Need help with powersupply.

[Andersonix]

Originally posted by AndrewT
The wire you choose must be capable of passing that rated output current. Do not use a single very thick wire (2.5mm or 3mm diameter). Instead use parallel 1.6mm diameter enameled wires to give the same total area that you need.

Andrew, why should one not use a single fat wire when adding windings to a transformer?

[star882]

Originally posted by Tosh
Andrew, why should one not use a single fat wire when adding windings to a transformer?

The skin effect will increase the effective impedance at high frequencies and large wire is less efficient at using space. Take apart the transformer out of even a cheap ATX power supply and remember that if they can effectively cut costs by using one large wire for the secondaries, they will.

[AndrewT]

Originally posted by Tosh
why should one not use a single fat wire when adding windings to a transformer?

Hi,
just try winding the required length of thick wire on to a long bobbin to feed through the middle of the toroid.
Now, try to feed that bobbin through and around the toroid core and try to place that thick wire in neat parallel lays without any kinks.

I suspect the machines that wind toroids have a similar problem getting sufficient tension to straighten out the thick wire.

I can wind 1.6mm (6A) wire but 2mm (9A) is almost impossible for my hands.

We are working at 50/60Hz. Skin effect is a non starter at these low frequencies.
In fact the opposite is an advantage.
Thick wire will help attenuate the HF interference that comes in from the mains. If the winders could use very thick wire in the higher VA toroids it would remove one of the disadvantages of a toroid cf. EI types.

[Andersonix]

Right, I can imagine the physical difficulty. But one is usually winding on just a few extra volts, so maybe 10-15 extra windings with whatever fat-ish wire one has available. In my case it has been stranded wire, so not a problem physically.