House Fan Power Usage

[jeff88]

I was just wondering what kind of electricity a typical house fan uses. Does it use the ac current from the main house electricity or is it converted to something else, say, DC or PWM? I would like to know this for both a ceiling fan and portable fan, if possible.

Also, based on the answer to the above question, is there a more efficient way to control a fan? For example, if the fan uses AC, would it be beneficial for it to use PWM instead?

Thanks!

[Daox]

My ceiling fans use from ~15 - 100W when in use depending on the speed. My box fans use 70-120W depending on the speed. Pedestal fans are probably less.

Sounds like you should get yourself a kill a watt. They're great for tracking energy use and can easily save you money by helping you find phantom loads.

[jeff88]

I have a kill-a-watt, but I don't know how I can connect it to the ceiling fan. It's hard wired into the house power lines. I can't really plug the KAW in anywhere to find out the power usage. How did you find out how much wattage your ceiling fan uses?

I still would like to know what kind of power the fans use. AC, DC, PWM?

[Daox]

I have a TED. Its a whole house electricity monitoring device.

You could rewire the fan to plug into a KAW, but that would be a pain.

All the motors I've seen used on fans are AC motors. PWMing AC power is not the best idea. I'm no expert, but I don't see it working.

[jeff88]

Thanks for the link! I like the idea of being able to read the power coming into the house.

Yeah, I definitely don't want to be dealing with rewiring the fans, but if I ever get around to swapping them to different ones, I might do that before I finish the full install.

So a PWM AC fan wouldn't work. What about it is not a good idea? Would converting the power to DC than PWMing that be beneficial or would the inefficiencies of converting the electricity not be worth it?

Maybe if one has some forethought, they could use DC from a solar array and/or wind turbine and install DC fans. Would this be more efficient than standard AC fans? Also, in this case, would PWM be beneficial?

[Daox]

I really don't know the specifics. But, AC power is a sine wave, not a square wave like PWMed DC power. An AC motor is designed to use this smooth wave, not a square wave. Converting to DC power sounds like a huge pain. Any efficiency gain wouldn't be worth the trouble I can gaurentee you. Its not like AC motors are horrible inefficient.

I'm also unsure why you want to PWM your fans? Its not going to increase efficiency or anything, its just going to slow them down...

[mf70]

My understanding is that most 3-speed floor fans are wired with two sets of windings, one for each target power. I've got a whole-house fan on a heavy-duty dimmer, At very low power settings it hums loudly due to the spikes in the supplied power:

(look up google images on "lamp dimmer ac waveform")

A lamp dimmer usually uses the zero-crossings in AC power as trigger points for a triac switch. The large deviation from sine wave magnifies the hum, but efficiency is still fairly good. There are dedicated fan control switches, but I have not seen a voltage trace to see if that's what the do that is special.

The power usage of your ceiling fan will be on a placard somewhere, but is probably around 60 Watts.

Mark