17th March 2009 12:31 AM
Setting up Solid State Relay to Solenoid with Snubber Circuit
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/c.../s102t02_e.pdf) is the setup we are using.
17th March 2009 01:24 AM
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).
solid state relay,
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