Electrical question for the pro's (ceiling fans)

[Anthony Whitesell]

The only thing I can think of as to why each of three fans would run slower than the previous is if there was same odd series-parallel wiring combination. Possibly also impacted by the fan controller as well.

If the fans were at 50', 75' and 100' from the source. The difference in voltage from the source to the first and from the first to the third would be 3% each (or 3.6V). I find it hard to believe that a ceiling fan would run noticeably slower on a difference of 3.6V (or 116.4 vs. 112.8).

Seems like there is another, yet, unknown in the story. My concern with running 3 fans from the same controller would be overloading the controller itself.

[Mark Bolton]

The only thing I can think of as to why each of three fans would run slower than the previous is if there was same odd series-parallel wiring combination. Possibly also impacted by the fan controller as well.

If the fans were at 50', 75' and 100' from the source. The difference in voltage from the source to the first and from the first to the third would be 3% each (or 3.6V). I find it hard to believe that a ceiling fan would run noticeably slower on a difference of 3.6V (or 116.4 vs. 112.8).

Seems like there is another, yet, unknown in the story. My concern with running 3 fans from the same controller would be overloading the controller itself.

There are controllers out there rated for 5 fans. My only guess on the speed issue is the fans being such low amperage but again its a guess.

[Mike Heidrick]

This thread is funny to me. Fan in shop - dust will vary the speed a ton more than length of supply line.

[Bill George]

At 1 amp draw your voltage drop will not be a factor. I have never tried this but, set up each fan on its own controller and adjust the speed on each so they are the same. Feed all the controllers from 1 single pole switch and use it to turn the fans on and off at the same time. You would need to keep the speed fairly fast so the motors will start.

It was always my understanding that unless the motor was DC and its not, the frequency of the controller was the speed control.
This is the Only circuit I could find and its 220 volts > http://www.circuitstune.com/2012/01/...ontroller.html

[Lee Schierer]

Don't most fan speed controllers use sine wave clipping to control fan speed? If that is the case, wouldn't the input voltage to fan #1 be something less than 119 due to the clipping?

[Phil Thien]

An air scrubber mounted in a corner at about shoulder height and aimed (output) at the ceiling, will do an amazing job of equalizing the temps. Even on the lowest setting (which is fairly quiet). And you get the bonus of cleaning the air, too.

[Mark Bolton]

This thread is funny to me. Fan in shop - dust will vary the speed a ton more than length of supply line.

Dust varying the speed of a fan? Thats a funny one. I have been in peoples homes with tendrils of dust trailing off the blades.. doubt it slowed them.

I have seen the progressively slower fan issue first hand. Its completely obvious at all speeds but majorly obvious at very low speed (which is where my fans would mostly run). One instance I saw, at the lowest speed setting the first fan would run like youd think and the last was turning slow enough that you likely could have read something if it were written on the blades.

I was hoping to avoid three fan controls just for ease of installation and to keep it clean but I really dont want the speed ussue. If that's the route then that's the route but as was said, something has to be at play.

[Dick Strauss]

Mark,
I have an idea that might work for you. Use Lee's idea and wire to the center fan. Then add a loop of wire to the center fan circuit only that matches the lengths to the outer two fans. This loop of extra wire could be run into the attic area to hide it. The outer fans will be connected to the straight shot wire coming from the switch and distributed to them through the middle fan. The center fan motor will be connected to the extra loop (that is connected to the main wire feeding all three fans). This way all runs are the same length without messing with conduit lengths, etc, and all the speeds are as close to the same as the resistance in the respective motors.

Exceeding a 3% Voltage Drop
At less than 1A per motor x 3, there should be no reason to run anything bigger than 14g unless you have a run longer than 190 ft one-way. With a 2A total motor draw, you can have 290 ft of one-way run and still make the 3% voltage drop limit.

By the way, I'm not a pro so run it by the other guys to see if there might be an issue with my idea. I have no idea what lengths we are talking about but I know it isn't a good idea to coil too much wire together (it can't dissipate the heat from internal resistance) in the case of the added center loop.

