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Setting up Solid State Relay to Solenoid with Snubber Circuit

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excetara2

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I am setting up the Sharp ST102T202 solid state relays to the solenoid valves that operate at 120VAC and 10W. The recommended values for the snubber are 47Ohms and .022uF. I found cheap capacitors but what is the cheapest resistors to get because of the high voltage rating. Cheapest I could find were carbon composition for 2 dollars per resistor.

On page 9 of the datasheet (http://www.electro-tech-online.com/custompdfs/2009/03/s102t02_e.pdf) is the setup we are using.

Thanks.
 

i_build_stuff

New Member
The resistor can actually be a lot smaller than that--maybe like a 1/2 watt or so.

A 0.022uF capacitor will have a reactive impedance of about 120k ohms, so you're really only looking at about a milliamp of current when the thing is on. At turn off, there will be a spike of power that might get into the hundreds of watts, but it only lasts for like a microsecond, so the resistor doesn't need much of a rating.

If you want a pre-packaged solution, you could always go with a Quencharc. These ones might be a bit overkill for your application, but they are convenient and will definitely protect your SSR:

CORNELL DUBILIER|104M06QC100|Film Capacitor | Newark.com

For the cheapest option (assuming you have a lot of solenoids, and that's why you bring it up), I would go with 24VDC solenoids. Then, you only need a diode across the coil, and a transistor for drive it (instead of that SSR).
 
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