Question about wiring Toroid Trnsformer

[ericdwilso]

I have a toroid transformer that is rated 120V input / 39.8-0-39.8V 8.8A.

I want to have the full VA rating to run a single 56VDC circuit.

When I measure it I get 40 & 80V readings aross the various output wires (+'ve (or -'ve) to centre & +'ve to -'ve). Can anyone help me with how to wire the 2 output coils together?

I thought of using 2 bridge rectifiers and then switching the outputs from the rectifiers such that the pair 0VDC and the pair 56VDC lines are joined together... then connect to the capacitor. Will this work?

[Al_The_Man]

Unfortunately if it is a centre tapped winding i.e. all 4 ends do not come out, but just the three 40-0-40 then you will only be able to use the one half of the secondary to obtain the 56vdc.
You will be able to use the full VA capacity as long as the gauge of a single half of a particular secondary is sufficient to handle the current.
If you can identify the centre tap as two conductor ends connected together and be able to separate them, you can parallel the windings up, although it is best if they are wound side-by-side (bifilar) for exact balance.
Al.

[ericdwilso]

Thanks for the reply Al,

What is the reason that my suggestion would not work?

[pminmo]

Al,
Why can't he use a full wave center tap configuration?

[Al_The_Man]

Yes thats true but only one section of the secondary is conducting at any given time. So it is not as efficient as the full wave bridge.

Originally Posted by ericdwilso What is the reason that my suggestion would not work?

You will be shunting out a section of each bridge.
Al.

[ericdwilso]

Yes thats true but only one section of the secondary is conducting at any given time. So it is not as efficient as the full wave bridge.

If I use the configuration that pminmo suggested... will I be back to the same power output as using one of the secondaries? Or am I further ahead?

[Al_The_Man]

There are some small differences, one advantage with the FW centre tap that Phil shows is that you only have one diode volt drop, against a 2 diode drop on a bridge.
But essentially the VA availability is close.
Did you check to see if they bring all 4 ends out of the secondarys?
Al.

[ericdwilso]

I could only find 3 wires on the secondary. I did remove some of the covering to look in but the metal wrap around the outside prevents seeing much.