The Benefits of Three Phase AC Pumps For Solar Water Pumping

Johncfii

Solar Addict
I’ve been operating submersible well pumps for more than four decades. I’ve installed, repaired, and replaced many pumps. The reason for this post is to encourage anyone operating, or planning to operate a submersible pump on solar power, of the significant benefits of powering the pump with three phase, 230 VAC power. For a new or replacement install, it isn’t costly, and it isn’t especially complicated. You don’t need three-phase mains power. A Variable Frequency Drive generates the three phases.

The benefits:

1. NO starting surge current to overwhelm or stress your system. The variable frequency drive (VFD), that converts your 230-volt single phase power from your solar inverter to three-phase 230 VAC, is fully programable to provide a slow, linear, ramp up of motor speed. (I have mine programmed to steadily accelerate to full speed over 20 seconds). This is far superior to “soft-start” single phase motors.

2. NO high starting torque that has damaged many long down pipes, and many power leads over time.

3. Better motor efficiency. For any given HP rating, a three-phase motor is about 15% more efficient. A typical 1-1/2 HP single-phase submersible pump motor draws 10 amps at full load, which is 2300 watts at 230 VAC. A typical 1-1/2 HP three-phase motor draws 5 amps at full load, which is 1992 watts. (The formula to calculate three phase power is: 1.732 x amps x volts).

4. You will have fully variable motor speed that will allow you to reduce power draw in times of low sun energy. You can easily set your VFD to run the pump motor at 3/4 of full speed, or 1/2 of full speed. Water pumped is fairly linearly proportional to power consumed, down to about 50% of full speed. Some pump motors can even be operated with reasonable efficiency down to 25% of full speed if you are REALLY short on power reserves, and can make do with a smaller volume of water during hard times.

5. You can use smaller conductors down to the pump. Three-phase motors generally allow the use of one size smaller conductor. If your single-phase motor would require 10 ga conductors, a three-phase motor, all other things being the same, will only need 12 ga conductors. (This potential saving can be offset if your single-phase motor is 1-1/2 HP, or less, and is of the “two-wire” variety).

6. You can install your water system with a smaller, or even without, a pressure tank. This is possible because you can install a $130 pressure transducer that will send a 4-20 milliamp control signal to your VFD that varies linearly with system pressure. You program your VFD to maintain your chosen system pressure, and the pump speed will ramp up and down to maintain that constant pressure, as it reads the input from the pressure transducer. But this refinement is optional.

7. Three-phase motors cost about 10% less than single phase motors of the same HP. This is because their lower current demand allows the build with less total copper in the windings.

8. Most of these modern Variable Frequency Drives do not require a pure sine wave input. Whatever AC waveform you input is first converted to about 320 volts DC anyway. (Verify with your VFD vendor.)


The disadvantages:

1. You have to install an extra component in the form the VFD. But these are now amazingly affordable and reliable. A VFD rated for 3HP costs less than $300. I recommend selecting a drive rated for twice the HP rating of your motor. The incremental cost is very small. This increases reliability because the system runs cool, with little stress. I have both Fuji and Hitachi drives that have been in daily service for eight years with no trouble.

2. Some VFD manuals will recommend that a “line reactor” be installed at the drive output for long wire runs. Not a big deal. A $50 to $100 added cost.

3. As a DIY system, this can save you a ton of money compared to buying prepackaged system of the same components from Grundfos. But it does require some study, and some electrical understanding. If you managed to DIY your solar system, you can DIY this.

4. 1-1/2 HP is about the smallest size three-phase submersible motor available.

We have three wells on our property, all with three-phase pumps running off of VFD’s. Before my conversion to three-phase motors and VFD’s, we had to pull and replace some system component, in one well or the other, about every two years. It was always either a pump motor, a pump, cracked PVC down piping, or damaged lead wires. It was so frequent that I built an A-frame for my tractor that allows my wife and I to pull and install any pump ourselves - by running a steel cable over a pulley at the top of the A-frame, and connected to the bumper of our pickup. She would drive forward 20 feet to pull 20 feet of down-pipe up out of the well. We got to be very fast at it.

