill"
wrote:

A neutral in a breaker box could have a loose connection. These
connections can heat up and cool down as more/less electricity is
used on the panel in question. And there may be a point where the
connection fails momentarily or arcs. Then if you lose the neutral
connection, 120 volt circuits become 240 volt circuits via other
circuits turned on in the panel on the other leg.

The solution to that problem is usually to have the electric
company or electrician retorque the main panel lug nuts to the
panel manufacturers tightness specifications in inch lbs. Note
POWER IS ALWAYS HOT TO THESE CONNECTIONS and this is NOT a DIY
thing!

A similar problem can be with what is called a MWBC or Multi-Wire
Branch Circuit. These are 2 separate 120 V circuits run to the same
area that share one neutral wire. So 2 hots and 1 neutral coming
from the breaker panel. A loose neutral connection with that one
wire and same problem.

MWBC is not legal for a furnace and never has been (at least in
Canada) and a main panel neutral problem should have manifested
iteself with light bulbs flaring/dimming or other indications of
"wonky" voltage elsewhere in the house.

I agree. Suggesting that the OP's problem is due to a buggy Edison
circuit (and why don't they just call them that, since that's what
everyone else calls 'em?) is just grasping at straws. Possible, sure,
but highly unlikely.


--
The current state of literacy in our advanced civilization:

yo
wassup
nuttin
wan2 hang
k
where
here
k
l8tr
by

- from Usenet (what's *that*?)

Yo! Neb!
S'appenin
In earlier post, he said it's 24 VAC, 35 VA.
Tnx
Ywlcm
by

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"David Nebenzahl" wrote in message
s.com...


Well, it's not exactly rocket science. And you can't hurt
anything,
unless you get a fuse that's too big (i.e., rated at too
many amps).

First thing you gotta figure out is how much current your
transformer is
rated at. Since your wiring diagrams don't say, we have to
take an
educated guess.

The only thing connected to the transformer is a thingamajig
called the
"integrated furnace control" (IFC). Even without seeing this
thing, I
can guess with confidence that it's an electronic circuit
board which
controls the operation of the furnace. Since it undoubtedly
does so
through relays (either mechanical or electronic), it's safe
to assume
that it doesn't draw much current.

Let's say 1 amp to start. We could be wrong, but that's a
good starting
point. So what we need is a fuse rated at *at least* 24
volts (could be
much more, up to 120 or 240 volts), and *exactly* 1 amp. To
be on the
safe side, let's get a "fast blow" fuse. Hey, fuses are
cheaper than
transformers, right?

So install such a fuse, run the unit and see what happens.

If the fuse blows right away, it's probably too small, so
use the next
bigger fuse; let's say 1.5 A.

Now you want to stop at some point, let's say 2-3 amps,
because now
you're getting up to where you may be exposing whatever
fault there is
with the unit and risking blowing the transformer again. If
this
happens, you're going to have to bite the bullet and find
out what's
wrong with the damn thing. But at least your 3rd transformer
will still
be intact.


--
The current state of literacy in our advanced civilization:

yo
wassup
nuttin
wan2 hang
k
where
here
k
l8tr
by

- from Usenet (what's *that*?)

On 4/9/2011 11:23 AM, Steve Turner wrote:
On 4/9/2011 10:59 AM, The Daring Dufas wrote:
On 4/9/2011 10:48 AM, Steve Turner wrote:
On 4/9/2011 9:12 AM, wrote:
On Apr 8, 10:05 pm, wrote:
On 4/8/2011 8:44 PM, Tony Hwang wrote:

Steve Turner wrote:
A continuation of the "Why does the 115V-24V transformer keep
blowing
on my Trane XB80?" discussion I started on 04/02/2011.

...

... Buy one of hevier one(bigger size and really heavier in
weight than stock) If it blows again, something on the load side is
wrong.

I'd venture something is already wrong...

--

I'd agree. Responding to his first post and before he put this
latest transformer in I recommended measuring
how many amps are being drawn on the low voltage side.
This is electricity 101. So, he comes here asking for advice
and instead of listening, he justs puts another transformer in
and blows it too..... Go figure. Time to either get educated
or hire a pro.

In case you hadn't noticed, I've been getting LOTS of (much appreciated)
advice from many people, but it's also been very contradictory with no
single suggested approach. It's been an interesting and informative
discussion, and I've been happy that nobody's been a jerk about it...
until *now*. And I DID listen; plenty of people suggested that the
original transformer was likely to be under-rated and to replace it with
something more heavy-duty. Also, it seems to me that having a working
transformer is a pre-requisite to following your advice of measuring the
amp draw on the low voltage side, no? Unfortunately, time constraints
prevented me from being there to perform those measurements when the
unit was running, and unfortunately again the transformer blew in my
absence. But of course, I'm repeating myself...


Steve I really hope you can figure out the problem with the furnace and
I can understand the bit about time constraints. Installing a fuse in
series
with with either side of the transformer is cheap insurance to
keep from losing another transformer. The fuse holders are inexpensive
and it's a lot less of a hassle to replace a blown fuse.

TDD

Yes, I would be more than willing to do that, but my electricity
training is not quite up to the 101 level that trader4 seems to think I
should have; can you suggest a specific fuse rating that I should use?
Thanks!


Most control boards have a place to plug in a low voltage blade fuse
just like the ones introduced to automobiles by GM years ago. The value
will vary from 3 to 5 amps. A one amp fuse should be sufficient for the
primary/120volt side. The primary fuse should be installed in series
with the black/hot wire of the transformer and the low voltage fuse
should be installed in series with the red/R wire OOPS! I just noticed
something from the pictures of the burned transformer! The wire colors
in the control system of air handler/furnace wiring can vary a little
from manufacturer to manufacturer and I just saw something that may be
a problem causing confusion. The transformer in the picture has a YELLOW
wire in place of the RED low voltage output. The black/hot and
white/neutral are for the 120vac connection and the yellow/R and blue/C
are on the other side of the transformer. The red and orange wires
should be taped up because they are for 208-240 volt connections. If the
red wire on that transformer were hooked to the red wire connections
shown in the wiring diagram, it will burn up. Yellow is usually the low
voltage wire color used for safety switches, pressure switches and
interlocks. The blue wire is the common 24vac and is often grounded to
the metal cabinet of the furnace. A seasoned HVAC tech would have seen
the anomaly immediately and it wouldn't have posed a problem.

TDD

TDD

On Sat, 09 Apr 2011 11:23:47 -0500, Steve Turner
wrote:

On 4/9/2011 10:59 AM, The Daring Dufas wrote:
On 4/9/2011 10:48 AM, Steve Turner wrote:
On 4/9/2011 9:12 AM, wrote:
On Apr 8, 10:05 pm, wrote:
On 4/8/2011 8:44 PM, Tony Hwang wrote:

Steve Turner wrote:
A continuation of the "Why does the 115V-24V transformer keep blowing
on my Trane XB80?" discussion I started on 04/02/2011.

...

... Buy one of hevier one(bigger size and really heavier in
weight than stock) If it blows again, something on the load side is
wrong.

I'd venture something is already wrong...

--

I'd agree. Responding to his first post and before he put this
latest transformer in I recommended measuring
how many amps are being drawn on the low voltage side.
This is electricity 101. So, he comes here asking for advice
and instead of listening, he justs puts another transformer in
and blows it too..... Go figure. Time to either get educated
or hire a pro.

In case you hadn't noticed, I've been getting LOTS of (much appreciated)
advice from many people, but it's also been very contradictory with no
single suggested approach. It's been an interesting and informative
discussion, and I've been happy that nobody's been a jerk about it...
until *now*. And I DID listen; plenty of people suggested that the
original transformer was likely to be under-rated and to replace it with
something more heavy-duty. Also, it seems to me that having a working
transformer is a pre-requisite to following your advice of measuring the
amp draw on the low voltage side, no? Unfortunately, time constraints
prevented me from being there to perform those measurements when the
unit was running, and unfortunately again the transformer blew in my
absence. But of course, I'm repeating myself...


Steve I really hope you can figure out the problem with the furnace and
I can understand the bit about time constraints. Installing a fuse in series
with with either side of the transformer is cheap insurance to
keep from losing another transformer. The fuse holders are inexpensive
and it's a lot less of a hassle to replace a blown fuse.

