I have a variable speed controller with a 500K potentiometer driving a DC 180v motor. The motor has an RPM of 4000 but I really only want to use a range of 50-400RPM. When using the potentiometer I'm finding it is overly sensitive and isn't giving me the control over the lower RPM that I need. Would adding a fixed resistor across the Pot reduce the range of RPM? If so what value resistor should I start experimenting with and which wires does it need to intersect?

 

If 500k produces the slowest speed you want with enough torque, replace the pot with 47k or 100k and add a 470k resistor in series with it.

 

If 500k produces the slowest speed you want with enough torque, replace the pot with 47k or 100k and add a 470k resistor in series with it.

The motor doesn't start up until I've turned the Pot about 20%. Then there is very little range between 0-400RPM, I only need to turn the Pot maybe 5% to go from0-400rpm. Ideally I would like to be able to set it to 50,100,150... etc. I won't really need anything above 400RPM. A gear reduction would be ideal but I'm hoping I can fix the issue through the Pot, I won't know about the torque until I load it up.

 

You need a Gear or Pulley Speed Reducer to let the Motor run closer to its designed RPM range.
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50 revs per minute is less than only 1 rev per second which is extremely slow for a small motor.

 

Thanks guys, I'll look at a pulley reduction system