But since my conversion to three phase pump motors, we have not pulled a single pump in the eight years since. I am convinced that this is because of low starting torque, no surge current, and a pump motor than runs cooler at higher efficiency. (We do have hot well water which is not good for long component life anyway).

In the summer, when we have an excess of solar power, the domestic water pump is set to run from our solar panels during daylight hours. This is when we do our garden/lawn watering.

Here is a link to one source for the VFD’s. Note that they come in a flavor that requires 3-phase input, and a flavor that will accept single phase input:

Here is a link to a pressure transducer that can be used to replicate the Grundfos tank-less system:

These are line reactors:

Feel free to send me a direct message if you would like some help in getting past any confusion about this approach to water pumping using solar power. I’ll try to help, to the extent that work allows.
 
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Roswell Bob

Solar Addict
I’ve been operating submersible well pumps for more than four decades. I’ve installed, repaired, and replaced many pumps. The reason for this post is to encourage anyone operating, or planning to operate a submersible pump on solar power, of the significant benefits of powering the pump with three phase, 230 VAC power. For a new or replacement install, it isn’t costly, and it isn’t especially complicated. You don’t need three-phase mains power. A Variable Frequency Drive generates the three phases.

The benefits:

1. NO starting surge current to overwhelm or stress your system. The variable frequency drive (VFD), that converts your 230-volt single phase power from your solar inverter to three-phase 230 VAC, is fully programable to provide a slow, linear, ramp up of motor speed. (I have mine programmed to steadily accelerate to full speed over 20 seconds). This is far superior to “soft-start” single phase motors.

2. NO high starting torque that has damaged many long down pipes, and many power leads over time.

3. Better motor efficiency. For any given HP rating, a three-phase motor is about 15% more efficient. A typical 1-1/2 HP single-phase submersible pump motor draws 10 amps at full load, which is 2300 watts at 230 VAC. A typical 1-1/2 HP three-phase motor draws 5 amps at full load, which is 1992 watts. (The formula to calculate three phase power is: 1.732 x amps x volts).

4. You will have fully variable motor speed that will allow you to reduce power draw in times of low sun energy. You can easily set your VFD to run the pump motor at 3/4 of full speed, or 1/2 of full speed. Water pumped is fairly linearly proportional to power consumed, down to 50% of full speed. Some pump motors can even be operated with reasonable efficiency down to 25% of full speed if you are REALLY short on power reserves, and can make do with a smaller volume of water during hard times.

5. You can use smaller conductors down to the pump. Three-phase motors generally allow the use of one size smaller conductor. If your single-phase motor would require 10 ga conductors, a three-phase motor, all other things being the same, will only need 12 ga conductors. (This potential saving can be offset if your single-phase motor is 1-1/2 HP, or less, and is of the “two-wire” variety).

6. You can install your water system with a smaller, or even without, a pressure tank. This is possible because you can install a $130 pressure transducer that will send a 4-20 milliamp control signal to your VFD that varies linearly with system pressure. You program your VFD to maintain your chosen system pressure, and the pump speed will ramp up and down to maintain that constant pressure, as it reads the input from the pressure transducer. But this refinement is optional.

7. Three-phase motors cost about 10% less than single phase motors of the same HP. This is because their lower current demand allows the build with less total copper in the windings.

8. Most of these modern Variable Frequency Drives do not require a pure sine wave input. Whatever AC waveform you input is first converted to about 320 volts DC anyway.


The disadvantages:

1. You have to install an extra component in the form the VFD. But these are now amazingly affordable and reliable. A VFD rated for 3HP costs less than $300. I recommend selecting a drive rated for twice the HP rating of your motor. The incremental cost is very small. This increases reliability because the system runs cool, with little stress. I have both Fuji and Hitachi drives that have been in daily service for eight years with no trouble.

2. Some VFD manuals will recommend that a “line reactor” be installed at the drive output for long wire runs. Not a big deal. A $50 to $100 added cost.

3. As a DIY system, this can save you a ton of money compared to buying prepackaged system of the same components from Grundfos. But it does require some study, and some electrical understanding. If you managed to DIY your solar system, you can DIY this.