TDD

Yes, I would be more than willing to do that, but my electricity training is
not quite up to the 101 level that trader4 seems to think I should have; can
you suggest a specific fuse rating that I should use? Thanks!
1.5 amp fast blow for the secondary, no more than 500ma for the
primary if the original was 35va. full rated load would be about .3
amps, so a 250ma would be boarderline. (but the transformer should NOT
be running full rated load, either)

Take the va rating and devide by the voltage to get the current rating
in amps. 40va at 24 volts= 1.66 amps. 40va at 115 volts = .347 amps.
40 va at 127 volts = 0.315, etc.

Yo!
Home!
Hangin, slick?
http://www.harborfreight.com/digital...ter-96308.html
Good enough for government work!
dude.
This one only goes up to 200 mA, needs higher range than
that.
http://www.harborfreight.com/ac-dc-d...ter-37772.html
Bummer.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"David Nebenzahl" wrote in message
s.com...


He still has the problem of finding an AC ammeter, since a
DMM won't
handle AC current.


--
The current state of literacy in our advanced civilization:

yo
wassup
nuttin
wan2 hang
k
where
here
k
l8tr
by

- from Usenet (what's *that*?)

You do make mistakes, now and again. This is one, such.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"David Nebenzahl" wrote in message
s.com...
On 4/9/2011 11:13 AM Stormin Mormon spake thus:

Agree, sounds like electrical problem, and the OP isn't
quite skilled enough to find it.

.... and you're certainly not competent to even comment on
it.


--
The current state of literacy in our advanced civilization:

yo
wassup
nuttin
wan2 hang
k
where
here
k
l8tr
by

- from Usenet (what's *that*?)

On 4/9/2011 2:21 PM Steve Turner spake thus:

The specs on the original transformer we Class 2, 115V primary (60hz), 24V
(35VA) secondary. Any chance you could point me to some _exact_ fuse solutions
for this application? There's a virtual six-pack of beer in it for you. :-)

Guess I missed that.

35 VA/24 V = 1.45A, so you need a 1.5A fuse. Fast-blow.

Get the kind that'll fit in an in-line fuse holder (the little glass
jobbies with metal contacts on the ends). Should be available even at
Radio Shack.


--
The current state of literacy in our advanced civilization:

yo
wassup
nuttin
wan2 hang
k
where
here
k
l8tr
by

- from Usenet (what's *that*?)

On 4/9/2011 1:13 PM, Stormin Mormon wrote:
Agree, sounds like electrical problem, and the OP isn't
quite skilled enough to find it.


I just saw it in the picture and posted what the problem is.
I would have seen it immediately if I was hands on. Look at
the wire colors on the transformer especially the YELLOW, it
is taking the place of the RED wire for low voltage. Notice the
yellow and blue are on one side of the transformer. I don't know
why I didn't notice it before. ^_^

TDD

On 4/9/2011 4:52 PM, The Daring Dufas wrote:
On 4/9/2011 11:23 AM, Steve Turner wrote:
On 4/9/2011 10:59 AM, The Daring Dufas wrote:
On 4/9/2011 10:48 AM, Steve Turner wrote:
On 4/9/2011 9:12 AM, wrote:
On Apr 8, 10:05 pm, wrote:
On 4/8/2011 8:44 PM, Tony Hwang wrote:

Steve Turner wrote:
A continuation of the "Why does the 115V-24V transformer keep
blowing
on my Trane XB80?" discussion I started on 04/02/2011.

...

... Buy one of hevier one(bigger size and really heavier in
weight than stock) If it blows again, something on the load side is
wrong.

I'd venture something is already wrong...

--

I'd agree. Responding to his first post and before he put this
latest transformer in I recommended measuring
how many amps are being drawn on the low voltage side.
This is electricity 101. So, he comes here asking for advice
and instead of listening, he justs puts another transformer in
and blows it too..... Go figure. Time to either get educated
or hire a pro.

In case you hadn't noticed, I've been getting LOTS of (much appreciated)
advice from many people, but it's also been very contradictory with no
single suggested approach. It's been an interesting and informative
discussion, and I've been happy that nobody's been a jerk about it...
until *now*. And I DID listen; plenty of people suggested that the
original transformer was likely to be under-rated and to replace it with
something more heavy-duty. Also, it seems to me that having a working
transformer is a pre-requisite to following your advice of measuring the
amp draw on the low voltage side, no? Unfortunately, time constraints
prevented me from being there to perform those measurements when the
unit was running, and unfortunately again the transformer blew in my
absence. But of course, I'm repeating myself...


Steve I really hope you can figure out the problem with the furnace and
I can understand the bit about time constraints. Installing a fuse in
series
with with either side of the transformer is cheap insurance to
keep from losing another transformer. The fuse holders are inexpensive
and it's a lot less of a hassle to replace a blown fuse.

TDD

Yes, I would be more than willing to do that, but my electricity
training is not quite up to the 101 level that trader4 seems to think I
should have; can you suggest a specific fuse rating that I should use?
Thanks!


Most control boards have a place to plug in a low voltage blade fuse just like
the ones introduced to automobiles by GM years ago. The value
will vary from 3 to 5 amps. A one amp fuse should be sufficient for the
primary/120volt side. The primary fuse should be installed in series with the
black/hot wire of the transformer and the low voltage fuse should be installed
in series with the red/R wire OOPS! I just noticed
something from the pictures of the burned transformer! The wire colors
in the control system of air handler/furnace wiring can vary a little
from manufacturer to manufacturer and I just saw something that may be
a problem causing confusion. The transformer in the picture has a YELLOW
wire in place of the RED low voltage output. The black/hot and white/neutral
are for the 120vac connection and the yellow/R and blue/C
are on the other side of the transformer. The red and orange wires should be
taped up because they are for 208-240 volt connections. If the
red wire on that transformer were hooked to the red wire connections shown in
the wiring diagram, it will burn up. Yellow is usually the low
voltage wire color used for safety switches, pressure switches and interlocks.
The blue wire is the common 24vac and is often grounded to
the metal cabinet of the furnace. A seasoned HVAC tech would have seen
the anomaly immediately and it wouldn't have posed a problem.

Not to worry; I read the directions. The red and orange wires were indeed
taped up and not used; only the white and black wires on the input side were
hooked up in the normal fashion. The blue and yellow wires on the 24V output
side of the transformer were hooked to the blue and red wires (respectively)
leading to the control board. I measured input and output voltages after
installing the transformer, and I ensured that I was getting 24V on the output
side before I hooked those leads to the control board. The control board then
came up with it the flashing red LED to indicate normal ("no call for heat")
operation.

On 4/9/2011 5:05 PM, Steve Turner wrote:
On 4/9/2011 4:52 PM, The Daring Dufas wrote:
On 4/9/2011 11:23 AM, Steve Turner wrote:
On 4/9/2011 10:59 AM, The Daring Dufas wrote:
On 4/9/2011 10:48 AM, Steve Turner wrote:
On 4/9/2011 9:12 AM, wrote:
On Apr 8, 10:05 pm, wrote:
On 4/8/2011 8:44 PM, Tony Hwang wrote:

Steve Turner wrote:
A continuation of the "Why does the 115V-24V transformer keep
blowing
on my Trane XB80?" discussion I started on 04/02/2011.

...

... Buy one of hevier one(bigger size and really heavier in
weight than stock) If it blows again, something on the load side is
wrong.

I'd venture something is already wrong...

--

I'd agree. Responding to his first post and before he put this
latest transformer in I recommended measuring
how many amps are being drawn on the low voltage side.
This is electricity 101. So, he comes here asking for advice
and instead of listening, he justs puts another transformer in
and blows it too..... Go figure. Time to either get educated
or hire a pro.

In case you hadn't noticed, I've been getting LOTS of (much
appreciated)
advice from many people, but it's also been very contradictory with no
single suggested approach. It's been an interesting and informative
discussion, and I've been happy that nobody's been a jerk about it...
until *now*. And I DID listen; plenty of people suggested that the
original transformer was likely to be under-rated and to replace it
with
something more heavy-duty. Also, it seems to me that having a working
transformer is a pre-requisite to following your advice of
measuring the
amp draw on the low voltage side, no? Unfortunately, time constraints
prevented me from being there to perform those measurements when the
unit was running, and unfortunately again the transformer blew in my
absence. But of course, I'm repeating myself...


Steve I really hope you can figure out the problem with the furnace and
I can understand the bit about time constraints. Installing a fuse in
series
with with either side of the transformer is cheap insurance to
keep from losing another transformer. The fuse holders are inexpensive
and it's a lot less of a hassle to replace a blown fuse.

TDD

Yes, I would be more than willing to do that, but my electricity
training is not quite up to the 101 level that trader4 seems to think I
should have; can you suggest a specific fuse rating that I should use?
Thanks!


Most control boards have a place to plug in a low voltage blade fuse
just like
the ones introduced to automobiles by GM years ago. The value
will vary from 3 to 5 amps. A one amp fuse should be sufficient for the
primary/120volt side. The primary fuse should be installed in series
with the
black/hot wire of the transformer and the low voltage fuse should be
installed
in series with the red/R wire OOPS! I just noticed
something from the pictures of the burned transformer! The wire colors
in the control system of air handler/furnace wiring can vary a little
from manufacturer to manufacturer and I just saw something that may be
a problem causing confusion. The transformer in the picture has a YELLOW
wire in place of the RED low voltage output. The black/hot and
white/neutral
are for the 120vac connection and the yellow/R and blue/C
are on the other side of the transformer. The red and orange wires
should be
taped up because they are for 208-240 volt connections. If the
red wire on that transformer were hooked to the red wire connections
shown in
the wiring diagram, it will burn up. Yellow is usually the low
voltage wire color used for safety switches, pressure switches and
interlocks.
The blue wire is the common 24vac and is often grounded to
the metal cabinet of the furnace. A seasoned HVAC tech would have seen
the anomaly immediately and it wouldn't have posed a problem.

Not to worry; I read the directions. The red and orange wires were
indeed taped up and not used; only the white and black wires on the
input side were hooked up in the normal fashion. The blue and yellow
wires on the 24V output side of the transformer were hooked to the blue
and red wires (respectively) leading to the control board. I measured
input and output voltages after installing the transformer, and I
ensured that I was getting 24V on the output side before I hooked those
leads to the control board. The control board then came up with it the
flashing red LED to indicate normal ("no call for heat") operation.

Well, that blew that theory! ^_^

TDD

On 4/9/2011 2:55 PM Stormin Mormon spake thus:

You do make mistakes, now and again. This is one, such.

No.

I make mistakes. You're an ignoramus.

See the difference?


--
The current state of literacy in our advanced civilization:

yo
wassup
nuttin
wan2 hang
k
where
here
k
l8tr
by

- from Usenet (what's *that*?)

On 4/9/2011 4:28 PM, David Nebenzahl wrote:
On 4/9/2011 2:04 PM Steve Turner spake thus:

On 4/9/2011 2:58 PM, A. Baum wrote:

On Sat, 09 Apr 2011 14:41:05 -0500, Steve Turner wrote:

But measuring and understanding the ramifications of current
(amperage) is where I get a little fuzzy. Would you help me out?
That's why I came here.

I advised you the last time to measure the 24 volt circuit amperage
draw and convert that to the specs (volt-amps) of the transformer.
If the draw is out of bounds of the specs then the 24 volt circuit
is the problem. You can't put a band-aid on a bullet wound.

Yes, you did, and thanks for the suggestion. I've never used my meter to
measure amperage before, and I don't know how to do that conversion, but I
will study up on it.

It's not a "conversion".

To measure current (which, properly speaking, is what you're measuring, not
"amperage"), you have to break the circuit and put the ammeter in series with
the circuit, so that all the current goes through the meter. (As opposed to
measuring voltage, where you put the meter *across*, or in parallel with, the
thing whose voltage you want to know.)

In your case, since you want to see how much current is being drawn from the
transformer, you'd put the ammeter between one of the transformer secondary
leads (doesn't matter which one) and whatever wire from your unit that's
supposed to connect to that lead.

Since you're measuring AC current, you'll need an AC ammeter, which rules out
most digital multimeters, which only are designed to measure DC current. Not
sure where you'd (quickly, easily) get an AC meter. Maybe others can suggest?
But that's how you do it.

Interesting; thank you. My meter is an Extech MN26T:

http://www.extech.com/instruments/re...ls/MN26_UM.pdf

According to the operating instructions, my meter supports "AC or DC Current
Measurement"

On 4/9/2011 4:37 PM, David Nebenzahl wrote:
On 4/9/2011 2:21 PM Steve Turner spake thus:

On 4/9/2011 3:43 PM, Smarty wrote:

On 4/8/2011 8:52 PM, Steve Turner wrote:

A continuation of the "Why does the 115V-24V transformer keep
blowing on my Trane XB80?" discussion I started on 04/02/2011.

Yep, My A/C unit blew another transformer. Pictures (and wiring
diagram) he

http://www.flickr.com/photos/bbqboye...7626457562742/

Trane's manual for the unit is here (for perhaps better viewing
of the wiring diagrams that I also copied to my above flickr site
as jpg images):

http://www.trane.com/webcache/un/fur...7_04012009.pdf


As you can probably see in the pictures, there is visible charring of the
115V leads going into the transformer, and of course the 115V circuit is open
(again). If you didn't see my first thread, this is the third transformer the
unit has blown. In the previous discussion, it was discussed that perhaps the
first one just blew because of old age (6 years), and the second blew because
it wasn't a proper replacement (poor quality, made in China, etc.). This
third unit is most certainly a proper replacement, and it's most certainly
indicative of a real problem I have somewhere else in the unit. I didn't see
any such charring on the previous two units, at least not like this.

I never got a real chance to test out the system after installing this third
transformer. We had cool weather for several days, and I never tried to force
the system to come on so I could monitor it; that was probably a mistake.
Unfortunately, I was also absent from the premises during the extended times
when the unit was most likely operational, so that didn't help either.
However, my family tells me that it WAS working and cooling the house rather
nicely, for at least a day, perhaps two. I'm getting 115V in all the right
places, so it doesn't look like an over-voltage condition to me. Perhaps it's
an overheating condition? It looks to me like the only real load on this
circuit is the blower motor; could the motor be causing this? The blower
spins freely when I turn it by hand. Start capacitor on the motor maybe?
Relay on the control board perhaps?

If you are not comfortable with taking current measurements, or do not have an
ammeter, or do not wish to sit there waiting for some unusual condition which
is drawing too much current, you could temporarily install an in-line fuse
holder and automotive cartridge fuse rated at or above the secondary side
amperage which the transformer is rated. With this fuse installed on the
secondary side, in series with the load, you could then determine if the load
is indeed drawing too much current from the secondary and burning out the
transformer, versus primary side excess voltage being the problem.

A rough guess would be that the contactor coil should maybe be drawing about a
quarter to a half an amp of current at 24V. The transformer secondary should
not need to source a lot more than that amount of current to provide adequate
power to the coil of the contactor.

Fuses are a lot cheaper than transformers......

There may be an intermittent short in the wiring to the coil, a short in the
coil itself, a breakdown of the coil insulation allowing a short to ground when
the coil heats up or cools or vibrates, etc.

Yes Smarty, I would very much like to try this approach because I don't want
to zap any more transformers. Lots of people have suggested it, but there
appear to be more types of fuses than there are insects, and I have no idea
what *exact* type to look for.

Well, it's not exactly rocket science. And you can't hurt anything, unless you
get a fuse that's too big (i.e., rated at too many amps).

First thing you gotta figure out is how much current your transformer is rated
at. Since your wiring diagrams don't say, we have to take an educated guess.

The only thing connected to the transformer is a thingamajig called the
"integrated furnace control" (IFC). Even without seeing this thing, I can guess
with confidence that it's an electronic circuit board which controls the
operation of the furnace. Since it undoubtedly does so through relays (either
mechanical or electronic), it's safe to assume that it doesn't draw much current.

Let's say 1 amp to start. We could be wrong, but that's a good starting point.
So what we need is a fuse rated at *at least* 24 volts (could be much more, up
to 120 or 240 volts), and *exactly* 1 amp. To be on the safe side, let's get a
"fast blow" fuse. Hey, fuses are cheaper than transformers, right?

