I bought a home (existing construction) with a 3-speed ceiling fan on a dimmmer switch. An electrician doing some work for me made a comment to my wife how that’s bad for the fan motor, but why? (Luckily, the variable aspect of the dimmer switch doesn’t work.) I wasn’t there to ask why is this so bad?
Could it have burned out the variable resistor within the dimmer switch, perhaps? If so, how? Could it have the potential to burn out the fan motor? If so, how?
Motors draw a starting current during spinup which is much higher than their normal operating current. I believe this higher current tends to burn out dimmer switches and, if the switch prevents the motor from drawing adequate current, the motor itself may overheat.
I’m sure an electrician doper will be by with more facts…
IANAE, but what micco said. I’ve installed a few fans in rental properties and my house. Everyone of them said DO NOT use with a rheostat or dimmer switch unless specifically provided.
Don’t hook a regular ‘ol dimmer switch to a ceiling fan. A ceiling fan has an induction motor, and as such you cannot vary its speed using a phase-fired proportional controller (which is what a dimmer switch is). Not only will it not work, it could also damage the motor, as the sharp voltage transitions (particularly at half power) will make the coils vibrate.
this is a WAG, but since the current turns on more sharply than without the dimmer, the motor keeps turning off and back on, which is giving it lots of little current ‘spikes’, which can hurt the motor…
We have several ceiling fan/light combos hooked up to dimmer switches. The dimmer switch only controls the lights, however, and doesn’t affect the fan motor (I think we’ve got combo dimmer/toggle switches is how, but I’m not entire sure - I don’t do wiring).
You can do that without any problems, evidently. As least our electrician-nephew OKd it.
AC motors (such as a ceiling fan uses) are line-synchronous. The speed of the moroe is determined by the frequency of the AC power. A dimmer won’t change the frequency of the line power, so it won’t change the working frequency of the fan motor. What it will do is reduce the motor torque by cutting out part of the phase. When you reduce the power to the fan enough, the fan will no longer have enough torque to turn at line-synchronous speed, buzz loudly, and heat up a lot. This is not recommended.
To do this properly, you would need a variable-frequency motor controller and a 3-phase fan motor. That costs a lot, but it’s how variable-speed industrial fans and pumps are run.
