> > I have a timer assembly here that uses transformerless power. The
> > 680n X2  type capacitor is probably not much smaller than a transformer
> > and much less versatile, especially as the timer has a VFD, so needs
> > multiple voltages.
> >
> > I think more than 10mA is questionable.
>
> My power supply reference book states that 1uF will pass 70mA. The
> few supplies I've built that use caps as the dropping element would
> bear that out. Using low quiescent regulators rather than zeners or
> 78 series regs will mean a smaller cap. Even a 2u2 isn't all that big
> and if it's reclaimed from a PSU or monitor board the price is right
>
O.K. I'm a bit prejudiced due to a pair of expensive failures of delay
relays where the device has a 24v AC or DC input and a 240v AC input. Took
one apart and the capacitor, not X type, had half melted. I believe that the
failure was caused by the delay relay being on the same circuit as a
contactor coil, but nowhere does it say you can't do that. Whole thing
pointless as 24v DC was available anyway, also seriously considered putting
a pneumatic timer on the accessory plate.

I'm not saying it's always wrong, indeed I guess the circuit used on triac
controlled dimmers probably doubles up as a snubber for the triac.

Oliver.

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
use mailto:listserv@mitvma.mit.edu?body=SET%20PICList%20DIGEST