AC coil snubbers

All,
Please check my thinking. I'll be using zero-crossing solid state relays to fire some 120VAC solenoid valves. Since the SSR's are zero-crossing turn on/off, I shouldn't need transorb / snubber protection, correct?

I don't often deal with AC coils, and I'm used to putting diodes across DC coils.


-rpoet

You need snubbers. The back EMF is 90 degrees out of phase.

+1

Solid State outputs are always zero-crossing on turn-off, but that doesn't mean they don't have any noise.

keithkyll said:

You need snubbers. The back EMF is 90 degrees out of phase.

Click to expand...

TVS snubbers are cheap. I'll tack these onto the Mouser order:

http://www.mouser.com/ProductDetail...=sGAEpiMZZMuNo3spt1BaVxePKaRMsphF0NHb/SwEjv0=

Thanks,

rpoet

First, you need to check the specs of your SSR to see if any protection is built-in. Sorry didn't think of this in my first post.

Here's what Crouzet says about their SSR's. (Link )
"What is a snubber network and when would I use one?
A snubber network is a resistor and capacitor in series and is placed in parallel with the output of the ssr. Typically snubbers are required when the relay is placed in an environment that has electrical noise. Most manufactures incorporate a snubber network into their ssr’s. Crouzet uses an inductor along with transorbs to fill this role instead of a snubber network."


A TVS alone may not be enough, as shown in this paper from Crydom.
An RC type snubber is the first choice.
This type has an RC and MOV in one package from FM.