Hi-
I'd be interested in a schematic for such (and any other useful instruments :-)
Maybe in the PICLIST archives?
Thanks, David


Roman Black wrote:

> William Chops Westfield wrote:
> >
> >     > Isn't a 630V 1uF "milspec" poly cap somewhat ... large?  Say,
> >     > close to transformer sized?
> >
> >     A 1uF 250V X2-rated cap is 31 x 24 x 14mm, about 1/2 the size
> >     of a small mains Tx.
> >
> > So how much bigger is the recomended 630V cap? :-) I have sitting next to
> > me a 32 x 26 x 21 mm 1.5VA PCB mount transformer with a 15V 0.1A secondary
>
> I am going to risk being unconventional here, but I have
> a capacitive reactance supply here that uses two electro
> caps back to back, reversed. 2.2uF 400v. These caps are
> quite tiny compared to a poly or non-polarised cap suitable
> for 240vac use.
>
> It has worked fine for a few years, of course it has a
> series resistor dropping about 10% of the mains voltage.
> I build supplies like this all the time for testing
> things with a constant current like leds, and for trickle
> charging NiCds that a lot of our multimeters and test
> equipment use in the workshop. You can use a switch to
> switch different caps in and out of circuit to adjust
> total current, and my main system is to build them in
> old analogue multimeter frames, using the rotary
> switch to adjust current and the meter to display the
> current/voltage etc. The Xc supply is small and cool
> enough to do this even in those small cheap boxes.
>
> My favorite one is a zener tester, it injects 2mA
> to 50vdc and 0.4mA to 200vdc and will test zeners
> in-circuit most of the time, and show their zener
> voltage on the meter.
> :o)
> -Roman
>
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http://www.piclist.com hint: The PICList is archived three different
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