Transformer Question

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I have a 90W RMS sub amp, the cheap ones with bandpass, level control, phase switch, auto sense on etc, I purchased for next to nothing, a few bucks. The seller claimed it simply got too hot in a sealed box, and indeed the plastic housing had warped near the transformer. OK, for some reason I couldn't resist buying it to play with since it looked quite new indeed.

Anyway, to cut a long story short, the thing works perfectly, and what is getting hot is the transformer (laminated), as in way too hot, 50-60Celcius. And I say this because it's that hot even just sitting there idle, prior to autosensing a signal, in the free open air, no cover.

I have a question regarding the primary inputs. In that there is 5 of the suckers. This intrigues me. The secondary is standard X-0-X multitap output.

Any clues, comments. I'm curious. My guess is multi voltage transformer, ie 110V & 250V etc. It has of course, no labels on it (typical). What I noticed is that the the additional three wires have the red and black twisted together and a brown wire isolated.

Electronic stores being the friendly people they are in this part of the world are useless, selling only the usual double wire input transformers. At least here I hope I'll get a sensible answer. ie 'cheap tacky piece of &^$$ ditch it' or such.

P.S. It has not blown the 1A fuse in the system yet, regardless of how hot it's got. I'm going to disconnect it totally from the circuit and see what it does in regards heat.
 
Some info

Yes, dual voltage, the red and black twisted put the other two primary coils in series, allowing for doubling of the 115V to 230V for UK. And we have 250V, which could explain some warmth, but not all of it. But...I still don't know what the 5th brown wire does.

I knew I'd find it if I spent my life searching the web, through all those useless links. It's only taken 4 hours on my slow connection.
 
Hot Transformer

Usually when a transformer gets hot just sitting there, idling, there are only a few reasons why.

1. The transformer is mis-wired and one winding is shorted or wired in the wrong phase. Figure it out and fix it.
2. The transformer has developed a shorted turn and must be replaced.
3. The transformer designer skimped on the number of turns and/or the iron and you either live with it or you replace it with something else larger.

I suggest you at least measure the output voltage now while it is still functioning so you can replace it after it burns out. If you wait, it will be much harder to figure out the voltage.
 
...well I think it may be, that this transformer was designed very close to saturation. Then already a small increase of the input voltage will saturate it. This will cause higher losses in the core and due to current peaks also in the winding....
I you run the transformer naked without load, rectifier and caps and all other electronics disconected: Do you still find that heat? Do you find
remarkable peaks in the input current at this condition? If you find peaks in both directions then this indicates that the transformer is designed to close to staturation for your 250V. If you find peaks only in one direction, then this indicates some DC in your mains...., may be in
combination with a critical designed transformer.

I would agree to dmfraser:
Measure the voltages now while the thing is still working
and replace when you find time.

Cheers Markus
 
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