Transformer max temperature

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D605Eagle
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Transformer max temperature

Postby D605Eagle » Fri Apr 06, 2018 6:38 pm

I'm building a rather complex power supply with 6 different voltage outputs. 5 come from a large multi tapped transformer (ex army) and the 6th from a small stand alone transformer. I want to put thermal cut out protection on each of them, but I'm not sure what temperature is sensible. Under normal conditions I wont be drawing anything like the capability of each transformer but I do have a habit of forgetting to turn things off so some kind of protection in necessary. I was thinking about 50 deg C? What do you guys and galls think?

fourtytwo
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Re: Transformer max temperature

Postby fourtytwo » Fri Apr 06, 2018 7:08 pm

TBH thermal cutouts are of little use unless embedded within the winding, you would be better to ensure each secondary is protected preferably by a self resetting thermal current cutout close rated to the actual secondary current and a primary fuse in case some nasty accident occours. By the time you have heated up the whole trafo core to 50C the windings are long gone!
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Mountain
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Re: Transformer max temperature

Postby Mountain » Fri Apr 06, 2018 11:45 pm

Use a fan?

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D605Eagle
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Re: Transformer max temperature

Postby D605Eagle » Sat Apr 07, 2018 2:15 am

I was actually thinking of gluing the cutout to the coils as its a small plastic square. I had also thought about a fan as you can get normally open thermal switches, but from the last power supply I made it never got hot enough to warrant it.

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TimberSurf
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Re: Transformer max temperature

Postby TimberSurf » Sat Apr 07, 2018 4:55 am

Transformers are designed to get hot (at full load), but with such a mass, in the case of a overload, the windings will be melting internally, a long time before the heat reaches the surface! I have never seen a temperature device on a transformer yet! What you DO need is to select an appropriate fuse for the primary (NOT a 13A) and ditto for each secondary (because you have multi taps), fused at the max current value of each secondary.
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