Blowing transformers for low voltage kitchen lights

I installed one of the sets of low-voltage under the cabinet kitchen lights (string of 5) and I'm having problems with blowing out transformers.
The first time it went out, I checked the power before and after the transformer. Before the transformer was good and after was nothing so I replaced the transformer (had to buy a new set of lights) and everything worked OK. About 2 weeks later the lights were out again.
I have a few sets of these lights and only one set of transformers is blowing out. The others seem good although the lights seem to go out sooner than I would have thought they should. I had an electrician come infor other things and asked him about it. No clue without doing extensive testing. Thought maybe some of the neutrals on the breaker box may be loose and need tightening.
I'm also having some problems with other lights in the house frequently going out soon after replacing them. Other than crappy bulbs, any ideas on what may be causing this?
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What's the rating of the transformer and wattage of the bulbs?
Are you using made in China crap?
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Pls see inline:
:I installed one of the sets of low-voltage under the cabinet kitchen : lights (string of 5) and I'm having problems with blowing out : transformers.
===> HOW are the transformers "blowing out"? Simply stops working? Smokes? Pops? : : The first time it went out, I checked the power before and after the : transformer. Before the transformer was good and after was nothing so : I replaced the transformer (had to buy a new set of lights) and : everything worked OK. : About 2 weeks later the lights were out again. : : I have a few sets of these lights and only one set of transformers is : blowing out. The others seem good although the lights seem to go out : sooner than I would have thought they should.
===> Something doesn't sound right in either: # & type of bulbs used, transformer rating/size, xfmr location (no air flow), or applied primary voltage.
: I had an electrician come infor other things and asked him about it. : No clue without doing extensive testing. ===> Interpret that as "don't want to bother with it" or "you won't pay me what it;s worth". Whatever, it doesn't require "extensive" testing. Thought maybe some of the
: neutrals on the breaker box may be loose and need tightening. ===> That was blowing the transformers? Not very likely. It sound like maybe he had a no-fault-found service call and just wanted to move on.
: : I'm also having some problems with other lights in the house frequently : going out soon after replacing them. Other than crappy bulbs, any : ideas on what may be causing this?
===> Maybe crappy bulbs if you're buying them all at the cheapest location you can find and they're no-names. Another possiblity though is that your house voltage is either high all the time or goes high for long periods of time. THAT might amount to a little work to dig thru if it's intermittantly high voltages, but ... it's pretty easy to figure out in some ways, not always.
What did you measure at the input to the transformer? It should have been around 115 to about 122 volts. If it's 126Vac or more, then it's a high power into the house causing the bulbs to burn out quickly and, if the design were poor enough, might, not will, explain why transformers might give up. There is probably a fuse internal to the transformers which opens up. Not replaceable so don't even look; they're internal to the windings.
Do you have the right number of bulbs for the transformer you are using? Is the xfmr the one intended for that number of bulbs? What wattage are the bulbs? What voltage are the bulbs? What are the ratings on the transformer? It should be printed right on it. Do you ever notice any other lights going bright or dim in the house? Like when an electric motor starts.
It's possible, with a cheapie sysem, that one bulb blowing could cause damage to the transformer under "normal" voltages. Is there always a blown bulb when the xfmr goes bad?
HTH,
Pop
:
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all good points! The only indication of a problem is all the lights (5) on the string go out. Not being an expert electrician; all of the transformers and lights including bulbs are sold as a "set." When I mentioned checking the power I just checked to see if there was power before and after the transformer. The transformer (it's only 1x1x2 in) is mounted on the underside of the cabinet so it's not enclosed and has alot of air space. It's the transformer that came with the set. The wires connecting all the lights are located between the bottom of the original cupboards and a new bottom used to house the lights. There's a 1/2 in space between these two for air. I bought a new set to match the one with the bad transformer and "spliced" in new transformer. It was the only way I could do it since the power from wall switch comes through the back of the wall by the underside of the cabinet. Just could be that it's a cheap set of lights. Bought it at Lowes.
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Rick wrote:

I put some of these in for a client, three sets. I notice the transformers read 20VA. I have some other types in my own kitchen that have wall warts the same size but these are switch mode types and read 60VA. I actually replaced one set of 3 of these with a transformer unit thats 6 times the size but still reads 60 VA. I replaced the latter because the cheap supplies kept blowing out, except for one which is still working. The client wanted just one switch for all three sets so I replaced the 3 transformers with one switchmode type supply that I got from a local electrical distributor. As I recall it cost $80 and supplied 150VA. They had others that supplied more at an appropriate rise in cost. That electrician you hired should at least have pulled the cover on the box and inspected the neutral. I used to have a chart recorder that I used for long term monitoring like this. I have another client that has a similar voltage fluctuation problem. She's at the end of the feed coming from the transformer and I can count 3 splices from the transformer to her house. Now the problem is to convince the power company they have a problem. Richard
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For high current needed for the brighter bulbs a transformer would need to be physically quite large. The high cost of the copper inside and the shipping cost adds up quickly, for higher current a switching supply is definately more economical and if overloaded will self current limit to prevent damage to the load or supply. A transformer on the otherhand if overloaded will try to supply too much current, get hot and eventually fail. Where you mount the transformer and how well the heat can escape can have a strong effect on how quickly it would fail.
Barring voltage variation problems which are not very common, I would guess you have used bulbs of too high wattage for the selected transformer. Don't try and use all of the rated capacity of a transformer unless you have mounted it in a well cooled area. If you have it shut up in a small compartment you may need to derate its capacity by as much as 50%.
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many of these "transformers" are actually switching power supplies which is why they can make them so small and light weight
and they create radio and TV interference....
I took mine out and installed a 120 Volt lighting system...
Mark
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