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I_rock_well

Driving a 24V solenoid valve with a 120V MicroLogix 1763-L16AWA

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Just a quick question from a total noob: I have the ladder logic setup to drive a solenoid valve that takes 24VDC. The PLC I have takes 120VAC as the input, the output specifications just say "Relay".

Am I correct in thinking that I need some sort of 24DC power supply, or can I somehow set the output to supply 24VDC?

 

I hope I gave all necessary information, I am a mechanical engineering student and a little out of my comfort zone.

Thanks in advance.

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relay output can be used to switch either DC or AC loads as long as rating are not exceeded. 24VDC inductive loads require suppression device such as MOV or diode. this can work without diode as well but relay contact will be arcing a lot more and life will be shortened. since this is inside PLC, it is not considered serviceable part.

you will need 24VDC power supply. 

connect positive terminal to relay common terminal(s) on PLC (marked VAC/VDC).

connect output side of that relay (such as O/1) to one side of your solenoid

connect other side of solenoid to negative side of your 24VDC power supply.

add diode across solenoid (such as 1N4004, actually any 1N400x should work). note that diodes are polarized devices. make sure that end with silver/white ring connects to solenoid end that is positive (one connected to PLC output). connect other side of the diode to the other solenoid wire (one connected to negative side of power supply).

EDIT, here is manual for it"

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1763-in001_-en-p.pdf

 

 

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Thanks for your answer. I have a second question: I am using two push buttons with button relays. Do those take the voltage from the plc, or do they need to be connected to a power supply as well? If it comes from a power supply, this would need to be 120V, as the on state of the digital inputs is 79vac according to the manual, right?

 

This is for a senior design project btw, I will not do the installation myself, just need to make sure I have all the parts.

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Just now, I_rock_well said:

Thanks for your answer. I have a second question: I am using two push buttons with button relays. Do those take the voltage from the plc, or do they need to be connected to a power supply as well? If it comes from a power supply, this would need to be 120V, as the on state of the digital inputs is 79vac according to the manual, right?

 

This is for a senior design project btw, I will not do the installation myself, just need to make sure I have all the parts.

The first question is very simple.  They are relays.  In other words, they are switched contacts, or switches.  That means the PLC closes a pair of contacts to create continuity between two contacts.  The most important thing is to make sure you don't exceed the rated voltage or current of those contacts. 

 

You our should also keep in mind that relay contacts are physical and have a far shorter life span than transistor outputs.  I say that because if you're cycling the solenoid very often (I mean x times per minute), the life of the relay will be short.

 

The second question is a bit confusing.  Are you saying that you're using a push button switch to energize a relay?  If so, you go by the relays COIL voltage; it depends on what you buy or what the customer has already.  If your push button is going into a PLC input, you obviously need 120v.  I guess my question is, what are you "turning on" with your push button?  

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I apologize, I should have phrased the question better. I am using two push buttons which I guess open/close a button relay. This is the input for the plc.
The button relays are rated for 240ac. My question is, were does the electricity come from for the circuit which is opened/closed by the button relays? do they just need to be wired to the ac com and input terminal from the plc, can I just take 120v from the bus tap directly, or do they need a 120vac power supply?

 

 

 

 

 

 

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You will need to provide the power for the push buttons.

 

The inputs for your unit are 120vac.

 

Quote

two push buttons with button relays

I have never heard of such a thing. Do you have a part # or model #?

Your push buttons are probably just switches (maybe spring loaded). ( check to see if they are NO or NC.

Edited by Mickey

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