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Electric Bike

Discussion in 'General Electronics Discussion' started by ElectricMan27, Apr 5, 2016.

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  1. ElectricMan27

    ElectricMan27

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    Apr 5, 2016
    Hello i am looking to build a electric bike/motorbike if i were to use a power source of numerous deep charge batteries that total voltage would be 46V. And a 36V or 24V motor what sort of Variable resistor would i need to control the speed? Would i use a control board to control the motors, power and speed? If so what model or type would be best and where would i get it? How would i connect the batteries together?
    As you can tell i'm full of questions because my knowledge is limited but any help and input is gratefully appreciated
     
  2. BobK

    BobK

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    Jan 5, 2010
    You will need a motor speed controller board rated for the voltage and current used by the motor. Take into account that the stall current is much higher than the running current, and the speed controller must handle the higher stall current.

    You can find these at very reasonable prices (read as ridiculously low) on Ebay.

    Bob
     
  3. Gryd3

    Gryd3

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    Jun 25, 2014
    BobK Is right on the nose...
    Using a simple Variable Resistor will waste a lot of power... They work by simply adjusting the resistance in-line with the motor... the amount of power wasted can be HUGE! So you typically need a very large/expensive part for this. Think... at half speed, 18 - 23V will drop across the resistor, and if the motor pulls 3Amps, this part will get hotter than an incandescent light-bulb! (60+ Watts ... in this example. Real-world will be based on the actual draw of the motor)
    The parts Bob mention are active components that usually operate in with PWM, and run incredibly cool and efficient. They also have more features. You can find controllers that offer 'speed' control instead of simple voltage adjustment, as well as things like over-current protection to prevent you from burning out your motor if the motor stalls. (Usually at a higher price, but worth it!)
     
  4. Bluejets

    Bluejets

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    Oct 5, 2014
  5. ElectricMan27

    ElectricMan27

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    Apr 5, 2016
    Thank you everyone for your replies i was wondering if you could give me some links or details on appropriate speed controllers
     
  6. Gryd3

    Gryd3

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    Jun 25, 2014
    Well... there are tons of links, but google will show you that ;)
    Consider two types of controllers to begin with:
    - Linear or Analogue
    - PWM

    In the simplest form, you can use a rheostat or something like the fan control in a car... (Multi-position switch to a selection of high power resistors.)
    This method wastes a lot of heat, and is inefficient.

    The digital control uses PWM or an alternative switching technology and is much more stable and efficient.

    In any case.... the controller MUST be sized based on the needs of your motor.
     
  7. Bluejets

    Bluejets

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    Oct 5, 2014
    I thought I did...?
     
    davenn likes this.
  8. ElectricMan27

    ElectricMan27

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    Apr 5, 2016
    Could i give the controller more power than the motor needs and will it hold it back or will it fry the motors
     
  9. ElectricMan27

    ElectricMan27

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    Apr 5, 2016
    Say 48v to a 36v controller
     
  10. Gryd3

    Gryd3

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    Jun 25, 2014
    Depends entirely on the controller.
    If it has current / voltage sensing on the output then yes... otherwise it's a pretty stupid device that will typically just pass the full voltage to the motor if you crank the speed up.
     
  11. ElectricMan27

    ElectricMan27

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    Apr 5, 2016
    what do you think would be better for a motor 36v or 48v?
     
  12. BobK

    BobK

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    Jan 5, 2010
    Match the voltage to the rating of the motor.

    Bob
     
    Gryd3 likes this.
  13. ElectricMan27

    ElectricMan27

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    Apr 5, 2016
    If i used 48v for a 36v motor would the controller have power for longer than 36v to 36v
     
  14. ElectricMan27

    ElectricMan27

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    Apr 5, 2016
    Geared Motor or straight???
     
  15. Alec_t

    Alec_t

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    Jul 7, 2015
    ... you may well damage the motor :(.
     
  16. Gryd3

    Gryd3

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    Jun 25, 2014
    Based on the understanding you have of the subject thus far, I would strongly urge you against using a higher voltage for the motor than it's rating. Most motor controllers aren't very complicated, so using a 48V supply and a 36V motor would most likely end up in the controller sending 48V to the motor. This 48V may be pulsed, or in the form of PWM, but unless you understand the workings, it's a bad idea to even try.
    This is your preference and is highly dependant on the motor you plan to use. If your motor has low torque and high RPM, you will want it geared. Alternatively, if your motor is very high torque and low RPM then you may want this geared as well depending on the speeds you want to achieve.
     
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