So install such a fuse, run the unit and see what happens.

If the fuse blows right away, it's probably too small, so use the next bigger
fuse; let's say 1.5 A.

Now you want to stop at some point, let's say 2-3 amps, because now you're
getting up to where you may be exposing whatever fault there is with the unit
and risking blowing the transformer again. If this happens, you're going to
have to bite the bullet and find out what's wrong with the damn thing. But at
least your 3rd transformer will still be intact.

Great information David. Thanks!

On 4/9/2011 3:11 PM Steve Turner spake thus:

On 4/9/2011 4:28 PM, David Nebenzahl wrote:

Since you're measuring AC current, you'll need an AC ammeter, which
rules out most digital multimeters, which only are designed to
measure DC current. Not sure where you'd (quickly, easily) get an
AC meter. Maybe others can suggest? But that's how you do it.

Interesting; thank you. My meter is an Extech MN26T:

http://www.extech.com/instruments/re...ls/MN26_UM.pdf

According to the operating instructions, my meter supports "AC or DC Current
Measurement"

Yep. You've got a better meter than I, and it's up to this task. Just
connect it as I described (be sure to use the correct connectors on the
meter, the ones marked "10A" and "COM"), make sure it's on the highest
current range (10A), and you're good to go.


--
The current state of literacy in our advanced civilization:

yo
wassup
nuttin
wan2 hang
k
where
here
k
l8tr
by

- from Usenet (what's *that*?)

On 4/9/2011 5:21 PM, Steve Turner wrote:
On 4/9/2011 3:43 PM, Smarty wrote:
On 4/8/2011 8:52 PM, Steve Turner wrote:
A continuation of the "Why does the 115V-24V transformer keep
blowing on my
Trane XB80?" discussion I started on 04/02/2011.

Yep, My A/C unit blew another transformer. Pictures (and wiring
diagram) he

http://www.flickr.com/photos/bbqboye...7626457562742/

Trane's manual for the unit is here (for perhaps better viewing of
the wiring
diagrams that I also copied to my above flickr site as jpg images):


http://www.trane.com/webcache/un/fur...7_04012009.pdf



As you can probably see in the pictures, there is visible charring of
the
115V leads going into the transformer, and of course the 115V circuit
is open
(again). If you didn't see my first thread, this is the third
transformer the
unit has blown. In the previous discussion, it was discussed that
perhaps the
first one just blew because of old age (6 years), and the second blew
because
it wasn't a proper replacement (poor quality, made in China, etc.). This
third unit is most certainly a proper replacement, and it's most
certainly
indicative of a real problem I have somewhere else in the unit. I
didn't see
any such charring on the previous two units, at least not like this.

I never got a real chance to test out the system after installing
this third
transformer. We had cool weather for several days, and I never tried
to force
the system to come on so I could monitor it; that was probably a
mistake.
Unfortunately, I was also absent from the premises during the
extended times
when the unit was most likely operational, so that didn't help either.
However, my family tells me that it WAS working and cooling the house
rather
nicely, for at least a day, perhaps two. I'm getting 115V in all the
right
places, so it doesn't look like an over-voltage condition to me.
Perhaps it's
an overheating condition? It looks to me like the only real load on this
circuit is the blower motor; could the motor be causing this? The blower
spins freely when I turn it by hand. Start capacitor on the motor maybe?
Relay on the control board perhaps?

Steve,

If you are not comfortable with taking current measurements, or do not
have an
ammeter, or do not wish to sit there waiting for some unusual
condition which
is drawing too much current, you could temporarily install an in-line
fuse
holder and automotive cartridge fuse rated at or above the secondary side
amperage which the transformer is rated. With this fuse installed on the
secondary side, in series with the load, you could then determine if
the load
is indeed drawing too much current from the secondary and burning out the
transformer, versus primary side excess voltage being the problem.

A rough guess would be that the contactor coil should maybe be drawing
about a
quarter to a half an amp of current at 24V. The transformer secondary
should
not need to source a lot more than that amount of current to provide
adequate
power to the coil of the contactor.

Fuses are a lot cheaper than transformers......

There may be an intermittent short in the wiring to the coil, a short
in the
coil itself, a breakdown of the coil insulation allowing a short to
ground when
the coil heats up or cools or vibrates, etc.

Smarty

Yes Smarty, I would very much like to try this approach because I don't
want to zap any more transformers. Lots of people have suggested it, but
there appear to be more types of fuses than there are insects, and I
have no idea what *exact* type to look for. That's why I asked earlier
in this thread if this particular transformer:

http://www.pexsupply.com/White-Rodge...unt-14937000-p


with a built-in manual reset would be a much cleaner solution that
serves the same purpose, but I got no responses.

The specs on the original transformer we Class 2, 115V primary
(60hz), 24V (35VA) secondary. Any chance you could point me to some
_exact_ fuse solutions for this application? There's a virtual six-pack
of beer in it for you. :-)


It's not that hard, or that critical.

Put this on the primary:
http://www.radioshack.com/product/in...ductId=2103752

..25A

This on the secondary:

http://www.radioshack.com/product/in...rodsPerPage=60

1.5A

You can put them in this:

http://www.radioshack.com/product/in...rodsPerPage=60

But first do as I suggested in another thread,look carefully for
anything burnt and check the polarity of the line. Make sure the neutral
is neutral. You can measure from the ground prong. See the note in the
schematic. I'm not so sure this didn't arc to the transformer shell,
from looking at the pic. You may wish to measure voltage (AC) from the
transformer shell to a guaranteed neutral.

It is OK for the transformer to run a little warm, it shouldn't be hot.

There are two kinds of failures, one is a long term thermal failure
(which seemed likely when you said years had gone by), the other is a
transient short, or maybe not so transient. If that is the case then
something else will be bad. It may look burnt, or if it is a diode or
transistor it may just be shorted. You can Google how to test those.

Don't be afraid to put a quick finger on a transistor to see if it is
hot, or on the transformer.

As far as calculating what size fuse, you should know Ohms law. Current
* voltage is watts, or in this case V(olt)A(mps). 120V * 1/4A = 30 VA,
on the out side, 24V * 1.5 = 36 VA.

Note that there is a small surge when you turn on a device. So it may
peak higher at the instant of turning on. A fuse usually can absorb
that. The white ceramics are faster blowing and the slow blow ones
usually have a little coil inside the fuse to show it down and are
marked slow blow. When/if you fix this, leave in the fuses and we can
give you some guidance on more properly sizing them. But some fuse in
the ballpark is definitely better than nothing.

Jeff

In article ,
The Daring Dufas wrote:

On 4/9/2011 1:13 PM, Stormin Mormon wrote:
Agree, sounds like electrical problem, and the OP isn't
quite skilled enough to find it.


I just saw it in the picture and posted what the problem is.
I would have seen it immediately if I was hands on. Look at
the wire colors on the transformer especially the YELLOW, it
is taking the place of the RED wire for low voltage. Notice the
yellow and blue are on one side of the transformer. I don't know
why I didn't notice it before. ^_^

TDD

Hello? tap tap tap. Is this thing on? I mentioned that yesterday, duf.
Or maybe this morning. Time gets distorted on weekends.

"Steve Turner" wrote in message ...

A continuation of the "Why does the 115V-24V transformer keep
blowing on my Trane XB80?" discussion I started on 04/02/2011.

Yep, My A/C unit blew another transformer. Pictures (and wiring
diagram) he

http://www.flickr.com/photos/bbqboye...7626457562742/

Trane's manual for the unit is here (for perhaps better viewing of
the wiring diagrams that I also copied to my above flickr site as
jpg images):


http://www.trane.com/webcache/un/fur...7_04012009.pdf

As you can probably see in the pictures, there is visible charring
of the 115V leads going into the transformer, and of course the 115V
circuit is open (again). If you didn't see my first thread, this is
the third transformer the unit has blown. In the previous
discussion, it was discussed that perhaps the first one just blew
because of old age (6 years), and the second blew because it wasn't
a proper replacement (poor quality, made in China, etc.). This
third unit is most certainly a proper replacement, and it's most
certainly indicative of a real problem I have somewhere else in the
unit. I didn't see any such charring on the previous two units, at
least not like this.

