8x Parallel 12V Fans 2.0

158

04:05:00

Variable speed control.
Advice welcome.

I added an NPN transistor to reduce the load across the potentiometer from 600mA →6mA. 

But it seems to have dropped the speed/RPM of the fans by ~50%.

I understand that Pulse Width Modulation is a popular solution, but I'd really like to get this working before moving on to more sophisticated methods.

published 8 years ago

2ctiby

8 years ago

You are dropping 1.5v across the bjt (12v at collector, 10.5v at emitter). With roughly 600mA flowing through it .....Power=AmpsxVolts so the Power wasted as heat in the bjt is 0.6x1.5=0.9 Watts..... Notice also that this 10.5v is your supply voltage to the motors (no longer 12v), so you may need to alter that for each motor in the settings. If you then alter the pot, you would have a different supply than that 10.5v......see how by using this resistor method your realtime supply voltage alters as well as being inefficient in power usage....Is it any wonder that drills etc use PWM or other more efficient methods these days.

tjt263

8 years ago

Well, they're based on real 12V (100mA) DC fans, so I really can't just change their values. And yes, I see the problem. I'm just not quite sure how to deal with it. I'm going to look into PWM, I was just hoping I could come up with a more basic solution first. But at this stage it looks like it was better off before incorporating the transistor.

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