Capacitors for well pumps

lazzalazza Solar Expert Posts: 334 ✭✭✭
HI

I've seen 20µF capacitors put in well pump circuits (see photo) ... can anyone explain to me what they are for and how they work?

thanks
Larry

Comments

  • mike95490mike95490 Solar Expert Posts: 9,040 ✭✭✭✭✭
    Re: Capacitors for well pumps

    Well pumps. Big subject. I will only address common AC pumps, not solar or DC.
    Pumps come in 2 basic styles. Single phase, and Three phase. Any pump over 1 HP, 3 phase is more efficient.

    AC pumps can use 2 different types of caps. Nearly all have a START cap somewhere. This cap is only energized for a couple seconds to start the motor, and is then disconnected with a centrifugal switch in the motor.
    Some motors can have a RUN cap wired to help correct poor power factor. Electronic Pump control boxes generally do not allow for this. (but you do get stall and run dry protection).

    --

    Single phase pumps can be further divided into Two wire and Three wire.
    2 wire pumps have the motor start capacitor, miniaturized and packaged with the motor. When the cap goes bad, you
    have to open the well, pull the pump, and at this point, I'd install a new system, pointless to put a new cap into an old system when you have all the parts out of the well.
    3 wire pumps have the motor start capacitor in a control box. Some control boxes are a simple relay, some are electronic. It depends on how fancy you want to be. If this capacitor goes bad, it's easily replaced. They are generally more robust and live under more benign conditions than a cap crammed into a motor under water.

    Some motors can also use an optional RUN capacitor, but only if the control box has provisions for it.

    The Franklin Motor site has a lot of info about this stuff.
    http://www.franklin-electric.com/aim-manual.aspx

    some other sites -
    http://homeimprovement.lovetoknow.com/do-it-yourself-plumbing/submersible-well-pump-wiring-diagrams
    (has some links to schematics at the end of the article)

    http://www.franklin-electric.com/residential-light-commercial/controls/controls/control-box.aspx
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Capacitors for well pumps

    And re the MFD value of the start capacitor, that value is decided on by the designers of the pump motor to give the best results. Changing the value will almost always result in poorer results. This may not be so evident on grid power because of the relatively enormous power available to start the motor in spite of improper capacitor value. It will however be very obvious if starting off inverter power.
    BTW, in my experience with 3 wire single phase AC submersible pumps, the starter circuit is switched by one of four ways, neither of which use a in-motor mechanical switch. The older ones used a relay. One type monitored the run winding current. When the motor was not up to speed, the run winding current is high and would pull in the relay, connecting the start circuit. Once the motor is up to speed, that current decreases and the relay drops out. Another system has the relay connected across the start winding. As the motor is coming up to speed, that voltage is relatively low, so the relay is not activated, thus leaving the start circuit energized. When the motor reaches full speed, the start winding, through transformer-like action, has a substantial voltage rise which pulls in the relay, disconnecting the start circuit. Another system uses a simple timer, supplying start power for a set time, after which it is assumed the motor is up to speed. The final way I'm aware of is the little electronic triac circuit that electronically monitors motor performance and supplies start current as needed.
    In all cases, if the motor fails to start, an automatic reset overload cutout activates, cutting off power completely, and trying for another start after a short rest time.
    Also in my experience, the 3 wire pumps (3 wire + ground = 4 wires) are much easier to start than the 2 wire (2 wire + ground = 3 wires) which have the start circuit within the motor itself. Why this should be I do not know, but it is so. Thus if planning on running such a pump off-grid, go for the 3 wire + ground motor if at all possible.
  • BB.BB. Super Moderators, Administrators Posts: 31,082 admin
    Re: Capacitors for well pumps

    And if you choose a three wire or three phase pump, that gives you the option of looking into VFDs (variable frequency drives). Lots of interesting options there... Soft start, variable RPM based on water pumping needs (volume/pressure), etc...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Capacitors for well pumps
    BB. wrote: »
    And if you choose a three wire or three phase pump, that gives you the option of looking into VFDs (variable frequency drives). Lots of interesting options there... Soft start, variable RPM based on water pumping needs (volume/pressure), etc...

