Soft start options for a deep well pump?

wirenut
wirenut Registered Users Posts: 22 ✭✭
in Advanced Solar Electric Technical Forum #1
I have a customer with an Outback system that has 1 GVFX3648. One of the loads backed-up by this system is the 240v well pump. I'm using a step-up transformer to make the 240v. The pump uses 2,000 watts running. The inverter starts and runs the pump just fine if there isn't much other load. If there is a few hundred watts of load on the inverter when the pump starts the inverter shuts down with a low output voltage error.
I know I can just install a second inverter to cure the situation but that's over $2,000. I'm wondering if there is an economical way of adding a soft start device to the well pump. It is a 2 wire model so the start cap is down in the well. I don't know the HP rating but it pulls about 8.5 amps at 240v running.
I'd love to hear from anyone with experience in soft starting a deep well pump.

Thanks for your help.
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Comments

  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
    Re: Soft start options for a deep well pump?

    Don't know if it's too late to change the pump, but three wire pumps with the starter box and capacitor above ground are considerably easier to start. It's almost but not quite, as if the 2 wire pumps don't have a built in start capacitor. Not really noticeable when operating on grid, but all that changes when off grid.
    8.5 amp 240V is probably a 3/4 hp pump. The 1/2 hp pumps draw roughly 6 amps @ 240 V.
    Changing the pump would likely be a lot cheaper than a new inverter.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #3
    Re: Soft start options for a deep well pump?

    You don't get something for nothing. What usually happens with AC motor soft starters is you can reduce the peak current with the down side of longer start period at the lower current. Inverters will typically act as a soft starts during brief startup surges. Down side of this is lights dim and other devices like refrig compressor that may be running also sees the dip in inverter output voltage which is undesireable.

    You have look at the peak surge current capability of the inverter versus duration of surge. Generally, on inverter output, the soft starter will net no benefit because the lower surge current is still an overload and last too long.

    A second inverter setup as 240v stacked arrangement is the best solution. A step up transformer just adds more loss to an already marginal situation. It is better if pump has option to be configured as 120vac operation if you only have a 120v inverter.
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,020 ✭✭✭✭
    #4
    Re: Soft start options for a deep well pump?

    Grundfos soft start submersible pump would be a great option. I replaced a newer 240vac pump with one and don't regret it. Setup was similar to OP's, 120v inverter, autotransformer, 240v pump. The tranformer was wired so that it didn't start until the pump circuit was called for (presure switch), the lights would dim, the colour tv went black and white with smaller picture for a second, then ran. The Xantrex inverter display showed over 40amps draw, probably more. Now there's the pressure switch click, load starts at zero amps and goes up to 9 (it's a 1kw pump), no flickers etc. Maybe the cheapest option (less than 1/2 the price of another inverter).

    Ralph
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  • BillG
    BillG Users Awaiting Email Confirmation Posts: 7 ✭
    #5
    Re: Soft start options for a deep well pump?

    I know this is an old thread, but I have been just now looking for a solution to the same problem. I have what I believe is a 3/4hp 3- wire well pump that runs off an Outback single inverter, with a 240v auto Xfmr. Just recently (last couple or three months) I've been experiencing inverter shutdown when the well pump kicks in. Yesterday we checked the amperage draw on the pump, was 16amp on one leg. My thought was to either put a soft starter in line to the pump, or call the plumber and pull the pump out, thinking there may be an issue with the pump motor? it's always caused flicker when it starts, but this is getting tiresome, especially in Maine in the winter. Any suggestions are appreciated!
    Thanks, Bill
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Soft start options for a deep well pump?

    16 Amps @ 240 VAC is whopping big for a 3/4 HP pump. Or is that current measured on the 120 VAC side of the transformer?

    Since you've seen a change in performance over time it is likely that something has gone wrong. Possibly a failure of the start capacitor on the pump or mechanical obstruction of the rotor stack (wear and tear).

