output voltage

i'm planning on using a plc with pnp digital outputs.
the plc uses 24VDC.
i need to operate a few solenoind valves of 24VDC.
will the plc provide them the 24VDC they need, or will i need another relay?
if the plc uses 24VDC, does it mean i can connect to it loads up to 24VDC?

The outputs are isolated. They have nothing to do with the PLC operating voltage. The outputs don't supply voltage. Treat them as relay contacts - contact closure.
If you want to use 24DC valves, connect the positive leg of another independent 24DC supply to the Common of the output module. When you turn on an output, the associated PNP transistor will turn on, and 'Supply' the positive leg of your supply to the solenoid.

Just make sure that the current demands of your solenoids do not exceed the MAX current limit for the particular PLC output.

PLC 24v DC output

Barak,

Be sure to fuse your outputs, if the PLC has no internal fuses for each output. Also, In my experience I have found that the isolated semiconductor outputs, as opposed to relay outputs are more sensitive to voltage transients. If a relay is powered on and the contacts of that relay energize the solenoid, it provides additional protection to your PNP output card. The relay output is not as susceptible to voltage transients, but then you have the 1 million physical make/break limitation (before the relay goes bad in the PLC) and the slight lag in time that actual physical contacts take to make/break.

Just a thought.

Mike

Hi Barak.

Check if the DC output can drive the solenoid (Amps).

A relay is a cheap insurance. It is cheaper to replace a relay than a whole PLC or an output card.

In any case, remember to install surge suppressors over the coils.
Freewheeling diode, or zener diode.
It is not the connection of the coil that will kill the output or the relay, it is the disconnection of the coil!