I have a project I am working on which has a 300Watt AC/DC converter AC220V 230V to 24DC 12.5A - 15A power switching Transformer.
Which is connected to a EM - 285 DC motor speed regulator. 12/24v 20A, and then to a High torque electric motor DC 24volt 3000rpm 200 watts.
The electric motor has a pulley that with a drive belt can be attached onto a pulley that is on a drive shaft, which has a flywheel mounted on it.

First I did a test run of the set up with out the motor being attached to the dive shaft with the belt.
I turned on the speed controller very slowly and the shaft on the motor started turning slowly, but when I turned the speed up, the motor speed, started pulsing, right up to full speed.
I turned it down to zero, and the motor stop spinning, I then again turned the speed controller to set the motor spinning at a slow speed, and again it turn over with no pulsing, but as soon as I turned the speed up, the motor started pulsing.

I then attached the dive belt from the motor to the drive shaft, turned on the speed controller, so that the motor started to rotate very slowly, I slowly increased the speed, and there was know pulsing just a sooth acceleration, as I went from very slowly speed to high speed, and back down till zero, when it stopped rotating.

Can any one explain why the motor starting pulsing when I increase the speed from very slow, when a belt was not attached? Is it because the motor was not experiencing any resistants when rotating?

 

First IF the "15A power switching Transformer" is a SMPS, this is not the ideal source at all for controlling a motor.
The best source is a linear supply . Followed by a suitable PWM control.
Is this a PM brushed DC motor or a series or shunt field wound field?

 

I suspect the pulsing was due to the voltage converter, or the speed controller, going into self-protect mode by shutting down briefly because of current overload. A motor running slowly generates very little back-emf so draws more instantaneous current than when it is running at full speed.

 

A motor running slowly generates very little back-emf so draws more instantaneous current than when it is running at full speed.

Not quite so:
I have done some extensive empirical testing of brushed DC motors, large TM types etc, and when off loaded, if the voltage is applied slowly, then the BEMF to applied voltage ratio stays the same.
In other words, the current is exactly the same throughput the RPM range.

 

if the voltage is applied slowly

Interesting. I had in mind typical PWM control, where full voltage is applied in pulses.

 

Interesting. I had in mind typical PWM control, where full voltage is applied in pulses.

In PWM, the current does not follow a square wave as the voltage does, it is in fact a fairly small, peak-to-peak saw tooth, riding at some mean level
The level will increase with load, however.

 

First IF the "15A power switching Transformer" is a SMPS, this is not the ideal source at all for controlling a motor.
The best source is a linear supply . Followed by a suitable PWM control.
Is this a PM brushed DC motor or a series or shunt field wound field?

Thank you for your thoughts on what you think has gone wrong, and the solution you suggested, and I appreciate you taking the time out, to reply to my thread.

 

I suspect the pulsing was due to the voltage converter, or the speed controller, going into self-protect mode by shutting down briefly because of current overload. A motor running slowly generates very little back-emf so draws more instantaneous current than when it is running at full speed.

Thank you for your thoughts on what you think has gone wrong, and the solution you suggested, and I appreciate you taking the time out, to reply to my thread.

 

What form of technology does the motor take ?
DC brushed? BLDC? etc

 

If the controller was a closed loop control, where it reads the motor speed and adjusts the drive to hold a set speed, then running without any load was like turning up a servo gain much too high. Motor inertia matters a lot in closed loop feedback systems.

 

Can any one explain why the motor starting pulsing when I increase the speed from very slow, when a belt was not attached? Is it because the motor was not experiencing any resistants when rotating?

BLDC with no feedback may explain it?