Slowing down a box fan.  Low is still too high. - Page 1
Forum section: electronics / beginners

author: Peabody
author_rank: Super Contributor
timestamp: July 23, 2023, 02:40:05 pm
content: The Lakewood Kool Operator 7-blade fan was the world's best box fan. So of course they quit making it. So I'm looking at the 20" fans at Walmart, and they're all too noisy, even on the lowest setting. Since I would have no way to get another motor tap to get a slower speed, I wonder if there's any kind of dimmer or AC motor speed controller that would work. I guess an autotransformer would work, but I don't have one of those. Well, if it isn't obvious, I don't know much about AC motors, so any suggestions would be helpful, particularly if you know of a box fan that is vewy vewy quiet.

author: bdunham7
author_rank: Super Contributor
timestamp: July 23, 2023, 02:43:24 pm
content: Inline capacitor, which may be what they are using for the speeds anyhow. You just need a smaller one, say 2µF.https://www.ebay.com/itm/273467799023

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: July 23, 2023, 03:36:28 pm
content: "so any suggestions would be helpful, particularly if you know of a box fan that is vewy vewy quiet"Just make an array of noctua fans if you want to sleep near your fan, the is no commercial fan under 10 dB, only an undervolted array NF-P14s is able of that.

author: eugene
author_rank: Frequent Contributor
timestamp: July 23, 2023, 05:55:59 pm
content: Triac speed control works with shaded pole motors. Might be room to mount a light dimmer on the fan itself.I use one ofthesewith a small tabletop fan.EDIT: I understand that this is not an ideal way to control the speed of an induction motor, especially a shaded pole motor. However, I have found it to do exactly what I want with a small fan in the bedroom. The other option that I considered was replacing the motor with a BLDC motor that I already have. The light dimmer has worked fine for over two years, so I have no incentive to do anything else.

author: floobydust
author_rank: Super Contributor
timestamp: July 23, 2023, 07:03:44 pm
content: The chinese have completely taken over small electric motor manufacturing. They design for using minimum materials - minimum copper, steel, plastic on the blades. On low speed it's way too fast, the blades are noisy. The enclosure is huge but the fan inside is small. So their fans are basically cheap garbage. Get used to it, people want cheap.To slow them down to being quiet, I supply them with about 80VAC on low speed. You can use an autotransformer or variac.I did not see the capacitor that can be stashed under the hub, per the schematic.Using a light dimmer (phase-control) also slows the fan down- but it hums/buzzes loudly from the harmonics and the motor is still noisy. One manufacturer says don't do this, the motor will overheat.old 2011 Lasko Recalls Box Fans Due To Fire Hazardthe 115°C TCO did not work either...Lakewood Engineering & Mfg. Co. Chicago, Illinois is out of business, they had too many incidents with their cheap import oil heaters.

author: CaptDon
author_rank: Super Contributor
timestamp: July 25, 2023, 03:15:53 pm
content: There is a special type of dimmer device built for ceiling fans. They work and are quiet running but not cheap. A 24 volt center tapped transformer could be wired as a 12 volt or 24 volt buck voltage. They are easy to find and with a S.P.D.T switch you could select either voltage.

author: IanB
author_rank: Super Contributor
timestamp: July 25, 2023, 03:55:39 pm
content: Quote from: Peabody on July 23, 2023, 02:40:05 pmYou might want to look at Matthias Wandel's fan reviews on YouTube, if you are not aware of them. They are very comprehensive, and demonstrate some good alternatives to box fans:https://youtu.be/jbJPIRurJYEhttps://youtu.be/fe4O_O9jpCMhttps://youtu.be/q3FH3boEu04Alternatives may cost more, but you can certainly achieve slower and quieter if that is what you need.

author: elecdonia
author_rank: Frequent Contributor
timestamp: August 14, 2023, 03:33:16 am
content: I suggest trying a capacitor-type ceiling fan speed control with your box fan.I’ve looked inside several ceiling fan speed controls which contain series capacitors to reduce the speed.Highspeed applies full mains voltage to the fanMediumplaces a capacitor in series with the mainsLowspeed places 2 capacitors in series with the mains (these 2 capacitors are in series with each other)Typical capacitor values are from 2.2uF to 10uF for 120V mains. These are the same type of capacitors used as “run” capacitors in ceiling fans.For ceiling fans that run too fast I’ve had good results by reducing the uF of the series capacitors. I think this method would work just as well with modern box fans as it does with ceiling fans. Most of today’s box fans contain Chinese motors which are of the “capacitor run” variety as shown in the schematic posted earlier in this topic. This type of motor (in a box fan) should behave about the same as a ceiling fan motor (nearly all ceiling fan motors are “capacitor run.”)Vintage box fans used “shaded pole” motors which consume about 1.5x more power (Watts) and about 2x more line current (Amps) compared to “capacitor run” motors. The series capacitors needed for box fan with a shaded pole motor would need to be about twice the uF compared to the series capacitors for a capacitor run motor.If you have a Kill-A-Watt or similar mains power measuring device which can display power factor, you will observe that “capacitor run” motors have a power factor >0.9, sometimes close to 1.0. Note that a power factor of 1.0 provides the highest possible efficiency. Shaded pole motors have power factors between 0.5 and 0.6. Because of this the mains current is about 2x larger than a capacitor run motor of the same horsepower. This extra current increases the heat dissipated by the motor windings without increasing the mechanical power output.