control solenoid valves

rania_alv

Member
R
Join Date
Nov 2009
Location
cairo
Posts
3
i have a plc with relay outputs, and i need to control solenoid valves with coil 220vac 5VA,
i need to know if i can connect them to the plc outputs directly or not?
and i need to know the values of the RC circuit to protect the plc from surge current and if these values differ from load to another
 
Last edited:
I have a box (500mm x 3000mm x 1000mm) that I want to put in my car, can you tell me if it will fit?

You can't possibly answer the question unless you know the type of car and the specifications for the size of the doors. Same problem with your question, we can't possibly answer the question without knowing the type and specification of the PLC that you are using.

Bryan
 
So the relay is capable of 2 Amps at 220V. Your solenoid valve is 5VA which gives 5VA/220Volts = 0.023Amps approx (23mA). Even without any RC circuit the system should be more than OK unless you have a very high switching rate. I tend to fit RC circuits any way, I buy plugs for the solenoid valves that have RC circuits built in

The PLC has a number of output circuits with a common supply, obviously you can't have a mix of voltages on the same common.

Bryan
 
Mrs. rania , welcome to u in "PLCtalk.net", what is the function of the soleniod valve in your application?
u can use special type isolator "barrier" for this application , if u interest i can send to u the manual for this isolator.(y)
 
from the relay output of the PLC , connect a electro-mechanical relay or Solid state relay and drive the SOV through this. hazzle free , you dont need to worry about surges affecting the PLC output.
 
I find driving solonoids directly from PLC eventually burn their points making the PLC fail. Rather add external relays so easy to replace.
 
there is only one answer to this
As rdrast has said
the calculation earlier is a DC calculation
there is no allowance for inductive reactance.

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.
 
Relay to Solenoid

I have read this and many threads like it and had one question about the final circuit. Do you need anything in other than a direct connection from the output of the Relay to the solenoid? From what i have seen it seems you can drive a 220V AC solenoid directly from 220V AC source with no current limiters or other types of additional circuitry, is that correct? My biggest fear is making a rookie mistake and I ruin the solenoid I am trying to control.
 
Casmer said:
I have read this and many threads like it and had one question about the final circuit. Do you need anything in other than a direct connection from the output of the Relay to the solenoid? From what i have seen it seems you can drive a 220V AC solenoid directly from 220V AC source with no current limiters or other types of additional circuitry, is that correct? My biggest fear is making a rookie mistake and I ruin the solenoid I am trying to control.
Click to expand...
We answer these threads with the understanding that basic electrical knowledge is already known.
if we dont do this we will be an education site rather than a PLC forum.
welcome to the site.
Now to answer your question with a question.
If you have a hard wired device like a motor starter which is wired to a switchboard - (forget about PLC's) - would you use any form of current limiting
why would you use it.
Why is house wiring fitted with current limiting devices.
there are many reasons for current limiting.
this Forum is primarily controlling systems - Current limiting is expected and in most cases manditory.
 
A solenoid is only going to draw enough amps to operate it. Its based on the voltage applied and the resistance ( impedance) of the coil. It does not matter how much power you have available.

I would be more concerned about the relay contacts. What is the voltage and current rating of the relay contacts.

Its always a good idea to have short circuit protection though.

And you should always have surge protection across any inductive load. This will protect the relay contacts.
 

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