Tuesday, December 5, 2023

The Joys of Country Living

I went to the tap and turned it on. All I heard was a sucking sound.


After Quicksilver had been picked up, I grabbed a couple of screwdrivers, a multimeter and a headlight and went looking.

The first thing I noticed was that the breaker was tripped.

The second thing I noticed was....

One of the capacitors in the well-pump specific junction box had disassembled itself, presumably due to rapid temperature rise inside of the case. There was also arcing damage to the 1/4" spade connector.

That is what we call in the trouble-shooting biz "A clue".

The new part is ordered and is expected Thursday.

Arcane question to the smoke-hose guys:

We paid for a 3/4 hp pump down in the hole. I suspect that the capacitors in the generic junction are sized for the 1/2 hp pump "everybody" installs.

The blown start capacitor is 70 MFD. The internet suggests that it should be 108 MFD-to-130MFD for a 3/4 hp motor on 240V. (Link  3/4 hp is about 0.56 kW)

The reason I ask is that my 4000 Watt generator will not start the pump. I SHOULD have enough juice to do it even with 3X in-rush but maybe not enough if the starting coils do not have enough off-set from the run coils.

Is there a major downside to installing a 108-130 MFD capacitor IF the well contractor actually installed a 1/2 hp motor rather than the paid-for 3/4 hp?


  1. Yes, there is a downside for using a larger start capacitor than the motor is designed for. You'll be feeding a higher surge into the windings, and could burn the motor out. I'd split the difference and go with this one (or something similar):

    1. My understanding, as incomplete and flawed as it is, is that the start capacitor creates a phase shift so a single-phase feed can "look like" a second phase to the secondary, start windings. A single-phase is like trying to start pedaling a bike with the pedals at top-dead-center. It. Just. Doesn't. Work.

      Many motors have a centripedal switch that drops out the secondary once it reaches a given RPM. The rotational speed of the rotor creates the phase differential between the stator and the rotor that creates torque.

      The surge from capacitors is a discharge phenomena and I am not sure it applies to an AC environment.

    2. You are more or less correct in your understanding.

  2. Line length? Voltage drop ?

    1. I believe the pump is AT LEAST 60' from the top of the well, perhaps more but not more than 200'. The well is 50' from the junction box. 12 gauge wire. 3/4 hp is nominally 2.3 Amps at 240 Volts, which is chump-change. No significant voltage drop expected.

  3. Don't have enough info to comment.

  4. No, it won't really make that much difference. When in doubt, more is better (up to a point). All the capacitor does is cause a phase shift to the start windings to help the motor spin up faster.

    Don't go too far down the "wrong capacitor" hole though. Capacitors fail due to heat cycles from the inrush current. It may not be anything more than that....especially if the caps weren't replaced at the time of the well motor replacement.

    (BTW, don't pay someone to install a well pump motor, it is easy to do...)

  5. B,could you put out a good source of info. in regards to replacing a deep well pump?

    I have done plenty of shallows due to easy access but never did a deep,thanks for any info sources/ideas.

  6. James: Deep well is pretty much the same as a shallow well, just a longer supply line. I generally use a tractor bucket to get them started, and use a simple pair of pipe wrenches as stops. Once it get far enough out you can use an old tire rim to roll it out of the casing.

    I doubt that Joe has a well much deeper than 75 feet though, knowing where he lives.

    Two guys can pull a well and replace it in about an hour....maybe less. All you need is a handle to hold the well string (3/4 or half inch pipe, depending on the adapter and a torch to reseal the hose and the electrical crimps. Some bleach to sterilize and yer all set.

    1. Thanks B,will do a little more research and be ready ahead of time so feel better about doing it meself,as for tractor bucket start,hmmmmmm....,luckily me meighbor and I get along and .....,he has a tractor!

  7. Beware of counterfeit capacitors. Image link: https://www.electronicproducts.com/wp-content/uploads/images2-facm-cti-3-oct2012.gif


Readers who are willing to comment make this a better blog. Civil dialog is a valuable thing.