Understanding CompactLogix Power Supply Requirements

[monteran]

I have a CompactLogix PLC that I am looking to integrate into a new application. I see that the unit operates by taking power from the +/- 24V DC terminals as well as the +/- FP terminals. I believe the FP terminals are used to power the output pins, etc?


My question is this: For simple testing purposes, is there anything wrong with using a standard lab workbench power supply with +/- 20V DC hooked directly into the screw terminals on the device? I also see that the back of the controller has a metal contact for a DIN rail. I don't have any such setup currently - could I just put in a small cut from a DIN rail I have on hand and connect that with alligator clips to the ground of the power supply I have on hand?

Apologies if these are stupid questions. I'm not much of an electronics guy and he won't be back until next week. Thanks for any guidance.

 

[bjh]

It's fine to do pretty much what you're describing. I wouldn't even go as far as grounding the back of the controller as long as the power supply is grounded. And try to use 24vdc (is 20v a typo?) for your control power.

Just to be clear as well, the unit operates on +24vdc, not +/- 24vdc. - is neutral/0vdc in this case. Connecting +24 to the + terminal and -24 to the - might make the magic smoke come out.

 

[Dravik]

Grab the doc 1769-um021_-en-p.pdf for exact directions, but in general you are correct. For testing just the PLC, you can hook your DC power supply to the DC terminals on the terminal block.

 

[monteran]

Thanks for the hints.

I'm glad that you mentioned that the - terminal goes to ground in this case. I kept reading in that manual that you connect the supplies' +24V DC to the 24+ terminal and I assumed that the the 24V- terminal on the PLC meant it wanted -24 from the supply as well.

I've been thinking back to a transistors course I took back in college where we were often using +Vcc -Vee values...