I never got a real chance to test out the system after installing
this third transformer. We had cool weather for several days, and I
never tried to force the system to come on so I could monitor it;
that was probably a mistake. Unfortunately, I was also absent from
the premises during the extended times when the unit was most likely
operational, so that didn't help either. However, my family tells me
that it WAS working and cooling the house rather nicely, for at
least a day, perhaps two. I'm getting 115V in all the right places,
so it doesn't look like an over-voltage condition to me. Perhaps
it's an overheating condition? It looks to me like the only real
load on this circuit is the blower motor; could the motor be causing
this? The blower spins freely when I turn it by hand. Start
capacitor on the motor maybe? Relay on the control board perhaps?


Just a thought,

When you put the new transformer in does the "Diagnostic Light" LED
turn on ?
Does the LED blink or flash in one of the patterns indicated in the
"diagnostic codes" section that you posted a link to ?

The "diagnostic codes" imply that the control board can detect
several of the problems mentioned by others.
Maybe a good starting point as there is not enough time to test with
test equipment.

robb

"robb" wrote in
m:

"Steve Turner" wrote in message ...

A continuation of the "Why does the 115V-24V transformer keep
blowing on my Trane XB80?" discussion I started on 04/02/2011.

Yep, My A/C unit blew another transformer. Pictures (and wiring
diagram) he

http://www.flickr.com/photos/bbqboye...7626457562742/

Trane's manual for the unit is here (for perhaps better viewing of
the wiring diagrams that I also copied to my above flickr site as
jpg images):



http://www.trane.com/webcache/un/fur...oduct/22-1666-
07_04012009.pdf

As you can probably see in the pictures, there is visible charring
of the 115V leads going into the transformer, and of course the 115V
circuit is open (again). If you didn't see my first thread, this is
the third transformer the unit has blown. In the previous
discussion, it was discussed that perhaps the first one just blew
because of old age (6 years), and the second blew because it wasn't
a proper replacement (poor quality, made in China, etc.). This
third unit is most certainly a proper replacement, and it's most
certainly indicative of a real problem I have somewhere else in the
unit. I didn't see any such charring on the previous two units, at
least not like this.

I never got a real chance to test out the system after installing
this third transformer. We had cool weather for several days, and I
never tried to force the system to come on so I could monitor it;
that was probably a mistake. Unfortunately, I was also absent from
the premises during the extended times when the unit was most likely
operational, so that didn't help either. However, my family tells me
that it WAS working and cooling the house rather nicely, for at
least a day, perhaps two. I'm getting 115V in all the right places,
so it doesn't look like an over-voltage condition to me. Perhaps
it's an overheating condition? It looks to me like the only real
load on this circuit is the blower motor; could the motor be causing
this? The blower spins freely when I turn it by hand. Start
capacitor on the motor maybe? Relay on the control board perhaps?

a bad start cap would not affect the 24v control transformer,that just
powers the controller board and relays.
either something is loading the transformer or a problem with input
voltage.


Just a thought,

When you put the new transformer in does the "Diagnostic Light" LED
turn on ?
Does the LED blink or flash in one of the patterns indicated in the
"diagnostic codes" section that you posted a link to ?

The "diagnostic codes" imply that the control board can detect
several of the problems mentioned by others.
Maybe a good starting point as there is not enough time to test with
test equipment.

robb



a line voltage monitor may be needed to see if there's some short-term
overvoltage applied to the transformer,and a oscilloscope may determine if
the input waveform is sinusoidal or otherwise,because 60hz iron core
tranformers don't like extreme distortion on their input,it gets converted
to heat,not output voltage. a DMM will not show line distortion or short
term overvoltages.
are the wires burned close to the transformer,or over their entire length?

--
Jim Yanik
jyanik
at
localnet
dot com

On Sat, 09 Apr 2011 14:28:28 -0700, David Nebenzahl
wrote:

On 4/9/2011 2:04 PM Steve Turner spake thus:

On 4/9/2011 2:58 PM, A. Baum wrote:

On Sat, 09 Apr 2011 14:41:05 -0500, Steve Turner wrote:

But measuring and understanding the ramifications of current
(amperage) is where I get a little fuzzy. Would you help me out?
That's why I came here.

I advised you the last time to measure the 24 volt circuit amperage
draw and convert that to the specs (volt-amps) of the transformer.
If the draw is out of bounds of the specs then the 24 volt circuit
is the problem. You can't put a band-aid on a bullet wound.

Yes, you did, and thanks for the suggestion. I've never used my meter to
measure amperage before, and I don't know how to do that conversion, but I will
study up on it.

It's not a "conversion".

To measure current (which, properly speaking, is what you're measuring,
not "amperage"), you have to break the circuit and put the ammeter in
series with the circuit, so that all the current goes through the meter.
(As opposed to measuring voltage, where you put the meter *across*, or
in parallel with, the thing whose voltage you want to know.)

In your case, since you want to see how much current is being drawn from
the transformer, you'd put the ammeter between one of the transformer
secondary leads (doesn't matter which one) and whatever wire from your
unit that's supposed to connect to that lead.

Since you're measuring AC current, you'll need an AC ammeter, which
rules out most digital multimeters, which only are designed to measure
DC current. Not sure where you'd (quickly, easily) get an AC meter.
Maybe others can suggest? But that's how you do it.


Pardon? every one of my digital meters has an ac current range.. The
one on my desk right now has a 200ma and a 20 amp scale, while for DC
it has 2ma,20ma, 200ma, and 20 amp.

My "pocket" meter has 2 amp and 10 amp AC and dc

My "bench" meter has 300ma and 10 amp, both AC and DC.

The first digital meter I ever owned (and I still have it) has 2ma,
200ma and 10 amp ranges (and it is 30 years old)

And my"amp clamp" reads 200 or 1000 amps

On Sat, 9 Apr 2011 21:30:15 +0000 (UTC), "A. Baum"
wrote:

On Sat, 09 Apr 2011 16:04:32 -0500, Steve Turner wrote:

On 4/9/2011 2:58 PM, A. Baum wrote:
On Sat, 09 Apr 2011 14:41:05 -0500, Steve Turner wrote:

But measuring and
understanding the ramifications of current (amperage) is where I get a
little fuzzy. Would you help me out? That's why I came here.

I advised you the last time to measure the 24 volt circuit amperage
draw and convert that to the specs (volt-amps) of the transformer. If
the draw is out of bounds of the specs then the 24 volt circuit is the
problem. You can't put a band-aid on a bullet wound.

Yes, you did, and thanks for the suggestion. I've never used my meter
to measure amperage before, and I don't know how to do that conversion,
but I will study up on it.

An amp meter goes in series with the secondary (or primary) of the
transformer. You can convert amps to volt-amps by multiplying volts times
amps. 24 volts times 1 amp = 24 volt-amps. I don't remember if
transformers are rated differently for the primary or secondary or which
one is usually used. It might be in the technical data usually packed
with the transformer or stamped on the transformer somewhere.

If the spec is for the primary then it would be 117 x amps. Of course the
measurements should be taken while the unit is in heat mode.


The rating is "output" which means the secondary. Primary power will
always be slightly higher due to efficiency issues.

On Sat, 09 Apr 2011 14:37:10 -0700, David Nebenzahl
wrote:

On 4/9/2011 2:21 PM Steve Turner spake thus:

On 4/9/2011 3:43 PM, Smarty wrote:

On 4/8/2011 8:52 PM, Steve Turner wrote:

A continuation of the "Why does the 115V-24V transformer keep
blowing on my Trane XB80?" discussion I started on 04/02/2011.

Yep, My A/C unit blew another transformer. Pictures (and wiring
diagram) he

http://www.flickr.com/photos/bbqboye...7626457562742/

Trane's manual for the unit is here (for perhaps better viewing
of the wiring diagrams that I also copied to my above flickr site
as jpg images):

http://www.trane.com/webcache/un/fur...7_04012009.pdf

As you can probably see in the pictures, there is visible charring of the
115V leads going into the transformer, and of course the 115V circuit is open
(again). If you didn't see my first thread, this is the third transformer the
unit has blown. In the previous discussion, it was discussed that perhaps the
first one just blew because of old age (6 years), and the second blew because
it wasn't a proper replacement (poor quality, made in China, etc.). This
third unit is most certainly a proper replacement, and it's most certainly
indicative of a real problem I have somewhere else in the unit. I didn't see
any such charring on the previous two units, at least not like this.

