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Duffy
04-25-2018, 10:21 AM
My daughter has bought a ceiling fan that has a small problem:- it is too fast. The color and design are perfect, so changing is not in the cards. I have not put a tachometer on it yet, but it seems to be about 50-100 RPM too fast. The wall mount speed control appears to be a combination of a five-position rotary switch and a multi-tap transformer. From the size of the transformer, this motor cannot be very powerful.
I welcome any suggestions, but would an electronic controller work, and where does one buy it?

J Tiers
04-25-2018, 11:53 AM
There are really only a few ways these controls work.

1) Pole changing. This requires that the number of poles be selectable to a number that gives a suitable speed. I understand that you do not want to hear this, but....... If there is no acceptable speed provided with this type motor, your only choice is to remove the fan and replace with a different one that has suitable speeds.

2) Winding changing. the windings are tapped and the switch selects the speed by applying power to the appropriate winding tap. You must have the taps, but with this type, it is possible that a triac controller may work. You would then set to lowest speed, and use the triac controller to slow it farther.

3) A triac type speed controller. This is only suitable if the motor is one that will accept it. I do not know if it is, but it might be, as per "2".

mattthemuppet
04-25-2018, 11:55 AM
I don't know much about ceiling fans, but if the rotary switch controls voltage to the motor via the transformer then a big azz power resistor in series with the lowest speed transformer output should knock some speed off. Wouldn't hurt to figure out power at that output and cooling requirements for the resistor though.

BCRider
04-25-2018, 12:15 PM
I'm pretty sure that the box you have is not a transformer. With multi winding motors in the fans for speed control the box you have is simply a switch that applies power to the suitable wire from the motor. And that box with the multiple wires is up in the box in the ceiling, right? Then a wireless remote mounts in a clip on the wall?

You could try using a light dimmer and it may work if you only need to reduce the speed by a little. But if you need to reduce it by much there is a good chance that the motor will start to hum due to the way the triac chops the AC power to alter the "duty cycle" of the sine wave.

But if the triac did work then a resistor of the proper value and wattage would drop the power to that low speed winding and not introduce any hum. But the only way to determine the value to use is to take measurements of the current being used by the motor. If you want a number from us that's impossible to give without us doing the same measurements.

It won't be just a small resistor either. The wattage rating and need for airflow will depend on the voltage it needs to drop and the current passing through it. Again we have no way of saying what this would be without measurements.

Duffy
04-25-2018, 12:48 PM
I opened the control box and it turns out that the "transformer" is really a coil with five taps. I guess that Jerry's number 2 option is correct. Meanwhile, my grandson checked motor speed with a laser tachometer and found that it ran at only ONE speed! Methinks that there just MIGHT be an error in in hookup. More later, when I find out more. Thanks Guys!

J Tiers
04-25-2018, 01:50 PM
That may be "option 4", a variable impedance put in series. A low-loss relative of the "big azz resistor", (or the triac)

If so, then a triac will work, but I agree, first you need to see if it is hooked up right. I also suspect it is not, so there is your first point of attack..

PStechPaul
04-25-2018, 04:19 PM
It's probably a shaded pole induction motor. The best way to control speed is probably by varying the drive frequency and voltage (VFD with V/Hz), but that would likely be too complex and expensive. I have wondered if it would be possible to control speed of an AC induction motor by skipping every other full wave, or applying one positive half-wave, skipping a full cycle, and then a negative half-wave. Here is a simulation showing what that might look like with an inductive motor load:

http://enginuitysystems.com/pix/electronics/AC_Control_Skip_Half_Wave.png

I thought it might be done with a simple series SCR, but the inductance causes oscillations and high voltage transients when the drive is turned off. So I had to use a half-bridge. At that level of complexity, might as well use an H-bridge and full PWM. Or even a "modified sine wave equivalent" as produced by automotive 120 VAC inverters.

Here is a document on AC motor speed control:

http://www.me.ua.edu/me360/spring05/Notes/Topic17-AC_Motor_Speed_and_Other_Motors_sv.pdf

And for shaded pole motors:

https://www.electronicspoint.com/threads/speed-control-of-shaded-pole-induction-ac-motor.114240/

https://en.wikipedia.org/wiki/Shaded-pole_motor

https://electronics.stackexchange.com/questions/358562/shaded-pole-motor-speed-control

Probably too much techno-babble for this thread, but, hey, the engineer-devil made me do it!

