MPJA is sort of an interesting outfit worth keeping in mind.? They cover a LOT of ground including multiple pages of advertising in a Ham Radio magazine.? All the way to even selling a talking multimeter which isn't really a joke.? You may be in a position difficult to see the meter or want to focus on placing test leads carefully.? And the National Federation of the Blind stocked these at one time.

Charles E. "Chuck" Kinzer

On Thursday, February 8, 2024 at 11:27:33 AM PST, mike allen <animal@...> wrote:

Someone mentioned the car seat motors , these folks have them on sale & also have a controller on sale too

animal

On 2/8/24 10:42 AM, mike allen wrote:

I believe that with PWM nothing happens till 15% duty cycle & limits out at 85% duty cycle . That's in print somewhere out in internet land .

animal

On 2/7/24 10:08 PM, Evan wrote:

I haven't tried using a treadmill motor controller and cannot be specific but hope this is of some help.

Lets start with some calculations from your motor DC specs:
Power = 120 volt x 21 A = 2,520 watts
1 HP = 745 Watts so divide by 745 gives 3.38 HP?
Calculating backwards from 2.5 HP
2.5 x 745 =?1,862.5 Watts
Divide by 120 gives 15.5 amps at full output.
This discrepancy probably means that the motor can handle up to 21A when under load.

When running at its maximum speed of 7000 RPM the armature is acting like a generator creating a 'back-emf' ?or voltage of -120 volts opposing the 120 volt input and that is why it can't run any faster than 7000 RPM. (otherwise it could be a recommended limitation depending on the centrifugal/centripetal forces that the armature can handle without flying apart.)

My Pulse Width Modulator circuit displays amps and volts and I have a tachometer as well. The data from that may help answer your question. Under heavy load the motor slows down, the back EMF decreases at lower RPM and input voltage is able to push through more amps. Eventually as the amperage increases the driver circuit will cut off the power supply to avoid burning out its components. ?In addition to that, the PWM circuit tries to maintain power output by increasing average amps as it switches on and off.?

I think the solution is to alter the gearing/pulleys to allow the motor to run at higher RPM.

Note: the potentiometer used in these circuits operates on 0 to 5 or 0-10 volts, so is quite safe. It is still a good idea to have it grounded and/or insulated well.

--
Evan
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