PLC's, power supplies, and wireing

[keithkyll]

Wire the + side of the supply to ground. Positive common instead of negative common.

 

[leitmotif]

What do you mean 0 to -24vdc??? I don't understand how you can get -24 volts.

Take any two batteries of any equal voltage. Wire them in series additive. In the series connection between the two hook up a test lead. Read to the opposite terminal of each battery. You will get + X volts on one and - X volts on the other.

The series connection between the two batteries could be used as a common.

In the days of tube electronics these were called B+ and B-

Dan Bentler

 

[mjisaacs]

Sounds like more of a trick question than anything else. Two 24DC supplies, but one of them has + as the common. That's the only way you could get 48DC on the input.
PLC1 has relay output and soucing the -. +24 is wired to common return.
PLC2 has sinking inputs. -24DC is wired to common return (shared between the 2 supplies), and +24DC is wired to input common.

Does anybody tie +24 to ground? I don't think so.

You would be surprised! I have seen lots of Japanese machinery that has all the +24 tied to ground! ...and their drawings are

backwards