I never got a real chance to test out the system after installing this third
transformer. We had cool weather for several days, and I never tried to force
the system to come on so I could monitor it; that was probably a mistake.
Unfortunately, I was also absent from the premises during the extended times
when the unit was most likely operational, so that didn't help either.
However, my family tells me that it WAS working and cooling the house rather
nicely, for at least a day, perhaps two. I'm getting 115V in all the right
places, so it doesn't look like an over-voltage condition to me. Perhaps it's
an overheating condition? It looks to me like the only real load on this
circuit is the blower motor; could the motor be causing this? The blower
spins freely when I turn it by hand. Start capacitor on the motor maybe?
Relay on the control board perhaps?

If you are not comfortable with taking current measurements, or do not have an
ammeter, or do not wish to sit there waiting for some unusual condition which
is drawing too much current, you could temporarily install an in-line fuse
holder and automotive cartridge fuse rated at or above the secondary side
amperage which the transformer is rated. With this fuse installed on the
secondary side, in series with the load, you could then determine if the load
is indeed drawing too much current from the secondary and burning out the
transformer, versus primary side excess voltage being the problem.

A rough guess would be that the contactor coil should maybe be drawing about a
quarter to a half an amp of current at 24V. The transformer secondary should
not need to source a lot more than that amount of current to provide adequate
power to the coil of the contactor.

Fuses are a lot cheaper than transformers......

There may be an intermittent short in the wiring to the coil, a short in the
coil itself, a breakdown of the coil insulation allowing a short to ground when
the coil heats up or cools or vibrates, etc.

Yes Smarty, I would very much like to try this approach because I don't want to
zap any more transformers. Lots of people have suggested it, but there appear
to be more types of fuses than there are insects, and I have no idea what
*exact* type to look for.

Well, it's not exactly rocket science. And you can't hurt anything,
unless you get a fuse that's too big (i.e., rated at too many amps).

First thing you gotta figure out is how much current your transformer is
rated at. Since your wiring diagrams don't say, we have to take an
educated guess.

The only thing connected to the transformer is a thingamajig called the
"integrated furnace control" (IFC). Even without seeing this thing, I
can guess with confidence that it's an electronic circuit board which
controls the operation of the furnace. Since it undoubtedly does so
through relays (either mechanical or electronic), it's safe to assume
that it doesn't draw much current.

Let's say 1 amp to start. We could be wrong, but that's a good starting
point. So what we need is a fuse rated at *at least* 24 volts (could be
much more, up to 120 or 240 volts), and *exactly* 1 amp. To be on the
safe side, let's get a "fast blow" fuse. Hey, fuses are cheaper than
transformers, right?

So install such a fuse, run the unit and see what happens.

If the fuse blows right away, it's probably too small, so use the next
bigger fuse; let's say 1.5 A.

We don't need to guess here.
The transformer has a rating. NEVER fuse above the transformer rating.
If the transformer is a 40va 24 volt transformer the MAXIMUM fuse
rating is 40/24=1.66 amps - so a 1.5 amp fuse will protect the
transformer - a 2 amp fuse will NOT.

Now you want to stop at some point, let's say 2-3 amps, because now
you're getting up to where you may be exposing whatever fault there is
with the unit and risking blowing the transformer again. If this
happens, you're going to have to bite the bullet and find out what's
wrong with the damn thing. But at least your 3rd transformer will still
be intact.

On Sat, 09 Apr 2011 14:42:39 -0700, David Nebenzahl
wrote:

On 4/9/2011 2:30 PM A. Baum spake thus:

An amp meter goes in series with the secondary (or primary) of the
transformer. You can convert amps to volt-amps by multiplying volts times
amps. 24 volts times 1 amp = 24 volt-amps. I don't remember if
transformers are rated differently for the primary or secondary or which
one is usually used. It might be in the technical data usually packed
with the transformer or stamped on the transformer somewhere.

Using the primary side would be more conservative (= a bit safer), since
it will include any losses between primary and secondary sides. But it
really doesn't matter. And I'd much prefer to measure current on the
secondary side, rather than deal with 120-volt juice.

He still has the problem of finding an AC ammeter, since a DMM won't
handle AC current.

As noted previously, this is NOT the case. An AUTOMOTIVE DMM might not
have an AC current scale, but virtually all general purpose meters do.
They generally have a "third terminal" used with the common for the
high range, which will be what he wants to use since the low range
that uses the standard (vom) connections generally tops out at 300ma,
more or less.

On Sat, 9 Apr 2011 17:46:06 -0400, "Stormin Mormon"
wrote:

Well, the way I see it. If he FUSES the SECONDARY side, and
the transformer BLOWS, it might still be a BAD NEUTRAL. At
this point, MY best GUESS is some kind of problem with the
SECONDARY wiring. But, I'm NOT THERE to check.

He needs to fuse the secondary and meter the primary, and have someone
switch all the loads while he watches the meter. This will tell if he
has a neutral issue, because a load on the "other phase" will cause
the voltage to go up while a load on the "same phase" will cause the
voltage to go down.

Even simpler, when the blower motor comes on, if he has a neutral
issue the voltage on the primary WILL DROP. Absolutely no question.
(and more than 1 volt - virtually guaranteed)

On 4/9/2011 6:11 PM spake thus:

On Sat, 09 Apr 2011 14:42:39 -0700, David Nebenzahl
wrote:

On 4/9/2011 2:30 PM A. Baum spake thus:

An amp meter goes in series with the secondary (or primary) of
the transformer. You can convert amps to volt-amps by multiplying
volts times amps. 24 volts times 1 amp = 24 volt-amps. I don't
remember if transformers are rated differently for the primary or
secondary or which one is usually used. It might be in the
technical data usually packed with the transformer or stamped on
the transformer somewhere.

Using the primary side would be more conservative (= a bit safer),
since it will include any losses between primary and secondary
sides. But it really doesn't matter. And I'd much prefer to measure
current on the secondary side, rather than deal with 120-volt
juice.

He still has the problem of finding an AC ammeter, since a DMM
won't handle AC current.

As noted previously, this is NOT the case. An AUTOMOTIVE DMM might not
have an AC current scale, but virtually all general purpose meters do.
They generally have a "third terminal" used with the common for the
high range, which will be what he wants to use since the low range
that uses the standard (vom) connections generally tops out at 300ma,
more or less.

Well, all I can say is that *none* of my 3 general-purpose multimeters
(2 analog and 1 DMM) have AC current settings. But apparently this is a
non-issue in this case, as the OP's meter definitely has AC current
capability.


--
The current state of literacy in our advanced civilization:

yo
wassup
nuttin
wan2 hang
k
where
here
k
l8tr
by

- from Usenet (what's *that*?)

On Sat, 09 Apr 2011 16:57:57 -0500, The Daring Dufas
wrote:

On 4/9/2011 1:13 PM, Stormin Mormon wrote:
Agree, sounds like electrical problem, and the OP isn't
quite skilled enough to find it.


I just saw it in the picture and posted what the problem is.
I would have seen it immediately if I was hands on. Look at
the wire colors on the transformer especially the YELLOW, it
is taking the place of the RED wire for low voltage. Notice the
yellow and blue are on one side of the transformer. I don't know
why I didn't notice it before. ^_^

TDD


You are sure that's the problem??
There are NO STANDARDS when it comes to transformer wiring colours
(outside of the radio/communications industry, and even there, the
beauty of standards is there are so many to choose from)

He needs to go by the wiring diagram that came with the transformer,
and VERIFY IT WITH A VOLTMETER.

On Sat, 09 Apr 2011 17:11:31 -0500, Steve Turner
wrote:

http://www.extech.com/instruments/re...ls/MN26_UM.pdf
The instrument is definitely capable. Use the 10 amp scale, with the
leads in the common and 10a jacks.

