Soft-start inverter--is it bad for my well pump?

[Vigilant24]

I have a "regular" 1/2 HP, 120VAC submerged well pump I'd like to be able to run on an inverter (as a backup). It's a 2 wire unit (so, the start capacitor is at the pump, not in a box above ground). It's about 120 feet down the well, water level is typically 60 feet down. I measured the running current as about 7A, I can't measure the starting amps with my meter but the stated locked rotor amps (LRA) is 50 amps.

My solar/FLA/inverter setup is for emergency backup only. 99.9% of the time we'll be on grid power. So, turning off other loads, etc is no big inconvenience while we pump water once per day for a few minutes.

I've seen some high frequency inverters that have a claimed "soft start" feature that ramps up the voltage on big loads to reduce starting current of inductive loads. The instructions from the inverter company say to use the soft start feature users should:
1) Turn off the inverter
2) Hook up the device/appliance that has the big startup load
3) Turn on the inverter. The voltage will ramp up over a short time.

This big pump motor starting current is the >only< load I've got that exceeds 1000W. It would be great to be able to use a 2000W (soft start) inverter to cover this load and everything else. I'd prefer to avoid the expense of a dedicated soft start box for this "maybe never use it" case, or the expense (and high idle wattage) of a big LF inverter. Well, that is, if the inverter soft-start function will accomplish a similar thing.

My questions
1) Is this soft-start inverter likely to do the trick? Is there a way of knowing short of just trying it?
2) Will this likely damage my pump?
2a) Potential electrical damage to windings/etc from the nonstandard voltage/current profile?
2b) Potential mechanical damage to impeller/bearings? I'm under the impression that these depend on a thin film of water to keep the bits apart, and worried that a longer period of grinding away at low RPMs on startup will wear things out sooner.

When I eventually need a new pump, a Grundfoss model might be a prudent investment.

Thanks for any assistance.

Mark

 

[Mattb4]

You may be able to get by with not needing the soft start by running the well pump with no pressure discharge to it. That is other than the 60ft head it has to overcome. The water would just go to a open air tank. If you need to pump it from there there are several on demand pump that are low draw for amperage.

The inverter soft start may work fine but until you try it with your particular well setup it is unlikely anyone could guarantee it. I have a 2000w 24VDC 120AC PSW inverter that balks on trying to start a small air compressor (similar idea to a pump) even with the soft start though it will start a 15a circular saw.
So:
1. Considering the vagaries of inverter quality and also the demands of the pump the answer is no way until you try.
2. Try it out and watching to see if the pump starts quickly and runs OK I doubt you would see any damage. Be ready to stop if it appears to be having problems pumping.
b. mechanical damage due to insuficent electrical power is unlikely.

 

[Vigilant24]

Thanks much for the reply

You may be able to get by with not needing the soft start by running the well pump with no pressure discharge to it. That is other than the 60ft head it has to overcome. The water would just go to a open air tank. If you need to pump it from there there are several on demand pump that are low draw for amperage.

I think that'll be the plan. No matter how we get it out of the well (120VAC pump, hand pump, well bucket) it'll go into a barrel/tank. From there, if we need pressurized water (to filter it or just to move it somewhere more convenient) it'll be via a small 12VDC diaphragm pump.

The inverter soft start may work fine but until you try it with your particular well setup it is unlikely anyone could guarantee it. I have a 2000w 24VDC 120AC PSW inverter that balks on trying to start a small air compressor (similar idea to a pump) even with the soft start though it will start a 15a circular saw.
So:
1. Considering the vagaries of inverter quality and also the demands of the pump the answer is no way until you try.
2. Try it out and watching to see if the pump starts quickly and runs OK I doubt you would see any damage. Be ready to stop if it appears to be having problems pumping.
b. mechanical damage due to insuficent electrical power is unlikely.

Yeah, I think you are right. I'll buy the inverter from someplace with a convenient return policy and bring it back if it's not suitable.

I have also thought of trying this "caveman" idea of using an NTC thermister or two (in series) in a small box to briefly increase the resistance during the startup period.