Motor Speed and Electrical usage

[leehljp]

Basic question:
Does the speed settings (slow, med., fast) on motors (specifically box fans) affect the amount of electricity used?

My shed/shop is 9 x 12 and I just added a 20 in box fan (from Walmart, USA) in the ceiling to act as an attic fan. In the past, I have turned the AC on a 1/2 hour before I go work in it; sometimes I turn a small floor fan on. AND occasionally, I turn them on, don't get to work (and forget that they are on) and leave them on all night.

With Electricty costs here, I try to watch the usage. So my question is as listed above. I can tell a huge difference in our monthly electricity bills ($50 fall, winter, and spring, $100 in summer) just by using fluorescent bulbs.

So, If I leave the fan running on slow (versus med/fast) all day just to keep the walls from being roasters will it save any yen for me?

[LCHIEN]

I'm sure it does. I'll do a measurement for you...

--------------Low----Med-----High
Amps________.40____.51______.63
Watts________35_____43______54
VA___________49_____62______75

at 119V with my 3-speed 12" fan.

Move more air = more work...

[leehljp]

Thanks Loring. Somewhere in something, maybe from when I was a kid, it seems like - that electricity usage through resistors, transformers or what not, a change in speed did not reflect a change in electricity usage because electricity was diverted to something else - heat causing resistors or transformers etc.

THAT is nagging in my mind.

[LCHIEN]

Thanks Loring. Somewhere in something, maybe from when I was a kid, it seems like - that electricity usage through resistors, transformers or what not, a change in speed did not reflect a change in electricity usage because electricity was diverted to something else - heat causing resistors or transformers etc.

THAT is nagging in my mind.

You could regulate speed somewhat by using series resistors but that is an extremly inefficient way of controlling speed or load power. Would be a bad engineer that controlled speed that way in a commercial device. Transformers are theoretically lossless devices. But bulky heavy and expensive. Usually avoided, too.

[cabinetman]

This is an interesting topic. What else may affect efficiency is how clean you might keep the fan. I've bought and still use those 20" box fans. I can get them on sale here for around $16.00. They are so cheap I don't worry about them breaking. I've made floor fans out of them by building a stand, and some added casters.

But, I do notice a real lack of efficiency from the fan, at any speed, when the blades get all dusted up or gummed up from use. I've had to oil the shaft on occasion to get it to start freely. When used as a forced air aid, or as an exhaust it might be wise to regularly check to see how clean it is. I'm guessing that if additional load is applied, the cost of operation vs efficiency could be an issue.
.

[Hellrazor]

Keeping the fan blades clean in anything from a box fan, ceiling fan, exhaust fan to the fan in your A/C unit is important. Dirty blades cause extra stress on the motor, can increase power consumption and puts stress of the shaft and bearings because the fan is no longer balanced.

[linear]

here's some more data

These measurements were taken with a P4400 Killawatt meter. My fan is a Vornado 283 (uppity box fan ) nameplate rating 1.2A at 120VAC.

Low 33W
Med 58W
High 118W

So there you have it.