PWM Stir Plate

[jzamora3]

I'm building a stir plate but can't seem to get the fan to spin at lower speeds.

I'm using this PWM http://www.ebay.com/itm/112306248234 and just a regular 12v pc fan with three wires. I have it wired as indicated in the item description but the fan will only spin at 99 or 100. A slight movement about 88 but no spinning. Any idea what's going on here? I'm using a 9v power supply.

 

[day_trippr]

Perhaps this note provided by the seller is pertinent?
“NOTE: This can not be used to the brushless motor”
All of the peecee fans I've used over the last many years are brushless...

[edit] Aside from that, without knowing the VIN vs VOUT for that device it's hard to say that using a 9V power supply will provide enough output voltage to spin a 12V fan...

Cheers!

 

[jzamora3]

Perhaps this note provided by the seller is pertinent?
“NOTE: This can not be used to the brushless motor”
All of the peecee fans I've used over the last many years are brushless...

[edit] Aside from that, without knowing the VIN vs VOUT for that device it's hard to say that using a 9V power supply will provide enough output voltage to spin a 12V fan...

Cheers!

I used the same controller as the guy did in the post https://www.homebrewtalk.com/showthread.php?t=575715.

I'll look to see what the details are on the device when I get home. Maybe using a higher voltage power source could help of that's the case?

 

[day_trippr]

Yes, if you fed that box with 12 VDC it should produce at least a solid 11 volts at the output whether there's a linear or buck regulator inside.

As for the original note thing, I can't imagine why a PWM supply wouldn't work with a DC brushless motor.
Heck, 40 years ago we had PWM model train controllers working with brushless motors

Cheers!

 

[jzamora3]

Yes, if you fed that box with 12 VDC it should produce at least a solid 11 volts at the output whether there's a linear or buck regulator inside.

As for the original note thing, I can't imagine why a PWM supply wouldn't work with a DC brushless motor.
Heck, 40 years ago we had PWM model train controllers working with brushless motors

Cheers!

So here's some more info on the device.

PWM
6-30VDC
8a Max

Fan
12v
0.18a

Power supply
9v
1.8a

So maybe not enough juice. I tried a 5v power supply and it didn't spin at all. I have a 12v-750mA power supply. Think that would make it work?

In the earlier post the guy used a 12v 3a power supply. Not sure if that's the same as the 12v I have now.

Thanks again for your help and knowledge!

 

[augiedoggy]

So here's some more info on the device.

PWM
6-30VDC
8a Max

Fan
12v
0.18a

Power supply
9v
1.8a

So maybe not enough juice. I tried a 5v power supply and it didn't spin at all. I have a 12v-750mA power supply. Think that would make it work?

In the earlier post the guy used a 12v 3a power supply. Not sure if that's the same as the 12v I have now.

Thanks again for your help and knowledge!

The 12v 750ma is plenty for a 180ma pc fan.... 9 v not so much... your already underpowering it and slowing it down even at 100 on the pwm controller its still only 75% of the power it was designed to run on.
Add the drag from the magnets and well its struggling to get out of its own way.. This is why your going to use a pwm controller instead of actually adjusting the voltage to control the fan speed... Pwm just pulses the 12v on and off quickly and varing speeds so the fan still have enough power to move it reliable whereas if you just lowered the voltage from 12v down to say 9v the fan goes slower because its struggling to move not because the pulse is turning the motor on and off... hope that makes sense.. I know its not the best explanation.

 

[jzamora3]

The 12v 750ma is plenty for a 180ma pc fan.... 9 v not so much... your already underpowering it and slowing it down even at 100 on the pwm controller its still only 75% of the power it was designed to run on.
Add the drag from the magnets and well its struggling to get out of its own way.. This is why your going to use a pwm controller instead of actually adjusting the voltage to control the fan speed... Pwm just pulses the 12v on and off quickly and varing speeds so the fan still have enough power to move it reliable whereas if you just lowered the voltage from 12v down to say 9v the fan goes slower because its struggling to move not because the pulse is turning the motor on and off... hope that makes sense.. I know its not the best explanation.

Thanks for the explanation. So I tried with my 12v power supply and same issue. Either 100 or nothing. With the 12v there was some minor "twitching " of the fan at about 55 but nothing happened besides that. Any idea what's going on here? Maybe a stronger power supply more more amps?

 

[augiedoggy]

Thanks for the explanation. So I tried with my 12v power supply and same issue. Either 100 or nothing. With the 12v there was some minor "twitching " of the fan at about 55 but nothing happened besides that. Any idea what's going on here? Maybe a stronger power supply more more amps?

Maybe the magnets are disturbing the motors magnetic field? try it without them if they are not already mounted. you may need to add a spacer as an insulator.

 

[jzamora3]

Maybe the magnets are disturbing the motors magnetic field? try it without them if they are not already mounted. you may need to add a spacer as an insulator.

Hmmm. Tried with no magnets and same thing. Seemed simple enough when I started this project. The only thing I see different between my setup and the one I'm trying to duplicate is that he used a 12v 3a power supply.

Any other idea what might cause this? I can't use it at 100 because the speed is too fast and throws the stir bar almost instantly.

 

[augiedoggy]

Hmmm. Tried with no magnets and same thing. Seemed simple enough when I started this project. The only thing I see different between my setup and the one I'm trying to duplicate is that he used a 12v 3a power supply.

Any other idea what might cause this? I can't use it at 100 because the speed is too fast and throws the stir bar almost instantly.

Is he using the same fan?

im pretty sure the power supply I use with mine is only like 800ma..

 

[jzamora3]

Good catch. He's using a different fan. Hmm may need to rethink this project. I thought I could use a simple pc fan but looks like he used a PWM fan. They sell for about 10 bucks. I may or may not keep trying with this project. I have an old stir plate was just hoping to upgrade with this one.

But I guess if I do proceed, I'd just have to buy a new fan and use existing power supply and all should be perfect. Seems easy enough.... that's what I said when I started this haha

 

[getack]

PC DC fans are brushless. They are essentially 3-phase motors with circuitry built in to convert the 12v dc into the correct 3-phase sine profile.

Some fan models allow you to change it's speed by changing the voltage. Some don't. Normally the fans with 4 wires have built in pwm circuitry and you are required to have stable 12v on the power line, with the pwm going in through one of the other wires. IIRC the typical pin-out on a 4wire PC fan is power, ground, pwm and tach.

This gadget you bought seems to apply pwm directly to the motor's power line. This will not work reliably with all fans and as noted, it won't work with BLDC motors. It's designed to work with brushed motors such as drills or vacuum cleaners.

The post from which you are copying fails to give a wiring diagram, but the fan he uses is one of those 4-pin PWM fans I'm talking about. It is very likely that he has the fan power lines wired directly to the power supply, with the pwm connected to the pwm output of the controller.