Toroid transformers

[Meerkat 77]

Good afternoon everyone. I just joined this forum and would like some assistance with a couple of Toroid Transformers that I was given that have 5 wires on the primary. One a brown wire is labeled fuse. I have never encountered this before and I assume it is an internal thermal fuse. The transformers are Chinese from Mei Ha Industries HK Ltd..

I have wired lots of Toroids with dual primaries but never one like this.
Is there to test where this wire goes, or what is the proper hook up. No on seems to know and the manufacturer is no where to be found, the transformers came from Russound amp model DPA 4-8.
Any help would be appreciated , these are big units which I would like to use.
Thanks Wayne

 

[canadaelk]

Russound does not recognize the model # given. What are the colours of the other wires (including the secondary. Read resistance (give value) between wires. E

 

[Diver300]

It could be that there are two 110 V windings, and one of those has a 20 V section in series.

I would connect one of the windings to a low voltage ac supply, probably from another transformer. Then you can measure all the voltages without risk of electric shock or burning things out.

If you power a 110 V winding from 12 V ac, then all the voltages will be just over 10% of the intended voltages.

 

[Diver300]

The instruction book is at https://www.manualslib.com/manual/389335/Russound-Dpa-4-8.html
It says that it can work on 115 or 230 V, with some internal setting. The transformer might have a thermal fuse in series with one winding. That would make more sense than a 20 V winding.

 

[schmitt trigger]

It could be that there are two 110 V windings, and one of those has a 20 V section in series.

I would connect one of the windings to a low voltage ac supply, probably from another transformer. Then you can measure all the voltages without risk of electric shock or burning things out.

If you power a 110 V winding from 12 V ac, then all the voltages will be just over 10% of the intended voltages.

That is exactly the technique I also use when attempting to figure out an unknown transformer.
If you don’t have available low voltage AC but only mains, then Another technique is to wire in series a 40 watt incandescent bulb. If it lights dimly your supply voltage is correct for that winding. If it lights brightly, then you have applied a mains voltage to a low voltage secondary.

 

[Diver300]

That is exactly the technique I also use when attempting to figure out an unknown transformer.
If you don’t have available low voltage AC but only mains, then Another technique is to wire in series a 40 watt incandescent bulb. If it lights dimly your supply voltage is correct for that winding. If it lights brightly, then you have applied a mains voltage to a low voltage secondary.

Whether it is bright or dim the current won't be sufficient to damage anything and you can measure all the voltages while it is connected like that.

 

[schmitt trigger]

Indeed, that is the reason I keep a handful of vintage incandescent bulbs, as “fully visual” current limiters.