I'm building my first arduino project, and I could use some help building up the relay portion.
My goal is to control a water pump that's running at 110V, 3/4hp, rated at 9A, and measured to run at 500 watts.
Initially I selected a 10A relay module from Sainsmart:
However, after reading about motor loads, I'm worried that I undersized the relay. Now I'm looking at:
A 20A EM relay:
- Is this enough of a safety factor for my motor size
- Would the Arduino have enough current to drive the coil, would I need additional circuitry to drive it?
A 25A SS relay:
- Pro, comes with a heatsink
- Would the 25A really be enough to support the startup spike of the pump motor?
A 40A SS relay:
- Does not include heatsink. Do I really need a heatsink for a constant 9A running through a SS relay?
How about a flywheel diode? I'm guessing that for an EM relay I should include a flywheel diode. I've seen reference that SS relays normally include snubber circuitry. Is this the case, and would either of the SS relays basically be drop-in with my application (5V arduino logic pin, directly to VDC side, 110VAC hot line through the VAC side).
I've read that EM relays are beefier and more reliable than SS. And I've also read that EM tends to fail open, whereas SS fails closed (potentially destroying my pump). However, the idea of a relay with no moving parts, zero-crossing switching, and an onboard snubber is really attractive.
What's your recomendation? Thanks for your help in choosing.