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I have an old Siemens motor with this specification : 220V 80W 0.65A

I need to reduce the speed (slow down) of this motor.

I know it's easy with something like an inverter, but I'm just wondering how about with just a resistor? If it is possible what are consequences? Is it bad for motor (damage or crash?)

If no, let me know how to slow down with resistor or something you suggest, please.

enter image description here

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2 Answers 2

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You can't really change the speed without changing the frequency of the AC. That's a synchronous motor - it rotates at a fixed multiple of the line frequency.

If you lower the voltage (or reduce the current) but keep the load the same it will be forced to run slower - it hasn't got the power to force the load to rotate at its designed speed. That is a bad thing.

If you lower the voltage some, then it will run slower under load but overheat and burn out. If you lower it more, then it will stop and burn out under load. If you lower it enough then it won't burn out, but it won't rotate, either.


I used to live in a house with low voltage (outlet voltage was like 90V when it should have been 110V.) The synchronous motor in the water pump (we had our own well) burned out like three times in a year before my father could convince the power company to do sonething about the low voltage.

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    \$\begingroup\$ Why should it be a synchronous motor? It should rotate at 3000rpm than. It is an Asynchronous motor! \$\endgroup\$
    – JG97
    Aug 10, 2019 at 9:23
  • \$\begingroup\$ thanks a lot 1++ \$\endgroup\$
    – Freeman
    Aug 10, 2019 at 10:26
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The motor is almost certainly an induction motor with a capacitor permanently connected to the auxiliary winding, a permanent-split-capacitor (PSC) motor. There is a marking that appears to be the capacitor rating (.1uF 400V?) in the lower left area area of the rating plate. It is possible to control the speed of such a motor to some extent by reducing the voltage with a series resistor or other means. That will work over a limited speed range it the load is a fan or a centrifugal pump that does not have too much static head. That would tend to increase the operating temperature of the motor, but that tendency is offset to some extent by the reduced torque load at reduced speeds. There are several similar questions here that have answers providing additional information.

speed-control-for-psc-induction-motor

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  • \$\begingroup\$ thank you so much , rep 1++ \$\endgroup\$
    – Freeman
    Aug 10, 2019 at 10:26

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