    I don't know which OB inverter you have so can't say how well it should work to begin with. A 3648 as in the OP's case should have no trouble with a 3/4 HP deep well pump. That said, a lot of factors go into it including how hard the pump is working (deeper well = more effort for the pump and a larger one might actually work better) what the wire size/length is, and the battery bank capacity (smaller bank stretched to supply power to begin with, capacity is reduced over time; situation gets worse).

    If you had all the specs from when it was installed and working you could check them against what presents itself now and see what's gone wrong.
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  • BillG
    BillG Users Awaiting Email Confirmation Posts: 7 ✭
    #7
    Re: Soft start options for a deep well pump?

    Yes, that looks like a lot of amps to me too. I'm only guessing on the pump HP. I will have to do some research there might be some paperwork from installation (around 2005) somewhere. We measured the amperage on the breaker in panel when the pump started. I'm suspecting a problem with the pump, since it's a fairly new issue. The well is 180-200ft deep. I'm wondering if I have to pull the pump anyway, is there a good replacement? Outback 24v system with a single inverter. Another possibilty is the battery is getting sulfated and can't handle the load that it could originally? Sounds like it may be a fairly expensive solution no matter what I do!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Soft start options for a deep well pump?

    So probably an FX3524 inverter.
    If that pump is pulling 16 Amps @ 240 VAC that's 3840 Volt Amps which the inverter would not be able to handle for long. If the 16 Amps is on the 120 side it's 1920 Volt Amps which it could manage. It's still a lot of power. Translate that into DC Amps @ 24 Volts and it's 80-ish Amps (not including other loads and the inverter itself). If the battery bank is on the small side it could be incapable of supply that much current on a sudden demand. What you want to look at here is the DC Voltage at the inverter when the pump starts; see if it is dropping below the low Voltage disconnect point set on the inverter.

    The other likely fault shut down would be from over-current on the AC OUT due to pump demand.
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  • BillG
    BillG Users Awaiting Email Confirmation Posts: 7 ✭
    #9
    Re: Soft start options for a deep well pump?

    Yes, FX3524. Do you think the problem would more likely be in the pump, or in the battery. This system has 12 Rolls 2.6v batteries in series. No markings on the batteries and I'm going from memory I think they are 395AH each. I'll try to get back later today and check the AC out and the DC voltage.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Soft start options for a deep well pump?

    Without knowing the exact batteries, their age, and what the wiring is it's hard to say. If they are 395 Amp hour, not very old, and the wiring is good then they should certainly handle the pump.

    There's just a lot of different problems that can produce the same symptoms.
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  • BillG
    BillG Users Awaiting Email Confirmation Posts: 7 ✭
    #11
    Re: Soft start options for a deep well pump?

    I think what I'll do is have a plumber come pull the pump out and check that. Could be something there, and if it is my thought is to replace it with either a 110v pump or spring for something designed for this application, like a Grundfos. That's after checking inside to make sure I don't have some other problems.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,606 admin
    #12
    Re: Soft start options for a deep well pump?

    But do check the DC battery bus right at the Inverter's DC power lugs when starting the pump. If the voltage drop to near 21 volts or less, then your DC system is not able to keep up with the power demands.

    Note that Power = Voltage * Current. If the battery bank is showing its age (or even you have some dirty/loose wiring connections), as the voltage falls, the current must rise to meet the AC Power demand from the inverter (AC Inverters are "constant power" devices). So, as the battery bank begins to fade, the DC current requirements actually increase.

    It may be well worth your time and money to look at a getting a VFD (variable frequency drive) to soft start/limit pump RPM (if pump is over sized for your water flow needs). VFD's are not that expensive (many are less than $300) and would probably be worth experimenting with. If nothing else, it could reduce the light flicking once any other issues are resolved.

    Getting a hand full of different starting capacitors may help too (use a smaller value capacitor that can still reliably start your pump to reduce peak surge current).

    See if your well guy has any VFD/Soft Start experience.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: Soft start options for a deep well pump?

