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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?
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!
Does the pain of N gauge steam ever end!
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.
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.
Lumsdonia <--- Hit link to go to my website for full story and wiring advice!
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