I was called today to assist the burner repair guy with an electrical problem in one of the apartment houses I work in. He wasn't able to get correct voltages at one of the zone valves.

I heat my home entirely with wood, so first let me say that what I know about heating systems could fit into a very small vessel. But I offered my assistance as an electronics technician.

There was a bank of 24 volt transformers, each feeding two apartment's zone valves. And two of these apartments had no heat. He told me that the transformer was a 40 volt unit, he went on to say that it was good, and attempted to demonstrate this by measuring across each secondary terminal and ground. When doing this he measured 40 volts from each secondary screw to building ground. I had to look twice at this to believe it. There was indeed from each screw to ground 40 volts!

So my next best guess was that perhaps it is a 40 volt unit and with a center tap to case ground. So half expecting to see 80 volts across the secondary I read 0 volts. However I did confirm the rating on the label. It was a 24 volt non tapped transformer and an ohm meter check between each secondary terminal and ground showed infinity. And interestingly the same check across the two secondary terminals showed 1 ohm.

We replaced the transformer with a new 24 volt unit and restored the heat in the two apartments. I asked for the transformer. I may have a chance to autopsy it after the guy shows it to his boss. Whether I'll notice anything would remain to be seen.

This problem seems to defy all logic. Does anyone have any thoughts as to what could be going on here? Lenny

wrote:


So my next best guess was that perhaps it is a 40 volt unit and with a
center tap to case ground. So half expecting to see 80 volts across the
secondary I read 0 volts. However I did confirm the rating on the label.
It was a 24 volt non tapped transformer and an ohm meter check between
each secondary terminal and ground showed infinity. And interestingly the
same check across the two secondary terminals showed 1 ohm.
VERY strange. My guess is there was a failure of the primary that
shorted a spot on the primary to the secondary. (This should NEVER
happen!) The primary was open, the secondary was being energized
from a spot on the primary where there was a lot of inductance, therefore
it didn't go all the way to 120 V. That would explain all the readings
you got, but this sort of short should NOT be possible. You may find
a non-infinite resistance reading between one of the primary wires
and the secondary.

It is also possible that there was enough capacitance between primary
and secondary to give the 40 V reading without an actual short.

Jon

On 9/04/2014 8:41 AM, Jon Elson wrote:


It is also possible that there was enough capacitance between primary
and secondary to give the 40 V reading without an actual short.

**BINGO! That is the only explanation which makes sense.


--
Trevor Wilson www.rageaudio.com.au

In article ,
Trevor Wilson wrote:

On 9/04/2014 8:41 AM, Jon Elson wrote:


It is also possible that there was enough capacitance between primary
and secondary to give the 40 V reading without an actual short.

**BINGO! That is the only explanation which makes sense.

Everybody today thinks that a digital multimeter is the be all to end
all.

Give me a good old Simpson 260 any day.

CP.

On 4/8/2014 8:24 PM, Pilgrim wrote:
In article ,
Trevor Wilson wrote:

On 9/04/2014 8:41 AM, Jon Elson wrote:


It is also possible that there was enough capacitance between primary
and secondary to give the 40 V reading without an actual short.

**BINGO! That is the only explanation which makes sense.

Everybody today thinks that a digital multimeter is the be all to end
all.

Give me a good old Simpson 260 any day.

CP.


Fluke makes a small cube that plugs into the meter and the leads plug
into it. It has a resistor that lowers the impedance of the meter.

On 9/04/2014 12:24 PM, Pilgrim wrote:
In article ,
Trevor Wilson wrote:

On 9/04/2014 8:41 AM, Jon Elson wrote:


It is also possible that there was enough capacitance between primary
and secondary to give the 40 V reading without an actual short.

**BINGO! That is the only explanation which makes sense.

Everybody today thinks that a digital multimeter is the be all to end
all.

Give me a good old Simpson 260 any day.

CP.


**I have a Simpson 260.

I never use it. It is purely decorative. Same as my AVO 8 and AVO 7 meters.

--
Trevor Wilson www.rageaudio.com.au

On Thu, 10 Apr 2014, Trevor Wilson wrote:

On 9/04/2014 12:24 PM, Pilgrim wrote:
In article ,
Trevor Wilson wrote:

On 9/04/2014 8:41 AM, Jon Elson wrote:


It is also possible that there was enough capacitance between primary
and secondary to give the 40 V reading without an actual short.

**BINGO! That is the only explanation which makes sense.

Everybody today thinks that a digital multimeter is the be all to end
all.

Give me a good old Simpson 260 any day.

CP.


**I have a Simpson 260.

I never use it. It is purely decorative. Same as my AVO 8 and AVO 7 meters.

The only analog meter I had was some Japanese import, used when I got it
and missing the back cover. It lasted no more than six months, my fault.
The usual problem, trying to measure voltage when in the ohms position.
Or too much voltage. Soon the needle was bent, from hitting the stop too
hard too many times, and then later it practically wrapped itself around
the stop.

