[move] How determine if transformer secondary can handle given amount of current

[rwind]

Hi,
attached is the circuit diagram of a old Pioneer receiver SX 1500. I am planning to reuse the transformer. In the picture (the thick black lines on the right top) pin 11 seems to be center tap and 13 and 9 are the other 2 ends of the winding. Between 11 and 13/9 I measure 33 V. But I don't need 33 V, all I need is about 18V which is what I measure between 12/10 and 11 the center tap. The fuse rating for the old amplifier says 2.5 A and is designed for about 100 W.

When I measure the resistance between 13 and 12 it shows almost as short, it looks like they are connected.

Can I use 12/10 with 11 for the PSU for a 50 W amplifier?



Thanks

 

[barry]

A transformer winding can have very low DC resistance; it doesn't mean it's defective. But there's really not answer to your question. You don't say what the current rating of the winding is, and you don't say what the current requirement for your amp is. 50W could be 25V at 2Amps,or 1 volt at 50Amps. The second case is not very likely, but you get my point.

But my GUESS is that it would possibly work, but I'd investigate a little more.

 

[jiripolivka]

A transformer winding can have very low DC resistance; it doesn't mean it's defective. But there's really not answer to your question. You don't say what the current rating of the winding is, and you don't say what the current requirement for your amp is. 50W could be 25V at 2Amps,or 1 volt at 50Amps. The second case is not very likely, but you get my point.

But my GUESS is that it would possibly work, but I'd investigate a little more.

Using an old transformer for a new load can be done but can be tricky.

First if you measure a secondary voltage without the nominal load, you must test some loads on it to see voltage drop. If your new load is taking more current than the old one, you cannot reuse the transformer.
You can try the new load on the secondary while monitoring the voltage AND temperature rise of the transformer, winding as well as the core. If the rise is higher than 55 deg.C after an hour, do not use the transformer with THAT load, it will burn sooner or later.

I would advise to buy a new transformer made to your new load. Some experts can rewind the transformer to your specification, possibly for a lower cost.