Slowing down a pedestal fan - Page 1
Forum section: electronics / projects

author: TomS_
author_rank: Frequent Contributor
timestamp: April 23, 2020, 07:21:50 am
content: Mains voltage is not my forte, and I'd rather not mess with it before asking people who know better...My parents have a fan which they use in their living room. The lowest speed setting produces quite a reasonable breeze. A bit too reasonable really.We'd like to try and slow it down a bit, and the best idea I've come up with so far is to take one of the speed controllers you would typically use for a ceiling fan, put it in a box of some sort, and wire the lead for the pedestal fan through that.The theory being that we can set that controller to one of the lower settings and hopefully then when we switch the fan on using it's own control it will be at a much lower speed.Does this sound like a reasonable thing to attempt? Or is there a better way to achieve this?Thanks!

author: taydin
author_rank: Frequent Contributor
timestamp: April 23, 2020, 12:27:29 pm
content: Speed settings for such fans are done by putting extra inductance in series with the motor. For example, you can start with the secondary winding of a transformer (make sure to isolate the primary winding well so that it won't zap you. Or you can remove all windings and just wind a secondary).

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 23, 2020, 12:36:24 pm
content: Put a reusable air filter on it. Slows down the flow and cleans the air as a bonus.

author: David Hess
author_rank: Super Contributor
timestamp: April 23, 2020, 01:08:42 pm
content: A common phase control light dimmer will probably work but is not ideal. Some of them are specified for motor loads.A better way is to use a variac and last year I mounted a small variac in an extended outlet box to do exactly what you described.

author: TomS_
author_rank: Frequent Contributor
timestamp: April 23, 2020, 09:28:50 pm
content: Quote from: NiHaoMike on April 23, 2020, 12:36:24 pmWhile reduced flow is the goal, it wouldn't slow the fan itself down much I don't think.I suppose the fan noise itself is a second issue that would be solved by slowing it down.

author: TomS_
author_rank: Frequent Contributor
timestamp: April 23, 2020, 09:31:29 pm
content: Quote from: David Hess on April 23, 2020, 01:08:42 pmCan't see where you are from in the mobile web interface, but it's quite common in Australia to have a similar kind of control for fans that are mounted on the ceiling. Looks like a dimmer but controls the speed of a motor instead. That's the one I'm thinking of using.

author: David Hess
author_rank: Super Contributor
timestamp: April 25, 2020, 06:17:40 pm
content: Quote from: TomS_ on April 23, 2020, 09:31:29 pmThe difference is that the one for motors is designed to operate into an inductive load which requires better snubbing and some additional derating. For small motors like you find in fans, common phase control lamp dimmers work but may be electrically noisy.

author: james_s
author_rank: Super Contributor
timestamp: April 25, 2020, 06:55:28 pm
content: A variac will work for the sort of motors typically used in domestic fans but it's not really ideal. A phase control motor speed controller is a simpler, cheaper and more efficient solution. Exactly the sort of thing sold for controlling ceiling fans and furnace blowers. Similar to a light dimmer with a few modifications to better handle inductive loads.

author: David Hess
author_rank: Super Contributor
timestamp: April 26, 2020, 03:36:09 pm
content: Quote from: james_s on April 25, 2020, 06:55:28 pmVariacs just being transformers are pretty efficient. Their disadvantages are higher cost and greater weight and size. Their major advantage is that being a passive device, they are robust and electrically quiet. I have burned out phase control dimmers on motors before but never a variac unless the load shorted.

author: wizard69
author_rank: Super Contributor
timestamp: April 27, 2020, 01:01:04 am
content: It depends upon the motor in the fan if it is even controllable in a simple manner. Since you mentioned "pedestal fan" and many of those are run via capacitor start, induction run motors there is no simple speed control solution. Induction motors rely upon the AC wave form to set a running speed. The speed being related to the synchronous speed of the motor minus the required slippage to generate torque.Beyond that many motors are simply not designed to run much slower than rated speed due to cooling issues. You could easily be creating a fire hazard if the motor should over heat. I wouldn't slow down any such fan unless it was known that it was safe to do so, at the very least that means a thermally protected motor no matter what type it is. There are some AC motors that can be varied via voltage control but one can't say what type of motor is in this fan.

author: Electro Detective
author_rank: Super Contributor
timestamp: April 27, 2020, 01:21:27 am
content: If you're going to use an external fan speed come dimmer controller, I would suggest running the fan at it's full setting,and use the controller to vary the speed, to avoid any possible conflict/loss/heat issuesthat other members can explain better than meSimilar to this I've run variable speed equipped brush powered power tools on the fastest/highest setting,and used a variac to slow start and 'fine tune' running the way I need, and ramp down to OFF etcwhilst paying attention to current draw and the load on the motor etcDrop some photos here of the fan and candidate controller so we can see what the scenario is,and vote it a go or no go.