I was lucky, got the use of an HP410B, which actually went back to the
owner at some point, then became mine when he was moving and getting
ridding of the "excess" (I think he had two other 410Bs).

I have a Voltohmyst that I solid stated, and then a few years ago found
another Voltohmyst lying by itself in a box on a busy street with no other
garbage near it. I hadnt' gone along that street in a long time, yet
there it was for me.

And a Radio Shack DMM in 1984, so I've never looked back. Yes, in a few
circumstances an analog meter is more useful, but not by much. And there
are ways of checking to make sure you aren't getting a phantom reading.

Note that a VOM wouldn't put much of a load on the circuit. Weren't the
good ones generally 20,000 ohms per volt? Assuming a 100volt range,
that's 2megs. A fifth of a 10meg input DMM or VTVM. Maybe enough, maybe
not.

Michael

wrote in message
...

I was called today to assist the burner repair guy with an electrical
problem in one of the apartment houses I work in. He wasn't able to get
correct voltages at one of the zone valves.

I heat my home entirely with wood, so first let me say that what I know
about heating systems could fit into a very small vessel. But I offered my
assistance as an electronics technician.

There was a bank of 24 volt transformers, each feeding two apartment's zone
valves. And two of these apartments had no heat. He told me that the
transformer was a 40 volt unit, he went on to say that it was good, and
attempted to demonstrate this by measuring across each secondary terminal
and ground. When doing this he measured 40 volts from each secondary screw
to building ground. I had to look twice at this to believe it. There was
indeed from each screw to ground 40 volts!

So my next best guess was that perhaps it is a 40 volt unit and with a
center tap to case ground. So half expecting to see 80 volts across the
secondary I read 0 volts. However I did confirm the rating on the label. It
was a 24 volt non tapped transformer and an ohm meter check between each
secondary terminal and ground showed infinity. And interestingly the same
check across the two secondary terminals showed 1 ohm.

We replaced the transformer with a new 24 volt unit and restored the heat in
the two apartments. I asked for the transformer. I may have a chance to
autopsy it after the guy shows it to his boss. Whether I'll notice anything
would remain to be seen.

This problem seems to defy all logic. Does anyone have any thoughts as to
what could be going on here? Lenny





I would hazard a guess that the secondary winding had shorted into the
primary winding.


Gareth.

pretended :
I was called today to assist the burner repair guy with an electrical
problem in one of the apartment houses I work in. He wasn't able to get
correct voltages at one of the zone valves.

I heat my home entirely with wood, so first let me say that what I know about
heating systems could fit into a very small vessel. But I offered my
assistance as an electronics technician.

There was a bank of 24 volt transformers, each feeding two apartment's zone
valves. And two of these apartments had no heat. He told me that the
transformer was a 40 volt unit, he went on to say that it was good, and
attempted to demonstrate this by measuring across each secondary terminal and
ground. When doing this he measured 40 volts from each secondary screw to
building ground. I had to look twice at this to believe it. There was indeed
from each screw to ground 40 volts!

So my next best guess was that perhaps it is a 40 volt unit and with a center
tap to case ground. So half expecting to see 80 volts across the secondary I
read 0 volts. However I did confirm the rating on the label. It was a 24 volt
non tapped transformer and an ohm meter check between each secondary terminal
and ground showed infinity. And interestingly the same check across the two
secondary terminals showed 1 ohm.

We replaced the transformer with a new 24 volt unit and restored the heat in
the two apartments. I asked for the transformer. I may have a chance to
autopsy it after the guy shows it to his boss. Whether I'll notice anything
would remain to be seen.

This problem seems to defy all logic. Does anyone have any thoughts as to
what could be going on here? Lenny

What did you measure the 40 volts with ? Digital volt meter I suppose.
Why did the Tech (Electrical?) tell you they were 40 volt units when
the label said 24 volts?

Since end to end of secondry is 1 ohm, of course the volts to ground
will be the same both ends. :-?
It is most likely the primary is open and all the volts are just
coupling from the line to the secondry.
You did not tell us the continuity of the primary. :-?

--
John G

This problem seems to defy all logic.

** The reading is normal.

Does anyone have any thoughts as to what could be going on here?


** There is about 100pF of capacitance from primary to secondary.

The primary winding is all at 120V AC since the neutral end is not
onnected - due to corroded wire, open thermal fuse etc .

The meter has a 10Mohm input impedance.


..... Phil

On Tuesday, April 8, 2014 5:33:59 PM UTC-4, wrote:
I was called today to assist the burner repair guy with an electrical problem in one of the apartment houses I work in. He wasn't able to get correct voltages at one of the zone valves.



I heat my home entirely with wood, so first let me say that what I know about heating systems could fit into a very small vessel. But I offered my assistance as an electronics technician.



