On Friday, April 8, 2011 5:52:06 PM UTC-7, 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/bbqboyee/sets/72157626457562742/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?

Hello, I am having the same exact problem and have replaced the transformer a third time with one of the correct rating as the manufacturer (70VA). The second time I replaced it with a 40VA because I assumed the one i replaced was the correct size. The Primary side keeps getting burned up. What causes that?

On Tuesday, June 17, 2014 9:34:20 AM UTC-4, wrote:
On Friday, April 8, 2011 5:52:06 PM UTC-7, 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/bbqboyee/sets/72157626457562742/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?



Hello, I am having the same exact problem and have replaced the transformer a third time with one of the correct rating as the manufacturer (70VA). The second time I replaced it with a 40VA because I assumed the one i replaced was the correct size. The Primary side keeps getting burned up. What causes that?

If the correct size was 70 and you replaced it once with a 40, then you have one or two unexplained failures, not 3. You can ignore the last part of that thread where he speculates about the blower motor load being the problem. The tranformer doesn't power blowers, it's used for the thermostat circuit, contactor circuit, control board power, etc.

Have you measured the current draw and voltage on the output of the transformer?
Made sure it's not exceeding the 70VA? My first suspicion would be that it's just cheap, crap parts. The other fellow talked about that. And just because you get it from Trane, doesn't mean it's not a cheap, China part. A few years ago I had a Sears dehumidifier where the fan died. It was only a few years old, so I bought a new fan for $50 from Sears. That fan lasted about a year. Still not having learned my lesson, I bought yet another fan. That one smoked when it was first turned on. When I finally did what you did, ie google, I
found that for 7 years people had been having the exact same thing happen. It's clearly a case of bad parts and Sears either not having a process to even know it, or not caring.

If it were me, I'd see if I could find a transformer that will fit from
another source, preferably American made, definitely avoid China if possible.

if the OP has the original failed transformer they could try looking for a thermal fuse buried in the primary wiring coil.

OP sghould look at the temperature where the transformer lives. perhaps the temp in the area is too hot, causing the transformer to fail.

OP could shop for a higher current transformer rather than 40 or 70 watts how about 150 watts.

the transformer with the obvious charring was likely a manufacturing defect.

On Saturday, April 9, 2011 12:23:47 PM UTC-4, 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!

Fuse depends on the transformer rating. Typically they specify a va rating on the secondary. Sometimes an amperage. If you have a secondary amperage then that's the fuse size you want. If they give you a va rating, say 50 divide that by the voltage to get the fuse amps. You can get an inline fuse holder and a fuse at radio shack. Use a slo-blo because there will be a surge when the outside unit contactor gets pulled. Most likely you will end up with a 2 amp fuse.

In the ac mode the transformer is powering the control board and the compressor contactor in the outside unit. If you have a smart thermostat that doesn't run on batteries then it's powering that too.

Most vom's won't measure amperage high enough to check it on the secondary side. You can measure the amperage on the primary and multiple by 4.8 to get the approximate secondary amperage.

You have a gas furnace so you only have 115 at the furnace. So fluctuating 115 would have also causes light bulbs to burn out around the house.

On Tuesday, June 17, 2014 10:47:48 AM UTC-4, jamesgang wrote:
On Saturday, April 9, 2011 12:23:47 PM UTC-4, 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!



Fuse depends on the transformer rating. Typically they specify a va rating on the secondary.

He said it's 70VA.

Sometimes an amperage. If you have a secondary amperage then that's the fuse size you want. If they give you a va rating, say 50 divide that by the voltage to get the fuse amps. You can get an inline fuse holder and a fuse at radio shack. Use a slo-blo because there will be a surge when the outside unit contactor gets pulled. Most likely you will end up with a 2 amp fuse.


I agree, that's a good idea, except it should be 3 or 4 amps. It would rule out any long over-current draw as the cause.






In the ac mode the transformer is powering the control board and the compressor contactor in the outside unit. If you have a smart thermostat that doesn't run on batteries then it's powering that too.



Most vom's won't measure amperage high enough to check it on the secondary side.

70VA is 3 amps at 24V. IDK about most. Maybe some won't do that,
but all the ones I've used will, including cheap ones. Any decent one
should. But I guess all that's a moot point, based on his last
response.


You can measure the amperage on the primary and multiple by 4.8 to get the approximate secondary amperage.



You have a gas furnace so you only have 115 at the furnace. So fluctuating 115 would have also causes light bulbs to burn out around the house.

