Speed Control for AC Electric Motors

Can anybody tell me how to build a controller to adjust the speed of an 110VAC electric motor, ( ex: blower motor, fan motor ) I was cautioned about using a light dimmer. bill

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MEAlvis1 month ago

Wall light dimmers use Triacs to block all current flow when applied voltage is low and continue to block all current flow for a variable time after the applied voltage rises above zero, then rapidly switching on, timed to the rising voltage of the applied alternating wave of applied voltage: 0 up to 155 V peak positive, back to zero, up to 155 V peak negative and then back to zero 60 times/second.

JoeK282 months ago
it might not be good for a motor, depending on the motor type and size, but again, no you are wrong. open a wall dimmer up and you will see that all it does is run the voltage thru resisters cutting the voltage....no blinking occurs lol wow
ngines19 months ago

Why is a light dimmer bad? Im trying to figure out the same thing now.

Yonatan24 ngines13 months ago

A dimmer (PWM) lowers the brightness by blinking the light at extremely fast speeds. This can ruin a motor.

The starting current of a motor can also be higher than what the dimmer can handle (Example if I'm not mistaken: a 2A motor can have a 3A starting current)

JoeK28 Yonatan242 months ago

rotfl um no it doesnt lol it does it by limiting the voltage to the light thus dimming it. thanks for the laugh though

You might have had a good laugh but you are still wrong LOL
Standard, old style dimmers cut the sine wave either at the front or at the back, so they reduce the average voltage this way.
Modern dimmers, for example those for LED systems do exactly what Yonatan said.
They create a PWM signal in the kHz range and the puls width determines the actual output voltage.
In either case a dimmer is not a good choice for a motor as the sine wave is incomplete.

I have a 110VAC 1hp motor, it has 2 brown leads running off to a capacitor. There is the white/common, with 5 assorted wires colored by speed, all in a bundle runnig from the inner windings, and finally, a green earth ground lead attached to the body. Is there an instructable to craft a multi polar/variable switch for this, or should I make one?

Where did you find it? (If not buy it)

Those motors are not very common for the hobbiest.
But just for the understanding of things it would be good to have an ible for it.
Especially if it includes how to figure out the right wires for the different speeds.

ShahidulI57 months ago

what are the present limitation for speed control of motor?how can i speed control of dc motor?

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