raising transformer va

[PRR]

> can I wind it over the two secondaries already present

Re-read post #20

a) fully unwind secondary.
....
d) wind bifilar , holding both wires side by side in your hand.
Only GUARANTEE that both windings will have ....exact same turns.

 

[bansuri]

Thanks for the replies, much appreciated

Got some enameled wire now.

So far: the toroid transformer has two 15volt secondaries. I have taken turns off each secondary to give me the required 8 volts.
Now with so much wire removed the toroid is half empty. Since it is good practice, should I spread out the secondary turnings to cover the empty surface.
I want to keep the voltage at 8volts but raise the current by making another secondary, can I wind it over the two secondaries already present. Just this post here states winding more secondaries will not raise current.
https://www.diyaudio.com/forums/power-supplies/299824-toroidal-transformer-rewind.html
What should i do.



Thanks.

The transformer has 2 limits, the max magnetic flux before saturation and a thermal limit.
When it saturates the inductance goes to 0 and with it the output current as well, it will make a humming noise just like at start up.

The input- and output current will create heat across the ohmic resistance of the windings, this limit is higher with good cooling, mounting it on a bigger alu sheet or a fan.
I think just with your 8V windings you can take out at least 50-60% more current as is, you can gain a bit more with a Schottky bridge at those low voltages, so you can go to 2x 7.5V.

 

[goodsguys]

Thanks.
Going back to post 19, half the toroid is empty at the present, what if i wound a new secondary over the empty area measuring the voltage as i go along until it is exactly the same as the first secondary, then parallel the new and first secondary together. As long as both voltages are the same it may be okay

 

[goodsguys]

What do you think. Is it okay to judge by secondary voltages, rather than turnings. Make sure both voltages are exactly the same.


Thanks

 

[goodsguys]

The label states that the transformer is 15volts and 7.5 amps per secondary.

With two secondaries paralled this should give 15 volts and 15 amps.
As i have removed turns and halved the voltage does this mean the amperage will double, so that it is now 8 volts and 30 amps.
The stock wire used by the manufacturer is 1.5mm, so with the two secondaries paralled this should be the same as using 3mm wire. Will the 3mm wire be sufficent thickness for 30 amps.
Thanks.

 

[amplidude]

Carver used triac to modulate primary windings, would altering frequency produce higher current ability? I'm not sure.

 

[goodsguys]

Anyone have an idea

 

[richie00boy]

Current rating is governed by wire diameter. If the secondaries provided 15V 7.5A each and now you unwound turns to lower the voltage you will get 7.5V 7.5A each.

If you want more current strip the secondaries off totally and rewind with the appropriate wire gauge. Which is not 3mm by the way. Think about pi and diameter vs area.

 

[goodsguys]

If not 3mm what would you say it is?


To update, i have measured the current and cannot get it to go any higher than 28 amps. It seems the va rating cannot be increased from stock value. Lowering the voltage only lowers the voltage and does not affect current