Powering well pump with a generator

[steve tym]

If you buy something other than a Franklin drive for your pump, be very careful. As valveman stated, if you don't reach 30 Hz (half speed) in one second or less, you will damage the bearing in the bottom of the motor. The Kingsbury thrust bearing hydroplanes for lubrication. This doesn't happen until half speed, get there as quick as possible. A 3hp well pump will need to be 3 phase to make it variable speed, so that means a new motor and drive.
If you do a Franklin SD30 (for the 3 hp) you can do a 3 phase motor (cheaper than 1 phase) a 1.5 hp pump (because it will overspeed) and smaller wire (becasue of the 3 phase) and the drive unit. It would be a nice system and your generator will thank you.

 

[LouNY]

That 3 hp 240 volt motor that shows 42 amps on a clamp on meter is likely to be closer to 49 amps on startup. So at a bare minimum a 12KW generator may start it with nothing else running of course the surge load on the generator is going to bog it down quite a bit.
As far as a PTO generator not providing clean enough power for, I've read that here before and it must be a pretty cheap two pole unit to have poor power quality.
I've been using my 25KW pto generator for over 25 years and have had any problems with any kind of electronics when using it. Including UPS which I use to compensate for poor utility power.
Any generator is dependant on the power plant to drive it, doesn't matter if it's a 3600 rpm screamer on a 2 pole generator or a 1800 rpm driving a 4 pole generator. Usually the 4 pole will provide better power quality then a 2 pole.
PTO generators can be found in 2 pole or 4 pole versions they just use different gearboxs to get the correct generator speed to get your 60Hz power.

 

[arcteryx]

Thanks for the additional info. Based on the info posted, I don't think I will do the well pump easy start. The ROI is much longer with it, I was hoping for a few hundred dollar unit like the Micro-Air.

@ponytug I have researched solar, would love to do that but my power company is not solar friendly, they want to charge a higher rate for solar and have lowered the wholesale price for those who have it. It would take 17 years before I break even, which is ridiculous. It should be 5-7 years. I have discussed this with others who would like solar and standby batteries and they have also come to the same conclusion.

Still mulling things over and researching but I have to get the Micro-air hooked up first to understand the load. I suspect that the well pump will take as much if not more amps than the rest of the house, meaning the pump may take a 10KW generator but I could run everything else with a 10KW (or less) generator.

 

[mikester]

Get a real 10kW CONTINUOUS DUTY genny. Careful with the sales BS specs.

 

[Valveman]

I was looking at an old Franklin AIM manual that said only needed a 4KW "internally regulated" generator for a 3HP. But with "externally regulated" it says you need a 10KW. Was just on the wrong line, sorry. I can start a 1.5HP with a 3500 watt, but it lugs down pretty good. With a 10KW you shouldn't have to worry about soft start and all the problems that go with.

Here is a new AIM manual with genset sizing on page 5.

https://www.rcworst.com/Shared/content/mfr/franklin_electric/docs/franklinsubmersiblemotorguide2022.pdf

 

[MAX-24-Dean]

A 3HP single phase submersible has a locked rotor amperage of 71 and takes at least a 4KW generator to start.

From the motor ampacity tables in the NEC (Art 430). It gives the running load amps for a 3 HP motor at 12 amps. Inrush current is typically 6 times the running load amps.
12 amps x 6 =72 locked rotor amps.

General rule of thumb for sizing a generator for a single motor load is the amount of HP times 1000 volt amps x 3.

So 3 HP x 1000 = 3000 VA
3000 VA x 3 = 9000 VA
Minimum generator size for the 3 hp load wouild be 9Kw.

Some generator engineering tables will tell you you can start a 3HP motor with a 7.5Kw genrator if it is the only load. Tried this and it doesn't always work.
The rule of thumb above has always worked.
EDIT: this works for residential motor loads with 4 ton A/C or less and 4 HP or less electric loads.