In article ,
"Arfa Daily" wrote:



Hi Smitty
Peak DC out is root 2 (1.414) *times* the RMS AC in, so with a resevoir
cap of sufficient size, and not too much loading and source impedance,
that's about the level of DC that you would measure on a normal multimeter.
You are thinking of calculating the AC RMS figure from the DC where you
*divide* the DC level by root 2 (or multiply by 0.707).

The fact that there is no resevoir cap, throws a bit of a spanner in the
works when it comes to measuring the 'DC' out from the bridge because,
whilst by strict definition it *is* DC, what you will actually have is a
train of unipolar pulses, which the meter will make some attempt to
integrate into a DC level that it can display. Obviously, this will be a
misleading figure, and may even differ between an analogue, and a digital
meter. The meter reading of "12" might well have been 'correct' in this
case - if you see what I mean !

I wonder what additional circuitry this supply is powering ? It can't be
anything 'electronic', as such a raggedy-arsed rail would play havoc ...

Arfa

Thanks Arfa, and others. School was over many years ago, and never
having made the subject into an occupation, as I had planned, the theory
quietly slipped away ...

Friend obliged my request for another reading, and now shows 28 VDC out
of the unfiltered bridge, with his Fluke handheld meter. Would have
saved us all a lot of bother if I'd recognized that 12 VDC as faulty
right off, rather than thinking it was spot on.

N. Cook is correct, the DC only drives a relay to operate the carousel
on command.

Smitty