    -Bill

    But keep in mind that unlike a 3 phase pump, a "3 wire" single phase pump has only two windings, one for run, the other for start. One wire is the common of the two coils, and the two coils have different resistance readings, one coil is meant to be continuously powered, the other only for a very few seconds while the motor comes up to speed.
  • lazzalazza Solar Expert Posts: 334 ✭✭✭
    Re: Capacitors for well pumps

    Thanks for the info.... however this capacitor, and as I have seen in other well pumps here, appears to be constantly connected to the live and neutral wires... it's a separate, added part of the system and doesnt come with the pump. How does this affect the running of the pump?
  • mike95490mike95490 Solar Expert Posts: 9,040 ✭✭✭✭✭
    Re: Capacitors for well pumps
    lazza wrote: »
    Thanks for the info.... however this capacitor, and as I have seen in other well pumps here, appears to be constantly connected to the live and neutral wires... it's a separate, added part of the system and doesnt come with the pump. How does this affect the running of the pump?

    It's likely a aftermarket "Run Capacitor". They have a small micro farad size, and a large voltage rating. They slightly improve the efficiency of the motor, and should only be connected when the motor is on, otherwise they mess up the power factor for the rest of the household.

    This link talks about RUN capacitors
    http://www.franklin-electric.com/aim-manual/page-15.aspx
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Capacitors for well pumps

    Power factor correction. Might well help reduce the current load (but not the wattage) which would help ease the strain on off-grid inverters once the pump is up and running, and to a lessor extent, when it's starting. But you'd have to use something like a Kill-A-Watt meter to find the proper value capacitor for your particular pump.
  • Texas WellmanTexas Wellman Solar Expert Posts: 153 ✭✭
    Re: Capacitors for well pumps

    Franklin 2-wire motors have a BIAC switch in them and do not have a start capacitor. Faradyne (goulds and pentair) motors do have a capacitor built into the submersible motor for 2-wire pumps.

    3-wire pumps come in different flavors. With a regular QD (quick disconnect box) there is only a start capacitor. This is the type of box you will see on a typical 1/2 HP-1 HP 3-wire motor. There is also a Deluxe box that comes with a run cap and start cap. The big box lets the motor run on fewer amps because it keeps the start windings partially engaged while running.

    The deluxe box has external overloads you can manually reset.

    I am told by Franklin that the capacitors shift the voltage phase from the current phase. This creates a rotating magnetic field to start the motor. Once the motor is started the start-cap can be disengaged.

    I'm not sure how you connect a VFD system to a regular well pump using solar but I would suggest the Grundfos SQ flex instead. The SQF has VFD technology built right into it and will run on any voltage, AC or DC, from 90-230VAC or 30-300 VDC. It's that simple. No extra equipment necessary.

    BTW: Franklin 2-wire motors require 2x the starting power that a 3-wire pump requires. Once they are started they use slightly more electricity.
    mike95490 wrote: »
    Well pumps. Big subject. I will only address common AC pumps, not solar or DC.
    Pumps come in 2 basic styles. Single phase, and Three phase. Any pump over 1 HP, 3 phase is more efficient.

    AC pumps can use 2 different types of caps. Nearly all have a START cap somewhere. This cap is only energized for a couple seconds to start the motor, and is then disconnected with a centrifugal switch in the motor.
    Some motors can have a RUN cap wired to help correct poor power factor. Electronic Pump control boxes generally do not allow for this. (but you do get stall and run dry protection).

    --

    Single phase pumps can be further divided into Two wire and Three wire.
    2 wire pumps have the motor start capacitor, miniaturized and packaged with the motor. When the cap goes bad, you
    have to open the well, pull the pump, and at this point, I'd install a new system, pointless to put a new cap into an old system when you have all the parts out of the well.
    3 wire pumps have the motor start capacitor in a control box. Some control boxes are a simple relay, some are electronic. It depends on how fancy you want to be. If this capacitor goes bad, it's easily replaced. They are generally more robust and live under more benign conditions than a cap crammed into a motor under water.

    Some motors can also use an optional RUN capacitor, but only if the control box has provisions for it.

    The Franklin Motor site has a lot of info about this stuff.
    http://www.franklin-electric.com/aim-manual.aspx

    some other sites -
    http://homeimprovement.lovetoknow.com/do-it-yourself-plumbing/submersible-well-pump-wiring-diagrams
    (has some links to schematics at the end of the article)

    http://www.franklin-electric.com/residential-light-commercial/controls/controls/control-box.aspx
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Capacitors for well pumps
    Franklin 2-wire motors have a BIAC switch in them and do not have a start capacitor. Faradyne (goulds and pentair) motors do have a capacitor built into the submersible motor for 2-wire pumps.