Duffy
04-25-2018, 06:13 PM
My grandson and I tried just about everything, even opening and checking the rotary switch! I finally hung the unit, minus blades, from the ceiling in my shop, and we "jury wired" the speed control to it. The fan motor runs at ONE speed, regardless of the selector setting, about 440 rpm according to my laser tachometer. We bought this unit at Loews, and I think that I am going to have a chat with someone, even though I no longer have the packaging. The only thing I did not check was the capacitor, and I now give up!
Thanks for all your suggestions.

J Tiers
04-25-2018, 06:20 PM
The capacitor was good, or it would not run.

PStechPaul
04-25-2018, 09:36 PM
If the fan also has a light, maybe the wires are switched, so the selector is trying to dim the lamp instead of adjusting motor speed. If it is a non-dimmable LED lamp, it won't change much until it gets to a very low setting, where it might flicker.

But the capacitor seems to indicate a PSC induction motor, rather than shaded pole. The capacitor complicates matters because it supplies lower current at low speeds and torque will drop rapidly. It may be possible to design a VFD with a third leg to the auxiliary winding, replacing the capacitor. It might even run on three phase.

More links, for PSC motors and fan motors:

http://www.tcf.com/docs/fan-engineering-letters/speed-control-for-fractional-horsepower-motors---fe-1000.pdf?Status=Master

https://electricmotorwarehouse.com/speed-control-kb-electronics/

http://www.practicalmachinist.com/vb/general/adding-variable-speed-control-single-phase-motor-303368/

Here is a video showing how to rewind a ceiling fan motor. It appears to have a total of 24 slots, which may be connected as a 12 pole induction motor, which would provide a speed of 600 RPM at 60 Hz or 500 RPM at 50 Hz. It would probably be fairly easy to rewire the belts for three phase.

https://www.youtube.com/watch?v=OfAIok7hpcI

lugnut
04-25-2018, 09:59 PM
For a few dollars more you could have bought a fan with speed control. Even the elcheapo models have at least 3 speeds. Mine in the house has a variable speed control and the one in my little shop has 3 speeds via a pull chain switch.

tmarks11
04-25-2018, 10:51 PM
Sure the fan doesn't have a chain-pull switch inside it to switch between speeds? I have seen few fans that don't.

I prefer to wire them to wall mounted speed controls, and set the chain-pull setting at the intermediate speed, which has the effect of reducing the speeds the fan runs it when the wall mount control is used.

wmgeorge
04-26-2018, 08:56 AM
Now that you have screwed with it and voided the warranty and lost the packaging your more or less screwed without a wiring diagram. The smart thing would have been take it back and get a new one. Yes it has a speed controller, no it does not work and is it worth messing with?
Changing the voltage on an AC motor does not change the speed, changing the frequency does or number of poles selected will however.

J Tiers
04-26-2018, 09:33 AM
.......
Changing the voltage on an AC motor does not change the speed, changing the frequency does or number of poles selected will however.

That type of AC motor DOES change speed, with a fan type load.

wmgeorge
04-26-2018, 10:17 AM
That type of AC motor DOES change speed, with a fan type load.

Yes and if you continue to let it run with not enough power and cooling it will over heat and you know that. The true speed control is by frequency or clipping the waveform.

J Tiers
04-26-2018, 10:31 AM
Yes and if you continue to let it run with not enough power and cooling it will over heat and you know that. The true speed control is by frequency or clipping the waveform.

Actually, the fan motors are designed to be higher slip. You can operate them all day on any of their settings without overheating.

Remember, the slip is associated with lower current, due to a lower applied voltage, or a series impedance, so the possible heating is less. It's ancient, ho-hum technology that has worked fine since the 1920's, although it is not as efficient as newer methods. Works with PSC and shaded-pole motors.

The fan speed curve is such that the fan always finds the highest speed it can operate at given the available power. If there was no load, the motor would operate close to synchronous speed.

You may be thinking of cases where the motor has to hold a given load, but voltage is reduced. Then, to obtain the same power, current must go up, and that CAN overheat the motor. But the fan load is a variable load, dependent on fan rpm according to a "cube law".

lakeside53
04-26-2018, 10:37 AM
My ceiling fan has 1990 speed control (6 speeds, switched). It is just a series of switched inductors that have the effect of lowering voltage to the motor. Two wires to the motor. Works perfectly.

BCRider
04-26-2018, 11:13 AM
Before you give up take note of Jerry's info about the "slip". It's quite possible that without the blades attached that it will run at the one speed all the time. But the drag of the blades moving air will allow the motor to "slip" and not match up to the line frequency.

The other thing is are you working with the originally supplied wiring diagram? If not then some searching for the make and model as found on the fan's info label should turn one up from the internetz.

wmgeorge
04-26-2018, 11:31 AM
http://www.me.ua.edu/me360/spring05/Notes/Topic17-AC_Motor_Speed_and_Other_Motors_sv.pdf

J Tiers
04-26-2018, 12:43 PM
Thank you for agreeing with me.

