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Speed control of cooling fan


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Hey All,

I'm playing with one of my home projects where I have a 6" "boxer" fan (120vac 85W) cooling some components.

The fan is currently controlled from my PLC with a PNP output turning on a random crossing SS relay (AD-SSR810-DC-48R).
I would like to slow down the speed of the fan, and seems it should be just a matter of adding HSO/PWM to the output?

But I've not done this before, so before I let the smoke out of things here, I figured I'd ask for opinions...

What do you'all think??    :unsure:

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John, different motors need different speed controls.  I don't know the term "boxer" (you americanos not talking aussie) but perhaps it means shaded pole?  I doubt that it's going to work immediately without something else.  It's a bit of a minefield.  One of the reasons motors are hard is that the windings and the way they work is essentially an inductive device that generates all sorts of odd things.  Couple that with all the different starting methods and caps involved or not and it gets messy. 

My first phone call is to the maker if possible.   Even then, my final hardware backstop for some speed control of motors that supposedly can't be done is multi-tap transformers.....a seemingly long forgotten method that's been replaced by electronics.....except they often generate hum that the tranny doesn't!

However, put your clamp meter on the line at full speed, do some measurements and then play, starting at the lowest PWM you can and increase slowly.  See what the fan does and whether current draw seems odd for what is being achieved.  If it IS a simple motor then it might just work if the draw bears a linear relationship to speed.  If you have an infrared temp gun, check the motor body as well for anything odd compared to normal full speed running.  Don't forget that fans rely on the inherent flow over the motor to keep things cool.  Even though at slower speeds the motor should be using less power, sometimes it isn't enough flow to compensate.

A zero-crossing ssr might also help, but you can imagine the conflicts involved if your pwm is not near the line Hz rate.

You wanted a simple answer, but sadly not as easy as one might think.

cheers, Aus

 

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I'll try to fantasize a little on this topic. You have an AC fan. There are two points in such devices.

The first - the fan is guaranteed to start only after reaching a certain supply voltage.

Second - by slowing down the fan you can go to a voltage lower than the starting voltage and the fan will still rotate.

Therefore, I recommend determining the PWM at which the fan will start if you gradually add voltage. Conversely, determine the PWM when it stops when the voltage drops. I think that's all you need to know.

By setting the adjustment within (minimum starting voltage + some margin) up to 100% PWM - you will have everything your fan can.

However, in general, it is said that it is illogical to apply a voltage below 40% of the nominal voltage to the fan - because the fan no longer creates an air flow.

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On 6/19/2021 at 6:43 PM, Ausman said:

John, different motors need different speed controls.  I don't know the term "boxer" (you americanos not talking aussie) but perhaps it means shaded pole?  I doubt that it's going to work immediately without something else.  It's a bit of a minefield.  One of the reasons motors are hard is that the windings and the way they work is essentially an inductive device that generates all sorts of odd things.  Couple that with all the different starting methods and caps involved or not and it gets messy. 

My first phone call is to the maker if possible.   Even then, my final hardware backstop for some speed control of motors that supposedly can't be done is multi-tap transformers.....a seemingly long forgotten method that's been replaced by electronics.....except they often generate hum that the tranny doesn't!

However, put your clamp meter on the line at full speed, do some measurements and then play, starting at the lowest PWM you can and increase slowly.  See what the fan does and whether current draw seems odd for what is being achieved.  If it IS a simple motor then it might just work if the draw bears a linear relationship to speed.  If you have an infrared temp gun, check the motor body as well for anything odd compared to normal full speed running.  Don't forget that fans rely on the inherent flow over the motor to keep things cool.  Even though at slower speeds the motor should be using less power, sometimes it isn't enough flow to compensate.

A zero-crossing ssr might also help, but you can imagine the conflicts involved if your pwm is not near the line Hz rate.

You wanted a simple answer, but sadly not as easy as one might think.

cheers, Aus

 

Aus...

Sorry for the confusion, we Americanos also call them "muffin"fans...