You would think so and also, voltage would have to fluctuate a lot to screw the transformer. Given that others are having similar problem, my money would be on these just being cheap, crap parts, but who knows.

wrote:
On Friday, April 8, 2011 5:52:06 PM UTC-7, 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/bbqboyee/sets/72157626457562742/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 mot
or maybe? Relay on the control board perhaps?

Hello, I am having the same exact problem and have replaced the transformer a third time with one of the correct rating as the manufacturer (70VA). The second time I replaced it with a 40VA because I assumed the one i replaced was the correct size. The Primary side keeps getting burned up. What causes that?

Hmmm,
I never had 24V AC x-former blown in any appliances. If it keeps
blowing, take logical steps B4 just keep replacing it. It must have
a reason why it is blowing. Probably overloading, El Cheapo x-former,
Bad or partially failing component on the load side(control board)
When the unit is running, does it feel hot? Did a careful inspection
on the board for any component with color change, sign of over heating,
cracking, etc.? Checked thermostat inside? Measured the current in full
load to see it is within specs.? I perused eBay for a x-former. Price
varies from 5.00 to 100.00.
Try to buy a NOS good stuff paying for it's value. That is even a fire
hazard. I'd also Google the issue to see if it is common problem. Good luck.

Tony Hwang wrote:

Hmmm,
I never had 24V AC x-former blown in any appliances. If it keeps
blowing, take logical steps B4 just keep replacing it. It must have
a reason why it is blowing. Probably overloading, El Cheapo x-former,
Bad or partially failing component on the load side(control board)
When the unit is running, does it feel hot? Did a careful inspection
on the board for any component with color change, sign of over heating,
cracking, etc.? Checked thermostat inside? Measured the current in full
load to see it is within specs.? I perused eBay for a x-former. Price
varies from 5.00 to 100.00.
Try to buy a NOS good stuff paying for it's value. That is even a fire
hazard. I'd also Google the issue to see if it is common problem. Good
luck.
P.S.
I wonder why fuse did not blow B4 x-former blew? Make sure all the
connections related to x-former are not loose including crimped pins
inside Molex connector. Triad Magnetics old vintage x-formers
are floating around at eBay. They are good stuff.

On Friday, April 8, 2011 5:52:06 PM UTC-7, 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/bbqboyee/sets/72157626457562742/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?

Hello, I am having the same exact problem and have replaced the transformer
a third time with one of the correct rating as the manufacturer (70VA). The
second time I replaced it with a 40VA because I assumed the one i replaced
was the correct size. The Primary side keeps getting burned up. What causes
that?



*Is there any chance that water is somehow dripping on the transformer?
Moisture could cause it to burn out over time. Maybe try relocating it.

On Tuesday, June 17, 2014 2:45:58 PM UTC-4, John G wrote:
On Friday, April 8, 2011 5:52:06 PM UTC-7, 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/bbqboyee/sets/72157626457562742/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?



Hello, I am having the same exact problem and have replaced the transformer

a third time with one of the correct rating as the manufacturer (70VA). The

second time I replaced it with a 40VA because I assumed the one i replaced

was the correct size. The Primary side keeps getting burned up. What causes

that?







*Is there any chance that water is somehow dripping on the transformer?

Moisture could cause it to burn out over time. Maybe try relocating it.

That seems highly unlikely. Condensate is the possible water source and fresh water, though eventually damaging, would be obvious long before it did any real damage to the transformer.

Either he's using too small/too cheap transformers or something is drawing too much current.

jamesgang posted for all of us...

And I know how to SNIP

Either he's using too small/too cheap transformers or something is drawing too much current



+1
--
Tekkie

On Tue, 17 Jun 2014 06:34:20 -0700 (PDT), wrote:

On Friday, April 8, 2011 5:52:06 PM UTC-7, 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/bbqboyee/sets/72157626457562742/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?

Hello, I am having the same exact problem and have replaced the transformer a third time with one of the correct rating as the manufacturer (70VA). The second time I replaced it with a 40VA because I assumed the one i replaced was the correct size. The Primary side keeps getting burned up. What causes that?
Use a 90va or better transformer and fuse the secondary. Buy a good
brand name transformer. Eiuther you are overloading the transformer or
the transformer is junk.

wrote:
On Tue, 17 Jun 2014 06:34:20 -0700 (PDT), wrote:

On Friday, April 8, 2011 5:52:06 PM UTC-7, 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/bbqboyee/sets/72157626457562742/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?

