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Question DetailsAsked on 7/22/2014

Why my transformer in 12V track getting overheated when I switch bulbs to LED bulbs?

I got 5 bulbs in track light. Each of it was 20W, so I decided to switch them to LED bulbs. After about 1-2 hr the light of that track went off. I touched the transformer and it was very hot. Am I saving energy or using even more in this case? What is going on?

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5 Answers

Voted Best Answer

As Don said - the transformer should have a rating on it, in Watts. Your total lighting bulb load on the system should not exceed about 80% of that wattage. Where you get in trouble with LED and CFL bulbs is the rated wattage for the bulb is not the total wattage it draws - the controlling electronics pulls some power too - I checked a CFL bulb for instance, and an 18W bulb was pulling 21W.

So, even thought the rated wattage of the bulbs does not exeed about 80% of the rating of the transformer, the total load might.

Also - I am presuming this is not on a dimmer - because most CFL and LED bulbs do not work on dimmers - they overhead and increase their power demand.

One other issue might be a transformer rating - commonly these days UL is letting them put the maximum capacity on transformers as if it were the rated load - so they run at near-failure heat when they should be running at maybe75-80% maximum of that load. And, commonly, they come with lamps whose wattage equals the transformer rating, so by the time you put in line losses and connection losses and such, they are actually pulling more power than the transformer is rated for right out of the factory.

If the transformer is getting to hot to hold your hand against indefinitely, it is too hot and shoulde considered a risk under that condition.

Answered 6 years ago by LCD


Something seems wrong here. If you have a transformer the only bulbs that are LED that I have seen in local stores are not low voltage. I may be wrong but I would check the package to see what the voltage of the new bulbs are.


Answered 6 years ago by ContractorDon


Hi, I am using 12V LED bulbs, but I guess I added up one bulb than original one was made. I took this bulb off and I see that helps. But I still don't know how much power my transformer is using even that I am using 4x3W LED bulbs. Can somebedy unswer me this? If I hear more noise from transformer using dimmer does that mean the transformer is working harder using more power?

Source: robaczek2000

Answered 6 years ago by robaczek2000


Oops- I forgot to ask if on a dimmer. Most LED and CFL bulbs cannot handle dimmers, and those that can commonly require a specific type of electronic dimmer.

If you hear a noticeable hum from the transformer tht likely means it is working harder than it should - and pulling a lot more juice. It is highly likely that a LED/CFL bulb life will drop VERy dramatically, because when on the dimmer the electronics are trying hard in their startup mode - except continuously. Like a flourescent bulb trying to start but can't when it is old - continuously trying to start so uses a lot more juice.

Check your bulb packaging or read intructions on manufacturer website as to whether they can be used with a dimmer - my guess would be no.

As for watrage - your bulb load should not be more than 80% of transformer rating, marked on the transformer - or on the head if integrated transformer/head. Originally you had 5 - 20W bulbs, so 100W bulb load, so transformer should have been rated for 120W or more. With the new bulbs you have 4 - 3W = 12 watts so way less bulb wattage, which would be OK IF not on a dimmer.

Answered 6 years ago by LCD


I was using 5 bulbs 20W each and had no problem with the transformer. Now when I switched to 5 LED bulbs 3W each my transformer is getting hot and after aproxemetely 2 hr it is shutting iff. I am not sure what kind of dimmer I have (LED compatible or not) but when I dimm my light I do not see any blinking effect. It is continuous. So what is going on that my transformer is getting so hot with15W usage? Maybe the Amps have to play the main role. Please help!

Answered 6 years ago by robaczek2000


Did not see your last post when it was posted for some reason - you are talking about a dimmer on the system, so I am guessing you are using LED bulbs that cannot work on a dimmer system - as you turn the dimmer down, the voltage to the CFL bulb drops down to the point where it goes into continuous start mode, burning up a lot of juice (like a flourescent bulb starting up), causing transformer overheating. This is going to burn out the transformer and the LED bulbs and maybe dimmer switch too, whether or not they are flickering - not to mention a fire hazard from the overheating.

Check lighting manufacturer info on suitable types of bulbs - but I am guessing your system says incandescent only, no CFL or LED - or if and old system may not address that at all. May also be that the transformer/lighting system can handle it, but the dimmer combined with the LED bulbs is the problem, which may only be solveable by getting dimmer-compatible LEd bulbs, which are rare and more costly.

Your only solution may be to stay with incandescent or halogen bulbs (whatever you had), or change out the fixtures and/or dimmer. Electrician should be able to figure it out too - maybe, many are not too up to speed on LED and CFL fixtures.

Answered 5 years ago by LCD

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