[Ole Anderson]

Before you do this, take time to measure the difference in air temp up and down. I bet you will find that you are wasting your time. Air movement in the summer is of course a whole different matter. I installed three 3 bladed fans in the peaked ceiling (24') of our church 24' on center and we actually used them last night to help cool the choir during rehearsal. And the fans were daisy chain wired. All seem to spin at the same rate off a simple VS fan controller. I think everyone is overthinking this one. Besides even if the air is 5 degrees warmer, the perceived cooling effect of moving air will negate the warmer temp.

[Mark Bolton]

At 1 amp draw your voltage drop will not be a factor. I have never tried this but, set up each fan on its own controller and adjust the speed on each so they are the same. Feed all the controllers from 1 single pole switch and use it to turn the fans on and off at the same time. You would need to keep the speed fairly fast so the motors will start.

It was always my understanding that unless the motor was DC and its not, the frequency of the controller was the speed control.
This is the Only circuit I could find and its 220 volts > http://www.circuitstune.com/2012/01/...ontroller.html

Bill,
My entire motivation for the single speed control and feeding from one end (like you'd feed any simple circuit) was just for ease, cost, and clean/simple install and operation. If I have to go to any extremes I will simply three controls and feed to through the single conduit. I was just looking for the optimal solution.

I think both you, and Lee, are on to what may likely be the real culprit here with regard to the progressively slower fans Ive seen. I never had any idea what control they were using on these fans but Im now wondering if the clipping Lee mentions, and your post with regards to the frequency being use to control speed, is what may be at play here. It wasnt my job to do so but it would have been interesting to eliminate the fan control temporarily and see how they ran. For all I know it may not have even been a multi fan control.

It all interesting none the less, and its just a simple little job, but Id rather only fool with it once ;-). Im not a fan of having to go back on things when Im done.

[Mark Bolton]

Before you do this, take time to measure the difference in air temp up and down. I bet you will find that you are wasting your time. Air movement in the summer is of course a whole different matter. I installed three 3 bladed fans in the peaked ceiling (24') of our church 24' on center and we actually used them last night to help cool the choir during rehearsal. And the fans were daisy chain wired. All seem to spin at the same rate off a simple VS fan controller. I think everyone is overthinking this one. Besides even if the air is 5 degrees warmer, the perceived cooling effect of moving air will negate the warmer temp.

Ole,
I experience this on a regular basis. I have high storage in the building and its sweltering up there when its cool down on the floor. I was planning on reversible fans so there really would be no moving air hitting anyone in the space. The fans would be pushing the air down the outside walls of the building (just like your heating system is designed to curtain the exterior walls). Im not saying its an ideal situation, and weatherization would be a much wiser investment. But even if I opted for non-reversing fans, I could do this job in perhaps 4 hours, for 350 bucks or so. That doesnt go too far with weatherization and with the work I have to do the 4 hours as opposed to a longer option, is very pretty serious motivator.
Having the fans running in the summer doing some cooling would be very nice too.

I have wall mounted air moving fans at the moment that help immensely and on one end of the shop I have a modine that moves a lot of air and I keep the fins pointed fairly low which helps. That said, these fans are very directional and they leave a lot of areas of the shop fairly cool.

One entire wall of the shop all overhead doors which is a massive loss. Two of those are going to be eliminated, framed in and insulated, which will make a big difference. That said, we are back to the free time to work on my building as opposed to produce work issue. Hiring it out gets even worse.

Thanks.

[Bill George]

Mark you are on the right track, voltage has little to do with the speed of an AC motor. The speed is controlled by the number of poles in the motor (fixed) and the frequency of the supplied alternating current to the motor. The sine wave clipping is a form of frequency control.

What I have done in the past when working on a control project is do a mock up in the shop and try some ideas. Once again, as Dick has pointed out and proved by the math, at the low amp draw of this circuit voltage drop is not a factor.

[James Tibbetts]

Just reading through the posts, and using a handy online calculator, here's what I think.
Run from panel to junction box at center point of fans. (assuming worst case of 100' run to junction box; 10 ga wire @ 15 amps, 8 ga. @ 20 amps. 3% voltage drop for both.)
Voltage drop from there to the farthest fan on a 12 ga. feed is less than 1 volt.
I'm assuming that the current draw of about .5 amps per was the run current.
Remember that your controller and wiring would need to be rated to handle the start-up draw of 4 loaded motors.