Dual rail bench psu

[chrispbass]

hi everyone

Having a sort through my collection of bits and bobs and came across a couple of 24v toroidal tx's i'd bought of ebay. These were mistakenly listed as having dual primarys, but actually only have a 110v primary and 2 x 24v secondarys. They cost next to nothing so I didn't kick up a fuss as they were being sold as part of a deseased grandfathers lot. Anyway,  was wondering what to do with them, apart from possibly using them in reverse in some valve project perhaps, but then I thought that I could possibly use them to make a variable dual rail psu.

Would it be ok to connect the primarys of the 2 tx's in series for 220/240 v and then parallel up the secondarys of both tx's (after connecing the 2 x 24v in series on each tx)?

I then found this schematic

http://sound.westhost.com/project44.h

Seems pretty simple. The idea is to make this without spending a bean as I've probably got all the bits i need already and have a 25v panel meter and loads of old cases i can recycle.

Just wondered what your thoughts were?

cheers

Chris


 
   

 

[JohnRoberts]

That would be fine if every winding is perfectly identical but any errors in turns ratios on primary or secondary could lead to the paralleled windings fighting each other.

I would suggest using two sets of diode bridges on the secondary side (Ok to normal the two secondary center taps) so the two output windings only add to each other and never subtract. 

JR

 

[chrispbass]

That would be fine if every winding is perfectly identical but any errors in turns ratios on primary or secondary could lead to the paralleled windings fighting each other.

I would suggest using two sets of diode bridges on the secondary side (Ok to normal the two secondary center taps) so the two output windings only add to each other and never subtract. 

JR

Thanks for the reply John, so would that lead to potential over heating? I can easily add another bridge rectifier.

Just noticed the above link isn't working properly  http://sound.westhost.com/project44.htm

cheers
Chris

 

[JohnRoberts]

Yes, shorting two windings together trying to make two different voltages at the same time will push/pull current into each other causing IR losses in the windings. If the voltage error is small some extra heat, if the voltage error is larger, some smoke.

JR