We have three wells on our property, all with three-phase pumps running off of VFD’s. Before my conversion to three-phase motors and VFD’s, we had to pull and replace some system component, in one well or the other, about every two years. It was always either a pump motor, a pump, cracked PVC down piping, or damaged lead wires. It was so frequent that I built an A-frame for my tractor that allows my wife and I to pull and install any pump ourselves - by running a steel cable over a pulley at the top of the A-frame, and connected to the bumper of our pickup. She would drive forward 20 feet to pull 20 feet of down-pipe up out of the well. We got to be very fast at it.

But since my conversion to three phase power, we have not pulled a single pump in the eight years since. I am convinced that this is because of low starting torque, no surge current, and a pump motor than runs cooler at higher efficiency. (We do have hot well water which is not good for long component life anyway).

In the summer, when we have an excess of solar power, the domestic water pump is set to run from our solar panels during daylight hours. This is when we do our garden/lawn watering.

Here is a link to one source for the VFD’s. Note that they come in a flavor that requires 3-phase input, and a flavor that will accept single phase input:

Here is a link to the pressure sensor that can be used to replicate the Grundfos tank-less system:

These are line reactors:
Great assessment! Thanks for the intel.
 

Hedges

I See Electromagnetic Fields!
I've used a Hitachi VFD with a 2 HP 3-phase pool pump for about 15 years.
At default switching frequency it made audible noise, so I increased it to 15 kHz (which derates output a bit.)

When running off-grid with a SB 10000TLUS (transformerless) PV inverter and Sunny Island, I saw an error from the PV inverter. I think the poor PF of the VFD caused that, so didn't use them together off-grid anymore. I'm using transformer type inverters now.

For someone with a high-frequency transformerless inverter, the VFD might be a problem.

Johncfii - what kind of inverter do you use?

 

Johncfii

Solar Addict
Hedges ... good additional information. Thank you.

I have only ever used an Outback VFX series inverters with capacity that is almost 4x the full load power consumption of the pump motor. I have seen cautions that indicate that a VFD can cause problems for a power supplying inverter that is marginally sized with respect to the VFD Load. But your 10,000 watt SB inverter wouldn’t seem to suffer from being under sized.
 
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Hedges

I See Electromagnetic Fields!
Outback would have a low-frequency transformer, which would isolate the inverter somewhat from the higher harmonics of 60 Hz that are generated by a non-linear load.

That 4x (or I say 5x) requirement could be to meet starting surge for induction motor without VFD. With VFD, no surge and I think DC direct from PV or from an MPPT could feed the VFD capacitor. (for PV direct, Voc and Vmp would have to be within input voltage range.)

My PV inverter had maybe 6kW of PV available to it. Four Sunny Island battery inverters could provide 23kW continuous, and frequency was shifted to reduce PV output to match load at the time I saw an error.

More recently I used a scope and current transformers to measure current draw in AC line and battery. I turned off the PV inverter when running the VFD and off-grid.

Third plot, top trace shows current measured by a current transformer around AC line, fed by Sunny Island and powering VFD for 2 HP pump.
Instead of drawing sine wave current like a resistive load would, current draw is zero except for where it follows peaks of sine wave and draws +/-28 or 29A (shown as V on scope).

Bottom trace shows the ripple (but not DC current) coming from battery for one Sunny Island, multiply 4x to get total.


I think the error message from transformerless Sunny Boy was "IGBT error", but don't find that in the manual.
Maybe a reactor (inductor) or transformer on AC input would help filter the current. Pump switch could turn it off so not powered all the time.

I had heard that VFD can cook motors not rated to be used with them, so I did get a 3-phase reactor which I put between VFD and motor. That should attenuate higher frequency harmonics getting into motor. I think one issue is circulating currents in laminations causing heating. Another could be imbalance of current from the three phases finding a return path through ground and shaft bearings. Now that my work experience covers similar behavior for EMI, I realize a common-mode choke would be good to confine return currents to the three wires (three windings around one core.)

What we would like is a VFD with 1.0 power factor, one which draws a full sine wave current to charge its capacitors instead of just clipping tops of sine wave with diode. Most power-factor corrected power supply designs just try to actively cancel harmonics, rather than presenting a "Real" (simulated resistive) sine-wave load.
 
