Questions on Single Phase VFD for well pump


I have been looking at VFDs for my home well pump.

We just recently replaced our pump. The "pump guy" did the job on a Saturday and, basically, he installed what was on the truck. The "pump guy" said that "new" pumps don't need the controller (starting unit).

The old pump was a capacitor start (current relay). It worked just fine for 30 years.

The replacement is just two wire. Since it's about 120' underwater I don't suspect it has any moving parts other than the rotor itself.

The new pump has two problems I didn't see with the old pump:

1) When it runs it transmits quite a bit of 60Hz "hum" back to my basement. We can hear it from the next floor. There is over 200' of pipe between the pump and our basement but that noise comes through loud and clear!

2) When it stops it creates quite a bit of water hammer. You can SEE the pipes move when it shuts off.

From an electrical view it seems to be working OK. Whatever starting transient it has, it's over is a fraction of a second. It draws just less than 10 amp at start and increases to just below 11 amps at shut off.

I would like a CHEAP package that would:

1) Start the pump a little slower taking about 1 second to ramp up.

2) On stop, take about one second to slow down.

3) Offer protection from "short cycling" with a two minute minimum OFF time.

4) When running in the steady state, it would operate the motor at specs (60 Hz, 240 volts).

5) On/Off would be controlled by contact closure (2 pole pressure switch) If it would "work" the pressure switch can just switch the 240 volts as it does now.

6) Any "programming" would have to survive an indefinite power outage.

Because of point #4, I don't expect any VFD to change the amount of "hum" making its way back to the tank. I suppose I might "play around" with the SS frequency/voltage to see if I can cut back the noise within it's performance envelope. Seems to me that once it's up to speed it might make sense to drop the voltage a bit to the just above the point where the motor slows down and the current increases.

I see VFDs with prices below $200. That's my upper limit.

For $700 to $1000 I can have them pull out the well string and put into any kind of pump I want (including, I suppose, the 3 phase delta, or whatever.) If I pay to pull a working pump, I will first open up my options. But for now, I am stuck with the pump that's nearly 200' down and 180' below water.

SO: Has anyone here used these relatively small VFD to "soft start/soft stop" and otherwise protect an "ordinary" 2 wire induction motor?

Is there a CHEAP one that will do all the above for me?

Are the "cheap" ones basically well made? IOW: will they last about as long as your basic TV?

Reply to
John Gilmer
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The water hammer could be caused from not enough ballast air in your storage tank, or maybe settlement in your tank. Not sure about the hum..

Reply to

Reply to
Rheilly Phoull


The air volumn control works just fine. You can hear the "slug" of air enter the tank on each start up. As soon as the air bubble is in the tank the lous hum starts.

When you lose a pump you end up with oil in the well. I have drained the tank more than once just for the oil. In any case, as the tank drains from the bottom in "normal" use, "settlement" just isn't a problem.

Reply to
John Gilmer

Could very well be. Like it or not, the pump is whatever it is.

That's all very good for "next time." But "this time" I have a pump thats in a 200' deep hole in the ground. The pump has a 5 years replacment guarantee but I have to pay to have it pulled if it fails.

The check valve is part of the pump and it's 200' (actually, slightly less) under ground. The new pump is a bit shorter than the old pump so I guess

30 years of progress have made a difference. Likely, the new pump has a lower moment of inertia for its rotating parts. This means that it will stop and start quicker. The water pressure tank is about the ultimate "anti-air-hammer" device. There is only about 20' of above ground pipe before the pressure tank.

I don't routinely work with motors. I note that all the motors in my HVAC system and in my sole window air conditional are capacitor run. All other things being equal, are capacitor start motors quieter than whatever technology (shaded pole?) makes for 2 wire motors?

I really was hoping that someone here has had experience on small VFDs. Frankly, it would be a heck of a lot easier to install a VFD than to make any serious changes to the plumbing.

Reply to
John Gilmer

You can use a VFD, just get ready to get up off your wallet.

Reply to

Before you do anything else, realize this:

When you see adds for "1 phase VFDs", they are selling VFDs that take a 1 phase input, but the OUTPUT is 3 phase! If you do not have a 3 phase motor these will NOT work for you.

