24v ps for IO board

[miljnor]

I was just double checking this.

If you don't have a filter cap on a PS then the VDC will be same (or little lower) than the input AC. I did a rough test with a torroidal and widow maker via a voltmeter. and it came out about 2-3volts lower that the ac.

the reason I am asking is I have a 24v a/c trans and the rutex board will take a 24vdc and in their docs they say ac. and looking at thier layout it dosn't look like it has any smoothing cap so the voltage will be at the lower vdc.


http://www.rutex.com/pdf/R990IO.pdf

this is the link with the schematic.

or should i buy a 18vac or switch to dc input.

[Al_The_Man]

They use a 1000µfd after the bridge, then into voltage regulators, so I would say the 18v is not critical, they will finsh up with around 24vdc into the regulators, but it depends what max they recommend, BTW with a bridge, you can also feed in DC of the same value if you wish, so if you had a 24VDC supply, you could connect that into it, polarity does not matter, the bridge will take care of it.
Al.

[NC Cams]

A neat trick about installing a full wave bridge in front of a DC circuit, to which you'll apply DC, is that input polarity becomes irrelevant.

A good trick to know if you are trying to idiot proof a circuit.

NOTE: if you do this, keep in mind the votage drop across the diodes.....IE: 10vdc in won't quite be 10vdc out.