Solid-State Relay instead of a contactor?

What a great project! How big is the tank?

I do not think that you can get solid state relays much cheaper than contactors. You need what, two 25 amp relays like Crydom D2425? That's about same as a 40-75 amp contactors -- about $20 with shipping if you are patient.

Also, I may be wrong but if you go the solid state route, pick a SSR that has zero crossing properties.

If I may offer another suggestion, add a 30 watt or 50 watt or so muffin fan to cool your pump when it is running. It will cost you basically nothing and may substantially increase reliability of your setup. A 30 or 50 watt muffin fan moves A LOT of air. An incredible amount.

SSRs need a decent heatsink for that current (16A or so @240VAC). If the SSR fails on (which they are wont to do) you'll be testing the safety relief valve. I don't see a lot of advantage to using an SSR in this application- the compressor is noisy anyhow and the life probably won't be an issue. Sometimes they have trouble turning off with motor loads- try to get the kind that is "back to back SCRs" rather than the triac kind.

Best regards, Spehro Pefhany

I have an SSR on my 2 Hp compressor. I had the first one blow (shorted) so I used a much higher rating and have had no further problems. The motor has an 11 A @ 240 V rating, and I'm using a 600 V 50 A SSR.

Jon

They are available cheap on eBay, but mostly these are used units swapped out from planned maintenance.

There are new and old ones oavailable on ebay, and both kinds are not cheaper than contactors on ebay.

Not a good application for 25-amp SSRs. Start current on an induction motor, particularly one with a compressor load, can exceed

Don't understand why you want a SSR.The only advantage of SSR is they are quiet.Try a mercury relay

On an inductive load? Good way to get a mercury-laden explosion unless they are specifically rated for that load (few are).

Best regards, Spehro Pefhany

I have a small supply of new in the box Crydom 2425s. $10 each, that includes shipping in the continental US. They were for a project that never happened.

this is a sensible deal actually.

Yes, indeed! The contactor that was in my compressor was actually louder than the compressor, and every time the motor started, I'd jump a foot! Now, there's no huge clang when it starts.

Jon

Thanks for the offer. I've put a bid in for a contactor, which I might get, but I'm still interested in trying some SS relays. OTOH, as someone said, I probably should go with something in the 40-50 amp range. My motor is a