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Variable speed from a 24 volt battery bank

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Well-Known Member
G'day Guy's,
With my cnc I'm using a deep cycle 24 volt bank as the primary power supply and for the spindle which is a 300 watt motor I was thinking just say a 5K pot would do the trick for varying the voltage to the motor. Now would this be right or am I on the wrong path.

Les Jones

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Most Helpful Member
If you mean putting the 5K pot in series with the motor it wil not work. A 300 watt motor at full load on 24 volts will take 300/24 amps = 12.5 amps. (These figures are based on 100% efficiency. It will probably only be about 80% efficient.) The current through a 5K pot with 24 volts across it will only be 24/5000 amps = 0.0048 amps. What you would need to do is build a PWM (Pulse width modulator.) speed controller. You could use the 5K pot to control the duty cucle of the PWM controller.

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Most Helpful Member
Pull the speed controller out of an old 18+ volt cordless drill and modify that to use a potentiometer rather than the sliding trigger.


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Bryan! Good to see you, mate! It's been a while!
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