The link agrees 100%.

And, did you see the point about the load varying? That applies directly to fans, with their cube law power/speed relation.

Tapped windings are really a form of voltage control... varying the slip, since the extra windings change the motor to need a higher voltage to produce the same power. Therefore the slower taps are really power reductions analagous to a straight change in voltage, or insertion of a series impedance..

In the case of shaded pole, or PSC motors, those are really 2-phase motors "on the inside" due to the capacitor or the pole shading, and have torque that is more constant than a straight single phase induction motor. So they are not as dependent on the inertial carry-through mentioned in the link.

In any case, now that you agree with me, we are done. Thanks

wmgeorge
04-26-2018, 12:51 PM
Just making a point for the folks who think they can take a regular AC motor and half the voltage and expect it to run at 1/2 the speed with the same power and without overheating. These cheap Fan motors are "special" and not the same as a motor on say your table saw. My advise to the OP was get a wiring diagram or try to return still stands.

J Tiers
04-26-2018, 01:03 PM
Before you give up take note of Jerry's info about the "slip". It's quite possible that without the blades attached that it will run at the one speed all the time. But the drag of the blades moving air will allow the motor to "slip" and not match up to the line frequency.

....

yes... you have the idea exactly


Actually, the fan motors are designed to be higher slip. You can operate them all day on any of their settings without overheating.

.....
The fan speed curve is such that the fan always finds the highest speed it can operate at given the available power. If there was no load, the motor would operate close to synchronous speed.

.....

In a heavily loaded motor, More slip = lower speed = lower back EMF = more current (more current is needed to make up he input power to exceed the load demand by the amount of the losses). Since those motors are not designed for the situation, they will very likely be "thermally damaged' (burn up) from the abuse.

But, "fan duty" motors are designed for, well, "fan duty"... And they are normally "air over" motors, meaning that they need the fan airflow to keep them cool. A lot of HVAC blowers have the motor right in the incoming air flow, and most floor fans, desk fans, etc are the same.

when series impedance is put in-line with the power to the fan, the current is limited, so the burn-up is prevented. But if you put too large a blade assembly on the fan, or operate certain blowers with "open flow", the load is so large that they DO burn up when set for max speed, because there is no current limiting device.

wmgeorge
04-26-2018, 01:09 PM
FYI for those reading, HVAC motors unless they are the new ECM ones with controllers or 3 phase with VFD I have never seen anything but multi winding for the speeds. Never the ones described above as Fan Duty. Fan Duty in HVAC/R is a air over motor with sometimes no internal fan for cooling.

Juiceclone
04-26-2018, 09:05 PM
u could try one of those ceiling fan speed controllers from some home center. My experience with them is they're "buzzy" at lower speeds....annoying..

BCRider
04-27-2018, 01:43 AM
FYI for those reading, HVAC motors unless they are the new ECM ones with controllers or 3 phase with VFD I have never seen anything but multi winding for the speeds. Never the ones described above as Fan Duty. Fan Duty in HVAC/R is a air over motor with sometimes no internal fan for cooling.

All the fans I've come across over the years ( a dozen or so) had control boxes that fit inside a regular octagonal box. Anything else would be an issue for MANY home installations. I know electronics is wonderful stuff but I've not yet come across a VFD that fits into one of those octagonal boxes and still leaves room for the connections needed. Are you saying there is such a thing?

wmgeorge
04-27-2018, 07:26 AM
All the fans I've come across over the years ( a dozen or so) had control boxes that fit inside a regular octagonal box. Anything else would be an issue for MANY home installations. I know electronics is wonderful stuff but I've not yet come across a VFD that fits into one of those octagonal boxes and still leaves room for the connections needed. Are you saying there is such a thing?
No.

Noitoen
04-27-2018, 08:29 AM
Hi.

Haven't read the hole thread but here is my 5 cents. I've worked with motors all my life including owned a motor repair shop. The thing with fan motor speed, in most cases, varying the voltage forces a change of speed. Most fan motors do this in the motor winding itself where additional windings change the motor's voltage to a higher setting, e.g. a 230 v motor is wound for 230, 280, 320 v. Since we only have 230 v to supply it, it will loose torque and run at a lower speed. Attention that this only happens with the fan blades mounted. Fan motors are built to support this abuse and usually they are not very efficient.

Another way to do this is to lower the supply voltage by means of a very inefficient resistor or an auto transformer which seems to be the case. When you change the switch, the motor supply voltage should lower by a few dozen volts.

