Hi guys, I want to make a circuit that controls a solenoid by using a 3V relay, and I will put the diode across the relay for protection, but my question is do I need to do anything for protection to the solenoid valve?
The problem is that the solenoid valve operates by 220 VAC, so I don't know what to do. The web is full of protection ways but the supply voltage was always a DC source not AC.
Thanks in advance.

 

It's not the solenoid that needs protection, but the contacts of the relay that switches the high voltage. Can you not substitute a solid-state relay? That would solve the problem. If that isn't possible, I think the best protection is a varistor across the contacts, selected to exceed the line voltage (and remember that it's the peak that counts, not an average or r.m.s. value) and with the ability to absorb the maximum energy that the circuit can be storing. The solid-state relay is much easier to deal with.

 

There are actually a few types of protections when you talk about relays.

protecting the contacts is one where ZNR's or unidirectional TVS diodes or snubbers can be used for AC. For DC ZNR's, or unidirectional TVS's can be used.

The bigger problem is protecting the solid state device driving the DC coil. This is where a reversed biased diode is placed across the oil to essentially allow the voltage created when the coil turns off to be absorbed by the coil instead of killing the solid state device activating the coil.

generally no special precautions are used for turn-on for AC coiled relays. I think random firing is recomended for triac driving of relay coils.

 

It is common when using low voltage control for AC relays and solenoids to add an RC snubber across the solenoid coil.
Max.

 

You could also use the 3 volt relay to control a larger relay that can survive the voltage and current better. You have not said anything about the current the solenoid uses. I suspect that 3 volt relays wouldn't have massive contacts in them.