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!

[EDIT] Just some more info on the batteries: there are ten 1.2V and 1700mAh batteries, which makes it a 12V battery pack. The question arising from this:

  1. Can it be that the battery pack is not charging because it is a 21V charger on a 12V battery pack? Do I need to put a resistor in between? And if so; what kind of resistor?
  • \$\begingroup\$ Battery details would be useful. \$\endgroup\$ Mar 29, 2013 at 9:22
  • \$\begingroup\$ @LeonHeller - Unfortunately I've got no more details on the battery. It was inside the dustbuster and it has no information on it.. \$\endgroup\$
    – kramer65
    Mar 29, 2013 at 9:38
  • \$\begingroup\$ Check the batteries and see what voltage they should be at when fully charged. The individual voltages should be marked on them. Then work-out if they are wired in series or parallel or combinations of ser/par. From that, work out what you expect the battery pack to deliver when fully charged. It might be in the order of 8V rather than 5V. If you conected the chrger (at 16V) across the motor, ask yourself if this might have (a) damaged the motor or (b) damaged the charger or (c) it didn't hurt either. Do you have a multimeter because you're prob gonna need one for the kite project. \$\endgroup\$
    – Andy aka
    Mar 29, 2013 at 9:41
  • \$\begingroup\$ Also, have you checked the fuse close to the bat-pack? Why is there a battery missing and why is there a cut-wire? \$\endgroup\$
    – Andy aka
    Mar 29, 2013 at 9:45
  • \$\begingroup\$ Is this the motor that wasn't designed to run well in reverse, in a recent question? \$\endgroup\$
    – user16324
    Mar 29, 2013 at 10:01

2 Answers 2


Chargers only deliver enough current for charging a battery over several hours, which is far less than the current required to run the motor.

If the charger is only supplying 16V and is marked 21V, it is probably faulty and won't charge the battery properly.

  • \$\begingroup\$ Thanks for your answer. Just to clarify; what do you mean by saying the battery is "faulty"? It was the charger which came with the dustbuster, do you mean it is broken? \$\endgroup\$
    – kramer65
    Mar 29, 2013 at 9:27
  • \$\begingroup\$ Yes, it might not be working properly. That is likely if it is only giving 16V. \$\endgroup\$ Mar 29, 2013 at 9:31
  • \$\begingroup\$ Ah alright. So I suppose I can just use any general 21 Volts charger? Or should it have some minimum of mA? Would a 12V charger also work (but would it only charge the battery to 12V)? \$\endgroup\$
    – kramer65
    Mar 29, 2013 at 9:39
  • \$\begingroup\$ You need the correct charger for the battery. That is why I asked for the battery details. \$\endgroup\$ Mar 29, 2013 at 9:45

Why is the DustBuster "broken" in the first place? Chances are the batteries weren't taking a charge due to being permanently in the cradle connected to a cheap nasty power supply they pass off as charger. Batteries have a finite life and have to be charged correctly to maximise it. Consumer products generally have poor chargers to keep costs down (they only have to last a year or two).

You'd be better off buying a small RC Li-po battery and charger for use in your project. The charger will be able charge almost any battery you use in the future too.

  • \$\begingroup\$ It was "broken" because the powerswitch turned out broken. Since the dustbuster was taken apart and my sister already had a new one she simply wanted to throw it away. That's were I came in to take it home. At first the motor functioned perfectly well with the batteries, but once they were empty I simply couldn't charge them anymore. In the dustbuster there were some electronics which I threw away (stupid), but probably there was a resistor in it that I now miss. My question is now: Could it be that the battery doesn't load or is broken because of the higher voltage of the charger (21V vs 12V? \$\endgroup\$
    – kramer65
    Mar 29, 2013 at 11:48
  • \$\begingroup\$ It's impossible to say. Why don't you bin it and start with a new motor, battery and charger? \$\endgroup\$ Mar 29, 2013 at 12:10
  • \$\begingroup\$ Hmmm, that might be a better option indeed. The main reason for this is the fact that I like to keep it low budget. If I buy a new motor (€22) and a (LiPo)battery (€12) I also need a LiPo charger (€20), which will cost me around €50 total. But yeah, maybe it is the only way to go.. :S \$\endgroup\$
    – kramer65
    Mar 29, 2013 at 12:15
  • \$\begingroup\$ It's difficult to judge with out a schematic. It's possible that the PCB was a charge controller but I think your main problem is that the "charger" is shot/unsuitable. Even if the battery pack is good, you've proven that it won't charge them or run the motor. Get yourself an old PC PSU (often for free) for testing purposes, then worry about batteries and charging when you're further ahead with the project. \$\endgroup\$
    – Outsider
    Mar 29, 2013 at 12:55
  • \$\begingroup\$ @PaulCrouch - That is a brilliant advice. I think you mean that I use the PC PSU for running the motor (not for charging this old battery pack right)? \$\endgroup\$
    – kramer65
    Mar 29, 2013 at 14:17

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