There was a bank of 24 volt transformers, each feeding two apartment's zone valves. And two of these apartments had no heat. He told me that the transformer was a 40 volt unit, he went on to say that it was good, and attempted to demonstrate this by measuring across each secondary terminal and ground. When doing this he measured 40 volts from each secondary screw to building ground. I had to look twice at this to believe it. There was indeed from each screw to ground 40 volts!



So my next best guess was that perhaps it is a 40 volt unit and with a center tap to case ground. So half expecting to see 80 volts across the secondary I read 0 volts. However I did confirm the rating on the label. It was a 24 volt non tapped transformer and an ohm meter check between each secondary terminal and ground showed infinity. And interestingly the same check across the two secondary terminals showed 1 ohm.



We replaced the transformer with a new 24 volt unit and restored the heat in the two apartments. I asked for the transformer. I may have a chance to autopsy it after the guy shows it to his boss. Whether I'll notice anything would remain to be seen.



This problem seems to defy all logic. Does anyone have any thoughts as to what could be going on here? Lenny

I never thought to look at primary resistance, or for that matter resistance between primary and secondary. That could be a pretty serious failure, especially if you weren't expecting it. If I get this thing back I'll do some more tests on it and let you guys know. Lenny

On Tuesday, April 8, 2014 5:33:59 PM UTC-4, wrote:
I was called today to assist the burner repair guy with an electrical problem in one of the apartment houses I work in. He wasn't able to get correct voltages at one of the zone valves.



I heat my home entirely with wood, so first let me say that what I know about heating systems could fit into a very small vessel. But I offered my assistance as an electronics technician.



There was a bank of 24 volt transformers, each feeding two apartment's zone valves. And two of these apartments had no heat. He told me that the transformer was a 40 volt unit, he went on to say that it was good, and attempted to demonstrate this by measuring across each secondary terminal and ground. When doing this he measured 40 volts from each secondary screw to building ground. I had to look twice at this to believe it. There was indeed from each screw to ground 40 volts!



So my next best guess was that perhaps it is a 40 volt unit and with a center tap to case ground. So half expecting to see 80 volts across the secondary I read 0 volts. However I did confirm the rating on the label. It was a 24 volt non tapped transformer and an ohm meter check between each secondary terminal and ground showed infinity. And interestingly the same check across the two secondary terminals showed 1 ohm.



We replaced the transformer with a new 24 volt unit and restored the heat in the two apartments. I asked for the transformer. I may have a chance to autopsy it after the guy shows it to his boss. Whether I'll notice anything would remain to be seen.



This problem seems to defy all logic. Does anyone have any thoughts as to what could be going on here? Lenny

I forgot to mention, yes we did use a digital meter to look at this. I thought about bringing my 260 in to look at it and probably should have just to make sure I wasn't looking at noise. I will check it with a low impedance meter when I get it back. Lenny

On Tuesday, April 8, 2014 5:33:59 PM UTC-4, wrote:
I was called today to assist the burner repair guy with an electrical problem in one of the apartment houses I work in. He wasn't able to get correct voltages at one of the zone valves.



I heat my home entirely with wood, so first let me say that what I know about heating systems could fit into a very small vessel. But I offered my assistance as an electronics technician.



There was a bank of 24 volt transformers, each feeding two apartment's zone valves. And two of these apartments had no heat. He told me that the transformer was a 40 volt unit, he went on to say that it was good, and attempted to demonstrate this by measuring across each secondary terminal and ground. When doing this he measured 40 volts from each secondary screw to building ground. I had to look twice at this to believe it. There was indeed from each screw to ground 40 volts!



So my next best guess was that perhaps it is a 40 volt unit and with a center tap to case ground. So half expecting to see 80 volts across the secondary I read 0 volts. However I did confirm the rating on the label. It was a 24 volt non tapped transformer and an ohm meter check between each secondary terminal and ground showed infinity. And interestingly the same check across the two secondary terminals showed 1 ohm.



We replaced the transformer with a new 24 volt unit and restored the heat in the two apartments. I asked for the transformer. I may have a chance to autopsy it after the guy shows it to his boss. Whether I'll notice anything would remain to be seen.



This problem seems to defy all logic. Does anyone have any thoughts as to what could be going on here? Lenny

So this "cube", does it present a low impedance to the meter and maintain the high impedance to the circuit, or is it the opposite? Is this an active or passive device? And if a passive device how can something like this not affect the reading? Lenny

wrote:
So this "cube", does it present a low impedance to the meter and
maintain the high impedance to the circuit, or is it the opposite?
Is this an active or passive device? And if a passive device how
can something like this not affect the reading? Lenny

From the description, it's purpose *is* to affect the reading. Think
about the case you described: if you had used a low impedance meter,
you would not have gotten a 40v reading due to interwinding
capacitance. Sometimes you *want* to load the circuit.