Lowering voltage to a brushless motor

Nov 28, 2005 2 Replies
R

I have a brushless motor powering a water pump for a PC. It starts up @12 volts, but not 7. How can I lower the voltage to around 8 (BTW, I have ground, +5, and +12 available)? I tried 5 Ohms of resistance, but it still wouldn't start. Would a capacitor after the resistor help anything? I'm guessing the motors resistance is not constant due to the switching in a brushless motor. So would a capacitor make the input voltage more stable?



I know all about PWM circuits, but I'm looking for something simple. PWM is either expensive and bulky (around $30), or cheap (IC), but you need to purchase 100 of them.



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F

On 27 Nov 2005 20:57:48 -0800, "randino" put finger to keyboard and composed:

If the motor current is less than 1A, use an LM7808 regulator or equivalent.

The motor's current would vary with the load. A resistor is not the way to go.

Brushless motors use electronic commutation. I haven't tried it, but I suspect that PWM would play havoc with the motor's Hall effect sensor(s). At the very least you would need to smooth the output with an L and a C.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

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