There are a few VFDs (3 maybe?) made to work on 1 phase motors. These will NOT be the ones you see in the $200 range, they are significantly more expensive. They also only work on a very narrow type of 1 phase motors, namely PSC (Permanent Spilt Capacitor) or Shaded Pole. It is highly unlikely that you would have a shaded pole motor on a

200' submersible, but it might possibly be a PSC.

Assuming you can do this, the next problem is the distance from the controller to the motor. VFD output is noisy from an electrical standpoint and can create high voltage pulses on the motor windings, up to 3 times the line voltage rating. In the world of standard AC motors we typically don't worry about 240V systems having this problem because motor mfrs use the same insualtion for 240V or 480V motors, so the insulation is typically 1000V rated, and 3 x 240V is still under that. In the submersible world however, all bets are off because they design these motors to be very small, so they often use thinner insulation, rated only 500V or less. In that case, standing wave pulses from VFDs can damage the windings in short order.

The next problem is the pump itself. If not specifically designed for variable speed operation, taking too long to accelerate it may in fact damage the pump. There are breaing systems that rely upon hydrodynamic lift in order to come off of their resting place, and the hydraulic pressure is used as the brearing. Slow acceleration allows those types of systems to rub too long without a bearing, wearing them out extremely fast. Most submersible pump manufacturers will consider your warranty void if used with any starting method other than they designed it for.

So don't embark on this process without a thorough consultation with the pump manufacturer first.

Reply to
Bob Ferapples

You need a soft start controller such as:

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for control of starting. One of the main failure modes of motors is winding fatigue from starting surges. This device reduces surges. Also used to operate from inverters and small generators that can not provide the requiring starting surge.

There are short-cycle protectors for air conditioning compressors that you should consider.

A second check valve at the tank may help with the water hammer on stop.

Bill Kaszeta Photovoltaic Resources Int'l Tempe Arizona USA

Reply to
Bill Kaszeta / Photovoltaic Resources

I agree.

I "thought" I saw one that had a single phase output.

Frankly, looking at every single ad at every website is tedious. I was hoping that I would find someone with the facts as his fingertips or in his head.

I my brief look when I got to the details they all seemed to be 3 phase output even when the "intro" implied a single phase option for that line.

But from my OP you can see I want some other features. I have never used one of these gadgets. I know that they have some "smarts" and I know that with the right kind of "smarts" they could do exactly what I want. What I don't know for sure is whether I can get what I want for moderate cost with a single phase output and with the "smarts" that can do what I want done. If I need a PC to "program" the beast, for example, I can even bring one of my computers to the basement.

Unless the manufacturer built in the capacitor into his pump (could be?) then it ain't a PSC. There are only two wires going down there. The original pump was capacitor start and that was the standard for deep well pumps. There was always a "control box" associated with them.


That hurts! I definitely don't want to overstress the insulation. That's a BIG blow to my ambition.

I understand this. That's want I only want to slow down a start/stop "a little" to someone on the order of a second or less.

Maybe a better solution for me might be some PTC and NTC thermisters. The PTC would be across the contacts and would cause the motor to take "a little longer" to slow down.

The NTC would be in series with the pump and slow down the start "a little bit."

I'm sure that's correct. Fortunately, the maker didn't anticipate this. In any case, I don't want to drag out start/stop forever but just for the better part of a second.

Well, "if I ask" and he says the warrantee is off ...

Frankly, I don't see how a less than one second slow stop could do any harm.

Reply to
John Gilmer

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I will check it out. Thanks for the link.

winding fatigue from starting surges. This device

that can not provide the requiring starting

That definitely would be nice. We who get our water from private wells don't have the most reliable electric service. It would be nice to be sure than I can start my pump from a crappy and small generator.

should consider.

I was "kinda" hoping that it would be in one package.

Frankly, I don't see how. The pump stops and the water stops (on a dime). The check valve will not keep the water flowing. I suppose I would try getting and extras surge tank for the point where the water pipe first pops out of the concrete.

Reply to
John Gilmer

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The price is over $500!

WAY too much.

Maybe I will "solve" the water hammer by just blocking the pipe to keep it from moving.

