controlling three phase 1hp pump motor

Thread Starter


Joined Mar 22, 2020
I am looking ideas to control three phase 1hp pump motor for lifting water into well.

What should I keep in mind to design circuit ? Please recommend any good circuit


Joined Feb 20, 2016
What do you mean by controlling the motor?
Is it variable speed or just on and off?
Is it controlled by water level or timer?
Please post a bit more detail as you can use just a switch or a computer system or between the above.


Joined Jul 1, 2009
If this is AC, which it must be, SCRs won't work, because they will be turned off, every time the wave-form crosses zero, and the MCU would have to turn them back on- this is the fundamental process behind light dimming switches.

Instead, power-transistors, rated for the proper power of the circuit (Watt's Law), with opto-isolation for control of them to keep your circuit from actual direct connection to MAINs, would work really well for you. In the event there is a fault, the pump should also be connected to a breaker to disconnect it should something go wrong.


Joined Jul 18, 2013
What is wrong with the customary 3ph motor contactor?
Or am i missing something?
Simple I/O for both water level and coil switching, the latter can be either 24v using Mosfet or small relay,


Joined Jan 15, 2015
For simple On/Off you can use a simple relay type motor starter rated for 1 HP with a thermal overload trip. Available from any industrial supply house. There are also three phase SSRs available. Float switches could likely be used for level detection but unless you spell out more data it's hard to make suggestions. I see no need for a uC to run a simple On/Off pump.



Joined Jul 18, 2013
Also when using a modern contactor O/L there is a N.O, contact included which in this case can be used as an indicator/annunciator lamp etc, that comes on if the pump ever stops due to O/L.
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Joined Jan 23, 2018
I am wondering what part of the control scheme a computer would have. To switch the motor the correct scheme is to use a 3-phase contactor, as Max already stated. Those contactors made for switching the compressor of an AC outside unit wil probably be the least expensive.