Uwe Langmesser wrote in message ...
Wonderful, I might learn something here.
Here are some more details about the existing parts.


I use an existing center tapped transformer which gives twice 10.7 V. I also
have 4 caps of 167 000mF at 7.5 V (which are currently hooked up for 15V max
voltage) and two fat diodes. The transformer is probably good for 25 to 30A
( it has a 3.5 X 4.5 X 6 inch core).

If the 15 V I get right now at my filter stage is barely enough for decent
regulation I could double that (and also use a bridge rectifier) but then I
would have to regulate that higher voltage down to the 13.8V I will most
often use.

I looked at the design http://www.rason.org/Projects/powsupply/powsupply.htm
that Tracy had suggested and it looks manageable to me (the Astron design
someone suggested have additional windings on their transformers which I do
not have on mine) but I do not have the expertise to change parts in the
design to accommodate the higher voltage and current I could get out of my
transformer. I am not sure if I only have to change the current limiting
resisitor at the 723 as well as the resistors which determine the output
voltage or if more elaborate changes involving the 2N3055's are necessary.

This transformer is so close to the desired 13.8 volt output that I
would be tempted to use it unregulated. But you might want ot hang a
big 12 volt, 5 watt zener and a 10 ohm 2 watt resistor (in series)
across it to provide a minimum load. It will have some ripple
voltage, but it should do for most loads designed to operate from an
automotive charging system (which also has considerable variation).

If you want a regulated output, this transformer is not a very good
fit, unless you go with a switching regulator.