Explain pump motor start switch

Hi all, I helped my neighbor disassemble a pump motor, we had to remove the centrifugal assembly from the shaft. The centrifugal assembly opens a switch when it gets up to speed. Opposite of what I thought would happen. The motor has a start capacitor.

I just did a Google search thinking I might just answer my own question, but all I did was confirm what I thought I knew.

So, why does the switch open when the motor gets up to speed?

What is the circuit before the switch closes vs. after the switch closes.

Yes, I'm sure the switch is closed at stall and is pushed open when the weight swings. Mikek

Reply to
amdx
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The start winding draws a lot of current, and is only needed to get the motor started. That start capacitor is a non-polar electrolytic. It can only take intermittent service without blowing the vent. The start capacitor causes a phase shift to the run winding, which provides the torque required to start the motor. At least it isn't using a potential relay. :)

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Reply to
Michael A. Terrell

Why did you think the switch should close at speed ??

Reply to
Rheilly Phoull

Never mind. I don't know how I got my logic mixed up. Thanks, Mikek

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Reply to
amdx

That switch is for the start winding. The start winding should not be energized for more than a few seconds because it will overheat. Make sure the start switch goes back in the same location on shaft. Depending on how the switch is actuated the wrong location will either prevent the switch from opening or else the switch will always be closed. So if the motor just hums when it is powered up then the switch is open, and if the motor does start correctly make sure it doesn't get hot real fast, because that will mean the switch is always closed. Eric

Reply to
etpm

Centrifugal force. The spring that is holding the contacts together will be pulled back via the linkage that gets forced to the outside of the spin.

And also, you only want the cap in circuit on initial start.

You can get add on switchings to hang on shafts to do these wonderful things.

An electronic starter will monitor the current and when the initial current drops off, the electronic switch disconnects the starting cap. Those types of electronic switches normally use a reed switch with a couple of turns of wire around the read to sense current. The switch turns on a triac. Also, you may see a washer wrapped up in the turns to create a shaded pole to prevent the reed from chattering.

Jamie

Reply to
Maynard A. Philbrook Jr.

Just a slightly off topic note, one can make a cheap rotary converting with a cap start/run motor. You simply start the motor and let it run and then use the starter winding as the third leg..

It does not work as well as using a 3 phase motor but it does work! :)

Jamie

Reply to
Maynard A. Philbrook Jr.

How much current can you draw from this setup? I have made several rotary phase converters that were properly balanced and in fact my shop runs with one (that I bought before I understood well how to make one) that runs modern CNC equipment. I just can't see how it would be worth the trouble trying to get enough current...wait, I see now. You really only need the manufactured phase to get the three phase motor started. It will then draw enough current from the single phase line and won't really need the current from the third phase unless really loaded. Nevertheless, I wouldn't bother. With only a little more work and some oil filled caps from my box-o-caps I could whip up another with motors I have already. As an aside, it is interesting how a person can learn and understand a lot about a particular aspect of a certain subject, namely AC electricity and poly phase motors and generators, and yet understand practically nothing about the subject of AC electricity as a whole. Especially how radio waves propagate, reflect, and travel down wires to and from antennas, and how antennas themselves work. For me it's kinda like voodoo. Eric

Reply to
etpm

I have already explained, I got my logic backwards. I understand how it works. Then my question was poorly ask. What I meant to sask, what is the function performed when the switch opens at speed? Ans. Stops current flow in the start winding.

nuf said, Mikek

I'm embarrassed, well, a little bit.

Reply to
amdx

No, you're very red in the face! :)

Jamie

Reply to
Maynard A. Philbrook Jr.

You use a cap run motor, the phase angle on the cap line will shift ~

90 degrees, not exactly the 120 you need but it does work for basic operations. you start it, and simply use the starter/run wire as your third phase.

You do need to up size the motor, like 1.5 to 2 times the expected load.

Jamie

Reply to
Maynard A. Philbrook Jr.

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