Hello, I am having the same exact problem and have replaced the transformer a third time with one of the correct rating as the manufacturer (70VA). The second time I replaced it with a 40VA because I assumed the one i replaced was the correct size. The Primary side keeps getting burned up. What causes that?
Use a 90va or better transformer and fuse the secondary. Buy a good
brand name transformer. Eiuther you are overloading the transformer or
the transformer is junk.

Hi,
There are a few listings at eBay for a brand name NOS x-formers at
around 90VA rating. Not Chinese El Cheapo ones. For ~25.00.

"jamesgang" wrote in message news:041ed581-b187-

stuff snipped

Either he's using too small/too cheap transformers or something is drawing
too much current.

Is the circuit board possibly being subjected to back EMF from the furnace
motor? It's hard to tell without seeing a wiring diagram what's connected
to what but this seems to be a very intermittent issue. What series of
events could come together to burn out a transformer every few months?

One thing that comes to mind is that all day yesterday, my UPSs were
chirping like demented crickets. It was the first very hot day of the
seasons and ACs were drawing so much juice that the power company was
reducing the voltage substantially during the day. That's the kind of rare
event I would look at when considering why a transformer took so long
between replacements to burn out.

--
Bobby G.

On Wednesday, June 18, 2014 8:09:19 AM UTC-4, Robert Green wrote:
"jamesgang" wrote in message news:041ed581-b187-



stuff snipped



Either he's using too small/too cheap transformers or something is drawing

too much current.



Is the circuit board possibly being subjected to back EMF from the furnace

motor?

If it was, you'd expect components on the electronic board to fail,
not the transformer. You would think any decent transformer is going
to be among the components most resistant to a surge from a motor like
that.





It's hard to tell without seeing a wiring diagram what's connected

to what but this seems to be a very intermittent issue. What series of

events could come together to burn out a transformer every few months?


Crappy, cheap Chinese parts? As I stated previously, I saw 3 fan motors
for a Sears dehumidifier fail. Original lasted a few years, one lasted a
year, one smoked when installed and
turned on. Just simple two speed 120V motors, nothing to account for
those failures either. And when I googled, I found a lot of people with
exactly the same thing. Nothing I know of that accounts for a new 120V
fan smoking right out of the box, except that it's cheap China junk.

Not saying for sure that's what's going on here, only that it's not
unheard of and I don't see anything obvious. But then the OP hasn't
taken any current readings either.

On Wednesday, June 18, 2014 8:09:19 AM UTC-4, Robert Green wrote:
"jamesgang" wrote in message news:041ed581-b187-



stuff snipped



Either he's using too small/too cheap transformers or something is drawing

too much current.



Is the circuit board possibly being subjected to back EMF from the furnace

motor? It's hard to tell without seeing a wiring diagram what's connected

to what but this seems to be a very intermittent issue. What series of

events could come together to burn out a transformer every few months?



One thing that comes to mind is that all day yesterday, my UPSs were

chirping like demented crickets. It was the first very hot day of the

seasons and ACs were drawing so much juice that the power company was

reducing the voltage substantially during the day. That's the kind of rare

event I would look at when considering why a transformer took so long

between replacements to burn out.



--

Bobby G.

On the vast majority of air handlers the furnace blower motor is started via a cube style relay on the control board. The contactor out on the compressor is a pretty big relay (hvac guys call them contactors) and it's pulled by 24vac via the thermostat calling for cooling and what little emf it generates should not hurt a transformer. Once pulled, the outside contactor current draw is pretty small as the impedance goes up a good bit with the arm pulling into the coil.

Generally speaking hvac systems electrical/electronics is designed to be pretty forgiving as it has to operate in a wild range of conditions and is expected to work 24/365 without issue for many years.

A current check would be a good test. As others have said installing a known quality high current transformer may solve the problem. It might also cause a failure at whatever is drawing too much current. But then the problem will be more obvious.

On Friday, April 8, 2011 at 6:52:06 PM UTC-6, 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?

Our XR90 furnace did the same thing, I installed a 50W transformer instead of the stock 40W just in case it was underrated. I measured the operating output current during cool or heat and it maxes at .6 amps when 2.0 would be the limit. I cleaned up all the sloppy wiring from the installation and so far no blown fuses but with such an intermittent problem you never feel like you got it for sure. The only problem I could find was during heat call the red light would blink for 3 times indicating a problem with the safety pressure switch (enough gas pressure?). I temporarily bypassed the switch then it would latch and the heat would work fine. The only thing I can figure is that it the unit tries many times to turn on the heat and the pressure switch never makes the board commits suicide and deliberately blows the fuse so that you have to call a service man???? Sounds crazy but I wonder. I'll replace the pressure switch and see if the problem ever returns. For now I have a bunch of 2 amp (instead of 5A) fuses on hand to keep from blowing the transformer again. From the many web posts this seems like a common problem.

