On Wed, Feb 15, 2006 at 03:58:55PM +0200, Vasile Surducan wrote:
> Not that I am totally sure about those numbers,
> > that's just assuming that the amp meter on my testing power supply
> > works. The motors are not synchronized to each other. To be exact, they
> > play Conways Game of Life...
> >
> > The the problem is as follows. I built a linear power supply using a 28A
> > 6.3V transformer from digikey. 237-1255-ND. 4x LM396K 10A regulators in
> > parallel through load-sharing resistors regulate the voltage. For my
> > first attempt I used a standard 50A 600V diode bridge, MP506W-BPMS-ND
> > That didn't work, the final voltage at the "5V" line ended up being
> > about 3.5V, causing the master PIC controller to crash.
> 
> 6.3V ac is not enough to get 5V/25A dc stabilised with any schottky
> diode ever built.

I know now... I screwed up my calculations somewhere, fortunately I'd
planned ahead for such screwups and designed the circuits to work with a
fairly wide voltage range, they are all LF series PIC chips for
instance.

> > My second bright idea (ha!) was to try to reduce the voltage drop by
> > using those fancy schottky diodes I noticed in the catelogs... So I
> > ordered three 115CNQ015ASL-ND 15V 110A and made them into a diode
> > bridge. (they are two diode packages) That worked beautifully, giving me
> > a usable 4.2V line, until after about 30 minutes of running I heard a
> > loud bang. The main AC fuse had blown, though not the 40A DC fuse, and
> > the after some testing the diodes were found to have developed internal
> > shorts. All three seem to have done this at once!
> 
> three dual diode diode in a bridge, are you using tri-phase mains supply ?

No, just single, the diodes are arranged as follows:

          AC
    |-->--|
    |-->--|
    |     |-->--|
- --|           |- +
    |     |-->--|
    |-->--|
    |-->--|
           AC
	 
AC in the top and bottom, positive out the right, negative on the left.

The diodes are packaged as two diodes with common cathodes.

-- 
pete@petertodd.ca http://www.petertodd.ca
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist