Shop Fan - SPEED CONTROL - Bad for Motor?

[jonnymacuser]

My shop fan says DO NOT use with a speed control.
I would like to use a speed control, and run the fan at a slower speed.
Is this bad for the motor?
Will the motor windings get too hot?
Is this unsafe?
I might use this speed control, which says do not use on a brushless type motor. I believe my fan is an AC induction type electric motor. This might not even work with my fan?

[Hobbytime]

your asking a question you already answered..the fan says dont use one and the controllers say dont use on a brushless motor..how much more info do you want that says its a BAD idea??? most likley if you do it will burn up the motor and get so hot a fire could start in the windings...it looks like your fan has a high and low speed setting..if thats not good buy another fan..

[M J D]

Pretty much like using a toaster around water. Even if it was safe, would I really want saturated toast?

[albrightree]

My shop fan says DO NOT use with a speed control. - Don't

I would like to use a speed control, and run the fan at a slower speed. -Why

Is this bad for the motor? - Yes

Will the motor windings get too hot? - Yes

Is this unsafe? - Yes (only from the standpoint of you failing to heed the directions/warnings)


The fan will overheat fairly quickly , which will cause the one time overcurrent protection to fail. It is a tiny fuse soldered into the winding requiring disassembly to repair. Why not use a small $20 box fan instead , it would be far simpler if you wanted less air flow.


Its a hundred dollar fan why ruin it , you might need it for something else later. Why do you want to slow down a High Velocity Fan, it already has 2 speeds ?

HTH

[Insaneride]

I've used those controllers. Big differance in cheap vs more expensive.

That maybe a brushless fan and won't work a controller. An alternative would be to make a two foot extension cord with a 20 amp diode inline. Should make the fall run half speed. I don't know how efficient it will be on the motor. It would be worth a try

[Insaneride]

I've used those controllers. Big differance in cheap vs more expensive.

That maybe a brushless fan and won't work a controller. An alternative would be to make a two foot extension cord with a 20 amp diode inline. Should make the fall run half speed. I don't know how efficient it will be on the motor. It would be worth a try

Something like this but cut the black or white wire and splice diode in. I showed two diodes because I don't amps of either without looking it up.

[Hobbytime]

I've used those controllers. Big differance in cheap vs more expensive.

That maybe a brushless fan and won't work a controller. An alternative would be to make a two foot extension cord with a 20 amp diode inline. Should make the fall run half speed. I don't know how efficient it will be on the motor. It would be worth a try

thats the same thing as a speed controller except you just cut the speed in half rather than have variable... you are cutting the amount of power going to the motor..so it will over heat the same and possibly burn up..poof..

[ronsii]

thats the same thing as a speed controller except you just cut the speed in half rather than have variable... you are cutting the amount of power going to the motor..so it will over heat the same and possibly burn up..poof..

I think a lot of the 'issues' come into play when you compound the 'electronics' (in fan)on top of more 'electronics' (in speed controller) most of those speed controllers use an SCR or TRIAC to 'chop' the power on the downside of the sine wave curve... so while you are 'cutting' power from the fan motor you are not really lowering the peak voltage going to it... but you are lowering the RMS voltage to it... and if the fan already counts on full RMS voltage to make the electronics do thir thing once you affect that then bad things will happen I have not seen the latest/greatest chinese offerings in their fan motors but have worked on the older ones... they had an actual two speed motor so you could run a speed controller on the full speed set of windings... or at least I did without problems

[Hobbytime]

I think a lot of the 'issues' come into play when you compound the 'electronics' (in fan)on top of more 'electronics' (in speed controller) most of those speed controllers use an SCR or TRIAC to 'chop' the power on the downside of the sine wave curve... so while you are 'cutting' power from the fan motor you are not really lowering the peak voltage going to it... but you are lowering the RMS voltage to it... and if the fan already counts on full RMS voltage to make the electronics do thir thing once you affect that then bad things will happen I have not seen the latest/greatest chinese offerings in their fan motors but have worked on the older ones... they had an actual two speed motor so you could run a speed controller on the full speed set of windings... or at least I did without problems

I have a few of those chicom fans, the small ones, and the motors are sealed..you cant crack them to even try and fix them..the fan is just disposable....well most of the chicom electronics are disposable..