On Wednesday, June 21, 2017 at 7:15:34 PM UTC-4, wrote:
On Friday, April 8, 2011 at 6:52:06 PM UTC-6, 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?

Our XR90 furnace did the same thing, I installed a 50W transformer instead of the stock 40W just in case it was underrated. I measured the operating output current during cool or heat and it maxes at .6 amps when 2.0 would be the limit. I cleaned up all the sloppy wiring from the installation and so far no blown fuses but with such an intermittent problem you never feel like you got it for sure. The only problem I could find was during heat call the red light would blink for 3 times indicating a problem with the safety pressure switch (enough gas pressure?). I temporarily bypassed the switch then it would latch and the heat would work fine. The only thing I can figure is that it the unit tries many times to turn on the heat and the pressure switch never makes the board commits suicide and deliberately blows the fuse so that you have to call a service man???? Sounds crazy but I wonder. I'll replace the pressure switch and see if the problem ever returns. For now I have a bunch of 2 amp (instead of 5A) fuses on hand to keep from blowing the transformer again. From the many web posts this seems like a common problem.

so i know this is an old thread but i will add this

I've had 24V xformer burn out and it was due to a shorted wire.

There is a lot of vibration in HVAC equipment and if there is a wire touching
a bracket or anything, it may eventually wear through the insulation and
create a short, often these are intermittent and hard to see. The short blows the xformer.

I was lucky to spot the bad wire in my case. I repaired the short, installed a new xformer and added a PTC fuse device in series with the secondary just in case. A regular fuse rated for an amp or so above the xformer rating is a good idea. Also tie wrapped all the loose wires so none were rubbing on anything.
m

On Thursday, June 22, 2017 at 9:11:09 AM UTC-4, wrote:
On Wednesday, June 21, 2017 at 7:15:34 PM UTC-4, wrote:
On Friday, April 8, 2011 at 6:52:06 PM UTC-6, 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?

Our XR90 furnace did the same thing, I installed a 50W transformer instead of the stock 40W just in case it was underrated. I measured the operating output current during cool or heat and it maxes at .6 amps when 2.0 would be the limit. I cleaned up all the sloppy wiring from the installation and so far no blown fuses but with such an intermittent problem you never feel like you got it for sure. The only problem I could find was during heat call the red light would blink for 3 times indicating a problem with the safety pressure switch (enough gas pressure?). I temporarily bypassed the switch then it would latch and the heat would work fine. The only thing I can figure is that it the unit tries many times to turn on the heat and the pressure switch never makes the board commits suicide and deliberately blows the fuse so that you have to call a service man???? Sounds crazy but I wonder.. I'll replace the pressure switch and see if the problem ever returns. For now I have a bunch of 2 amp (instead of 5A) fuses on hand to keep from blowing the transformer again. From the many web posts this seems like a common problem.

so i know this is an old thread but i will add this

I've had 24V xformer burn out and it was due to a shorted wire.

There is a lot of vibration in HVAC equipment and if there is a wire touching
a bracket or anything, it may eventually wear through the insulation and
create a short, often these are intermittent and hard to see. The short blows the xformer.

I was lucky to spot the bad wire in my case. I repaired the short, installed a new xformer and added a PTC fuse device in series with the secondary just in case. A regular fuse rated for an amp or so above the xformer rating is a good idea. Also tie wrapped all the loose wires so none were rubbing on anything.
m

And other times, it's just that the supplier of the part is making
crap and it just keeps failing. I had that experience with a Sears
de-humidifier. The fan burned out, so I bought a replacement one.
It lasted less than a year. Then foolishly I bought one more.
That one burned out when it was first powered up. And yes, it was
wired in right, it was just a simple AC two speed motor.

Finally I started googling and saw that so many other people were
having exactly the same problem. But Sears just kept buying crap
from whoever the supplier was. Posts complaining about it went
back many years.

One choice might be to find a different Xformer supplier, even a slightly
different one as long as it can be mounted and the specs are equal
or better.

On Thursday, June 22, 2017 at 12:44:45 PM UTC-4, trader_4 wrote:
m

And other times, it's just that the supplier of the part is making
crap and it just keeps failing. I had that experience with a Sears
de-humidifier. The fan burned out, so I bought a replacement one.
It lasted less than a year. Then foolishly I bought one more.
That one burned out when it was first powered up. And yes, it was
wired in right, it was just a simple AC two speed motor.