On 4/9/2011 6:28 PM spake thus:

On Sat, 09 Apr 2011 16:57:57 -0500, The Daring Dufas
wrote:

On 4/9/2011 1:13 PM, Stormin Mormon wrote:

Agree, sounds like electrical problem, and the OP isn't quite
skilled enough to find it.

I just saw it in the picture and posted what the problem is. I
would have seen it immediately if I was hands on. Look at the wire
colors on the transformer especially the YELLOW, it is taking the
place of the RED wire for low voltage. Notice the yellow and blue
are on one side of the transformer. I don't know why I didn't
notice it before. ^_^

You are sure that's the problem??
There are NO STANDARDS when it comes to transformer wiring colours
(outside of the radio/communications industry, and even there, the
beauty of standards is there are so many to choose from)

Ain't that the truth!

He needs to go by the wiring diagram that came with the transformer,
and VERIFY IT WITH A VOLTMETER.

Which he has already done, if you'd bothered to read all his postings.


--
The current state of literacy in our advanced civilization:

yo
wassup
nuttin
wan2 hang
k
where
here
k
l8tr
by

- from Usenet (what's *that*?)

On Sat, 09 Apr 2011 19:22:57 -0400, Jeff Thies
wrote:



But first do as I suggested in another thread,look carefully for
anything burnt and check the polarity of the line. Make sure the neutral
is neutral. You can measure from the ground prong. See the note in the
schematic. I'm not so sure this didn't arc to the transformer shell,
from looking at the pic. You may wish to measure voltage (AC) from the
transformer shell to a guaranteed neutral.

It's AC so there is no polarity. It's single output, non grounded, so
it doesnt matter which direction either the primary or secondary are
connected. Good to have the white on neutral and the bloack on live,
but it will have NO EFFECT on the operation. - or the life of the
transformer.

It is OK for the transformer to run a little warm, it shouldn't be hot.

There are two kinds of failures, one is a long term thermal failure
(which seemed likely when you said years had gone by), the other is a
transient short, or maybe not so transient. If that is the case then
something else will be bad. It may look burnt, or if it is a diode or
transistor it may just be shorted. You can Google how to test those.

Don't be afraid to put a quick finger on a transistor to see if it is
hot, or on the transformer.

As far as calculating what size fuse, you should know Ohms law. Current
* voltage is watts, or in this case V(olt)A(mps). 120V * 1/4A = 30 VA,
on the out side, 24V * 1.5 = 36 VA.

Note that there is a small surge when you turn on a device. So it may
peak higher at the instant of turning on. A fuse usually can absorb
that. The white ceramics are faster blowing and the slow blow ones
usually have a little coil inside the fuse to show it down and are
marked slow blow. When/if you fix this, leave in the fuses and we can
give you some guidance on more properly sizing them. But some fuse in
the ballpark is definitely better than nothing.

Jeff

On Sat, 09 Apr 2011 19:29:30 -0500, Jim Yanik
wrote:

"robb" wrote in
om:

"Steve Turner" wrote in message ...

A continuation of the "Why does the 115V-24V transformer keep
blowing on my Trane XB80?" discussion I started on 04/02/2011.

Yep, My A/C unit blew another transformer. Pictures (and wiring
diagram) he

http://www.flickr.com/photos/bbqboye...7626457562742/

Trane's manual for the unit is here (for perhaps better viewing of
the wiring diagrams that I also copied to my above flickr site as
jpg images):



http://www.trane.com/webcache/un/fur...oduct/22-1666-
07_04012009.pdf

As you can probably see in the pictures, there is visible charring
of the 115V leads going into the transformer, and of course the 115V
circuit is open (again). If you didn't see my first thread, this is
the third transformer the unit has blown. In the previous
discussion, it was discussed that perhaps the first one just blew
because of old age (6 years), and the second blew because it wasn't
a proper replacement (poor quality, made in China, etc.). This
third unit is most certainly a proper replacement, and it's most
certainly indicative of a real problem I have somewhere else in the
unit. I didn't see any such charring on the previous two units, at
least not like this.

I never got a real chance to test out the system after installing
this third transformer. We had cool weather for several days, and I
never tried to force the system to come on so I could monitor it;
that was probably a mistake. Unfortunately, I was also absent from
the premises during the extended times when the unit was most likely
operational, so that didn't help either. However, my family tells me
that it WAS working and cooling the house rather nicely, for at
least a day, perhaps two. I'm getting 115V in all the right places,
so it doesn't look like an over-voltage condition to me. Perhaps
it's an overheating condition? It looks to me like the only real
load on this circuit is the blower motor; could the motor be causing
this? The blower spins freely when I turn it by hand. Start
capacitor on the motor maybe? Relay on the control board perhaps?

a bad start cap would not affect the 24v control transformer,that just
powers the controller board and relays.
either something is loading the transformer or a problem with input
voltage.


Or just another crappy transformer.
You do not just ASSume it is the transformer


Just a thought,

When you put the new transformer in does the "Diagnostic Light" LED
turn on ?
Does the LED blink or flash in one of the patterns indicated in the
"diagnostic codes" section that you posted a link to ?

The "diagnostic codes" imply that the control board can detect
several of the problems mentioned by others.
Maybe a good starting point as there is not enough time to test with
test equipment.

robb



a line voltage monitor may be needed to see if there's some short-term
overvoltage applied to the transformer,and a oscilloscope may determine if
the input waveform is sinusoidal or otherwise,because 60hz iron core
tranformers don't like extreme distortion on their input,it gets converted
to heat,not output voltage. a DMM will not show line distortion or short
term overvoltages.
are the wires burned close to the transformer,or over their entire length?

Transient overvoltages of less than 20% or there-abouts are unlikely
to blow the transformer primary of the furnace without manifesting
themselves elsewhere in the house - and over 20% would definitely
manifest themselves elsewhere.

On 4/9/2011 7:29 PM, Jim Yanik wrote:
wrote in
m:

"Steve Turner" wrote in message ...

A continuation of the "Why does the 115V-24V transformer keep
blowing on my Trane XB80?" discussion I started on 04/02/2011.

Yep, My A/C unit blew another transformer. Pictures (and wiring
diagram) he

http://www.flickr.com/photos/bbqboye...7626457562742/

Trane's manual for the unit is here (for perhaps better viewing of
the wiring diagrams that I also copied to my above flickr site as
jpg images):



http://www.trane.com/webcache/un/fur...oduct/22-1666-
07_04012009.pdf

As you can probably see in the pictures, there is visible charring
of the 115V leads going into the transformer, and of course the 115V
circuit is open (again). If you didn't see my first thread, this is
the third transformer the unit has blown. In the previous
discussion, it was discussed that perhaps the first one just blew
because of old age (6 years), and the second blew because it wasn't
a proper replacement (poor quality, made in China, etc.). This
third unit is most certainly a proper replacement, and it's most
certainly indicative of a real problem I have somewhere else in the
unit. I didn't see any such charring on the previous two units, at
least not like this.

I never got a real chance to test out the system after installing
this third transformer. We had cool weather for several days, and I
never tried to force the system to come on so I could monitor it;
that was probably a mistake. Unfortunately, I was also absent from
the premises during the extended times when the unit was most likely
operational, so that didn't help either. However, my family tells me
that it WAS working and cooling the house rather nicely, for at
least a day, perhaps two. I'm getting 115V in all the right places,
so it doesn't look like an over-voltage condition to me. Perhaps
it's an overheating condition? It looks to me like the only real
load on this circuit is the blower motor; could the motor be causing
this? The blower spins freely when I turn it by hand. Start
capacitor on the motor maybe? Relay on the control board perhaps?

a bad start cap would not affect the 24v control transformer,that just
powers the controller board and relays.
either something is loading the transformer or a problem with input
voltage.


Just a thought,

When you put the new transformer in does the "Diagnostic Light" LED
turn on ?
Does the LED blink or flash in one of the patterns indicated in the
"diagnostic codes" section that you posted a link to ?

The "diagnostic codes" imply that the control board can detect
several of the problems mentioned by others.
Maybe a good starting point as there is not enough time to test with
test equipment.

robb



a line voltage monitor may be needed to see if there's some short-term
overvoltage applied to the transformer,and a oscilloscope may determine if
the input waveform is sinusoidal or otherwise,because 60hz iron core
tranformers don't like extreme distortion on their input,it gets converted
to heat,not output voltage. a DMM will not show line distortion or short
term overvoltages.
are the wires burned close to the transformer,or over their entire length?