author: amyk
author_rank: Super Contributor
timestamp: April 27, 2020, 01:27:00 am
content: Quote from: wizard69 on April 27, 2020, 01:01:04 amIt depends how big the fan is, but a typical pedestal fan would probably not be using a CSIR motor; or anything that has a starting switch, for that matter. A larger one is likely to be PSC, a smaller one may be shaded pole.

author: glentek
author_rank: Regular Contributor
timestamp: April 28, 2020, 04:30:26 am
content: I've used a triac controller, and it works perfectly, plus it fits where the buttons were.https://www.ebay.com.au/itm/1PCS-2000W-220V-SCR-Electric-Voltage-Regulator-Motor-Speed-Control-Controller/301920016934

author: Whales
author_rank: Super Contributor
timestamp: April 28, 2020, 05:44:41 am
content: Quote from: taydin on April 23, 2020, 12:27:29 pmReally? I thought they used switchable series capacitors. At least that's what ceiling fan control boxes here seem to use.

author: TomS_
author_rank: Frequent Contributor
timestamp: April 28, 2020, 07:47:23 am
content: I grabbed another fan controller and tried putting it inline with the fan. This one uses capacitors which get switched in, or none for full speed.Turned the fan itself to full and tried using the external controller but it was only rotating very slowly, barely able to start spinning on the lower setting.So perhaps it is a different setup to a standard ceiling fan. I haven't bothered to take it apart to see what it is doing to control it's speed. Perhaps a different type of controller might work, this was a cheapie $20 unit, but an electrical supply shop had a fully variable unit for about $80, though that was a bit too much for a test.Might just have to throw this in the f**k it bucket for now, was a nice idea if it would have worked. I'll be heading back home (to the UK) in a few days so not likely to have much time to try anything else this year.

author: Electro Detective
author_rank: Super Contributor
timestamp: April 28, 2020, 08:21:12 am
content: Hit on some Youtubes, I've seen a few tubers either doing it somehow,or explaining why it won't happen in certain circumstances

author: Psi
author_rank: Super Contributor
timestamp: April 28, 2020, 08:29:35 am
content: My sister had this exact issue.She had a fan where even speed 1 was too fast/noisey.We tried my variac, which worked fine, but she didn't want to spend that much money getting her own variac.The solution we came up with was a cheap $30 220-110v step down transformer.She just runs the fan from 110v instead of 220v.One word of warning, if you drop the voltage too low the lowest speed setting may not have enough torque to start spinning the blades.They may stall and the fan just sit there humming, this is bad and may cause the motor to overheatSo keep that in mind. Fan on but not moving = bad. <Insert usual disclaimer about not burning down ones house>

author: Electro Detective
author_rank: Super Contributor
timestamp: April 29, 2020, 01:32:46 am
content: A lot of those ' cheap $30 220-110v step down transformer' MIC in the last few years are a safety worry,every one I've had the displeasure of opening up, had wiring, assembly and shoddy labor issues as well as crappy crumbling brittle output connectorsThis is on top of the fact they are not isolation transformers and dangerous to begin with, especially in a flipped Active/Neutral mains scenarioThe older or vintage stepdown gear is the way to go, some are actually isolatedbut still open them up, dust out and check before using,and wack in a fuse on the output and input to be sure, if none presentGood for years, plug in, walk away..

author: Prehistoricman
author_rank: Regular Contributor
timestamp: April 29, 2020, 12:21:30 pm
content: Quote from: Electro Detective on April 29, 2020, 01:32:46 amWhy is this dangerous? Appliances should use earth for the chassis and not neutral so I don't see why this could be an issue.

author: TomS_
author_rank: Frequent Contributor
timestamp: April 29, 2020, 10:24:20 pm
content: Quote from: Psi on April 28, 2020, 08:29:35 amYeah this is pretty close to what I was seeing, so I turned it off pretty quickly. It was barely able to get started and was only turning very very slowly. I dont feel like burning my parents house down (as happened a couple of weeks ago just one street away), especially since my dad has a habbit of falling asleep on the couch while watching TV and could sleep through a world war.Need to find another solution, but I suspect at this stage it'll be waiting until I am back here next time, whenever that happens to be given the whole coronavirus mess. My dad doesnt seem so bothered by it, so it was more of a "for me" thing anyway.

author: Electro Detective
author_rank: Super Contributor
timestamp: April 29, 2020, 10:50:39 pm
content: Quote from: Prehistoricman on April 29, 2020, 12:21:30 pmYou'll understand it one day when it bites you or someone you know, playing with earthed metal chassis stepdown transformer/auto transformer equipment that's not isolated,and one has a wiring mix up or flip, or a DUT has. Please don't be that guy to find out the hard way!If they are all wired correctly and confirmed as such, what you typed above works fineBut that's not how things go in the real world, and many people get 'earthed' permanentlybecause of wiring assumptions, random wiring flips, neglected faults, and cheapskate DIY ignorance

author: Zero999
author_rank: Super Contributor
timestamp: May 01, 2020, 04:07:12 pm
content: Try a fluorescent tube ballast in series.