    With a 200' deep well you are probably not going to find a 120 Volt pump to use. The depth alone means some significant wire length which would result in too much Voltage drop to be practical to run at 120. What's more, switching pump Voltages to the lower value offers no advantage to supplying the power from the inverter & batteries. The little extra consumed by the transformer is made up in the more efficient long run and lower current of the 240 VAC.
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  • BillG
    BillG Users Awaiting Email Confirmation Posts: 7 ✭
    #14
    Re: Soft start options for a deep well pump?

    Thanks folks, I will inspect the systems wiring connections and the DC voltage. Yesterday we only checked AC. I'll also check on the VFD. I'll let you know how I make out with all this.
    Bill
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #15
    Re: Soft start options for a deep well pump?

    Some VFD's will also convert 115V single phase input to 230V 3 phase output, e.g.: http://dealerselectric.com/item.asp?cID=28&PID=4587

    I start our 1.5kW 3 phase pump using one, although we're 230V in and 230V out- peak power draw at startup is 2kW and the startup time is set to about 15 seconds. You can configure the startup time, so it could be made very slow and gentle, I would think that a startup time of 60 seconds or so would hardly show any power surge.
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  • michaelwmauser
    michaelwmauser Registered Users Posts: 1
    #16
    Re: Soft start options for a deep well pump?
    Cariboocoot wrote: »
    .... A 3648 as in the OP's case should have no trouble with a 3/4 HP deep well pump. That said, a lot of factors go into it including how hard the pump is working (deeper well = more effort for the pump and a larger one might actually work better) what the wire size/length is, and the battery bank capacity (smaller bank stretched to supply power to begin with, capacity is reduced over time; situation gets worse).

    I'm getting ready to install a 1.5 Hp Goulds 5GS15 pump thinking that my system with two Outback VFX3648 inverters should handle it. My battery bank is 8 Trojan L16H so I think it should do it. Pump will be at 600 ft (30 ft below water level) and discharge will be to an open tank. Wire is to be #8. Am I OK or is there a better option out there? I was thinking of a Grundfos SQE pump (5SQ10C-450) which uses a DC motor but my installer advised against it because of the potential for sanding damage. He suggested a variable frequency drive. Any thoughts?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #17
    Re: Soft start options for a deep well pump?
    michaelwmauser wrote: »
    I'm getting ready to install a 1.5 Hp Goulds 5GS15 pump thinking that my system with two Outback VFX3648 inverters should handle it. My battery bank is 8 Trojan L16H so I think it should do it. Pump will be at 600 ft (30 ft below water level) and discharge will be to an open tank. Wire is to be #8. Am I OK or is there a better option out there? I was thinking of a Grundfos SQE pump (5SQ10C-450) which uses a DC motor but my installer advised against it because of the potential for sanding damage. He suggested a variable frequency drive. Any thoughts?

    You have the two VFX's stacked for 3.6 kW @ 240 VAC?
    1.5 HP pump motor will draw a massive amount of current on start-up. It could, with other simultaneous loads, exceed the surge limit for the Outback. Much depends on how hard the pump is actually working. That is a really big pump, and it's trying to lift water from 270 feet. The soft-start variable frequency drive sounds like a good idea to me, especially if your pump man knows of one for the application.

    The Grunfos will not suffer from sand damage any more so than any other deep well pump. But it is probably a lot more money than the VFD for the pump you already have.
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  • Texas Wellman
    Texas Wellman Solar Expert Posts: 153 ✭✭
    #18
    Re: Soft start options for a deep well pump?

    FYI, in reponse to an earlier post on this thread most 2-wire pumps (Franklin Motors) do not have a start-cap. They have a BIAC switch inside the motor. They take 2X the start current of equivalent 3-wire pumps.

    I would go with the Grundfos soft-start. I'm not aware of any sand issues that would not affect the goulds but would affect the Grundfos.

    Goulds makes a good pump but that 1.5HP will take a lot of juice to start. FWIW I believe that Centri-pro (goulds own sub motor) 2-wire versions use a start-cap in the motor.
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