The house I moved into has a well. I find that the inrush current to the pump is some 26 Amps (normal running is between 6 and 7 amps). The pump is a 240-volt, 2-wire pump. No start capacitor can be seen at the top of the well or in the house. I don't know what kind of pump is down there, though Google Earth suggests the well was worked on around 2019, so the pump may be newer.

I am considering putting a soft-start on the pump, so my generator, which might barely push 20 amps at 240 volts into space heaters based on my tests, will have a chance of starting the well pump. (The generator is a Pulsar HD6580B at 5500W max on gas, 4950W on propane; the heater test was run on gas fuel.)

If this pump had an accessible start cap I'd be OK with adding a soft start that replaces starting caps (like this https://www.microair.net/products/easystart-364-3-ton-single-phase-soft-starter-for-air-conditioners ). But I don't know if the pump has a start cap down at the pump, or what a soft-start might do on a motor that has a start cap.

I am considering something like a Schneider Altistart ATS01N1. https://www.se.com/ww/en/product-range/779-altistart-01/ PDF for one possible unit: https://download.schneider-electric.com/files?p_enDocType=Instruction+sheet&p_File_Name=ATS01_IS_ATS01N1--FT_1624685_07.pdf&p_Doc_Ref=1624685 Other ideas would be appreciated.

Will adding a non-start-cap-replacing soft-start to a motor that has a built-in inaccessible start cap cause trouble?

  • I have done some web-searching on this but I can't hit the correct search terms to differentiate away from the usual replace-the-start-capacitor soft-starts. Nov 25, 2022 at 17:23
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    Would be best to figure out what you have for a pump. A two-wire well-pump VFD controller (also sold as "constant pressure controller") may be an option that will lower starting surge as well as offering other benefits, but they are not inexpensive. Still, if less than a new generator, might pay off.
    – Ecnerwal
    Nov 25, 2022 at 17:55
  • You could try calling local well/pump contractors to ask if they have worked at this property/address and have documents regarding what was installed, if you can't find something like a state database of wells that will tell you which contractors have worked there to shorten your list. Usually the pump info is stuck on or near the pressure tank.
    – Ecnerwal
    Nov 25, 2022 at 18:15
  • That's on my list for Monday, @Ecnerwal, thanks! Hopefully the town has records of what was done. Nov 26, 2022 at 16:34
  • Wells with start capacitors up top need a fourth wire in the cable going down the well. That would be costly on a deep well. Dec 26, 2022 at 22:44

1 Answer 1


I feel probably the best solution is to get a bigger generator. What you are trying to do may work it may fry your pump. There is a reason it needs the current. From your question It appears to be a submersible pump that also has to overcome the back pressure on the line, that takes energy. With a soft start it may never get to speed.

I have no idea what you are looking at or what is connected but I have found generators use less fuel if they are not fully loaded. I have no idea how much load you will put on it. You may find you will not use much more fuel with the next size generator. Also generators have a surge rating that should take care of a motor start.

  • I appreciate the idea, Gil, and I am worried what the soft-start might do. I lean a bit away from a more powerful generator, though, since I have limited fuel, no natural gas at the house, only what gasoline or propane I can bring in. A more powerful genny will use more fuel on idle... There are pumps with soft-start built-in, so it's apparently possible if done correctly. Nov 26, 2022 at 16:37

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