variable speed drive

Discussion in 'General Electronics Chat' started by georgewood, Sep 20, 2012.

  1. georgewood

    Thread Starter New Member

    Sep 20, 2012
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    0
    Should I be using a 180 v,7.5 A dc motor to make an electric bike. Using 5, 36 volt lithium batteries.
    Also I have no idea how to adjust the voltage as in an accelerator device.
     
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
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    180V * 7.5A = 1350W. Average ebike (bicycle frame) is around 500W; 1000W is "sporty."

    That's ok though, if you already have the motor, it will work.

    For speed control you're going to want to PWM the motor with a big IGBT.
     
  3. Rbeckett

    Member

    Sep 3, 2010
    205
    32
    George,
    Strantor is correct. An IGBT set up for PWM would handle the load and any possible surges or inrush current spikes and give you full torque at low rpm all the way to full RPM. Have a good long read on PWM so you grasp that you are not controlling voltage, you are merely controlling the actual amount of time each pulse lasts in a specific period of time. That will give you the power you need to get started off and as you increase you speed or shift through the gears you can maintain a pretty linear acceleration curve with a minimum of heat which is wasted energy. Hope this helps.
    Wheelchair Bob
     
  4. georgewood

    Thread Starter New Member

    Sep 20, 2012
    3
    0
    Thankyou for the response.
    I have no idea what that all means ,I will google pwm and igbt.
    I was concerned about using the wrong size motor, will I be wasting energy as heat.
    The motor has an rpm of 4500 and even 3 batterries half charged packed a punch, I probably don't need to use all 180 volts ??
     
  5. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I trust you've already googled the buzzwords, so I won't provide definitions.
    The motor, I assume is a permanent magnet motor (only 2 wires coming out of it)? If that's the case then speed will be proportional to voltage. Depending on your gearing, you may or may not need 4500rpm. However, I suspect that you won't, and therefore going down in battery pack voltage is not a bad idea. the PWM is to control the "effective" voltage between 0 and max (max = 180V, 100V, 72V, etc - whatever you decide on) so that you have some sort of control over the speed instead of just ON/OFF.
     
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