Reply to
John Gilmer

A VFD for a single phase motor is rare. But a 'soft-start' motor would help on the starting. It wouldn't help with the 'hammer' though.

Water hammer is strictly a mechanical/hydraulic issue. It is caused by water flowing in a long pipe suddenly stopping against a solid obstruction. When your pump shuts off, the flowing water *should* have a soft cushion to slow to a stop in the form of the tank bladder. But it may reverse flow back out the tank if the check valve at the pump is the wrong type. So the height of the water, and the tank pressure accelerate the water backward for a second or so, and then the check valve seats. The reverse-flowing water suddenly slams into the closed check valve and 'hammers'. An accumulator right at the check-valve outlet is one fix, but not practical down a 200' well. Another fix is changing to a different style check that can shut quicker before reverse-flow develops. Or, as you've surmised, some way to have pump discharge pressure decay more slowly so the valve can seat before a lot of reverse flow occurs. A check valve at the tank inlet might help some, by stopping reverse flow out of the tank, but it won't help for the

200' column of water.


Reply to

From my view, the "soft start" would make little difference. (The first thing into the tank is a large "bubble" of air. The air bubble takes a few seconds to travel from the top of the well to the tank.) What I really want is the "soft STOP." I figured that with a VFD the "soft start" would be a motor saving bonus.


Actually, since the water is under some pressure, you can "stop" the flow at the sending end and the effect is the same as suddenly shutting things off at the received end. That's what's happening in my case.

Well, I have an air over water tank but it's the same effect.

From my class on Fluid Dynamics (over 40 years ago), I remember that the "hammer" forces are the same regardless of the direction of flow. The "hammer" happens right after the pressure switch opens. A reverse flow problem would cause a "two hammer" signature: once as the fluid stops the first time and the second from the reverse flow.

Anyway, I was pretty sure from the time of my OP that a "soft stop" would be useful. That's what I am look for.

Does anyone still following this thread have any experience using PTC thermisters to allow the power to taper off for a fraction of a second?

Reply to
John Gilmer

"John Gilmer" wrote


Are you sure that you have suficent air in the tank?

If the air over water tank is working corectly and absorbes the incoming water slug at shut off, then that just leaves your revers flow stop (the check valve).

You may also want to just look at the cut off pressure point.

Stephen B.

Reply to
Stephen B.

The only way you would get hammer when the forward flow stops, is if there is not enough air in the tank and the water is hitting a 'solid tank'.. With the pump running, forward flow, then the air is squeezed 'solid'. Pressure would spike upward rapidly and *that* ends up tripping your pressure switch. But that is easy to fix, just make sure there is enough air in the tank to not go 'solid' before the pressure rises to stop the pump.

After pump stops, watch pressure gauge and *slowly* open a small water outlet. If pressure drops rapidly and then tapers off to a nearly steady value, that is the tank going from 'solid' back to a 'bubble'. Means you need more air (or if you have a bladder type, the bladder has ruptured).

The more likely event is pump stops and pressure in tank reverses flow until valve at pump stops the reverse flow. That needs a different kind of check valve, or a pump whose pressure decays more slowly when shut off (either more inertia, or 'soft stop').

I'd double check to make sure your 'hammer' is not caused by a lack of air in the tank. You mentioend it didn't used to do this with the old pump, so either you have a different check valve, this pump is a lot smaller, or your tank is going 'solid' when the pump fills it.

Don't see how a thermister would help. Lowering the voltage applied to the motor slightly won't 'soft stop' it.


Reply to

Pretty sure.

The system brings in a "slug" of air each time the pump starts. The air level control vents excess air when the air level is midway up. In the "steady state" the pump starts because a dropping water level activates the air bleed valve which quickly drops the pressure down to the kick in level. To a good approximation, when the pump starts about 50% of the tank is AIR. If the air level control fails you either end up with water on the floor or air coming out of the faucet so I know it's OK. I can HEAR the air bubble coming in.

I will reduce it. I had increased it to overcome the pressure drop of the filter we put in to catch the old pump's oil. Frankly, it's "nice" to have water over 40 psig. But reliability and reduction of "wear and tear" demand that I knock it down to 30-50.

I will also try to fix the incoming water pipe to the walls to at least cut the movement from the hammer.

