Transformer Help

Good Day,

I need to build a DC power supply for my project that has a voltage of anywhere between 9V and 15V but must be able to supply at least 25W.

I want to build a simple transformer into a full wave rectifier then filter cap system.

A local shop has this transformer **broken link removed**

can someone please explain to me what the 2x9V and 2x2.2A means? and can this be configured into 1x9v @ 4.4A? why does it have 2 outputs? would this transformer have three windings, one primary and two secondary?

Thanks,
StudentSA

This transformer has three windings; one primary, and two identical secondaries.

Just parallel the two secondary windings (observe correct polarity, both windings same direction) , and you will have 9V at 4.4A. This will require a full-wave bridge for rectification, with a loss of TWO forward diode drops.

Or, connect the two windings in series, ground the center tap, and use only two diodes to full-wave rectify. This has the advantage of using two less rectifiers, and having only only ONE forward diode drop.

Your choice.

Thanks Mike!

I got the transformer and it just occurred to me, how do I know the polarity of the two outputs? so that if I join them in parallel they are matched?

Also, If I connect them in parallel I assume that the two output windings are close but not identical, how will this effect the transformer?

Thanks,
StudentSA

it almost certainly runs as 0v 9v 0v 9v. join the two 0v terminals, and check you have 0v between the two 9v terminals. if you do, then join them up. if you have 18v then the connections are reversed

(9v will probably measure about 11v o/c)

Brilliant Grim!
Why did I not think of that...
Sorted and Thanks!

MikeMl said:

Or, connect the two windings in series, ground the center tap, and use only two diodes to full-wave rectify. This has the advantage of using two less rectifiers, and having only only ONE forward diode drop.

Your choice.

Click to expand...

However, you get the peak current taken by just one winding, while the with two windings in parallel, they only take half the peak current.

Depending on lots of factors, the extra voltage drop from a full bridge may be more than compensated for by the lower voltage drop in the windings.

On very small transformers, there is a lot of winding resistance, and on one project I had to rearrange from centre tapped to full bridge to get more voltage.