[Welder Dave]

It's a 2 speed high velocity fan. Live with it or get a different fan. This is like buying a tapped voltage Mig machine and wanting to make it a variable voltage. If you want variable, get variable.

[MinnesotaDave]

Why not use a small $20 box fan instead , it would be far simpler if you wanted less air flow.

That's what I use, full size cheap box fans. I even installed 2 in the ceiling of my shop.
They were there for 15 years and never burned up - but look horrible from all the smoke they exhausted

[Insaneride]

thats the same thing as a speed controller except you just cut the speed in half rather than have variable... you are cutting the amount of power going to the motor..so it will over heat the same and possibly burn up..poof..

I don't know Hobbytime, I think a diode inline would be more like switching the fan off and on 60 times a second.

ronsi gave a brief explanation of the scr controller. I will add that the scr can be triggered during the positive cycle and the negative. It seems to me that an scr should be able to control that fan.

I looked up data sheets for the diodes in my pic. One is 40 amp. The other is hi voltage low amps. I think I have a ceiling fan (brushless motor) somewhere. I'll give it a try and let you know how it works. I see no reason why it should not work other than cooling the motor.

[Hobbytime]

I don't know Hobbytime, I think a diode inline would be more like switching the fan off and on 60 times a second.

ronsi gave a brief explanation of the scr controller. I will add that the scr can be triggered during the positive cycle and the negative. It seems to me that an scr should be able to control that fan.

I looked up data sheets for the diodes in my pic. One is 40 amp. The other is hi voltage low amps. I think I have a ceiling fan (brushless motor) somewhere. I'll give it a try and let you know how it works. I see no reason why it should not work other than cooling the motor.

yeah, im not 100% sure a diode would work or not, but the diode in laymen terms slows down the current flow( they have other uses too)..so it may also depend on the quality of the motor if it has built in safteys for low voltage to avoid damage to the motor or just let it burn up...by reducing voltage or flow the fan may struggle to get started and burn up trying to get to full RPM...give it a try and see what happens...

[ronsii]

yeah, im not 100% sure a diode would work or not, but the diode in laymen terms slows down the current flow( they have other uses too)..so it may also depend on the quality of the motor if it has built in safteys for low voltage to avoid damage to the motor or just let it burn up...by reducing voltage or flow the fan may struggle to get started and burn up trying to get to full RPM...give it a try and see what happens...

LOL!!!!! you just used the words 'quality' and safety' in the same sentence when talking about a chinese motor LOL!!!!!!!!!!

[Hobbytime]

LOL!!!!! you just used the words 'quality' and safety' in the same sentence when talking about a chinese motor LOL!!!!!!!!!!

well I did say " it depends" on it..not that it was there....LOL

[Zebidiah]

A DC motor will take more circuitry (and money) to control it then if you just bought an AC motor and used your cheap speed switch. You are trying to defeat the basic laws of DC electronics.

[frieed]

I use a 2-speed, 24" whole house fan mounted in the ceiling...
https://www.homedepot.com/p/Master-F...S24M/100018252

[ronsii]

Get one of the bigassfans, they move any amount of air you need moved!!! and they're quieter than pretty much any other way of moving air

HD, lowes and just about everyone else sells them.
https://www.lowes.com/pl/Big-***-fan...ent=4294389884

[danielplace]

If you put a diode in AC circuit you create DC. A cheap AC fan motor may not run on DC.

[Insaneride]

If you put a diode in AC circuit you create DC. A cheap AC fan motor may not run on DC.

Wrong. You do not get DC. You get one half the power of AC. You could filter with a cap and use a full wave bridge (4 diodes) to get DC but a single diode is going to supply half cycle of 50 or 60 Hz.

Look it up.

[ronsii]

Wrong. You do not get DC. You get one half the power of AC. You could filter with a cap and use a full wave bridge (4 diodes) to get DC but a single diode is going to supply half cycle of 50 or 60 Hz.

Look it up.

Actually..... Alternating current reverses polarity... Direct current does not... so a diode(regular diode) will prevent the current from reversing one direction..... hence it is now DC.... albeit pulsating DC but DC none the less

[Insaneride]

Ok so it's 60 Hz DC. It still is fluctuating from zero to half wave peak AC no?