Reply to
John Gilmer

I figured that the PTC device would lower the voltage to near ZERO as the PTC approaches "open."

Reply to
John Gilmer

The problem with your PTC / NTC solution is that it involved dropping the voltage to the motor, and that involves a rapid loss of torque. Torque is reduced by the square of the voltage reduction, and a pump stops pumping within a relatively narrow band width of torque, so it is highly unlikely that you would attain any appreciable water hammer reduction by doing this with a resistor that has little or no means of adjusting the time frame. I use soft starters and VFDs to reduce water hammer all the time, and my experience is that it takes a gradual reduction of between 15 and 30 seconds to notice anything useful in a deep well pump. You usually have to play with it and adjust it several times because the hydraulic conditions are different for every installation.

Forget the soft starter for a 1 phase motor by the way, it has the same limitations I mentioned for the VFD and costs the same or more.

if your motor does not have an external starting cap any longer, it might well be a PSC motor. Post the manufacturer's name and model number, I can probably find out for you. That may be the best bet in actuality. Also, what country are you in and I'll post some links to 1 phase VFD suppliers for you.

Reply to
Bob Ferapples

Yikes! Even 15 seconds is a LONG time. As far as the PTC device is concerned, I figured that the loss of torque will allow the motor to slow down. It's been some time since "fluid dynamics" but now tha I think harder I suppose to torque required while the pump is still pumping depends mostly on the pressure head. Thus, the motor would still shut down rapidly as soon as the available torque falls below some value. IOW: there is still be a "clunk."

Yeah. I figured that would happen. As far at the ramp down time is concerned I still believe in my situation and ramp down time on the order of a second or two would cause the pipes to just return to "battery" slowly. On that line, I picked up some 1" tube strapes and will see about arresting the pipe to that it doesn't have a chance to react to the flow reduction.

Well, since the VFD's seem to be "smart" I figured that would be the way to go.

I THOUGHT I knew something about AC motors. What do you mean by a PSC motor. I thought is was a "capacitor run" type motor. Unless the makers decided to seal run capacitor in with the pump, it's some kind of split phase using pole shading or an auxilary high resistance winding (like motors in modern clothes washing machines and older dishwashers had.

Okey Dokey:

First, I live in the USofA. Pump is 240 volts and draws about 10 amps (a little less at turn on and a little more at shut down).

The Maker is "Red Jacket Water Products" of Seneca Falls, NY, USA.

Part No.: 100F21112G14 "1HP 1/60/230 2W 14STG GRIZ".

I believe it's rated for 12 gallons/minute.

At the minimum I would enjoy looking at the VFDs you come up with. Some question from my OP include: 1) do any of them have built in "short cycle" prevention? 2) do they "remember" programming after a power outage?

If the answer to both is YES and the cost is reasonable, I will get one just for fun.

BTW: Do you have anything to offer on the VERY loud hum? In the room above the water tank it is louder than that of the cheap ceiling fans we have about the place.

Reply to
John Gilmer

Sorry it took so long to get back, I was busy elsewhere.

That pump originally came with a Franklin submersible motor. Franklin's standard design is split phase cap-start / cap-run, with the caps being external to the motor in a "control box". In one of your early posts I thought I read that someone had "modified" yours to no longer need the external caps. That means that they probably changed it to Franklin's "2 wire" design, which means that the starting components are integral to the hermetically sealed motor, but it is still a split phase design with a start switch, so you will NOT be able to use a VFD on it, they will not work and you will damage the VFD and/or the caps.

For future reference, the best 1 phase VFD out there right now is make in the UK by Invertek, but is sold in the US by Bardac

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and Anacon
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Again, only if it is a PSC motor.

When you use a VFD you no longer need to worry about "short cycle" protection because the VFD does not stress the motor windings on startup. Still, there is probably something like that in the Invertek drive, I just have never used it.

Yes, all VFDs will retain all of their memory after a power failure.

An option for you is to replace that motor with a 3 phase version, then get a VFD with a 1 phase input / 3 phase output. Check out Frankiln at

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you can get any inexpensive 1HP 230V VFD and use it as a phase converter. I recommend the Teco FM50 for low cost and reliability.

Reply to
Bob Ferapples

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