I want to remote control (WiFi/Zigbee) a water pump AC motor, 1 phase or 3 phase depending on the case, with the smallest board size possible.
I have used large motor AC contactor in past, it works fine but it is also very heavy, bulky, and it has significant "bump" when activating, it also need a relay to control the coil which is in 240V AC, I cannot use that here for these reasons.
The load is a water pump AC motor, 240V AC 1 phase or 3 phase (so 240V between a phase and neutral or 400V between phases), the maximum power of the pump is 3.5HP, but if I can handle 3HP it would be OK too.
As of now there are two options I can think of, either a circuit based on three triacs (for example BTA41-800B) with MOC3083 to drive them, or a circuit based on 30A relays (model SLA-05VDC-SL-A).
The triac solution looks good but I have two concerns with it, first is heat, I don't know how much heat to expect from the triacs, I can add a small heatsink for the 3 triacs tabs (tab is insulated), for example 70*20*10mm but not very much bigger. The second concern is what will append when the capacitor on the pump motor fails and the triac will see pretty much a short circuit, I plan to add some high power (130A) hall current sensors in the circuit for monitoring so I could use that to stop the triac within an half wave in case of short but sadly I also know the triac cannot be turned off elsewhere than zero current cross, which will not append with a short, I also think a fuse will not help since the triac will likely blow before the fuse has a chance to melt.
The second option is 30A relays, 1 per phase, they are given for 30A @ 240V AC. They are rated 1-1/2HP, which to my understanding mean 1.5HP, now I wonder if I use one relay per phase on a 3 phase motor what is the total power it can handle? is it still 1.5HP total or 4.5HP total?
Does it look like a good plan to use such relays? Any advice would be very welcome.
After more input it looks like triac or back-to-back SCR is not really an option since for 20A each phase will have to dissipate 30W, which is too much for the heatsink surface I can provide here.
Now one question remains about the 30A relay, with one relay per phase, each relay rated 1.5HP / 30A@240V, should I consider the system capable of driving 3.5HP or only 1.5HP?