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I've just rewound a single-phase, 1/4 hp, 4-pole top-load washing machine motor identical to this one.

It was originally wound in AWG 22 aluminum wire, and I rewound in AWG 23 copper wire, which should have about 80-85% of the resistance of the original winding, which isn't so much lower that the capacitor value should be readjusted.

What I found strange is that its no-load current, with the original 40 μF capacitor, was too high. 2.8 A, 90% of rated current.

And it was heating horribly, it reached 100 °C in a couple minutes.

Then I noted something strange. By braking it with my hand, the current fell.

The current consistently fell, even at low speeds well below the breakdown torque, the current was still much lower, it fell to 1.9 A at its lowest.

What's the logic of this?

I never found anywhere online mentioning this behavior, and for all I know this makes no sense.

Perhaps these motors have a non-ideal behavior because of the way they're wound?

Instead of having an auxiliary winding with lower L/R ratio, it has two identical windings, same gauge, same number of turns, pitch etc.

It's wound exactly like an old two-phase motor would be wound, with two identical sets of windings made to be fed with phases in quadrature.

It's wound like that so it can be reversed by changing switching only one contact, changing which winding is fed through the capacitor and which is fed directly by the mains.

Or, perhaps, this happens because its capacitor is not optimized for nominal slip?

It's a permanent capacitor, so you'd expect it to be optimized for nominal slip, but as this motor needs to quickly reverse its rotation during the washing, it needs a decent starting torque too.

So perhaps its value is larger than that you'd use if this motor didn't have to do that and only ran in a single direction at nominal speed all the time, like fans do.

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  • \$\begingroup\$ Did you count the turns correctly? Was the copper wire insulated (basic question I know)? \$\endgroup\$
    – Andy aka
    Jan 14, 2023 at 20:44
  • \$\begingroup\$ Yes and obviously yes. I mean, how would it be even possible to use non-insulated copper wire? How would it even work to begin with if it wasn't insulated? \$\endgroup\$ Jan 14, 2023 at 20:50
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    \$\begingroup\$ You'd be surprised what some people will do (even on this site) LOL. \$\endgroup\$
    – Andy aka
    Jan 14, 2023 at 20:51
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    \$\begingroup\$ @PStechPaul It isn't 220 VAC, I forgot to mention, it's 127 VAC. And If I had done that then the motor wouldn't run. Plus, I've measured the capacitor with my multimeter, and tested other two that are 35 and 50 uF, all of them give similar values and have the exact same behavior of having a larger current in no-load when compared to some load (it gets higher again when its almost stopping). Plus, if I measure the current in the winding connected to the mains alone, yes, connecting the capacitor to the other winding does reduce the current on it. But the total current still behaves like that. \$\endgroup\$ Jan 15, 2023 at 7:10
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    \$\begingroup\$ @PStechPaul Insulation breakdown is very unlikely, they'd make the two identical windings differ, and I've ran tests changing them and it behaves virtually the same with either being directly on the mains and the other on the capacitor. What I'm starting to believe is simply that the original already ran too hot. Firstly because I have a brand new washing machine with the same motor and it heats so much I can feel the heat radiating on my foot when its by the side of its bottom. And I can smell it too. And it originally uses insulation class H, one of the highest temperature classes out there. \$\endgroup\$ Jan 15, 2023 at 7:12

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So, I found out what happened.

I accidentally measured the current on the main winding only and not the total current, the current flowing through the capacitor wasn't being added.

When measuring the total current, then it gave a more reasonable value and behavior, going from 1.8 A empty to 2.8 A on full load.

This also implies the phase difference was greater than 90° in no-load, cause the sum of the two currents was lower than the current on each winding separately.

I tested swapping this motor with the original motor in my washing machine, and then I tested the original motor, and found out that yes, it just heated that much originally.

It reaches 120 °C in a 28 °C room temperature with no load, so a 92° C rise.

It was just very hot to begin with.

Thankfully, I rewound it with class H insulation wire.

But, I used electrical tape to protect the tips of the thermal protection element, because its original plastic was tearing, and I'm afraid it may fail at those temperatures.

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