On Tue, 15 Sep 2009 17:12:41 +0100, Andy GD1MIP wrote:

Hi I am building a (240volt in) 13.8 volt (out) PSU along the lines of
this plan..
http://www.warc.org.uk/proj_psu.php it is very similar to the old
Marchwood practical wireless unit from the early 1980's using 2n3055
transistors.

My question. The spec says the transformer must have a secondary of 16.5
volt. Now when I last built a PSU using a similar plan the transformer
output could be much higher, in the region of 15 to 20 volts.

I have a Talema branded toroid I want to use, its spec is as follows
(from maker)
+++++
Toroidal transformer type 5028-P3S03: Prim: 0-110V-230V-240V
orange-yellow-violet-blue Sec1: 20V/6A green-red
Sec2: 20V/6A black-white
Sec3: 55V/2,5A braun-braun
If you use only the 2x20V you can get out 9A of each winding (no load on
the 55V)
+++++


as you can see the secondary output is 20 volt, now folks do you think
this transformer will suffice at 20 volts, or should I removed a little
winding to bring it down?

73 Andy

PS the variac is just there for scale.

If you _really_ want to do some work you could remove all the secondary
windings and replace them with a single 16V winding; that'll give you 25%
more current just from the drop to 16V from 20V, plus whatever extra
power you can take because you used the space formerly taken up by the
55V winding to put in bigger wire.

Lots -o- work, though.

--
www.wescottdesign.com