Based on my research so far, I've concluded that a relatively low-cost, yet reasonably reliable way to control operation (on/off) a motorized water pump, is a well spec'd EM-relay with flyback diode. I might also put in an opto-coupler for isolation, if that improves safety. The whole thing would be assembled on a general-purpose phenolic veroboard, with point-to-point connectors.
Given the pump motor's specs, I wanted help checking if the selected relay would fit the bill, or should I look for another.
The pump's specs (the relevant parts):
Self-priming 1.0HP mono-block pump Operating voltage: 220VAC +/- 6%, single-phase 50Hz kW / HP: 0.75 / 1.00 Current: 5A Cap. run: 20uF 440V
The operating characteristics are about 100 on/off cycles per month, with each "on"-cycle being about 60mins long. AC power quality is not that great, with voltage fluctuating 10-12% around 220V, and line frequency fluctuating by 6-7% (as told by a local friend, who is knowledgeable in power electronics).
The EM-relay specs:
General-Purpose 1Pole Heavy Load SPST-NO Power Relay Coil Voltage: 12V Coil Resistance: 185 Ohm Contact current: 25A Switching voltage: 250VAC Life: Resistive-Load: 100 x 10^3 operations Motor-Load: Min. 200 x 10^3 operations, given (250VAC inrush 80A, cosφ=0.7, cut off 20A, cosφ=0.9)
Does that sound good enough ? The above mentioned relay has 3 variants -- Standard, High Isolation, High Current. For the moment, only 'Standard' one is readily available. Would that suffice ? Just curious, what might be the other 2 variants good for.
A surprising observations was that the EM-relay has longer life with motor-load, than resistive-load. Is that normal ?
Also, the readily available part is a "PCB mount" relay. Is that acceptable, or should I really try to hunt for the socket-mount / tab-terminal kinds ?
Finally, is it fair to assume that I do not need any kind of "snubber circuitry". PS, I understand very little of "snubber" though, but it has appeared few times in the material I've read so far.
Edit: Signs of aging, and some carelessness. Had asked this question exactly a year back, when I had just began working with relays, and forgot all about Russell's excellent answer. It does cover many of the questions I re-asked here. Thought of linking this together.