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Pump Question

Had a call with a Munchkin F05 lockout (supply temperature exceeds 230F) and found that the impeller on the primary pump wasn't spinning.  I carry Taco replacement cartridges and slipped a new one in and this one didn't spin either even though I could feel the motor being energized.  I ended up replacing the motor as well and of course, it worked fine after that.



I'm curious as to what goes wrong with a pump to cause this problem.  The impeller would start spinning if you gave it a flick with your hand, but not on its own.  Maybe a bad capacitor?  Like I said, this pump is on a primary circuit, so it's got a easy life.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

Two btu per sq ft for degree difference for a slab

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 22,899
    There are several ways...

    to get an electric motor to spin on single phase AC (it's easy on three phase!).  Now I've not taken a Taco motor apart, so I can't be sure, but my feeling from looking at the literature is that it's a capacitor start motor.  Which means that there are two sets of field coils; one directly energized and one energized through a capacitor.  The capacitor makes the magnetic field in its coil lead the other coil slightly, giving a spin to the field, which creates torque on the armature and off you go.  Bad cap?  No spin, no torque, and it sits there humming.  Until you spin it by hand, when oddly it will run just fine up to a point.  It might also be capacitor start/induction run which is similar, but the capacitor cuts out once the motor is up to speed; those have a switch on the armature which can fail with the same result.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • SWEI
    SWEI Member Posts: 7,356
    edited February 2013
    single phase circulators

    Conventional wet rotor circs are mostly PSC.  Most of the three-piece designs have centrifugal cut-outs.
  • Paul48
    Paul48 Member Posts: 4,469
    This is what it is....

    Permanent-split capacitor motor

    One way to solve the single phase problem is to build a 2-phase motor, deriving 2-phase power from single phase. This requires a motor with two windings spaced apart 90o electrical, fed with two phases of current displaced 90o in time. This is called a permanent-split capacitor motor in Figure [u][color=#0066cc]below[/color][/u].



    Permanent-split capacitor induction motor.

    This type of motor suffers increased current magnitude and backward time shift as the motor comes up to speed, with torque pulsations at full speed. The solution is to keep the capacitor (impedance) small to minimize losses. The losses are less than for a shaded pole motor. This motor configuration works well up to 1/4 horsepower (200watt), though, usually applied to smaller motors. The direction of the motor is easily reversed by switching the capacitor in series with the other winding. This type of motor can be adapted for use as a servo motor, described elsewhere is this chapter.
  • Capacitor

    So, it might just be a bad capacitor?  Is that the device that's in the Taco wiring box?  Can you get replacements?



    Can you think of any reason why they fail?  This happens quite often on pumps that are not that old.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • MikeJ
    MikeJ Member Posts: 103
    I have a

    taco wet rotor in the shop with a bad capacitor, got a price from taco for a new capacitor. Price was high, better off replacing the whole thing. I should get that out and look at it, again. was always going too look elsewhere for one, but never have.
  • Jamie Hall
    Jamie Hall Member Posts: 22,899
    Capacitors die...

    they just do.  Some sooner than others, even in exactly the same application.  Of course, it is possible to kill them, too -- a healthy voltage spike might do it, but you'd see other problems in other connected equipment.



    It's just one of the things that capacitors do do.



    Sometimes the replacements are inexpensive, relative to the motor -- or at least they used to be, but then that was back aways.  I've replaced a few on motors around the farm here, but that's rather different.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Paul48
    Paul48 Member Posts: 4,469
    Capacitors

    I'd stop at a motor shop and see what they had. They're not usually expensive. The one you get, may not have the same plugs, and may have to be wire-nutted, but who cares.
  • Pumpguy
    Pumpguy Member Posts: 628
    Most

    common failure on capacitor start single phase motors is the centrifugal starting switch. 



    Over time the contacts get pitted and don't complete the starting circuit.  A good motor repair shop should be able to sell you a replacement board and switch contacts.
    Dennis Pataki. Former Service Manager and Heating Pump Product Manager for Nash Engineering Company. Phone: 1-888 853 9963
    Website: www.nashjenningspumps.com

    The first step in solving any problem is TO IDENTIFY THE PROBLEM.
  • Testing a capacitor

    I've gotten better at being able to use my meter for testing voltage and resistance, but don't know how to test a capacitor to see if it's any good.  Can one of you techies educate me?
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Paul48
    Paul48 Member Posts: 4,469
    Ebay

    Buy a cheap capacitor tester.Negative probe goes on the striped side of the cap, and it must be withing 10% of its rating,
  • Capacity Tester

    Thanks, Paul!  I'll get one.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • rick in Alaska
    rick in Alaska Member Posts: 1,452
    capacitor

    My meter has a capacitor checker built right in to it, which has helped me out a lot. And I didn't have to buy a separate meter.

    Try Radio Shack or similar for capacitors. I haven't looked myself, but I assume the numbers for the cap are written on it.

    Rick
This discussion has been closed.