Capacitors for well pumps

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.

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.

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

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

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.

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

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.