S7 200 PLC, sensor output...

I have a s7 200 CPU 222/AC/DC/RLY PLC. I am using 6 inputs and 5 outputs. Except for one NPN sensor input, rest are just contacts (switches and pushbuttons). Also 3 out of the 5 relay outputs are 24V LEDs.

The 24V sensor power output on the PLC is rated 180mA. The NPN sensor and indicators together are 140mA. My question is.. do the switches or pushbuttons consume any power? Am I ok using just the 24V sensor power for my I/Os instead of an external supply??

I am new to PLCs and glad to know there is a site dedicated to PLC users.

Thank you...

The PB's wont consume power but the plc may use some to light the led's, even if the leds are on 5v then a transistor or relay is used to turn it on.

If you have a small power supply available then it may be better to go ahead and use it. You are getting close to max...I try to avoid going over 75% of rated, less if possible.

rsdoran,

Thanks for your reply. I looked at the siemens S7 200 manual and it says the

"The CPU has already allocated the power required to drive the internal relay coils. You do not need to include the internal relay coil power requirements in a power budget calculation"

So I assume the 180mA is compensated for this?! Correct me if I am wrong.

Also, not all inputs will be on at the same time. Same with the output. The condition is such that only a max of 4 I/Ps and 1 O/P will be ON at the same time. Does this help?

As a precaution put a 180ma fuse in the line ...then go with it. IF the plc doesnt need any of the available 180ma then you are in good shape.