The usual noobie mistake -help please

[retiredsoldier919]

Today I installed a completely new 20 amp circuit.
Can you spot the new circuit?

New circuit

20160426_225250-1024x1365-600x800.jpg (90.1 KiB) Viewed 2046 times

This did nothing to improve my problem.
It's looking more like a bad motor.

[retiredsoldier919]

Although it is rarely the start capacitor, it is often the start switch.

That would be my next step.

The switch tested good following Jacob's Youtube video.

[retiredsoldier919]

It sounds like the motor is not starting properly under load, which points to: a) the start switch is bad or not making contact, b) the starting capacitor is bad or weak, or c) the start winding is open. If the start winding doesn't kick in, the motor wont develop enough torque under load and will slowly spin up, drawing lots of current.

Under no load, the motor may appear to start, but that's because it doesn't need much torque to come up to speed. I vote for a weak starting capacitor. If you have a multimeter, you can use the "ohms" setting to see if the start winding is open (infinite resistance). If it is, you might get lucky and spot a bad connection where the wires join to the winding; otherwise, the start winding may be burned out, but you would probably see lots of toasted insulation internally.

Good luck. Induction motors are pretty robust, so don't give up without a fight.

Since the circuit is definitely not the fault, I'm with you. Either the capacitor or windings are bad. I looked at the windings through the motor case openings and what i see looks good, but who knows. Unfortunately the motor is the Emerson with internal capacitor. I'm considering taking it to a local motor repair shop with Shopsmith experience.

[JPG]

Although it is rarely the start capacitor, it is often the start switch.

That would be my next step.

The switch tested good following Jacob's Youtube video.

Not having that video, I am curious how that is done.

I would not trust any resistance measurement made external to the motor.

P.S. You have a local motor shop with 'SS experience'?

[dusty]

What happens if, due to a malfunction, the motor remains in the start mode? In this configuration, both the start winding and the run winding are drawing current. Does this create an overload condition?

By design, at about 75% of run speed, the start circuit should be disconnected. If it does not disconnect, the most likely cause is the centrifugal switch; the contacts remain closed for whatever reason.

Unless you have the equipment and the know how, this problem should be evaluated by a reputable motor shop. Any motor shop will be able to evaluate the motor.

[johnm]

What happens if, due to a malfunction, the motor remains in the start mode? In this configuration, both the start winding and the run winding are drawing current. Does this create an overload condition?

By design, at about 75% of run speed, the start circuit should be disconnected. If it does not disconnect, the most likely cause is the centrifugal switch; the contacts remain closed for whatever reason.

Unless you have the equipment and the know how, this problem should be evaluated by a reputable motor shop. Any motor shop will be able to evaluate the motor.

If the start switch remains closed, the motor should speed up to rated speed, and the start winding will draw some current through the capacitor and the start switch. The capacitor probably isn't rated for continuous duty (those are usually those rectangular metal can capacitors), so it eventually it will fail. Since the motor starts and runs slowly and doesn't come up to rated speed, it says that it is just not developing any starting torque. If the starting winding is totally open (disconnected), you should be able to get the motor to run in the reverse direction by just spinning it in the reverse direction and turning on the power switch (try this with no load/no belt). If it reverses and goes in the right direction, that points to a weak capacitor.

[dusty]

A weak capacitor? Is that a capacitor that either does not take a charge or does not hold a charge?

[JPG]

I think changing the "W" to an "L" makes more sense. A more typical fail mode is open circuit or short (mechanical contact failure).

An interesting question re stuck on start switch. I do not know the answer, but it could possibly cause interference with the 'normal' currents in a running motor.

No I am not going to try it out.

After thought makes me consider that the capacitor wiring may be shorted.

[johnm]

A weak capacitor? Is that a capacitor that either does not take a charge or does not hold a charge?

The electrolyte inside dries out (due to heat, age). It basically just means that the capacitance value drops outside of the rated value on the label. Since these are AC capacitors, they don't really act to "hold a charge"...they just kind of "borrow it" for a portion of the AC cycle, so that the start winding has a current in it that is a bit out of phase with the running winding, and that gets the motor turning in the right direction.

The 3HP motor on my well pump is a capacitor start motor, and I've had the start capacitor replaced every few years. The well guy puts it on his magic meter and says "Capacitor looks weak...$80 please" :-) Usual symptom is that the well controller trips off due to high current, since the motor never gets running up to speed.

[JPG]

I think moisture contamination is a more likely cause of well pump motor start capacitor failing. Again the w vs l thing.

They do indeed hold a charge, but only for a short period since the applied voltage is reversing polarity 120 times/sec. Their purpose is to create a phase shift in the start windings. Without a charge, that would not happen.