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I have a swamp cooler motor which is single phase 3 speed motor, 1/7 HP i.e. 106 watts. I wish to reduce its speed (rpm) by 50%. Can I use this dimmer circuit to do so? This dimmer regulator is rated for 1000 watts exhaust fans. I only have school level electrical knowledge. I was thinking of connecting this dimmer regulator in between live (positive) wire, kinda like a ceiling fan regulator.

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This is the dimmer speed regulator

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3 Answers 3

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A 2-wire overhead fan controller would work. You can keep the 3-speed switch and put the speed controller in series with the lowest speed tap. That way you have all the higher speeds, and the LOW becomes a LOW-LOW.
In your photo, the heat sink seems small. If it gets too warm, add some metal or put the dimmer into the airstream. Remember, don't go too low on the speed setting. But if your motor is already turning when you switch it to LOW-LOW, then the setting can go a bit lower. It's like trying to drive your car using second gear. It helps if the car is already rolling.

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It should be possible as long as the power drawn by the motor does not exceed the absolute maximum ratings of the regulators switching device (triac).

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  • \$\begingroup\$ Thanks for replying. I have already stated that the motor is 106 watts and this triac dimmer regulator is rated for a load of 1000 watts. I asked the original question because normally experts say that single phase (or any induction) motor needs VFD which regulates both frequency & voltage to maintain same ratio for the motor. Simply reducing voltage will overheat the motor. Isn't that true for this motor? \$\endgroup\$ Mar 31, 2018 at 10:38
  • \$\begingroup\$ Yes, it should be possible but you may get side effects like overheating as you say, torq reduction... The best way to control speed in this kind motor is by frequency control. Anyway, it's worth a try to see if works ok for your application. \$\endgroup\$
    – user162889
    Jul 4, 2018 at 6:56
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If the dimmer circuit reduces the AC voltage and does not rectify it to DC, it may reduce the speed of your fan. The fan may not start with the voltage set too low. It may stall if you turn the voltage down too far. If you connect the motor to something other than the original fan, it may not work at all.

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