snubber circuit for a relay

I am trying to find a snubber circuit for a relay. I have no clue what to even get I keep looking at rc circuit I found some for sq d relays I think will work but not sure.

This is for 120vac relay coils.

Basically we are getting some transient voltage from a radio unit that is controlling inputs to some motor vfd's. causing relays to chatter

Anyone point me in the right direction.

Maybe a MOV/Varistor?

Usually relay manufacturers offer snubber circuits that be directly installed on the coils of the contractors or relay.
As far as I know snubber circuits are mainly used to protects contacts from excessive voltage when the contact opens.

I don't think that it will be helpful in your case as you probably need some kind of filter on the supply line to relay coils.

In pinball machines they just solder a 1N4001 diode across the coil. Not sure if that would help - but they cost pennies.

kallileo said:

Usually relay manufacturers offer snubber circuits that be directly installed on the coils of the contractors or relay.
As far as I know snubber circuits are mainly used to protects contacts from excessive voltage when the contact opens.

I don't think that it will be helpful in your case as you probably need some kind of filter on the supply line to relay coils.

Click to expand...

I agree, snubber circuit is useful to keeping down the "ARC" when contacts OPEN!

But in your case it sounds more like some type of interference, but don't assume the interference is causing the relay to chatter.

Could it be the interference is causing the 120vac relay coil supply to operate at a different frequency which in turn would cause the relay to cycle at that frequency? (Which would be the relay chatter)

Rson,

this is for a 120 volt relay.


you can buy mov terminal blocks from ab or automation direct.

james

I'm a bit fuzzy on something:

You believe you are getting "transient" voltages in VFD inputs and these are causing relays to chatter. So the VFD itself has 120V IO that is switching 120V relay coils?

use a 150V MOV trying to figure out the RC snubber on an aftermarket it a guessing game at best. You need to experiment with different one to see what works.
for DC use a diode on the coil

I'm a little bit suspicious about RF directly causing a 120V relay to operate. I'm sure in theory it would be possible but that would be one powerful transmitter. Either that or I don't fully understand the issue.

I've seen RF cause low voltage low current inputs to behave badly. One of the servo amplifier would take off at max speed when you used a radio in the vicinity of an open cabinet. But this was caused by a small offset in the feedback. We solved that by using ferrite beads and chokes on the input wiring to the amp.

I stopped using RCs years ago when I was having problems with an old turret lathe that was controlled by zillions of germanium transistor gates.


I have found Varistors work best because they clip the inrush voltage off at the value of the varistor. The problems I have had with RC circuits, and I watched this on an O'Scope, is the cap charges up to a point before the resistor shorts it. In the case I am referring to it was causing the turret to lift and and index without a command from the processor, As I watched on the scope I saw the signal across the rc, I replaced all of them with Varistors and the problem was solved, I could see the voltage getting clipped off with the varistor whereas the rc let it rise too high.