Under Cabinet Lights

A few years ago I installed a set of 5 "under cabinet" halogen light fixtures. These are the 12v 20 watt variety.
This week two of the 5 lights became inoperative - I suppose they "burnt out". I had two new unopened 12v 20 w halogens, that I installed in place of the burned out lamps. When I turned on the power, NONE of the 5 lights would turn on. I removed the "new" lamps, leaving 2 vacant sockets - and when turning on power, the three original lamps turned on. I took one of the "good" lamps and placed in it the socket that previously had one of the burned out bulbs, it worked fine. I went to the hardware store and purchased another fresh 12v 20w halogen...tried it.....no luck....same as before, all 5 lights were out.
I note that the transformer indicates 12v......I also measured about 12v ac at the sockets. I did not handle the bulbs with bare fingers.
I'M STUMPED........anyone have any idea of what's going on here? Any troubleshooting suggestions?
thanx =neal
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We have those lights too. Wish I had never seen them. They play hell with every radio (AM band) in the house when they are lit. Des

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I have them too and like them. Only problem I've had is with the 3 stage dimmer. I have an old 1980 cordless phone that I really like. Every time the phone would ring the lights would turn on to full power. UL listed or not, I don't like the idea of those lights being on full blast when I'm at work or on vacation...they do generate a ton of heat just a fraction of an inch away from the wood. Solution was to buy a new 2.4 ghz phone which sucks compared to my trusty 24 year old ITT.
To the OP:
That's an odd problem. My best guess would be that the transformer is on the way out. When you add the good bulb, the transformer can't handle the load and it drops out. You also mentioned 2 bulbs went out this week...more proof of something odd happening with the transformer. Possibly was hit with a voltage spike or it's just going bad. Was this a prepackaged kit? 5 lights on one transformer sounds like 2 too many. Not sure what your setup is like, but on mine each set of 3 lights is controlled by one transformer, for six lights I have 2 transformers and 2 distribution blocks. Both transformers also connect to a dimmer control box. I would first check all those connections, especially at the distribution blocks. If no problems are found there I would bet a new transformer will solve your problem.
George
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Neal Wessler wrote:

Could it be the lights were designed from lights less than 20W, like 10W maybe? Putting higher wattage lamps in there would draw more current and the power supply may be shutting down.
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Joseph E. Meehan

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Check that your 2 new replacement bulbs aren't the newer 120 volt variety. These "puck lights" have gone to line voltage now.
If it is you're causing a direct short by using a 120v bulb in a 12v transformer.
They're very pretty when lit, unfortunately, both varieties (12 & 120v) don't have a good long bulb life. I recommend replacing the bulbs with 10 watt bulbs of the 12v variety, they seem to last a lot longer and don't put out noticably less light.
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Here wrote:

I have yet to see a 20W 120V, but if there is one, it would not short out nor overload the supply, but just run very dim. It is use of lower voltage (higher current) bulbs on higher voltage supplies that causes problems.

10 watt normally produces 150 lumens. 20 watt normally produces 350 lumens.
If the 10 watt is almost as bright as the 20 watt, then the 20 watt is loading the voltage down or is a junky off-brand one. Are your failed bulbs showing a smoky appearance that indicates a sign of air leaking in? Possible causes: Bad bulb, bulb overheating due to poor fixture design, bulb contaminated by ash, salt or alkali is cracking (these materials leach into quartz if the quartz is hot enough, causing weak spots and stresses in the quartz).
- Don Klipstein ( snipped-for-privacy@misty.com)
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snipped-for-privacy@aol.com (HA HA Budys Here) wrote:

Actually no. It will light at 10% (if at all). A higher voltage bulb is no problem.
Putting a 12v bulb in a 120v outlet, is like a direct short, since it has 1/10 the resistance.
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Neal:
NW> A few years ago I installed a set of 5 "under cabinet" halogen light NW> fixtures. These are the 12v 20 watt variety. NW> NW> This week two of the 5 lights became inoperative - I suppose they NW> "burnt out". I had two new unopened 12v 20 w halogens, that I NW> installed in place of the burned out lamps. When I turned on the NW> power, NONE of the 5 lights would turn on. I removed the "new" lamps, NW> leaving 2 vacant sockets - and when turning on power, the three NW> original lamps turned on. I took one of the "good" lamps and placed in NW> it the socket that previously had one of the burned out bulbs, it NW> worked fine. I went to the hardware store and purchased another fresh NW> 12v 20w halogen...tried it.....no luck....same as before, all 5 lights NW> were out. NW> NW> I note that the transformer indicates 12v......I also measured about NW> 12v ac at the sockets. Strange! At this point you have told us part of what we need to know. The transformer is rated at 12v, and is putting out 12v -- under load or no load? If you measured without a load (bulbs off/removed) then try it with the bulbs. It is possible with the full load the transformer can no longer handle the load (thermal cut-off failure?) and either shuts off completely or put out a very low voltage.
Five 12v bulbs at 20 Watts is a 100 Watt load. Three is a 60W load.
It's possible when one of the failed halogen bulbs went out it overloaded the transformer's internal protection circuit which is now causing it to run OK at the 60W load but not 100W. (I don't recall reading if you tried four bulbs but since you want five doesn't really matter.) I would try replacing the transformer with one rated for above 100W service.
- barry.martinATthesafebbs.zeppole.com
* Man who run behind car get exhausted.Man run in front of car get tired
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Joseph:
JM> > A few years ago I installed a set of 5 "under cabinet" halogen light JM> > fixtures. These are the 12v 20 watt variety. JM> Could it be the lights were designed from lights less than 20W, like 10 JM> maybe? Putting higher wattage lamps in there would draw more current and JM> the power supply may be shutting down. But didn't the OP indicate the five halogen bulbs worked prior to the two burning out? Too much current could cause a transformer to trip if it had a built-in overcurrent device. I was thinking in my previous reply when the first bulb failed it could have damaged the overcurrent protection.
- barry.martinATthesafebbs.zeppole.com
* Do not use a toupee as a Frisbee.
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