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Johncfii

Solar Addict
Hedges, Thanks again for sharing your findings.

Years ago, when I was trying to track down a source of RFI that was interfering with my HF radio reception, I tried installing several forms of toroidal chokes around the input and output leads of the VFD. i could never detect any benefit. Checking for RFI during episodes of neighborhood grid failure, in frustration I concluded that the RFI problem was probably the pervasive presence of all sorts of modern electronics that generate a RFI. But with EMI being so pervasive, so many consumer complaints, and tighter eauipment standards imposed by veparious gevermrnt bodies, current versions of the VFD manuals have pages and pages of discussion about how to minimize EMI.

I had also read that VFD can potentially damage some motors, so I run a load reactor in the output leads to the pump for the same reason. But I haven’t installed a line reactor on the input. When I get home I will look at the waveform of the Outback inverter output when supplying a resistive load, compared to when supplying the VFD. An input reactor might be wise. While I don’t have a problem that I know of, I see that the current VFD manuals emphasize using an input line reactor even more strongly. Maybe there would be some benefit from any power factor improvement.
 
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Johncfii

Solar Addict
The first photo below is the output waveform from my Outback VFX3624 inverters when not powering a VFD.

The second photo is the waveform of input power being supplied to the VFD from the Outback inverters. While the audio frequency ringing imposed on the waveform has never caused any problems that I have detected, I’ve ordered a suitable reactor that might block the ringing from being fed back into my inverter and distribution system.
 

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Hedges

I See Electromagnetic Fields!
Looks like multiple traces shown overlapped on the screen.
Maybe driving the VFD, what we're seeing is that the high frequency switching/inductor used in Outback can't keep voltage up driving into the short circuit that is a capacitor (VFD front end.) There is resistance in the AC wiring, and for a moment voltage is raised by the pulse of current, but the current quickly goes away.

Do you have a current probe or current transformer so you can measure AC current draw?
If not, then differential voltage measurement across a shunt. That could be a length of wire. If you ran an extension cord back from the VFD to the inverter, voltage could be measured between hot on extension cord and hot at Outback, so entire length of AC is a shunt.

Measuring hots, that requires differential probe or subtraction of two two probes.
If load is line to neutral, then just single-ended measurement of neutral relative to ground would do it.

I'm wondering if current follows those high frequency pulses. My current measurement didn't; I should go back and measure voltage.

It is also possible your voltage pulses are from VFD drawing pulses of current proportional to voltage (poorly decoupled so seen on AC as well.) But I think that is unlikely because even if VFD is running 60 Hz it wouldn't be synchronized to AC input.

Hopefully reactor cleans that up.
 

Pyrofx

Flux capacitor builder
Great timing.
We start punching to 1050 feet next week.
Time for pump.
I can run my rotors phase to make 3ph on the 2 Sunny islands. It ran the mill and the lathe no problem.

I'd like to run a 3ph pump. Either 5hp , or 3hp. One gets lots of water ( 5gpm lol ) the other 3 and a lot less power. Really want the 5hp.

Watching this with anticipation!

Greg
 

Johncfii

Solar Addict
Looks like multiple traces shown overlapped on the screen.
Maybe driving the VFD, what we're seeing is that the high frequency switching/inductor used in Outback can't keep voltage up driving into the short circuit that is a capacitor (VFD front end.) There is resistance in the AC wiring, and for a moment voltage is raised by the pulse of current, but the current quickly goes away.
I should have taken a close photo of the wave form.

It is only one trace, with the pulses being the same frequency as the VFD switching frequency. When I get the line reactor installed, I will take before and after photos, with trace expanded to measure the pulse frequency. I’ll try to hook up some kind of shunt to also see/measure current response.
 

Wellbuilt

Solar Addict
Hmmmmmm , I have no clue what you guys are talking about ☹️
but I wish I did .
I’ve been trying to figure out how to pump water out of my well for 5 years .
I ended up with a grundfos SQF 6-3
I hope it holds up .
Im going to get it wet soon .
 

