Trouble powering motor

Discussion in 'The Projects Forum' started by Max Kreeger, Aug 20, 2015.

  1. Max Kreeger

    Thread Starter Member

    Oct 1, 2013
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    Hey guys,

    Recently I removed a motor from an Oral B Braun toothbrush, simply because the gears it had for oscillation were already set up and in a nice little housing. It was powered by a 2800mAh rechargeable battery.

    Now my problem is I can't seem to power it to produce results like it did with the battery. What I've tried so far:

    - I've noticed any DC supply with an output of over 1A results in the motor "chugging" regardless of the voltage being 5 or 12
    - A DC supply with 1A and 6V output has seemed to work best so far...it managed to supply almost the same amount of torque although the DC supply did burn out..
    - A DC supply with 700mA gets the motor going with good speed..but no torque..

    A note worth mentioning...these are all old DC supplies I have found from old devices which I have just cut the ends of and soldered directly to the motors contacts..maybe thats where I'm going wrong.

    To summarize, how would I go about finding the optimum voltage/current for this motor (I have tried searching for its spec sheet, no luck)

    Thank you in advance guys!

    Regards,
    Max
     
  2. tshuck

    Well-Known Member

    Oct 18, 2012
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    Are you sure the motor is a Brushed DC motor?

    I would expect a Brushless DC motor in such an application (it will not work with a simple DC supply).

    If you have a scope, you can probe the output wires of the toothbrush controller to the motor and observe the controller signals - which will tell you what kind of motor it is.
     
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  3. Max Kreeger

    Thread Starter Member

    Oct 1, 2013
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    That is an excellent question..I hadn't even thought of that. I don't have a scope unfortunately.

    Assuming it is a brushless..how would I go about things then?
     
  4. tshuck

    Well-Known Member

    Oct 18, 2012
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    If it was brushless, you would need to identify the number of windings you have and where they are in relation to one another. Then you would have to drive them in sequence.

    How many wires are coming out of the motor?
     
  5. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    This is probably just a cheap brushed motor and if a 6V 1A supply worked and then failed try a 6V DC supply with >1A. It cannot be a brushless motor as it would not work under any circumstances if fed directly with DC.

    Make sure that whatever supply you use provides smooth DC because some 'DC' supplies intended for charging batteries don't and will not drive the motor smoothly.
     
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    What was/is the battery voltage? What is the output from the battery charger for the toothbrush?
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Yeah, start with the details of the original power source, and work up from there.

    ak
     
  8. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Pretty sure I disagree with that, me and the gazillion brushless DC fans sprinkled around the planet.

    ak
     
  9. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    I was referring to a bare brushless motor with no electronics built in, primarily, in response to Post#2 and #4 which suggest that the TS may have such a motor and ignores the fact that the TS was able to run the motor with nothing more than a 6V DC supply.
     
  10. Max Kreeger

    Thread Starter Member

    Oct 1, 2013
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    The battery in it was a Ni-Cd 1N-600AA...which in search results gives me 1.2V 650mAh..although when I googled for replacement batteries for that same toothbrush they were all 2800mAh. I tried connecting the DC supply across where the battery terminals were on the circuit board, but no luck same results.
     
  11. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    So the motor needs around 1.2VDC at, probably, several amps. If you try to power it from a 6V supply, it's not surprising that bad things will happen to either the supply or the motor. Try running it from a 1.5V AA, C, or D cell.
     
  12. Max Kreeger

    Thread Starter Member

    Oct 1, 2013
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    Just hooked it up to a AAA (closest one I had to me)...ran quite well. So in short..I have to find a PSU @ 1-1.5V and 600mA?
    One more question..when I hooked the DC supply directly to the terminals of where the battery used to be...the motor came on automatically there was no need for me to press the power button..almost as if it was shorting the entire board. Could that be due to damage from previously trying high voltage/current supplies?

    Thank you again guys.
     
  13. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    The board is probably damaged from having 6V applied to it. I don't know how much current the motor requires (the capacity rating of the battery is not a particularly useful indicator) but due to the low motor voltage I would expect the current to be quite high. The only way to find out is to connect an ammeter is series with the motor and measure the actual current when it's running. I think you will struggle to find an off-the-shelf 1.2V-1.5V power-supply with sufficient current.
     
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  14. Max Kreeger

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    Oct 1, 2013
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    Would it be possible to design a buck converter to step the DC supply voltage down from 6V to 1.5V. Would that work?
     
  15. blocco a spirale

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    Jun 18, 2008
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    Yes. You just need a supply of the correct voltage and enough current to start and run the motor under load.
     
  16. Max Kreeger

    Thread Starter Member

    Oct 1, 2013
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    The only experience I've ever had with DC converters is of a theoretical nature (solving problems in my power electronics unit) and I've noticed I need Power and Frequency to be able to solve those circuits...so does that mean the Vin is an AC source? which defeats the name of DC-DC converter. A tad confused.

    Thank you for your patience :)
     
  17. blocco a spirale

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    Jun 18, 2008
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  18. Max Kreeger

    Thread Starter Member

    Oct 1, 2013
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    Thank you blocco! One last quesition:

    • Input voltage: 3.2V-40V
    • Output voltage: 1.25V-35V
    I'm guessing I adjust the output via the blue component in the picture?
     
  19. tshuck

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    Oct 18, 2012
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    ... And given the fact the TS doesn't know what he/she is talking about, it's entirely possible that there are electronics built in - hence the questions.
     
  20. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    Well, no.

    The TS said " A DC supply with 700mA gets the motor going with good speed..but no torque.."

    It doesn't take a genius to observe whether a motor is running or not so I think it is safe to assume that this is in fact the case.

    You then go on to say:

    "If you have a scope, you can probe the output wires of the toothbrush controller to the motor and observe the controller signals - which will tell you what kind of motor it is."

    "If it was brushless, you would need to identify the number of windings you have and where they are in relation to one another. Then you would have to drive them in sequence.

    How many wires are coming out of the motor?"

    Which contradicts the TSs observation that the motor runs when a DC supply is connected directly to it. Of course, it may be a brushless motor with a built-in controller but that is not what you were referring to because you wrote about the control signals coming from the toothbrush controller and speculated on the motor having multiple windings.
     
    Last edited: Aug 21, 2015
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