Solenoid and Relay Wiring

Hi everyone,

I am rather new to PLC's and I am looking to hook up an ASCO Redhat 24VDC solenoid using a relay to protect the output card. Is it possible to power the solenoid using the PLC's power source without frying anything. I am afraid it will draw too much current and burn something up. If it is possible, how would I go about doing this? Any advice is welcome and appreciated.

Thanks in advance.

Possibly. Is a single output on the card capable of supplying the in-rush & holding current required by the solenoid? If yes, then you can wire direct though I recommend fusing it AND adding a "snubbing" diode in parallel with the solenoid so that when the solenoid's field collapses it doesn't hurt the output. Otherwise use the intermediate relay.

and welcome to the forum.

(edit: those cheap little ASCO valves show up all the time in our water makeup circuit and I've never had a problem with them)

It is wise to use a separate power supply for I/O and PLC, especially with inductive loads that can cause voltage spikes.

It is also common to protect controlling devices from those DC loads with a reverse biased diode across the relay contact. The relay will last longer because the EMF generated by the collapsing field will go through the diode rather than try to arc across the opening contacts.

It might be okay to drive one solenoid from the same source the PLC is connected to, but we'd need to hear the specs on the power supply, the PLC in question, and the solenoid to be able to tell for sure.

Some newer valves have surge suppression built in...I doubt that's the case with the ASCO valve, but a part number would help to be certain.

Thanks for the responses.

It is an Allen Bradley Micrologix PLC, a Sola 24VDC:5A Power supply, and an Asco Redhat Solenoid Valve (Pt # 8210G002), 24VDC, 1/2" Inlet Pipe Size, 5/8" Orifice Size, Max operating pressure 125 psi.

Just one valve? I doubt you'll have any problems with that one valve and the Micrologix on the same power supply.

Paul

It is just one valve. We have decided to use a seperate power source to run the valve. It is a little extra money, but may cause a lot less headaches down the road.