Re: Variable speed motors
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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
Lathe: 1955 Boxford Model A with screw cutting
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?
Project to build a Greek Hero steam engine and measure its power
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