I peeled the insulation back from the hot and neutral wires and the burning
only occurred right at the terminals, no more than 1/4" into the wiring.

On 4/9/2011 6:54 PM, Smitty Two wrote:
In ,
The Daring wrote:

On 4/9/2011 1:13 PM, Stormin Mormon wrote:
Agree, sounds like electrical problem, and the OP isn't
quite skilled enough to find it.


I just saw it in the picture and posted what the problem is.
I would have seen it immediately if I was hands on. Look at
the wire colors on the transformer especially the YELLOW, it
is taking the place of the RED wire for low voltage. Notice the
yellow and blue are on one side of the transformer. I don't know
why I didn't notice it before. ^_^

TDD

Hello? tap tap tap. Is this thing on? I mentioned that yesterday, duf.
Or maybe this morning. Time gets distorted on weekends.

Steve wrote that the instructions pointed it out so another theory out
the window. Looks like it may be a intermittent floating neutral after
all. Oh tap, tap, tap, I don't think I've read all the posts so I may
have missed your brilliant deduction. I started reading the thread when
I noticed how long it was getting and no one was blaming BeeHO for it.
ROTFL

TDD

Steve Turner wrote:
On 4/9/2011 7:29 PM, Jim Yanik wrote:
wrote in
m:

"Steve Turner" wrote in message ...

A continuation of the "Why does the 115V-24V transformer keep
blowing on my Trane XB80?" discussion I started on 04/02/2011.

Yep, My A/C unit blew another transformer. Pictures (and wiring
diagram) he

http://www.flickr.com/photos/bbqboye...7626457562742/

Trane's manual for the unit is here (for perhaps better viewing of
the wiring diagrams that I also copied to my above flickr site as
jpg images):



http://www.trane.com/webcache/un/fur...oduct/22-1666-
07_04012009.pdf

As you can probably see in the pictures, there is visible charring
of the 115V leads going into the transformer, and of course the 115V
circuit is open (again). If you didn't see my first thread, this is
the third transformer the unit has blown. In the previous
discussion, it was discussed that perhaps the first one just blew
because of old age (6 years), and the second blew because it wasn't
a proper replacement (poor quality, made in China, etc.). This
third unit is most certainly a proper replacement, and it's most
certainly indicative of a real problem I have somewhere else in the
unit. I didn't see any such charring on the previous two units, at
least not like this.

I never got a real chance to test out the system after installing
this third transformer. We had cool weather for several days, and I
never tried to force the system to come on so I could monitor it;
that was probably a mistake. Unfortunately, I was also absent from
the premises during the extended times when the unit was most likely
operational, so that didn't help either. However, my family tells me
that it WAS working and cooling the house rather nicely, for at
least a day, perhaps two. I'm getting 115V in all the right places,
so it doesn't look like an over-voltage condition to me. Perhaps
it's an overheating condition? It looks to me like the only real
load on this circuit is the blower motor; could the motor be causing
this? The blower spins freely when I turn it by hand. Start
capacitor on the motor maybe? Relay on the control board perhaps?

a bad start cap would not affect the 24v control transformer,that just
powers the controller board and relays.
either something is loading the transformer or a problem with input
voltage.


Just a thought,

When you put the new transformer in does the "Diagnostic Light" LED
turn on ?
Does the LED blink or flash in one of the patterns indicated in the
"diagnostic codes" section that you posted a link to ?

The "diagnostic codes" imply that the control board can detect
several of the problems mentioned by others.
Maybe a good starting point as there is not enough time to test with
test equipment.

robb



a line voltage monitor may be needed to see if there's some short-term
overvoltage applied to the transformer,and a oscilloscope may
determine if
the input waveform is sinusoidal or otherwise,because 60hz iron core
tranformers don't like extreme distortion on their input,it gets
converted
to heat,not output voltage. a DMM will not show line distortion or short
term overvoltages.
are the wires burned close to the transformer,or over their entire
length?

I peeled the insulation back from the hot and neutral wires and the
burning only occurred right at the terminals, no more than 1/4" into the
wiring.


So the problem is the joint of the transformer wiring to the lugs. They
may have cold solder joints, or the lug may be slightly loose - enough
to crack the solder connection over time. Your transformer may still be
good!

When you are examining the transformer wire make sure it is stripped
enough to get good solder coverage. Burn off the insulation (enamel) -
do not sand, scrape, or try to erode it because if you scratch the wire
it will break at the scratch.

Re-solder the transformer connectors after first making sure the wire
has at least two complete wraps around the solder lug and the solder
makes a good meniscus joint to the wire and lug. Also use a good grade
of solder, not regular 60/40, find some 63/37 solder (Kester is best) -
this solder resists cold solder joints due to movement when cooling by
solidifying very fast.

John :-#)#

--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

On 4/9/2011 8:28 PM, wrote:
On Sat, 09 Apr 2011 16:57:57 -0500, The Daring Dufas
wrote:

On 4/9/2011 1:13 PM, Stormin Mormon wrote:
Agree, sounds like electrical problem, and the OP isn't
quite skilled enough to find it.


I just saw it in the picture and posted what the problem is.
I would have seen it immediately if I was hands on. Look at
the wire colors on the transformer especially the YELLOW, it
is taking the place of the RED wire for low voltage. Notice the
yellow and blue are on one side of the transformer. I don't know
why I didn't notice it before. ^_^

TDD


You are sure that's the problem??
There are NO STANDARDS when it comes to transformer wiring colours
(outside of the radio/communications industry, and even there, the
beauty of standards is there are so many to choose from)

He needs to go by the wiring diagram that came with the transformer,
and VERIFY IT WITH A VOLTMETER.

No it's not, Steve wrote that the included instructions pointed out the
difference in wire color. I may have to change a compressor tomorrow so
I'm sure I'll see all kind of colors when I get a whiff of phosgene gas
when I hit the lines with my torch. ^_^

TDD

"robb"


Yep, My A/C unit blew another transformer. Pictures (and wiring diagram)
he

http://www.flickr.com/photos/bbqboye...7626457562742/

http://www.trane.com/webcache/un/fur...7_04012009.pdf

As you can probably see in the pictures, there is visible charring of the
115V leads going into the transformer, and of course the 115V circuit is
open (again).


** From the damage to the tranny visible in the photos - the primary has
developed an internal short ( due to insulation failure) and since there is
no fuse link in series, the resulting current was high enough to make an
exposed wire leading to the terminals explode.

An internal short could develop due to heat alone because of an overload on
the tranny - but this requires a fault to exist on the secondary side which
seems not to be the case.

High voltage spikes on the primary could also cause insulation failure
leading to the damage seen in the pics - lightning does this sort of thing.
So also could back emfs from the blower fan if the is a bad connection in
the AC supply feed.

I suggest you provide the next replacement for that vulnerable tranny with
some "protection" - firstly an in-line fuse of say 1/4 amp AND a
capacitor wired across the primary of say 1uF rated for continuous use
across the AC supply.

If there is an overload on the tranny, the fuse will blow.

The 1uF capacitor should suppress spike voltages enough to save the tranny
from harm.



...... Phil

On 4/9/2011 1:37 AM, Smitty Two wrote:
In ,
Steve wrote:

snip

You might start at the beginning and make sure everything is hooked up
correctly. I mean, once you spring for yet another transformer. For
example, your latest fried transformer has six wires. The schematic
shows the secondary wire colors as blue and red. Given the location of
the blue and red wires on the pic of the transformer you have, that's
not quite intuitive.

And, it may not even be right. So I'd buy a new one, and check some
voltages on the bench. Put 120 into the black and white, and then
measure every other pair to make sure you understand which two wires are
really putting out 24 V.

Obviously, when you go to install it, clip and shrink tube the unused
wires, and make sure that leads are dressed so that they won't short
anywhere.

Then I'd be monitoring the damn thing, preferably with a voltmeter
perhaps on the primary and an ammeter on the secondary.

That 3rd transformer looks like a dual voltage (120/240) input.
If it is, it has two primary windings, and both need to be wire up to work.
Like this: http://www.eleinmec.com/figures/027_02.gif