From an old dust buster I've got this electro motor, the included battery pack and the charger:

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I ripped everything apart (the dust buster was broken) and the motor still works. After playing around with it for a while and letting it lying around for about two weeks it suddenly revs a lot slower. I supposed the battery pack was drained so I hooked up the battery pack to the charger and let it charge for a night. Unfortunately the motor still turns very slow.

Since I want to use this motor for my first home robotics project (making a kite fly with my computer), off I went to the local electronics store where they measured the charger to give 16V (even though it says 21V) and the battery pack to give about 5V. I then hooked up the motor directly to the charger, but unfortunately it doesn't even move an inch then.

So now I wonder:

  1. Why doesn't the motor spin at all when hooking it up to the charger? (Could that be because the 250mA is too low?)
  2. Why doesn't the battery pack charge at all? (this bothers me the most!)

All tips are welcome!


250mA states the maximum output current to drive the load. So check what the current rating of the 5V regulator is.

Check whether there is a voltage drop before reaching the motor. It might be that the motor is not spinning because of insufficient supply.

Change the adapter you are using. If it is marked 21V, the output from adapter will be around 20.5V to 21.5V.


If your charger is running at 16V instead of the 21V it's supposed to be operating at, then that is your problem.

Why your charger won't run the motor

Your charger should be fairly underpowered for running the motor. Most batteries strong enough to power motors are not meant to be charged as fast as they can discharge. This can be for several reasons, including:

  • Safety: some batteries will explode if charged with too much current
  • Longevity: some batteries will degrade if charged beyond what the chemistry can handle

A power supply capable of running the motor would be damaging (if not dangerous) to connect directly to the battery.

Other things to check:

It's possible that your batteries are running near the end of their lifetime (they have a finite number of cycles). When charged overnight and unplugged, are their voltages below what they should be?

It could also be that the problem is mechanical. Has debris been introduced into the motor assembly, or is it poorly lubricated?


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