How to control AC fan speed? - Page 1
Forum section: electronics / projects

author: eev_fan
author_rank: Contributor
timestamp: June 12, 2023, 09:45:43 pm
content: Motor is 220 volt and have 3 separate windings for low, med and high. I want to be able to lower the speed in the low setting.Have tried with a cheap wall mounted dimmer, but that did not work properly. Motor is giving off a humming noise and the dimmer have to be set at maximum to start it turning.Have found this:https://uk.rs-online.com/web/p/fan-speed-controllers/9196248Will it work?Any cheaper Chinese alternative? I do not need to adjust the speed once it has been set, but have to be sure the motor starts turning next time I switch the fan on.

author: james_s
author_rank: Super Contributor
timestamp: June 12, 2023, 09:50:21 pm
content: Interesting that an American company made 220V 50Hz motors.That looks like a shaded pole motor, I would expect a triac based motor speed controller like the one you posted would work, they're very similar to the light dimmer you tried but with some modifications that enable them to better handle inductive loads. Here you can find similar controls cheaper made for ceiling fans but I have no idea what's available where you are.

author: TimFox
author_rank: Super Contributor
timestamp: June 12, 2023, 10:24:16 pm
content: I worked for an American company before retirement, and we exported equipment to 50 Hz countries.One of our clients was a large Japanese company: due to the 50/60 Hz partition of Japan, all their factories had electrical switchboxes for both frequencies.This presumably gave them a small advantage for exporting.

author: Circlotron
author_rank: Super Contributor
timestamp: June 13, 2023, 12:06:25 am
content: I have an AC exhaust fan that I slowed down using about 10uF in series with the mains supply. Your motor may need 2 or 3 times that capacitance. Use a motor run cap. Not a motor start cap. Advantage of using a capacitor is the full sine wave still gets supplied to the motor so it should be quiet.

author: Kim Christensen
author_rank: Super Contributor
timestamp: June 13, 2023, 02:30:38 am
content: Quote from: eev_fan on June 12, 2023, 09:45:43 pmYou'll see a lot of multi speed fans set up that way... Speed controller is always in this sequence: OFF, High, Med, Low. Modify your dimmer so it does the same. (Swap outer legs of POT)That way, when you first turn it on, it always starts.

author: sparkydog
author_rank: Regular Contributor
timestamp: June 13, 2023, 04:25:39 pm
content: Quote from: Kim Christensen on June 13, 2023, 02:30:38 amObligatory explanation video:https://www.youtube.com/watch?v=hQ3GW7lVBWY.

author: Seekonk
author_rank: Super Contributor
timestamp: June 14, 2023, 12:14:51 pm
content: I replaced my old gravity feed furnace with a new one. The old ducts were over sized and even the slowest motor speed was too fast with little restriction. I used an auto transformer to lower the voltage slightly. That increased the motor slip. Too much and you can burn out the motor. It has been running for over 20 years, must have guessed right.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 14, 2023, 12:51:41 pm
content: Quote from: Kim Christensen on June 13, 2023, 02:30:38 amUnless the user rotates the pot too quickly past the HIGH setting... These things suck, and the buzzing triac dimmer noise from the motor is very questionable because usually the #1 reason to slow it down in the first place is to reduce audible noise.

author: David Hess
author_rank: Super Contributor
timestamp: June 14, 2023, 01:44:58 pm
content: A 240 volt variac or autotransformer will work to adjust the speed.

author: eev_fan
author_rank: Contributor
timestamp: June 14, 2023, 01:54:57 pm
content: Quote from: james_s on June 12, 2023, 09:50:21 pmIt's an Honeywell F59 electrostatic air cleaner. 8000 volts. Has served me for 40 years...Only problem is that the low speed makes to much fan noise. I "fixed" it back then by connection a 60W 220V lightbulb in series with the Low-winding.But todays focus on environment and energy prices made me look for a more efficient solution...Quote from: Kim Christensen on June 13, 2023, 02:30:38 amThanks, but I want to set the speed once and for all, not every time I turn on the unit.Also, with this dimmer the motor is noisy after being adjusted for low speed.

author: eev_fan
author_rank: Contributor
timestamp: June 14, 2023, 02:15:09 pm
content: I suspect my dimmer to be PWM.Would it be a better choice to go for anadjustable switch-mode supply?

