Just as a different way to express what I see as the problem. A doorbell
transformer is used for short bursts and not continued use, therefore
the 50VA that it is rated is probably not continuous duty, sort of like
a welder. Radio shack used to sell lots of parts for electronics
projects, but dropped them in favor of cell phone skins and other higher
volume parts. As someone else stated, you may have to find an
electronics parts store, but you can always order a transformer from
Digi-key or Mouser. Another place to try would be an A/C supply parts
store. They may have 24V transformers even though most furnaces I've
seen have been 12V. I would suggest looking for a 3A or 4A transformer.
Something else to try would be connecting a couple of car batteries in
series and measuring the current draw of the light. Remove the light
bulbs and make sure that the current drops to zero, indicating that the
wires aren't shorted.
Good luck and let us know what you find.
Peace,
Pat
Thusly spake Jim Stone:
> Thanks guys. I suspect this is the problem. I did discover shortly
> after posting this that I was mistaken about the transformers being DC;
> both the original one and the doorbell ones are AC. Fortunately, I
> decided to save the original one until I had permanently fixed the light.
> The
> original transformer output is 24VAC-50VA, while the doorbell one is
> 24VAC-20VA. Not four times as John suspected, but I am sure that 2.5 times is
> way too much. Plus, as everyone guesses, the doorbell ones are almost
> definitely not designed for a continuous load. Now, I just have to find the
> right transformer. I don't think any of the big box stores carry them; I'll
> do a little surfing and see what I can come up with.
>
> Thanks again.
>
>
>> From: rlwhitetr3b@hotmail.com
>> To: shop-talk@autox.team.net
>> Date: Sat, 1 Mar 2008 14:09:42 -0600
>> Subject: Re: [Shop-talk] Mystery of the blown transformers
>>
>> Jim,
>>
>> I think your problem is that the replacement transformer is not up to the
>> job.
>> As others has said you could calculate the cold resistance, but maybe it
>>
> would
>
>> be better to measure the current before dies.
>>
>> When picking out a replacement, you have to look at the continuous load
>> rating. A door bell would be a very short duration load and I would not
>> expect the transformer to handle its rated output continuously.Rich White
>>
> St.
>
>> Joseph, IL USA
>> '63 TR3B TCF587L
>> That ain't a scrap pile, that is my car!
>> See it moves!
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--
Pat Horne, Owner, Horne Systems
(512) 797-7501 Voice 5026 FM 2001
Pat@HorneSystemsTx.com Lockhart, TX 78644-4443
www.hornesystemstx.com
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