Door bell trans burning up

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mark32

mark32

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Currently in NJ
A GC told me today that he's recently gone through two 24v transformers that power the door bell chimes in a six apartment complex. He drew me a diagram as to how he hooked them up (At least how he believes he did) and it looked good but I've only done single family deals before so I'm unsure what one does in this situation. He said the transformer would get quite hot even though there was no apparent load on it.
 
mark32 said:
He said the transformer would get quite hot even though there was no apparent load on it.
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I cooked a doorbell transformer once, but only because I had a short circuit on it. It left a pretty nasty smell in the basement. :D

It sounds to me like there is a short somewhere.
 
mark32 said:
A GC told me today that he's recently gone through two 24v transformers that power the door bell chimes in a six apartment complex. He drew me a diagram as to how he hooked them up (At least how he believes he did) and it looked good but I've only done single family deals before so I'm unsure what one does in this situation. He said the transformer would get quite hot even though there was no apparent load on it.
Click to expand...

I believe that 24 volts will burn out the light bulb in most lighted buttons but I am not sure why it is burning out the trany unless it is wired wrong.

16 volts is pretty standard for bells around here perhaps he has a different system but I still believe it is shorting out the trany.
 
peter d said:
I cooked a doorbell transformer once, but only because I had a short circuit on it. It left a pretty nasty smell in the basement. :D

It sounds to me like there is a short somewhere.
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On two different jobs had door bell buttons stick, burnt the plunger in the chime up pretty good.
 
stickboy1375 said:
On two different jobs had door bell buttons stick, burnt the plunger in the chime up pretty good.
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Hopefully it wasn't one of those fancy chimes that cost $50. ;) I'm partial to the builders kit for $10.99 myself. :D
 
peter d said:
Hopefully it wasn't one of those fancy chimes that cost $50. ;) I'm partial to the builders kit for $10.99 myself. :D
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Interesting point here. I always use the Nutone LB 14 recessed chime. It cost about $40. The builders kit from Nutone is $10 or so. The internal parts of the recessed chime are the exact same guts as the cheap chime. When I have one go bad-- not very often- I replace it with the $10.00 kit.

Back to the topic. Have you all hooked up these chimes to 24 volts. I did that once on a tri tap trany and the buttons got very hot and bulbs did not last.
 
peter d said:
No great loss then. :D
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I dont replace them either, I just move the wire to the other plunger... :grin:



I found the problem to why the transformers keep blowing up....



mark32 said:
A GC told me today that he's recently gone through two 24v transformers that power the door bell chimes in a six apartment complex. He drew me a diagram as to how he hooked them up
Click to expand...
 
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There are certainly 24V doorbells, particularly in apartment buildings. Edwards style bells and buzzers, particularly, which are/were favored in apartment buildings. The guy really needs to ohm out the secondary side conductors to find out the real scoop. With no buttons pressed, there should be zero ohms. Anything more than that and you've got yourself a happy hunting trip for most or all of a day. :grin:
 
Dang you guys are fast tonight. Well despite the guy's claims of being an electrician as well as a GC, it didn't seem like he knew what he was doing. From what I gather, for some reason, he only hooked up one of the apartments so far and at first it didn't work. Then after some tinkering he got it to work but then the transformers started to burn up. On the way home the thought of there being a short did cross my mind, but hey, he did say he wired it right ;) Thanks again for the responses.

Mark
 
080522-0607 EST

Marc:

Did you mean to say infinite ohms instead of zero? But if there are lights in the buttons there will be some moderately low resistance, but not zero.

An 1819 pilot lamp is 82 ohms cold, and is rated 28 V @ 0.035 A or 800 ohms hot. These are approximately a constant current device relative to applied voltage. My guess is that a lamp in a pushbutton will have a lower current than the 1819. Thus, on a single pushbuttom I would expect less than 35 MA.

mark32:

Do Marc's resistance check and see if there is a short. Also measure a pushbutton alone and see what is it's cold resistance for comparison with your loop resistance check. Also you can check the current when the load is connected to the transformer. Note the pushbutton lamp resistance is in series with the chime resistance when you do the loop resistance check. If there are multiple pushbuttons on a single chime, then the multiple lamp resistances are in parallel.

What is the VA rating of the transformer? Note an 1819 lamp on 24 V would be about 24*0.035 = 0.84 VA. I expect the transformer rating is maybe 10 to 25 VA continuous duty. Also check the input voltage to the transformer.

.
 
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