Wellbuilt

Solar Addict
I sure hope so , there is a lot of talk about people changing pumps @10 years .
I’m 60 years old and never changed a well pump ( knock on wood )
 

Pyrofx

Flux capacitor builder
Is the goulds vfd pump controller just a glorified Hitachi?
Were drilling next week and I have to decide 3ph or not.
I can stack a vfd behind a rotary to try and clean it up. But that's a lot of added crap
 

Guido1

New Member
Hello
I'm pretty new to solar, but I have been trying to cram for 3-4 years using blogs such as this and books.
Wifey and I are finally retired and will move to our small ranch in East Texas. Lots'a sun and lots'a heat.
I'm trying to assemble a simple off-grid system with battery backup that can power our well pump and heat pump, particularly for cooling. I also have a woodworking shop with a few single-phase 220v power tools. No utilities on the ranch except grid electricity.
I like the 3ph well-water pump idea a lot. I like the idea of foregoing the massive inverter idea, as well, and it seems the VFD makes the boat-anchor inverter obsolete, at least as far as the well pump.
My pump guy says he has occasional issues with Grundfos pumps in the Roher aquifer where our well is located, so he's hesitant to install and warranty them. Going with a 3ph 1-1/2HP standard pump & motor greatly simplifies.
If one goes with Enphase micro-inverters, or possibly the LG NeON RACe PV panels, is there an easy means to obtain split-phase power for whole house utilities and HVAC? Do you simply pigtail two separate 110v "legs" off two groups of panels, and re-combine them downstream as needed for 220v use? I was originally gazing at an inverter with split-phase capabilities, but now I'm hoping to eliminate that component.
I realize that's probably an elementary question for you wizards, but heck, a fella's gotta ask at some point.
 

Johncfii

Solar Addict
A VFD that puts out 240-volt 3-phase power, does not actually require a split phase input. It only requires 240-volt single phase AC.

If you have a heafty enough supply, it would be possible to feed 120-volt single phase into either a conventional 2:1 transformer, or a somewhat less expensive auto-transformer, that will output 240 volts to feed the VFD. But you would probably have to pay something like $1000 on eBay for a used, functional, auto transformer of that size. You can buy a pair of new 4KVA Outback Power auto transformers for about $500 each, and run them in parallel. Look on ebay, sometimes such used items are pretty inexpensive because the market for used is so thin..

It might end up being more cost effective to just combine a pair of solar inverters, each putting out 120 volts. This would give you true 240-volt split phase.

I dont have any experience with micro-inverters, so don’t know how to wire them for 240 volts, and I’m hesitant to guess. One of the other brilliant minds around here probably does, though.

Just curious, does your pump guy explain what is special about the Roher aquifer that makes it hard on Grundfos pumps? Perhaps from sand, or high mineral content, or high water temperature?
 
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Guido1

New Member
A VFD that puts out 240-volt 3-phase power, does not actually require a split phase input. It only requires 240-volt single phase AC.

If you have a heafty enough supply, it would be possible to feed 120-volt single phase into either a conventional 2:1 transformer, or a somewhat less expensive auto-transformer, that will output 240 volts to feed the VFD. But you would probably have to pay something like $1000 on eBay for a used, functional, auto transformer of that size. You can buy a pair of new 4KVA Outback Power auto transformers for about $500 each, and run them in parallel. Look on ebay, sometimes such used items are pretty inexpensive because the market for used is so thin..

It might end up being more cost effective to just combine a pair of solar inverters, each putting out 120 volts. This would give you true 240-volt split phase.

I dont have any experience with micro-inverters, so don’t know how to wire them for 240 volts, and I’m hesitant to guess. One of the other brilliant minds around here probably does, though.

