current on unknown motor

Projects General Guidance
1

Hi, I have an old motor that I took out from an old RC car. All I know is it can take 9V from a power supply.
The power supply has a adjustable current up to 3A. I am wondering is too much current would burn out the motor, or the motor on draws cute as it needs such as when it has no load it draws less but when underload it draws more Am I correct?

2

The motor will draw whatever current it requires from the supply as long as the supply can source the amount required.

Set the supply to 9v and measure the free wheeling current then stall the motor for a very short time and see what it goes up to. These are then the currents you need to work with.

Weedpharma

3

Hi,

The power supply has a adjustable current up to 3A.

Doesn't you power supply have an Ammeter?

Tom.... :slight_smile:

4

Yes it does, it allows me to set Cthe current up to a wooly 5A! Initially I was just afraid to set the current too high, but after some experiment, I realized it is the voltage that would burn out the motor, not the current.

5

Actually, motors are really motor-generator - the motor takes in what current it needs to run and as it spins up, the back emf it generates (as a generator), counteracts the applied voltage with the end result is you get a much lower running current than starting current. When the rotor is locked, the "generator" part of the equation is "0", so you effectively end up with the maximum current the motor can pull (basically the DC resistance of the windings). Too long in an overloaded or locked condition will cause it to burn out from the current, applying too high a voltage typically can cause the armature to throw a winding etc. because it spins too fast. Your range of control for a given voltage needs to be able to handle the current all the way from the "locked armature" condition (stalled/starting) to the much lower current of running with no load on it.

6

I'd not assume that the motor will withstand 9V over a longer time, even if the power supply has 9V. Often a higher supply voltage is used to improve acceleration, with (PWM...) reduced voltage/current otherwise.