DC Motor (Connected Directly to PS) Starts Stops

Hi there,

I have This Motor connected directly to a 12v, 8.5A power supply.

The issue is that by applying power, the motor starts and stops at regular intervals.
From the research I’ve done, it appears the power supply is applying some sort of a power or heat protection from the back-EMF generated by the motor - thereby cutting power because of these spikes. This seems to be supported by the fact that the Power Suppy LED flashes on/off when doing this.

I assume I could be able to mitigate this by connecting the motor to a PWM regulator, but I don’t have access to one with such a high amperage input/output.

2 questions please:

  • Any way to get this working? Maybe with a capacitor? If so, how big of a capacitor?
  • The motor instructions warn against going over the recommended voltage (3.6-8.4V), what could happen if I continuously apply 12V?

Thanks!

What is the motor driving?

Since that's a motor that often runs at around 12-20A on 6-7V I doubt back EMF has anything to do with it. My guess is that it's simply drawing too much current and the power supply is shutting down intermittently. But that's what you'd expect when you run it on twice the design voltage. It will be trying to turn twice as fast as normal and using too much power and probably also ruining the bearings (which are just plain bushings).

A capacitor is not going to help.

Steve

slipstick:
My guess is that it's simply drawing too much current and the power supply is shutting down intermittently. But that's what you'd expect when you run it on twice the design voltage.

Wouldn't doubling the voltage halve the current though?

kenwood120s:
Wouldn't doubling the voltage halve the current though?

Very unlikely. If you somehow had a load which absorbed constant power then it would. But in most real world cases if you're turning something twice as fast that requires more power and it may easily be more than double the power. It certainly is with propellers where the power required is proportional to the cube of the rpm. Which is why I asked what the motor was driving.

Steve

slipstick:
Very unlikely.

Roger that

For that motor, you need a power supply of no more than the rated voltage of 8.4V, and capable of supplying the stall current, which is probably around 20 Amperes but may be higher.

Select an 8V, 200 Watt power supply to be safe, or use 2S LiPo batteries capable of 20A discharge.

Thanks for the replies everyone.
I will be driving a oscillating cutter to cut leather.

I'll try a different power supply and come back with the results.

I came to the realization that finding an affordable power supply with such a high amperage at low voltages is impossible. I will be looking for higher voltage motors.