Just curious, does your pump guy explain what is special about the Roher aquifer that makes it hard on Grundfos pumps? Perhaps from sand, or high mineral content, or high water temperature?
Hello, Johncfii

Thanks very much for the reply and suggestions.
So, the VFD's I was eyeballing (Hitachi, from a link you posted at top of this thread) 3HP for my 1-1/2HP pump (currently) as you had recommended) showed voltage requirements for 200V and 230V respectively, so I assumed they required +/- 220V AC with two hot 120V legs, which from what my history with 220V motors, is referred to as single phase. At least, as compared to true 3 phase service, with 3 hot legs in the circuit. I guess the true description for that service is 220V split-phase, as you allude to above.
But what I get from your response is they require 200V (+) from a single hot-wire AC circuit? That could certainly complicate the issue.
What is the typical source for that power? Can it be obtained from the grid somehow, or is it normal to expect the transformer solution described above in your response?
It still sounds easier and possibly cheaper to go with transformer(s) and VFD, and worry about the whole-house stuff later. Clean, obtainable drinking water is unquestionably the most valuable asset to have in a grid-down situation. Unclean H2O claims many lives in a very short period of time.
The paired, smaller inverters for household 220V/120V service sounds like a really practical suggestion, also. I'm just leery of the really big inverters, there seem to be horror stories abounding for most of them, although I know that for a price, reliability can be obtained.

My well/pump resident expert (he drilled the 460' deep original well) said he used to recommend and install Grundfos pumps throughout the area, then he was getting failure callbacks on about 1 of 6 that he had done. Minerals, I would expect calcium and such, was the culprit, but he said it was really unpredictable. One user would have issues, while their neighbors or another one of Brian's clients close by had no issues whatsoever. Chambers & Philips out of Tyler, TX were the drillers/installers. After that discussion, I purchased a PTO generator for the tractor and figured I'd worry about long-term solutions later. The Franklin "10 Series" 1-1/2HP pump/motor has been in since 2005, I'm thinkin' I'd rather replace it on my schedule than the pump's schedule. I'm still going to try and go with the VFD and anything else within reason to get it to work. I value reliability, especially with our drinking water, and from your description of your pumps with the VFD's installed, that's what I would like to have.
Thanks muchly for offering that advice, and even more so for your personal response.

Respectfully posted,
Paul
 

Hedges

I See Electromagnetic Fields!
A 3-phase motor doesn't care how the three wires are referenced to ground. Probably a VFD doesn't either (although one could design a device with surge protection clamping to ground that might care.) Whether VFD is fed +/-120V from 120/240V split phase or single 240V referenced to ground isn't likely to matter. The only difference is voltage between a wire and ground, which requires more insulation. But insulation is typically rated above 600V anyway. There would be some difference in current flowing through parasitic capacitance, again not a big deal.

On grid, you don't have the issues of starting surge, but you want to run off-grid during failures so there it matters. I think Grundfos is a 3-phase pump and VFD, so the question is whether a different brand of pump is less affected by calcium or whatever.

I've been seeing occasional issues with inverters and VFD. I have a 2 HP Hitachi VFD and 2 HP 3-phase pool pump. My SMA 10000TLUS once said "IGBT error" with pump running while off grid with Sunny Island. I thought transformer type Sunny Boy 5000US would be immune, but when it tried to connect to island grid with the same pump running it said, "Disturbance K1 close". After that it refused to connect even with pump off until I power-cycled its PV input. The system seems to operate with the VFD on, but has a problem with the GT inverter comes online with VFD already running. Ideally VFD would have 1.0 PF and present a simulated resistive load, drawing sine wave current. The cheap ones don't.

Is your PTO generator 3-phase? If you rely on a piece of electronics to make the pump work, would be good to have a backup. Is 3-phase available from the grid? If not, you'll be using your VFD daily. My Hitachi has lasted 15 years so far, but use is occasional.

If you want reliable off-grid power, consider getting a DC solar trailer (has two Sunny Island). Add one more Sunny Island if you want 3-phase. Make sure it has healthy forklift batteries. That's a good starting place with 2400W of PV, and you can AC couple up to 13kW more for grid-tie or 24kW for off-grid.
 

Johncfii

Solar Addict
Paul,

How to explain within this sometimes cumbersome teaching forum?