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 14, 2023, 02:29:42 pm
content: I also second the suggestion of using a capacitor in series with the winding. That is the way my ceiling fans lower their speed.Again, as others have mentioned, you have to use a capacitor rated for continuous “run” operation.How much voltage are you dropping actually with your light bulb? With that value and the current consumption, you can calculate the required capacitor reactance. And knowing the reactance, you can calculate the capacitance at your power line frequency.

author: bdunham7
author_rank: Super Contributor
timestamp: June 14, 2023, 02:35:25 pm
content: Quote from: eev_fan on June 14, 2023, 01:54:57 pmAs mentioned earlier, a capacitor in series is the way to go. Use the low-speed winding and add a 5-8µF (my best guess) motor run capacitor in series. You'll need to experiment to find just the right value.Phase-control for induction motors is not generally a good idea, although it may be marginally useful for short-duration applications.

author: eev_fan
author_rank: Contributor
timestamp: June 14, 2023, 02:42:29 pm
content: Quote from: bdunham7 on June 14, 2023, 02:35:25 pmYes, many thanks. But I haven't any of these capacitors to experiment with. My biggest unpolarized 220V capacitor is .47uF...

author: bdunham7
author_rank: Super Contributor
timestamp: June 14, 2023, 03:04:41 pm
content: Quote from: eev_fan on June 14, 2023, 02:42:29 pmPerhaps buy a few--or a multi-section version--so that you can get a variety of values depending on how you connect them. Here's an example:https://www.amazon.com/CEILING-CAPACITOR-CBB61-4-5uf-WIRE/dp/B017G5HKHMYou can get a number of values from about 2 to 15µF with that one unit.

author: Kim Christensen
author_rank: Super Contributor
timestamp: June 14, 2023, 03:26:57 pm
content: The light bulb was particularly well suited for this because it's low cold resistance would give the motor a voltage boost when the power comes on.You might want to experiment with a variac to make sure the motor will start at the required lower voltage without that "kick" to start it turning...

author: SeanB
author_rank: Super Contributor
timestamp: June 14, 2023, 05:24:39 pm
content: Quote from: eev_fan on June 14, 2023, 02:42:29 pmGo out and find the closest scrapped airconditioner, you will find the fan motor capacitor is between 6 to 10uF, which is a good start.

author: wraper
author_rank: Unknown
timestamp: June 14, 2023, 05:29:33 pm
content: Quote from: james_s on June 12, 2023, 09:50:21 pmUS has a split-phase system. So nothing surprising if it goes into high power device powered from double the normal mains voltage, electric stove for example.

author: james_s
author_rank: Super Contributor
timestamp: June 14, 2023, 09:07:49 pm
content: Quote from: Seekonk on June 14, 2023, 12:14:51 pmThat's a nice problem to have. Every old furnace I've replaced had ducts that were undersized for modern high efficiency furnaces and it has always been a challenge to get the static pressures as low as would be ideal. I've never encountered a gravity feed furnace, the oldest I've come across were mid 70s forced air models that were only 70% efficient. The lower efficiency forced air furnaces ran a much higher bonnet temperature so much less airflow per BTU was required.

author: james_s
author_rank: Super Contributor
timestamp: June 14, 2023, 09:09:44 pm
content: Quote from: wraper on June 14, 2023, 05:29:33 pmI'm very familiar with the split phase electrical system we have here. It is 60Hz though not 50, and it's 240V rather than 220. You'd never find a 220V 50Hz rated motor in any American appliance.

