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Old 01-17-2012, 12:08 AM   #1
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possible blown transformer, wiring problem?


I'm using a white rodgers 24v transformer in a control panel. The inputs are 120v white, 208v red, 240v orange, black com. I'm using the white 120v. Then on the 24v side is a blue wire and a yellow wire. The diagrams that came with it show the yellow being 24v out, and the blue being com.

I did have it wired incorrectly the first time I turned it on. I had the white connected to neutral, and the black connected to the 120v lead. I also had the blue and yellow switched. Could that have caused it to fry if that's what happened?

After wiring it up correctly and turning it on, I could hear a plastic crinkling like noise, and after a few minutes of it being on, I could see tiny wisps of smoke coming up from it. It also felt pretty warm. Does this mean the transformer is fried and no good? Why would it be doing this if it's now correctly wired?

**I just realized I didn't cover the red and orange wires' ends and they were touching slightly. I taped them up and tried it again. No crinkling on startup and it still isn't getting warm after a couple minutes of being turned on. I can still hear the hum though. So now I need to know if this thing is still good or not, since I did see a tiny bit of smoke before. To see if it works, can I just use a meter to see if the output voltage is around 24v? Would I connect the meter leads to the blue and the yellow, or would I have to connect the leads across a load?


Last edited by rtockstein; 01-17-2012 at 12:16 AM.
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Old 01-17-2012, 12:20 AM   #2
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possible blown transformer, wiring problem?


You probaly have a short in the low voltage side of system... thermostat, limit switch or gas valve, install a low voltage fuse(3amp or 5amp) inline with transformer common wire. then power up furnace, if fuse blows then you know you have a short. Then proceed to disconect wires from t-stat on circuit board and try again if fuse still blows then remove wires from gas valve and try and on down the line......

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Old 01-17-2012, 06:39 AM   #3
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possible blown transformer, wiring problem?


remove both sides of the TR in place and ring out (ohms setting) the wire pairs out each side 120V and 24V side if you don't get continuity on either it is shot...local grainger supply has then cheap and get on with a CB on the 24 side...your right on the 24V colors yellow is R... blue is C.sounds like it nuked out...on the low side.taping the un used primary wires is just for saftey but the common white is the only connection there between the 3 voltages...taps but a good practice but wasn't the cause if you have a control board within the furnace and the TR cooked be aware it shorted from there from the mis wire...
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Old 01-17-2012, 08:27 AM   #4
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possible blown transformer, wiring problem?


thanks for the advice from both! This should definitely help.
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Old 01-17-2012, 04:14 PM   #5
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possible blown transformer, wiring problem?


Quote:
Originally Posted by rtockstein View Post
thanks for the advice from both! This should definitely help.
I would guess it is fried, just went through the same thing on my heat pump...After it smoked it never worked again. I found the short in my heat pump outside. the 2 compressor wires were zip tied to a cooper tube and after 2 years they wore through to the wire

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Old 01-21-2012, 09:46 AM   #6
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possible blown transformer, wiring problem?


I used my meter and I've got continuity from the 120 hot to the 120 nuetral, and the 24 hot to the 24 neutral. I also wired it up correctly and measured 27V from the 24hot to the 24 neutral. So it's not fried, right?

Which is amazing, since I heard some crinkling and saw a tiny bit of smoke.
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Old 01-21-2012, 09:57 AM   #7
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possible blown transformer, wiring problem?


transformers and electrical motors all run on smoke.....but when the smoke gets out they are fried.

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