I‘m not sure, but I rather suspect the notion of a “hot leg” is complicating your thinking. We are used to that form of thinking because our power grid supply is constructed to make it easy for us to access both 120 and 240 volts AC for our various appliances. And to make it safe by having a way to connect the system to earth ground. Obviously, it is the big appliances in the home that are designed to operate from 240 volt supply,

We have two “hot legs” and a “neutral“ (the neutral which is tied to ground) in our main service panel because the “pole pig” transformer on your power pole has a center-tapped 240 volt secondary winding. It is the center tap that is tied to ground, and serves as the “neutral” leg. Thus we have 120 volt potential between each “hot leg” and ground, and 240 volt potential across the two “hot legs”. But this is all rather arbitrary by convention. This is where the strange, and imprecise, term “split phase” comes from. They really is no way to “split” a phase. You can only “tap
” a transformer winding to tap a portion of the full secondary winding voltage.

It would be perfectly possible to wire a home with only 240 volts AC with no “neutral”. Of course, all of your appliances would need to be built to operate on 240 volts. This would be done simply by elimination the center tap on the power pole transformer. Would we still think of them as “hot legs”? I‘m not sure. They are both definitely ”hot“ with respect to each other. This is analogous to what I am suggesting you can do to get 240 volts to power a VFD.

May I suggest that you Google “center tapped transformer”?

I am suggesting that you can create 240 VAC, to power the VFD, by “stepping up“ any 120 VAC supply. You would do it simply with a non-center-tapped 2:1 transformer, having a primary winding designed to be connected to 120 VAC source. Across the two secondary winding leads will appear the 240 volts that you need. The transformer just needs to be large enough to handle the load.

Or, you can use something a little different called an “auto transformer” which will do the same, but which does not have a secondary winding that is isolated from the primary. If interested, google “auto transformer“ to see the difference.

I‘m not recommending that stepping up your 120 VAC solar output, by way of a transformer, is the best way .... but it can be done.

I think all the VFD manual means when it mentions 200 volts and 230 volts is that it will work with any input voltage in that range. (230, 240, tomato, tomahto.)

I hope this attempt at explanation helps a little.
 
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Guido1

New Member
A 3-phase motor doesn't care how the three wires are referenced to ground. Probably a VFD doesn't either (although one could design a device with surge protection clamping to ground that might care.) Whether VFD is fed +/-120V from 120/240V split phase or single 240V referenced to ground isn't likely to matter. The only difference is voltage between a wire and ground, which requires more insulation. But insulation is typically rated above 600V anyway. There would be some difference in current flowing through parasitic capacitance, again not a big deal.

On grid, you don't have the issues of starting surge, but you want to run off-grid during failures so there it matters. I think Grundfos is a 3-phase pump and VFD, so the question is whether a different brand of pump is less affected by calcium or whatever.

Is your PTO generator 3-phase? If you rely on a piece of electronics to make the pump work, would be good to have a backup. Is 3-phase available from the grid? If not, you'll be using your VFD daily. My Hitachi has lasted 15 years so far, but use is occasional.

Hello, Hedges

Once again, I'd like to express my gratitude for all the volunteered wisdom provided.
Generally, experts are unwilling to divulge such info. freely. You folks show not only a great deal of expertise, but also a lot of class.

You bring up a very relevant point concerning the lack of backup power to the well motor if a VFD failure were to occur. My tractor PTO generator is a 27kw 120/240V single phase, I'd hope that would power a functional VFD in the event of a solar system outage, but I never really considered it.
I don't currently have 3-phase grid power service, although I suspect I could get it.
Would it be beneficial to have a backup VFD, in the event of a failure of the primary device? The Hitachi's, anyway, don't seem to be very expensive, and I'm all about redundancy, particularly when it pertains to drinking water.

You raise a valid question regarding the minerals fouling of Grundfos pumps vs. pumps of similar construction. I'm not that familiar with the internal design differences of Grundfos pumps that may make them more susceptible to fouling.
All I knew a few years ago when I had the conversation was Grundfos appeared to be the tip of the spear when it came to energy conservation, particularly during start-up. I was surprised to hear that they had such a chink in their armor.
Realistically, it could boil down to the profit margins of reselling various brands by the gentleman I spoke with.
I've never read or heard any similar opinions regarding such failure mechanisms specific to the Grundfos.

Thanks again for your observations and suggestions.

Respectfully posted,
Paul
 
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