I'm pretty sure this would be a shaded pole motor..

I've also done the tranny thing in the past, just thought as an experiment I'd try this as it seems I already have the hardware in place.

John

image.thumb.png.d39c84895b1e2f73c76de541eb40b999.png

 

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An 85W one of these things?   Are you sure that's right...not just a model designation?  A 6" one of these pulling 85W I've never seen, but if you've got one then I understand why you might be wanting to slow it down as I reckon it would be really loud!  You probably also have to have your flying suit and goggles on as you take off.  ✈️ 

These fan types are usually brushless with different methods involved, but they normallly tolerate variable voltage quite well.  However you can also get them with inbuilt PWM input signal method for speed control, which might suit your needs far better.

cheers, Aus

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Oh yeah... it's a healthy little fan, been sitting around my shop for years, don't remember where it came from.
and yes, it is loud.....

I had built a little enclosure out of foil faced foam-board to keep the sun off my swimming pool pump,
and have this fan blowing through the enclosure when it gets hot out, else the pump motor thermals out.
last week our temps hit 100F (yes, us americanos like to use the F word instead of the C word). 😳

Like I said, loud, you can hear it over the pool pump, so I wanted to see what happened if I slowed it down a bit.

And I do have smaller/quieter fans that I could use, but as I said, I'm experimenting...
Since I've retired from the working world I find myself wasting all kinds of time doing stuff "just because".  :rolleyes:

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image.thumb.png.82de03795a6e693851396c0a134a5e85.png

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3 hours ago, John_R said:

Since I've retired from the working world I find myself wasting all kinds of time doing stuff "just because".

And we all here only dream of such possibility.... :)

The pump is cooled by a fan, and the fan should probably be cooled by a slightly smaller fan and this smaller fan also needs to be cooled by something ...

100F in US

33C in EU.

 

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100°F!  Baa-Humbug!  You guys haven't lived in hot places.  That's nothing for my part of the world.  I once worked on a minesite in the middle of Aus where it reached just under 50°C every day for weeks on end.  And....my workshop area wasn't cooled.   🥵   The trick was to drink water early, and continue drinking before thirsty, as sweat was your cooling method that largely went un-noticed due to the really low humidity.  It all didn't really bother me too much, the main hassle was that many litres later you'd then have to wait until after midnight to have a shower, as the cold was still too hot due to the storage tanks from the reverse osmosis plant being in ambient, and the tanks would only cool enough by then. 

The solution I always use for a situation like yours John is to run a bit of correct sized flexible aircon duct onto the pump's fan shroud from outside the enclosure.  The outside end of the duct goes on the side that faces the general prevailing wind, whilst on the other side you have an exhaust grille.  Depending on location and needs, I often put a filter on the duct inlet as well.  Nothing nicer than having a clean motor system to work on in a really dusty environment.  Better for the motor, gearbox, drivetrain, human blah blah.

cheers, Aus 

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yeah, yeah yeah....

And when you were a kid, you walked to school in 4 feet of snow, 5-miles, uphill both ways, in just your knickers and a short sleeve shirt...😂

Is it still winter "down-under"??

:huh:

 

I'm surprised Joe hasn't chimed in, but I suppose he is ticked at me for retiring, and he has to go over to my old plant and figure out my ridiculous coding... :blink:

 

JohnR

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20 hours ago, John_R said:

I'm surprised Joe hasn't chimed in, but I suppose he is ticked at me for retiring,

I could never be mad at you, John.  😍  Your coding is not ridiculous, but I can't say the same about the expectations of your previous management.

1.  As kratmel said, you have an AC motor.  Single phase at that.  You can fiddle with it all you want with PWM-ness but I don't think you're going to be happy with the results as you can't keep the V/F ratio constant.  You need a DC fan to do what you want.  

2.  I just got back from a scout trip to the base in the Florida Keys, so I've been offline for a week and a half.  It was like Gilligan's Island as we had no electricity.  Google up "Big Munson Island".  

Joe T.

 

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