Subject: Re: V regulator input cap size?
Date: Thu, 24 Oct 2002 13:58:36 -0700
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On Thu, 24 Oct 2002 12:39:36 -0700, Lizard Blizzard wrote
(in message ):
> But I have used
> transformers similar to these control transformers, and they put out
> about 42 volts at the filter capacitor. You have to remember that the
> transformer gives 28VAC at full load, so at much lower load, the
> secondary AC voltage will be substantially higher. And after
> rectification, it can go as high as 44 or so VDC which is about 31 to
> 32VAC times 1.414. If a regulator with 40V max is used, it will still
> have an input voltage that exceeds its maximum.
I measured the control transformer voltage and with no load (HVAC off) at the
thermostat, where I will take the voltage - it measures 28v rms. I would
assume that under load it will go a bit lower, but as long as it doesn't go
above this measured value I think the 7824 and 7812 solution will be safe by
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