Transformer for dual rail supply

[technobreath]

I need some help, as I can't seem to wrap my head around it myself...

I need a xformer that gives me about 12v output with a centertap. I need to drive a 7809 and a 7909, and I want like 1 amp from each of the rails.

Problem is that I can't seem to find any transformers that fits this at the sites of the usual suspects (mouser, reichelt etc.) Elfa.se I don't even bother checking cause they are so shit expensive that I buy as little as possible from them, and they are slow.

If I were to use a dual output transformer and wire it so that I have a centertap - I mean - wire L on one output to N on the other, and there's my center tap.

If I wanted 12v output with centertap, am I correct that I should use a dual 6v on the secondary side, or should I still use dual 12v ?

Sorry my stupid question, but certain things I seem to have trouble with finding out myself... :rolleyes:

EDIT:

My stupidity haunts me. I found this site:

http://www.delabs-circuits.com/cirdir/electric/tables/tabl0007.html

Can someone verify for me that if I wire the two secondary outputs in parallel, the voltage I get from it is still 12v and twice the current capacity?

That is, if I want a 12V secondary with centertap and 2 amp, I can use a 12v dual secondary xformer @ 1amp each output?

Thanks for the help.

Edited April 11, 2012 by technobreath

[Janis1279]

http://www.delabs-ci...s/tabl0007.html

Can someone verify for me that if I wire the two secondary outputs in parallel, the voltage I get from it is still 12v and twice the current capacity?

That is, if I want a 12V secondary with centertap and 2 amp, I can use a 12v dual secondary xformer @ 1amp each output?

Thanks for the help.

Hi,

A nice link.

I do not recomended to connect the transformer two secondary windings in parallel. It can cause for more transformer heating ,than under normal usage conditions, no safe. Not every transformer manufacturer recomended do that way connections , the secondary windings are not so identical, I think.

Regards,

Janis

[technobreath]

Ah, I ordered a dual secondary transformer (a relativly cheap toroidal on ebay), and it's gonna be pretty easy to measure how symmetrical the windings actaully are ;)