    So THAT is why the Franklin 2 wire motors are so much harder to start, there is NO start capacitor in them! Kind of suspected that, but wasn't sure. Thanks for that info!
  • RCinFLARCinFLA Solar Expert Posts: 1,327 ✭✭✭
    Re: Capacitors for well pumps

    That is a run capacitor. It is connected all the time. The function is to provide a phasing delta between excitation winding. Best way I can describe it in not so technical terms is it is like holding a carrot on a stick in front of a horse while riding the horse.

    Run capacitor have to take continuous operation. Normally they are oil filled capacitor in a metal can.

    Start capacitors are often of dual polarity electrolytic because they will be much higher capacitance values (100+ uFd) and the electrolytic type gets much higher capacitance in a smaller package. The electrolytic start caps are often in a plastic can with a spline capture ring to hold its guts in the plastic can. They are only designed for short period operation to startup the motor. They are effectively taken out of the circuit once the motor is up to rotational speed. They will get very hot and blow the vent gasket if energized too long.

    You will often find starter caps on a water pumps, either under a hump can on the outside side of case or behind motor end cap. Refrigerators also often use starter caps.

    Just about all air conditioner compressors have a run capacitor on both the compressor and fan motor.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Capacitors for well pumps
    lazza wrote: »
    Thanks for the info.... however this capacitor appears to be constantly connected to the live and neutral wires.

    "Run capacitors" are wired across a winding other than what could normally be considered the run winding, often the start winding. The capacitor I understand the OP to be speaking of, was connected across the AC feed to the motor, which is typical for PF correction.
    However the OP may well have been mistaken as to where the capacitor was connected.
  • paul mwangipaul mwangi Registered Users Posts: 1
    i have a single phase submersible pump, with four wires and a capacitor how do i connect the capacitor?
  • BB.BB. Super Moderators, Administrators Posts: 31,082 admin
    Do you have a brand/model for your pump?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AguarancherAguarancher Solar Expert Posts: 309 ✭✭✭
    I assume your pump is 220v single phase pump. Do you have the control box? They are color coded for the connections at the control box.
    http://www.franklin-electric.com/irrigation-industrial/controls/controls/control-box.aspx#Controls
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    i have a single phase submersible pump, with four wires and a capacitor how do i connect the capacitor?

    If your pump is "4 wire", one of those wires, assuming this is a normal off the shelf single phase pump, will be to connect the outside shell of the motor to the house electrical ground to help prevent lightening damage. The other 3 wires come from inside the motor. One wire is "common", another supplies the run winding and the 3rd supplies the start winding. These pumps will not operate without a control box, and the control box will already have within it, the start capacitor, and IF the motor is of the capacitor run type, will also have a smaller value Run capacitor as well. The inside of the cover for the control box will have a wiring diagram showing which wire goes where and also where the capacitor is wired in. Any capacitors in that box will have already been selected at the factory to operate with the pump motor, so adding extra capacitors, or changing values of existing caps will only cause problems.
  • mike95490mike95490 Solar Expert Posts: 9,040 ✭✭✭✭✭
    Don't attempt to add a cap to any Franklin Electronic Control box. And their regular control boxes come with the proper cap for the motor. If you are buying parts and setting the thing up from scratch, then you will be learning a lot about motors and how Starting caps and Run caps function.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • ChangilaChangila Registered Users Posts: 1
    can i modify a single phase 220v well pump which have in built capacitor by fitting the capacitor externally? 
  • BB.BB. Super Moderators, Administrators Posts: 31,082 admin
    In general, the answer is no. You would have to "hack" the motor to bring out the capacitor wiring. If this is an in well/sealed pump--Would be hard/impossible to seal (I would guess).

    If this is an open frame motor--Perhaps you could bring the wiring out--But why do you want to do this?

    There are two types of "capacitor" motors--One with "Motor Run" cap, and for larger motors (typically) a "Motor Start" Capacitor.

    Motor Start capacitors typically have a centrifugal switch inside the motor to engage the capacitor for starting--Although (I believe) you can use a voltage potential relay to replace the mechanical switch.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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