Pump Question

Alan (California Radiant) Forbes

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.

Jamie Hall

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.

SWEI

single phase circulators

Conventional wet rotor circs are mostly PSC.  Most of the three-piece designs have centrifugal cut-outs.

Paul48

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.

Alan (California Radiant) Forbes

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.

MikeJ

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

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.

Paul48

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

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.

Alan (California Radiant) Forbes

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?

Paul48

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,

Alan (California Radiant) Forbes

Capacity Tester

Thanks, Paul!  I'll get one.

rick in Alaska

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