author: james_s
author_rank: Super Contributor
timestamp: June 14, 2023, 09:12:22 pm
content: Quote from: eev_fan on June 14, 2023, 02:42:29 pmBuy one. No need to experiment, just calculate the value. Measure the voltage across your 60W lightbulb and the current through it with the motor running and then use Ohms law to calculate the resistance of the bulb under those conditions. Then plug that value into the equation for calculating capacitive reactance and that will give you the value of capacitor you need.

author: eev_fan
author_rank: Contributor
timestamp: June 15, 2023, 06:00:02 pm
content: Many thanks.Voltage drop is 90v across the bulb and current 160ma. So it's not a big loss...Foundthis pagewhich says:QuoteMaybe the bulb solution is working because an incandescent light bulb, when switched on, only has around 1/15 of its operating resistance. And that's enough to get the fan started?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 15, 2023, 09:04:23 pm
content: One way of controlling motor speed is with a triac, then turn it on for a half or a full cycle, then turn it off for a few (half) cycles. Some 30 (+) year ago this used to be done with some 555's and but these days it's more logical to use a small uC for this, and you can probably find a few of such projects on those git collection websites.

author: james_s
author_rank: Super Contributor
timestamp: June 15, 2023, 09:33:17 pm
content: Quote from: eev_fan on June 15, 2023, 06:00:02 pmWell if you have a 560 ohm resistor that will be pretty close and you could try that, it will be dissipating almost 15 watts though. Fan motors require very little starting torque because fan doesn't draw any load from the motor until it gets spinning.

author: tooki
author_rank: Super Contributor
timestamp: June 15, 2023, 10:01:18 pm
content: Quote from: james_s on June 12, 2023, 09:50:21 pmThere’s this thing companies do, called “exporting”, where they sell things to customers in other countries. And to do that, they need to make the things the customers in those other countries want.Where you live, you can identify things that were exported to USA because the “made in ” declaration will name a country other than “USA” or “America”. For example, if you buy a real Swiss Army knife, the box will say “Made in Switzerland” (which is a real place, not a fantasy thing made up for a theme park!). Sometimes, manufacturers will leave off the “made in” part and just write a country name on the thing.

author: james_s
author_rank: Super Contributor
timestamp: June 16, 2023, 12:29:12 am
content: Quote from: tooki on June 15, 2023, 10:01:18 pmObviously I know that all that, I'm not an idiot. The USA has been far more well known for importing rather than exporting in recent decades though, I don't recall seeing much if anything made by well known American brands when I have visited elsewhere and even here in the USA it's far less common than I'd like to find domestic products. American appliances are rare in the typical smaller European homes, and there are loads of European brands. Obviously we must export some stuff still but I'm surprised to see something as mundane as a fan motor exported from here.

author: Zero999
author_rank: Super Contributor
timestamp: June 16, 2023, 02:24:39 pm
content: Quote from: Doctorandus_P on June 15, 2023, 09:04:23 pmThat's burst control and is not normally done for motors, because it causes vibration. Phase control is much more common for motors and is easier to do, with a TRIAC, DIAC and RC circuit.

author: eev_fan
author_rank: Contributor
timestamp: May 16, 2024, 01:10:20 pm
content: I ended up using a 220-110V transformer for the low speed winding.

author: brunoaduarte
author_rank: Newbie
timestamp: October 28, 2024, 07:53:44 pm
content: I have this 127V 60Hz air conditioner AC fan motor (AL) that also have the low/mid/hi wirings.Can you explain how you connected the transformer to decrease the low speed?

author: BILLPOD
author_rank: Frequent Contributor
timestamp: October 29, 2024, 06:10:42 pm
content: Yes, many thanks. But I haven't any of these capacitors to experiment with. My biggest unpolarized 220V capacitor is .47uF..Good Morning Eev_fan, I think the voltage rating for the capacitor should be at least 310 volts, which the peak your sign wave voltage will hit on your 220VAC system.