Problems with DC Motor Controller for 2 Wire Fan

[Solar Paul]

Hi All, A very new newbie and I'm having problems setting up a personal respirator (for use as a woodworker)

I've got a 12V DC power Supply (3500mAh Bosch cordless drill battery) and a fan (GDSTIME brushless Dual Ball Bearing DC 12V 0.5A). The fan works fine when connected to the battery supply but it is a little too strong and I would like to be able to control the volume of air supplied.

I bought a DC motor controller (PWM) rated at 2.0A and installed it in the circuit but the fan only twitches. I thought this might be too small so I bought a second rated at 5.0A 4.5-35V but this behaves in the same way.

I went and spoke to the guys at Jaycar but they were unable to help me.

I'm looking for ideas on how to diagnose the problem and get this working. It's the last step

Thanks in advance
Solar Paul

[james_s]

Even with the speed control set to max the fan only twitches? Have you tried another load such as an incandescent bulb to confirm that the speed control works and is wired properly?

[Solar Paul]

Hi James, no I haven't but I'll try that and get a multimeter to see what voltage is able to be read.
Cheers

[bidrohini]

Hi, which motor controller are you using? Is that an L293D?

[BillyO]

Brushless DC motors are really AC motors with drive electronics.  Some of these are a) not happy with speed controls of any kind.  b) extremely sensitive to the frequency of the supply voltage and expect DC and DC only.

You need to be sure the fan is okay with being controlled with a PWM controller.

[BeBuLamar]

Yes brushless DC motor won't work with DC drive. In fact the brushless DC motor that you have already has a drive but hardwired to maximum speed.

[james_s]

Lots of brushless fans work fine off PWM speed controllers, not all of them but most computer style fans do.

[coromonadalix]

maybe it needs a good kick to start and run and after  it will consume less

tried a few drill batteries substitutions in the past, the motor  kicked at 10 amps peak before running at 4 amps when drilling hard ??

[Solar Paul]

Hi All

Thanks all for the good advice and info. It took a while to get into town (we are in a regional area) to buy a multimeter and a 5W DC bulb. I've run some tests and here are the results:

• Voltage of battery when tests run was 11.26V
• Current draw of fan when connected directly to battery is 0.427A. I calc this as 4.8W. The fan is rated as 6W. I presume this is within tolerance but please let me know if this is not correct
• Current draw of bulb when connected directly to battery is 4.12A. I calc this as 4.6W. The fan is rated as 5W so presumably ok
• The DC motor controller added to the [bulb] circuit operated as a dimmer, with the potentiometer varying the brightness from off to appearing as bright as when connected directly. The current drawn varied from 0A to 0.412A (same as when directly connected)
• The DC motor controller added to the [fan] circuit failed to operate, with the fan only twitching as before. The current drawn varied from 0A to 1.2A as the potentiometer was dialled from off to max. Interestingly, the current drawn at max fell over time. This was consistent over multiple tests. I stopped tests when current draw fell to 1.0A (around 30 seconds duration) concerned that I would damage something
• I tried manually starting the fan but it really didn't want to spin
• bidrohini asked if it is an L293D I can't see that number anywhere on the controller. the board is stamped HW687. What I take to be the controller part (?) has two numbers on it D4184 above RY1A18. I don't know if these are helpful
• Given the comments around problems with DC brushless fans should I try to find a brushed fan with the same dimensions? Do they exist?

Any further advice or suggestions will be much appreciated

Regards
Solar Paul

[james_s]

I think you've got a typo there, I suspect the bulb is drawing 0.412A, not 4.12A.

Somebody might make a brushed fan but I don't think that's the solution, there are lots of brushless fans that can have their speed controlled by a PWM source. Have you tried using a variable voltage and see if the fan likes that better than raw PWM? You can get little buck regulator modules for next to nothing.

[Whales]

I can confirm that some computer-style fans do NOT work with PWM'd power.  They twitch and sing but do nothing. 

If you replace your PWM controller with an adjustable DC-DC buck converter then you will be able to control the speed of your 12V fan.  These buck converters output a constant, smooth voltage.  They only cost a few dollars.

It's also possible to fix your problem using a combination of diodes, inductors and capacitors; I did this on my 3d printer for a centrifugal fan that didn't tolerate PWM.

[james_s]

Adding a filter to a PWM controller is essentially what a buck converter is. There are adjustable buck modules you can get for about a dollar shipped from China, I've used them for various things and they work pretty well.

[Solar Paul]

I've ordered some buck controllers on eBay (10 for $15) and I found a utube video on mating them with a potentiometer.  I'll give that a go and let you know how it works out. I'll be able to screw up a few times while I build skills and knowledge
Thanks guys

[Whales]

Hope it works   

N.B. most cheap buck converters come with small screwdriver-adjustable pots already on them, if you buy the right ones then you don't have to add your own pot.  Post a link to the eBay item and I can take a look.

[BeBuLamar]

I don't know I think the fan won't run if you supply a voltage significantly lower than 12V like 6V and if you supply it with a voltage close to 12V like 11V it would still run at the same speed.

[james_s]

All of the computer style DC fans I've played with are controllable over a fairly wide range by varying the voltage. Maybe there are some that are not, but I would expect it to work.