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Old 11th January 2013, 10:19 PM   #1
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Default Parallelling torodial transformer output for full output power

Say I have a transformer such as this:

Avel Y236103 30VA 15V+15V Toroidal Transformer 122-605

I use the primary connections in parallel and input 115V, but at the output instead of 15/CT/15 I want only 15V at full power. Do I just parallel the two output windings?

And just to be clear, that means black/orange in parallel and red/yellow in parallel.
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Old 11th January 2013, 10:50 PM   #2
jaycee is offline jaycee  United Kingdom
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The transformer you link to is not centre tapped secondary, it is 2x15V. In this case, you would put both secondary windings in parallel - black+orange, red+yellow.

If you have a transformer that is 15-0-15 (3 secondary wires) then you cannot parallel them - you would create a short (i learned this one the hard way as a kid!). Instead you use two diodes, one for each 15v tap, and use the 0v tap as your ground:

File:Fullwave.rectifier.en.svg - Wikipedia, the free encyclopedia
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Old 11th January 2013, 11:10 PM   #3
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Thats what I thought, thanks
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Old 12th January 2013, 06:23 AM   #4
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When parallelling two transformers for full power, I recommend You to make the parallell connection AFTER the rectifiers.
This means you put one rectifier in each transformer and paralell-connect the + rail and the - rail. 0V is good to connect them all together.

The reason is quite simple:
Two transformers may have a slightly difference in the secondary windings.
Not much, perkaps one round or so,.
When parallelling the secondary windings of two transformers in this way, there will run current between the two transformers, "stealing" power from You.
It is actually possible to look at it as if one winding is done and the short cirquited.

So I recommend You to use separate rectifiers and then paralell-connect the rails.
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Old 12th January 2013, 10:07 AM   #5
sbrads is offline sbrads  United Kingdom
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Quote:
Originally Posted by TANDBERGEREN View Post
When parallelling two transformers for full power, I recommend You to make the parallell connection AFTER the rectifiers.
This means you put one rectifier in each transformer and paralell-connect the + rail and the - rail. 0V is good to connect them all together.

The reason is quite simple:
Two transformers may have a slightly difference in the secondary windings.
Not much, perkaps one round or so,.
When parallelling the secondary windings of two transformers in this way, there will run current between the two transformers, "stealing" power from You.
It is actually possible to look at it as if one winding is done and the short cirquited.

So I recommend You to use separate rectifiers and then paralell-connect the rails.
Agreed. The only time it's safe to parallel output windings is if they're bifilar wound.
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Old 12th January 2013, 10:21 AM   #6
AJT is offline AJT  Philippines
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Quote:
Originally Posted by Fusion916 View Post
Say I have a transformer such as this:

Avel Y236103 30VA 15V+15V Toroidal Transformer 122-605

I use the primary connections in parallel and input 115V, but at the output instead of 15/CT/15 I want only 15V at full power. Do I just parallel the two output windings?

And just to be clear, that means black/orange in parallel and red/yellow in parallel.
if you want just 15volts, series connect the primaries and parallel connect the secondaries...make sure you get your phasings correctly...
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Old 12th January 2013, 11:20 AM   #7
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You only have to worry about paralleling windings if they are from two separate transformers. A single transformer with two identical secondaries is designed so that it can have the secondaries paralleled.
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Old 12th January 2013, 12:33 PM   #8
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Quote:
Originally Posted by TANDBERGEREN View Post
So I recommend You to use separate rectifiers and then paralell-connect the rails.
If you want to be 100% you do that but normally it's no problem to connect the windings in parallel.
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