Wait a minute, you got several years out of a dehumidifier?

How the heck did you do that?

TimR posted for all of us...



On Thursday, June 22, 2017 at 12:44:45 PM UTC-4, trader_4 wrote:
m

And other times, it's just that the supplier of the part is making
crap and it just keeps failing. I had that experience with a Sears
de-humidifier. The fan burned out, so I bought a replacement one.
It lasted less than a year. Then foolishly I bought one more.
That one burned out when it was first powered up. And yes, it was
wired in right, it was just a simple AC two speed motor.

Wait a minute, you got several years out of a dehumidifier?

How the heck did you do that?

He turned it off and never turned it back on.

--
Tekkie

On Wednesday, June 21, 2017 at 6:15:34 PM UTC-5, wrote:
On Friday, April 8, 2011 at 6:52:06 PM UTC-6, 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?

Our XR90 furnace did the same thing, I installed a 50W transformer instead of the stock 40W just in case it was underrated. I measured the operating output current during cool or heat and it maxes at .6 amps when 2.0 would be the limit. I cleaned up all the sloppy wiring from the installation and so far no blown fuses but with such an intermittent problem you never feel like you got it for sure. The only problem I could find was during heat call the red light would blink for 3 times indicating a problem with the safety pressure switch (enough gas pressure?). I temporarily bypassed the switch then it would latch and the heat would work fine. The only thing I can figure is that it the unit tries many times to turn on the heat and the pressure switch never makes the board commits suicide and deliberately blows the fuse so that you have to call a service man???? Sounds crazy but I wonder. I'll replace the pressure switch and see if the problem ever returns. For now I have a bunch of 2 amp (instead of 5A) fuses on hand to keep from blowing the transformer again. From the many web posts this seems like a common problem.


A common problem is thermostat wires getting pinched behind the thermostat and causing an intermittent short circuit. I ran across it a lot when I was still working. ヽ(ヅ)ノ

[8~{} Uncle Shorted Monster

Thu, 22
Jun 2017 13:11:03 GMT in alt.home.repair, wrote:

I've had 24V xformer burn out and it was due to a shorted wire.

It shouldn't have happened the instant the short occured. More
likely, it damaged the insulation on the secondary/possibly the
primary windings due to excessive heat build up from the short
circuit condition.

There is a lot of vibration in HVAC equipment and if there is a
wire touching a bracket or anything, it may eventually wear
through the insulation and create a short, often these are
intermittent and hard to see. The short blows the xformer.

The short won't blow the transformer right away...See above. You
*should* notice if the transformer was being shorted in such a
scenario the unit as a whole wouldn't run properly due to some
voltage loss caused by the bad wire(s). A transformer isn't a fuse
and we're not talking about MV or HV transformers that can blow in a
short period of time due to a short circuit condition. And the reason
they go ahead and blow is because you're dealing with alot! more amps
with alot more voltage present. So, the heat build up they experience
during a short circuit is much much higher and occurs much faster.

I was lucky to spot the bad wire in my case. I repaired the
short, installed a new xformer and added a PTC fuse device in
series with the secondary just in case. A regular fuse rated for
an amp or so above the xformer rating is a good idea. Also tie
wrapped all the loose wires so none were rubbing on anything. m

It's a low voltage transformer, so, you shouldn't have experienced
transformer failure the moment you shorted out the secondary. It had
to have been an ongoing issue for sometime to cause enough internal
damage to the transformer for it to have failed. And, as I wrote
previously, it's due to insulation breakdown on the secondary and/or
primary windings. Eventually leading up to popping the fuse (if the
primary is severely damaged). But, by then, you've essentially
already killed the transformer. So, the fuse is a final 'safety' to
try and reduce the chances of an outright fire in the unit.



--
https://tekrider.net/pages/david-brooks-stalker.php

Some people act crazy, others aren't acting.

On Friday, June 30, 2017 at 12:03:59 AM UTC-4, Diesel wrote:

Thu, 22
Jun 2017 13:11:03 GMT in alt.home.repair, wrote:

I've had 24V xformer burn out and it was due to a shorted wire.

It shouldn't have happened the instant the short occured.

Who said that it did? From what I see in this thread, people are
having problems with them burning out, they put a new one in and
it lasts for days or months, then it fails.

If it were me, I'd put an appropriate fuse temporarily on the low
voltage side to find out if it's failing from overload or if it's
just failing because it's Chinese crap.