Why is my transformer so hot?

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goofeedad

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I have an AC transformer that reduces 110VAC to 36VAC it is rated at 1.5A, I'm runnning 2 seprate circuits off of it. Each circuit reportedly draws 0.66A or 1.32A for the 2 of them. My circuits run perfectly but, the transformer gets incredibly hot. I don't want the heat or the power lose to the heat.

Do I need a seperate transformer for each circuit to keep the heat down? Even though I know I will still be losing the energy from a transformer?

I plan on having 4 of the ciruits later and I just can't see having 4 of these transformers in my project.

Is a switching power supply my answer? And how do I make switching supply to handle the VAC and the current I need?

I know that was alot to ask but, any constructive help would be greatly appreciated.
 
Running a 1.5A transformer at 1.32A will generate heat. If you are concerned, get a bigger transformer for that load.
 
Mike2545 said:
Running a 1.5A transformer at 1.32A will generate heat. If you are concerned, get a bigger transformer for that load.
Click to expand...

Well, good answer but that's not really an option. I am trying to make a circuit like one I saw. It was powering similar circuits without a transformer (for the circuits anyway). It never generated any heat that I ever noticed (I'm sure there was some) and was all on a mid sized circuit board.
 
If it gets "incredibly" hot, I wonder if there is more to the story than meets the eye. A properly loaded transformer of the type you mentioned should not get "incredibly" hot. I would measure the voltage output of the transformer to see how much it differs from rated voltage. That will determine if it is being overloaded or not.
 
How are you saying is a 1.5A transformer.Have you coduct the load test on this transformer.Don't buy unbranded transformer.Better buy branded transformer like maxine etc....
 
Personal definition is not accurate. What an unfamiliar person will think is hot another that works with something regularly will think is normal.

Do you have an actual temperature reference to work with?

I have worked with commercial transformers that were rated at a temperature rise of 40 degrees Celsius with a 95 degree Celsius ambiant tempurature working limit.
That means that the top operating temperature was 135 C!
You could easily boil water on it and that was still within its working parameters!
 
What is the current waveform in the transformer secondary? If you are feeding a full-wave rectifier, the current waveform has a high peak to average ratio, and the transformer must be derated compared to its sinosoidal waveform RMS rating. In other words, a transformer rated to deliver 2A to a resistive load should only be asked to deliver ~1.2A DC out of a full-wave bridge/capacitor input filter type DC power supply.
 
Arumugam said:
How are you saying is a 1.5A transformer.Have you coduct the load test on this transformer.Don't buy unbranded transformer.Better buy branded transformer like maxine etc....
Click to expand...

Huh? 1.5A is what the manufacturer has stamped on it. What is "unbranded" and what is "maxine"? Thanks.
 

Well, the input is US house current measuring 112VAC, the output is right at what the manufacturer states 36VAC. Don't think this is the problem but I can't figure that it's anything else.

Any ideas on changing 110VAC to 36VAC any other way. I'm trying not to waste energy.
 

Your right. I never should have said "incredibly hot". After 1 hour of use the trans. gets so hot that I can't touch it for longer than about 1 sec. I'm sorry I can't be more precise, like with an actual thermometer. I can't find temp specs on the trans, but regardles I don't think I can use a power supply that emits such a high source of heat.

Any ideas on changing 110VAC to 36VAC any other way. I'm trying not to waste energy. I suppose I'll have to pose a Q for a power supply that doen't use a transformer. Thanks.
 

Well thank you but, unless I misunderstood you, I am not using a rectifier of any kind. I am taking ~112VAC and need to change it to 36VAC. I am not very familiar with differnt transformers but, I think just the fact that I have 112VAC flowing through unrestricted other than the resistance of the trans wires will cause major heat. Any ideas that might help would be appreciated.

Any ideas on changing 110VAC to 36VAC any other way. I'm trying not to waste energy. Thank you.
 

Transformers are pretty well the most efficient machines there are, but you're pushing that one far too hard - 1.5A is it's absolute maximum, so 1.32A is going to make it pretty damn hot.

Generally, the smaller the transformer the hotter it will get, and the lower it's efficiency will be.
 

Thanks, I guess I might have to just get a grip on reality and use 4 transformers, one for each circuit. Wow, that will make my project huge and very heavy.

Are switching power supplies only for AC - DC? I will post this question seperately, if youdon't want to address this question.

Again thank you.
 

No, it's AC - AC, you rectify it to get DC - but the AC is squarewave and high frequency.
 

You're not overloading it. The heat is likely normal for that transformer.

My first suggestion for dropping 110VAC to 36VAC is to use a triac "dimmer" circuit. It's efficient, small, cheap, and simple. The disadvantages are lack of isolation from the mains, and potential Electromagnetic Interference.
 
Assuming the common 40 C temp rise rating and an ambient room temp of say 22 C you would get a surface temp of around 62 C.
Very hot to the human touch is typically around 55 -65 C depending on the person. So your rough estimate wold put it at its normal expected range given the load its under.
I dont go by core touch temperature though when measuring transformers. I go by direct winding temp using an infrared thermometer. I have found most mid and low grade transformers, especially smaller ones under 100 VA to have core temps considerably higher than the winding temps. Small transformers are by nature less efficient and thus generate more heat in the cores.

A big multi KW transformer at full rated load will often be the reverse in actual operation. The core will be considerable cooler than the windings.
 

Just did a search for triac dimmer circuits. Looks like what I want / need. The heat is my main concern and the power loss is second. I will check into this see if it works for me.

Again thank you.
 
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