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I've got an electric split-phase motor (no capacitor) with a centrifugal switch.

Specs

Westinghouse electric motor manufactured in 76.
RPM 1725/1140
1/2 HP
115V 60Hz
Thermally protected L Type

It seems to me that the terminals are bypassed as the power cord is directly connected to the motor.

When plugging the motor I hear a humming sound and I have to hand turn the shaft to make it rotate (any direction).

That tells me that there is a problem with the start winding. So, I checked the centrifugal switch, cleaned it with sandpaper and still no automatic starting of the motor.

Here's the schematic of the motor as I see it since there is no schematic printed on the chassis.

schematic

simulate this circuit – Schematic created using CircuitLab

There are 2 terminals for plugging a kind of molex connector.

I don't know how to proceed from here.

Should I make connectors to connect wires between them?

Note than SW2 have a side not connected to anything!

Here's a table of all the motor interconnections between them with their resistance:

+--------+--------+--------+----------+--------+--------+
|        | Green  | Yellow |   Red    | Orange | Black  |
+--------+--------+--------+----------+--------+--------+
|  Blue  |    -   |    -   |     -    |    -   |    -   |
+--------+--------+--------+----------+--------+--------+
|  Green |        |   2.4  |    4.3   |    0   |    -   |
+--------+--------+--------+----------+--------+--------+
| Yellow |        |        |    5.6   |   2.4  |    -   |
+--------+--------+--------+----------+--------+--------+
|   Red  |        |        |          |   4.0  |    -   |
+--------+--------+--------+----------+--------+--------+
| Orange |        |        |          |        |    -   |
+--------+--------+--------+----------+--------+--------+

A - indicates infinite resistance, i.e no short circuit

Also, testing each motor input against the motor casing gives an infinite resistance.

The previous schematic shows the actual condition I got the motor and it used a bypass with a power cord.

I see that terminal A3 have a cut green wire so I guess that would be the same green wire from the motor connected with the line BLACK input.

Also, for terminal B1 the cut wire is yellow so this would be the same yellow from the motor and this would be connected with the line WHITE input.

The next schematic shows what it would have been before the "hack".

schematic

simulate this circuit

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Stécy
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  • Add the windings to the schematic, and mention at least their DC resistances. I think it's likely the start winding will be connected via the centrifugal switch to an external start capacitor. –  Jan 21 '17 at 15:52
  • About the windings, I am not sure which wires go to each of them... – Stécy Jan 21 '17 at 15:57
  • You have the motor. We don't. Do you have a multimeter? –  Jan 21 '17 at 16:03
  • Yes I have a multimeter. Since the green and yellow wires are connected to the power line I'm assuming that is the RUN winding. On that winding I get 2.4 ohms. For the start winding I'm assuming it would be the blue and red wires and I get no reading (infinite resistance, not connected). – Stécy Jan 21 '17 at 16:07
  • According to your measurements the Start winding is open circuit. That would prevent your motor starting without a physical turn. I wonder if that's why you were given it? – Jack Creasey Jan 21 '17 at 17:52
  • It might be a good idea measure the resistance from each motor terminal every other terminal. –  Jan 21 '17 at 17:54
  • Also check the resistance between each terminal and the motor housing. –  Jan 21 '17 at 18:00
  • @CharlesCowie : I added the resistances – Stécy Jan 22 '17 at 01:26
  • The usual fault with this kind of motor is that a bit of dust gets into the centrifugal switch. It takes a bit of disassembly and cleaning. Compressed air helps. – Whit3rd Jan 22 '17 at 06:31
  • @Whit3rd : I've done the cleaning and also sanded the contact points. – Stécy Jan 22 '17 at 10:59
  • I've corrected the question in light of further findings – Stécy Jan 23 '17 at 11:27

1 Answers1

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With the given information and discussion, I think the motor will operate with the following connection. The capacitor may not be needed. It the current in the start coil can be measured during start and it is relatively low with a capacitance value used for similar Hp motors, it might make sense to try a direct connection from the switch to the power line. There would be a risk of burning out the winding fairly quickly if it is designed for use with a capacitor.

Various electrical diagrams for washing machine are available on the internet. Some show motors that use a start winding with no capacitor and some show a capacitor. The extra centrifugal switch is shown on some as switching a function external to the motor. The extra contact on the starting centrifugal switch is shown as feeding power to an external function when the motor is up to speed.

enter image description here

  • It is what is setup right now and not an assumption. ;) – Stécy Jan 22 '17 at 02:21
  • So, what do you suggest for additional connections ? Is there missing connections ? Is the motor wired correctly for the START winding to work? – Stécy Jan 22 '17 at 02:23
  • Are you sure that a capacitor is needed? This motor does not seem to require one? – Stécy Jan 22 '17 at 11:00
  • If you want it to start without, hand turning the shaft, in the same direction every time, you need a capacitor. –  Jan 22 '17 at 15:35
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    Do you think that someone else might have changed the wiring on this before you got it? The arrangement seems unusual. –  Jan 22 '17 at 16:14
  • I've disassembled all the connections to be left with only the motor itself and made some discoveries. I've updated the question. – Stécy Jan 23 '17 at 11:10
  • The motor terminals are being bypassed by having the power cord directly connected to the motor as displayed in the diagram. – Stécy Jan 23 '17 at 12:00
  • I revised the drawing. I still wonder about the capacitor being switched over to the being across the power line in parallel with the run winding. I don't think that a motor starting capacitor would not be able to tolerate that. –  Jan 23 '17 at 13:44
  • There was no capacitor on the motor casing. I think this is a split-phase inducing motor so it does not need a capacitor. Besides, I am pretty sure the other wires (Blue and Black) should be doing something. I'll add another schematic with the missing terminal inputs as I discovered they were used before the power cord "hack". – Stécy Jan 23 '17 at 16:43
  • Motors that are mounted inside another enclosure like a heating or air conditioning equipment housing often have a capacitor separately mounted in the equipment housing. If the motor is split phase, there is a problem with the yellow and red wires connected to the centrifugal switch. I asked before if someone else could have changed the wiring before you got the motor. –  Jan 23 '17 at 16:55
  • The only apparent change is the power cord bypass. All the other connections to the centrifugal switch appears genuine. I've finished updating the question with an additional diagram and more text. – Stécy Jan 23 '17 at 17:28
  • Let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/52319/discussion-between-charles-cowie-and-stecy). –  Jan 23 '17 at 17:45
  • At the top of your drawing the "power" label refers to what part exactly ? – Stécy Jan 26 '17 at 01:51
  • That represents the 115V connection, but I made an error with that. –  Jan 26 '17 at 04:24
  • I revised the answer per discussion and corrected the drawing. –  Jan 26 '17 at 04:57
  • Alas it is not working. Motor still hums... I've tried different size of capacitors (88-108, 270-324)... – Stécy Jan 28 '17 at 15:30
  • Since this is a two-speed motor, you can be pretty sure that there is (or was) a third winding that is now not connected or open. It may not be worthwhile doing much more with the motor unless you can measure current and perhaps power. You could connect the start winding without a capacitor and see what happens. –  Jan 28 '17 at 16:24
  • With or without a start capacitor produces the same effect --> humming – Stécy Jan 29 '17 at 20:40
  • I am out of ideas. –  Jan 29 '17 at 22:12
  • I will try with smaller capacitor and see how it goes. After that, I'm declaring the start winding burnt or defective. – Stécy Jan 31 '17 at 02:29