In all fareness to danielplace, a diode and capacitor could make it DC with a whole lot of ripple and only for light loads of milliamperes. I've built several power supply's from scratch and repaired a few and have been shocked by a few. I've even used a diode and transformer to switch a solenoid that didn't mind half wave positive cycle only but it was still switching from peak to zero at 60Hz.

One power supply in a guitar amp that I repaired shocked the snot out of me after the caps were discharged. The choke had a warning label to discharge but I never thought a coil could store current when power was off. Apparently a magnetized coil can hold a charge. I used my cap discharger to bleed off the stored current. Caps store voltage, coil stores current if it's magnetized. I forget who (member here) schooled me about that. Voltage leads current in a coil and current leads volts in a cap.

[ronsii]

Ok so it's 60 Hz DC. It still is fluctuating from zero to half wave peak AC no?

In all fareness to danielplace, a diode and capacitor could make it DC with a whole lot of ripple and only for light loads of milliamperes. I've built several power supply's from scratch and repaired a few and have been shocked by a few. I've even used a diode and transformer to switch a solenoid that didn't mind half wave positive cycle only but it was still switching from peak to zero at 60Hz.

One power supply in a guitar amp that I repaired shocked the snot out of me after the caps were discharged. The choke had a warning label to discharge but I never thought a coil could store current when power was off. Apparently a magnetized coil can hold a charge. I used my cap discharged to bleed off the stored current. Caps store voltage, coil stores current if it's magnetized. I forget who (member here) schooled me about that. Voltage leads current in a coil and current leads volts in a cap.

In years past I have done a *lot* of electronics repair work and one thing I know 'a diode rectifies power!' I still do a considerable amount of repair work when someone brings me a device that they have a sentimental attachment to... or they just catch me at a weak moment when I can't say no to fixing a flatscreen TV that isn't worth two hundred dollars brand new!!! and I know I'll have a couple hours in it and it still won't be worth any more

Yes, coils or any inductive load can store great amounts of power!!! in fact this is one of the things that causes lots of damage in huge amounts of devices!!! another place for the proper use of diodes... as 'clamping diodes' they are put in circuit to shunt or shorth out the reverse spike coming from the coil as the supply current collapses.

[Insaneride]

I think of mains AC as a push/pull. The positive is is like the push and the negative is like the pull. Half wave of AC could be push or pull depending on polarity. If you chop or pulse DC you get a frequency. It's not really DC anymore because it's running at a frequency. It's alternating from off to on at frequency. DC is always on. Pulsing gives it a frequency and can then be put thru a transformer. DC won't work thru transformers. I believe inverter supply's use this technology to step up DC but I'm not abreast of the latest tech. They were originally called DC to DC converters.

When you chop or pulse DC, you can then run it thru a transformer to step it up. If you chop it into a hi frequency , you can decrease size of transformer and step up the volts. The old camera flash circuits work that way. A 1.5 volt AA battery can be stepped up and stored in caps to get 250 volts. Flash tubes ( xenon) work well with hi voltage. EG&G perfected this technology for hi speed photography and big azz light house lamps.

DC is always on. AC alternates on to off. AC can also go on to off to negative on to off. If it has a frequency, it's not DC.

Here's a pic of half wave AC circuit and waveform. You could instal a cap to to get a crude but exceptable DC with ripple. The cap maintains volts during the off cycle.
Second pic is same circuit with cap and rippled DC. True clean DC is a nice flat line but everyone already knows that.

The problem with using a diode to slow the fan down is, it woul be missing either push or pull ( polarity) and would have difficulty starting. A push or pull by hand or air blast would get it started and then the push or pull would keep it running.

I think the SCR controller the op showed would actually work on his fan. I noticed using those SCRs is you need to start out with full speed then back off to desired speed for some if not all motors. Trying to start at slow speed is hard on the motor. IMO.

[danielplace]

Wrong. You do not get DC. You get one half the power of AC. You could filter with a cap and use a full wave bridge (4 diodes) to get DC but a single diode is going to supply half cycle of 50 or 60 Hz.

Look it up.

Your right some wouldn't consider pulsating DC as DC at all.

It is still direct current by definition albeit pulsating DC. It isn't the more pure DC you get from a 4 diode rectifier but it is DC.