OT - Well pump VFD or soft start or ???

Our 1 hp submersible well pump runs @ 240VAC, about 8-9 amps.
Starting load is some unknown multiple of the 8A run.
When the utility fails, we run on the 21kw Perkins Diesel genset, starts the well pump fine.

(However, the new heat pump scroll compressor really zapped the genset for the start, I put a soft start kit on the compressor, fixed the startup load for the heat pump)

Now I am installing a small (7kw) solar power system, would like to know if it is possible to install a Teco Westinghouse VFD (or similar) on the well pump, so as to ramp up the starting load gradually.

Not sure if the VFD would go in front of or behind the well pump control box.
Guessing after (between the control box and the pump), so that the control box sees a normal waveform.
Or is there a better way to reduce the instantaneous overload on the solar inverter when the well pump starts? What do you think?
Frank in Florida

It sounds like your well pump is single phase 240VAC - and I'm not aware of a commonly-available VFD that supports single phase motors. Plenty will take single phase input and put out variable frequency 3 phase - so I suppose a well pump motor replacement to 3 phase might be one answer.

I'd think that if you added sufficient battery and inverter capacity to your solar installation, you could support the required starting current?

Yes, you are right, all the VFD’s I have now are running 3 phase motors from my single phase utility.
Guess beefing up the solar is the way to go, and keep it simple.

I was surprised to see this single phase in single phase out variable speed well controller on a job spec the other week. I haven't used one yet but I thought I would share it.
Goulds 1AS15, Aquavar Solo, Variable Speed, Constant Pressure Controller With Transducer, (230 Volts, Single Phase Input), 2 or 3 Wire Motors With 1/2-2 HP, 20/85 Min/Max PSI, Indoor/Outdoor NEMA3R

Your solar inverter, if it's gridtie only (implied) supplies power to the line from the solar panels. When your pump starts, it uses power from the line, not directly/exclusively from the panels. The synchronous inverter isn't required to supply all the power to the well pump, nor would it be wise to wire it that way. If it were, you wouldn't be able to pump water at night, for instance, or at any time there wasn't sufficient sun to start the pump.

Prob best to leave your solar installation out of the discussion, unless you want it to supply the pump when utility power goes out. Then, as Pete says, you will need to have a backup battery bank and an inverter (a standalone DC to AC, different from the one you have) to run the pump. And a transfer switch to protect the utility line from being energized from your side. There exist "opportunity" synchronous inverters that allow some use from solar when utility is absent, but even one of those is unlikely to be able to start your pump.

Lots of options and tradeoffs there - 220 or 110V pump? Two "stackable" inverters are generally needed to make 220V, and they'll need to be sized to handle the pump starting current. Only one inverter is required for a 110V pump. Or a DC pump run directly from batteries. Or maybe it's best to run the pump the way you are now. Hard to get a sense of the situation without more details.

The problem with single phase VFDs (I have designed a couple) is that they have to start the motor at full volts. That is the only way to get the capacitor of a PSC to pass start current. Most standard single phase motors are not suitable for VFD use, and would in any event have the same issue.

I think a shaded pole can be started at fairly low voltage, but since they are not useful at pump HP, I have never tried one.

One company has pump VFDs, or at least put out an RFQ for a single phase down-hole pump VFD. We got the RFQ, but it did not look like something we wanted to get into (and I think we were right).

However, theirs had a huge start surge requirement, it clearly was not soft starting.

Theoretically, the output from a 3 phase VFD could run any motor with a run cap and a 90 deg phase shift needed on the winding. You would have to reprogram the VFD, or else use a scott-T setup on the output, with no capacitor on the motor. It should soft-start, at least if it was unloaded at start.

If you get lucky, you will need only one transformer to drive a "single phase" 3 wire cap start motor from a 3 phase inverter, you need a 240v:120 volt tx.


The 240v coil goes along with the primary phase of your motor to phase 1 and 2.
120v output of transformer goes to phase 3 of vfd.
Third wire of motor goes to the 120v coil.

This will provide the motor 208volts at 90 degree phase shift on aux coil and 240v on primary coil. If 120v coil is connected backwards, you will get 268volts at a 30 degree phase shift. Thr motor might startup but the amps on the start winding will be high.

If 208 is not enough, use a buck boost transformer to add more volts.

fish123 said:

Now I am installing a small (7kw) solar power system, would like to know if it is possible to install a Teco Westinghouse VFD (or similar) on the well pump, so as to ramp up the starting load gradually.

Click to expand...

The Franklin Pump web site has a detailed description of what is required when using a VFD to drive a 3 phase well pump.

There are two main requirements.

The first is that the start ramp time needs to be less than one second to avoid damaging the pump thrust bearing.

The second is that a line filter after the VFD is required to prevent the motor windings from being damaged.

https://franklinwater.com/media/124113/Page-40-to-41.pdf

Franklin also makes a well pump designed specifically to run off a solar/ battery system.

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Thanks for all the replies! Single phase VFD is more complicated than I expected.

This solar system (off grid) has to to start & run the well pump, plus provide enough power to run some lights and a refrigerator.
There is going to be a 48vdc battery bank to contain the energy from the PV panels.

The pump is a Goulds 18GS10412C. 8.4 amps @ 240vac, running load.
The inverter is a Schneider Electric Conext XW Pro 6848.
Rated at 6800W.
Overload ratings: 30 min @ 8500w, 60 seconds @ 12,000w

It takes the pump about 30-45 seconds to recharge the 85 gal precharged water tank.
Cycles only a few times a day, unless we are doing laundry/showering.

It’s going to be a while before I finish building the system, will see if it can start the well pump w/ 12kw.

I see a 3 phase well pump in your future.....

Gohertz makes single phase VFDs. They bypass the start/run capacitors and connect to the start winding directly.