Solenoid valve

What voltage coil are you looking at and what current will it take?

A lot of people design it to drive a small relay from the PLC and then drive the solenoid from the relay.

Depending on the output card, some have the current capacity to drive the solenoid.
 
traditionally an AC coil inrush current is three times the run current.
- Still looks OK doesn't it.
Now the Issue comes
When a relay opens there is a back emf spark - This burns the contact.
Eventually causing it to stick then weld
the result is a prolonged intermittent fault period
followed by failure.

This is true with all contactors / relays
that is why they have a switching rating

Summing UP - use relays.


I Know I just posted this for AC solenoids but there is not much difference

- DC burns contacts harder - they pit quicker
A standard DC contact needs to be Gold Plated - general purpose relays are not.
 
I try to use transistor outputs whenever possible and have driven valve solenoids with them for many years without a problem (abiding by current ratings of course).

For 1.5A you will certainly need a relay though.
 
Yup -

Plc Controls Relay - Relay activates Solenoid

Plus... I always use Diodes when connecting relays to a PLC - and I always use relays even if the PLC has relays itself - because you can replace an external relay, an internal relay is a different matter :D

Ian
 
Yup -

Plc Controls Relay - Relay activates Solenoid

Plus... I always use Diodes when connecting relays to a PLC - and I always use relays even if the PLC has relays itself - because you can replace an external relay, an internal relay is a different matter :D

Ian
Seems that it would be more logical to use a DC output on the PLC to control your interposing relay with a proper DC coil.
Or, if the solenoid is small enough, use a DC coil there and eliminate the relay.
The fewer moving parts one has the fewer chances of failure. IMHO :)
 
Yes - if your referring to a Transistor output
you need to check the output voltage and current
 
The 1.5A requirement is higher than most Outputs for todays PLCs. Check the ratings of your Output Card carefully before hooking it up.

Stu....
 

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