J Tiers
04-27-2018, 02:53 PM
Hi.

Haven't read the hole thread but here is my 5 cents. I've worked with motors all my life including owned a motor repair shop. The thing with fan motor speed, in most cases, varying the voltage forces a change of speed. Most fan motors do this in the motor winding itself where additional windings change the motor's voltage to a higher setting, e.g. a 230 v motor is wound for 230, 280, 320 v. Since we only have 230 v to supply it, it will loose torque and run at a lower speed. Attention that this only happens with the fan blades mounted. Fan motors are built to support this abuse and usually they are not very efficient.

Another way to do this is to lower the supply voltage by means of a very inefficient resistor or an auto transformer which seems to be the case. When you change the switch, the motor supply voltage should lower by a few dozen volts.

Precisely correct!

danlb
04-27-2018, 03:52 PM
All the fans I've come across over the years ( a dozen or so) had control boxes that fit inside a regular octagonal box. Anything else would be an issue for MANY home installations. I know electronics is wonderful stuff but I've not yet come across a VFD that fits into one of those octagonal boxes and still leaves room for the connections needed. Are you saying there is such a thing?

I THINK that the Electronic Speed Control (ESC) modules used with BrushLess DC motors (BLDC) are essentially VFDs. From my reading, they change the frequency to drive the BLDC at varying speeds. Texas Instruments has a chip set (http://www.ti.com/solution/bldc_motor_drives) just for running large BLDCs for use in applications like ceiling fans.

Dan

Paul Alciatore
04-27-2018, 07:22 PM
Screwed? Not necessarily. Stores like Lowe's keep track of every sale in their computers. Even if you don't have the receipt, they can look it up. This is one good reason to give them your name, address, and/or phone number when they ask. If you even suspect that the unit is bad, talk to them BEFORE the return period (30 days?) has expired.

If you used a credit card then you have another avenue to approach a return or swap for a good one. Credit card companies will help you to reverse the charges if the item does not work. It is best to complain when the next CC statement comes in, but that is not strictly necessary and I have had charges reversed months later. This may or may not work if you used a debit card. I always buy everything possible with a CREDIT card. Not only do I get better protection that way, but I also get between $500 and $700 CASH back every year from redeeming the points accrued on the cards. Win, win, WIN! Of course I keep track of every purchase in my budget spreadsheet and I ALWAYS pay the full balance EVERY month so I never pay any interest or penalty charges. That's why I keep track with the spreadsheet: if I am short a few days before the due date, I move some money from my savings to the checking account to make that payment. But mostly, I am not short as the constant process of entering receipts keeps my spending with the cards under control. And if I have a major purchase I can always take advantage of a new CC offer with a year of more of zero interest. And I get a lot of points for them. As I said, win, Win, WIN!

I would notify Lowe's NOW. Then I would double check the wiring to be sure it is connected correctly. If it is properly wired, then it is likely defective and you should get your money back or a replacement.

Oh, You are under NO obligation to tell them that you "screwed with it". Just take it back, state that it only runs at one speed when it should have several, and politely ask for your money back. If they ask, tell them that you hooked it up, tried it, it ran at only one speed, you double checked the wiring and it was correct. So you brought it back. They are NOT experts on fan motors and will probably not even ask any technical questions.




Now that you have screwed with it and voided the warranty and lost the packaging your more or less screwed without a wiring diagram. The smart thing would have been take it back and get a new one. Yes it has a speed controller, no it does not work and is it worth messing with?
Changing the voltage on an AC motor does not change the speed, changing the frequency does or number of poles selected will however.

PStechPaul
04-27-2018, 09:39 PM
If they are unwilling to replace it or offer a refund, you could purchase another identical unit (perhaps at a different store), and then return the first, defective, unit.

Duffy
04-28-2018, 04:55 PM
To quote Jack Benny, WELLLLL! On what seemed like the 77th attempt, with the blades installed, The fan speeds range from about 270-420 rpm in five steps. The fan appears to doe what it is supposed to do. Whether the minimum speed is still too fast is not for me to judge. If it is, my daughter had better find a slower fan
Thanks again for all the help. You all have demonstrated one again why this is such a GREAT forum!

Noitoen
04-28-2018, 05:44 PM
Now all you need is a little zero crossing triac static relay and a oscilator circuit to cycle the power on and off to get an even lower speed :cool:

Glug
04-28-2018, 07:09 PM
Whether the minimum speed is still too fast is not for me to judge.

A friend once saw a drunk John Goodman stand on a chair in a New Orleans bar and stop a ceiling fan with his tongue.

Maybe he could help.