Well Pump Hookup

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Dennis Alwon

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Can a typical 3 wire well pump with a running winding and starting winding be run by wiring directly to the running winding and the common. I am talking about not using the control box that is normally used with them so the starting winding would not be used. What will happen if it is hooked up in this manner?
 

Dennis Alwon

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What would happen if you wired 240V directly to the starting winding and the common? I assume it will damage the starting winding but I don't quite know how the starting winding is different. I know that the starting winding gets the motor going and then switches to the running winding
 

GoldDigger

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What would happen if you wired 240V directly to the starting winding and the common? I assume it will damage the starting winding but I don't quite know how the starting winding is different. I know that the starting winding gets the motor going and then switches to the running winding
The most important difference about the starter winding is that it is mechanically offset somewhere close to 90 degrees of rotation from the run winding.
That means that if you drive out of phase with the run winding (via a series capacitor) you will get torque in a preferred direction, unlike the result with a pure single phase drive, even with the two windings.
It also has a different number of turns and DC resistance.
This is necessary since it is always driven through s series capacitor.
If you drive it directly, the motor still will not stsrt and it will overheat sooner.
Finally there has to be some way (timer or centrifugal switch) to cut it out of the circuit since it is inefficient and draws excess current.
(In some motors the capacitor fed winding is smaller and is designed to stay in circuit permanently.
Such motors are simpler but have less starting torque, I believe).
 

Jraef

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The problem with single phase is that there is no relative rotation of the magnetic fields. Once ALREADY spinning, the repulsion between the magnetic fields of the stator and rotor is against a moving mass, so it KEEPS it moving in that direction. But at a stand still, it just vibrates back and forth; it doesn't know which direction to rotate yet. The start winding is there to create that initial nudge to get it going in the direction you want it to spin, it does this by creating a virtual phase shift between the two sets of windings, using the capacitor (in the case of a cap-start motor), or a DIFFERENT capacitor (in the case of a cap-start / cap-run). That only needs to ESTABLISH that shift for a second to make the motor BEGIN spinning, then it becomes redundant. So the components for the Start winding are typically smaller than those of the main run winding since it is not really tasked with running the full load.

Bypassing the start winding sets up that "no rotation" situation and the motor does not spin. Without the rotor bars spinning through the magnetic fields of the stator providing mutual inductance to create impedance in the circuit, the windings look like a short circuit and blow the fuses or trip the breaker (or burn up).

If the motor was already spinning, it would work actually. the problem is, and especially with well pumps, if the motor is already spinning the WRONG direction, it will CONTINUE spinning in the wrong direction!
 

ActionDave

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What would happen if you wired 240V directly to the starting winding and the common? I assume it will damage the starting winding but I don't quite know how the starting winding is different. I know that the starting winding gets the motor going and then switches to the running winding
You would blow up the starting cap. You may or may not damage the starting winding.
 

Tony S

Senior Member
The three main types of SP motors.

The centrifugal switch can be done away with a timer.

CapacitorrunSync.jpg


Capacitorstart1.jpg



Capacitorstartcapacitorrun1.jpg
 

gar

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Ann Arbor, Michigan
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EE
150527-2234 EDT

All single phase motors are at least two phase for at least starting. If there were no starting winding and/or phase shifted running winding, then the only way to start the motor would be an external mechanical drive to the rotor.

A motor not mentioned above is the split-phase motor. This type does not use a capacitor. Rather the split-phase uses a starting winding with a different phase shift than the main winding. This is achieved by a different L/R ratio.

A capacitor start-run motor is the best of all in the following respects, two different capacitors are used:

High starting torque, and near unity PF on starting.
High torque, low torque ripple, and near unity PF while running.

See Chapter 17 of Alternating-Current Machinery by Bailey and Gault, 1951.

.
 

StarCat

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Moab, UT USA
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Imdustrial Engineering Technician - HVACR Electrical and Mechanical Systems
Additions

Additions

Something to add to Jraef's comments....
Scroll refrigeration compressors when powered down tend to back spool.
Sometimes a momentary power bump on a single phase machine happens and it will re-start running backwards then of course overheat and trip on internal.
Sensitive anti short cycle devices are helpful but even they can be fooled.
 

gar

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150529=1017 EDT

An additional comment on the capacitor run motor.

A capacitor run motor is a two phase motor with a rotating magnetic field. This will run in only one direction. To change direction the wires to the capacitor and its series coil must be reversed.

.
 

Dennis Alwon

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Thanks all...

The reason I asked was because my builder tore down an existing home to put up a new home. In the process the old well wire was taken apart. They had a control box along with a 3 wire cable going down to the pump. We had no idea how the pump was installed so my guys noticed that the wiring in the control box had some wires cut and they notice that the black feed and the black wire to the pump were under the same screw on the load side. We tested the pump and it appears that the 3rd wire was hooked up to nothing since we got no reading from it to any of the other wires. I decided that the pump was probably replaced with a 2 wire motor and the control box was really not used- bypassed. I told them to hook it up directly to the leads where we had continuity. The pump worked-- I was hoping since it worked we were good but wasn't sure if it could work and we still had something hooked up incorrectly.

If it were a 3 wire pump wouldn't I get continuity on all 3 wires thru the windings?
 
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