DIY build with DC Brushed Motor

Discussion in 'Electric Bikes' started by Loker, 19 Nov 2017.

  1. Loker

    Loker New Member

    Hi all,


    I’m studying electrical engineering at university and I’m working on putting together an electric bike for my senior project . I have an old brushed DC hub motor and three new rechargeable 12V lead-acid batteries that have a capacity of 15Ah each. I also have a bike frame that fits my hub motor and an ebike throttle I inherited from one of my dad’s old projects. I’ve looked extensively but I can’t find any specs on my motor online.


    The thing I’m struggling with is I have no idea how to build a control unit between the batteries and the motor. I think a buck converter whose output voltage is somehow regulated by the position of the throttle might work but I have a strong feeling that there’s more to it than that.


    Does anyone know of any resources detailing the typical circuitry between batteries and a brushed DC hub motor in the context of electric bikes?


    Any and all replies are appreciated!


    -Sean
     
  2. Tigerbiten

    Tigerbiten Veteran

    I think you'll find most motor speeds are now controlled by "Pulse Width Modulation" due to less power wastage.
    But that's about as much as I know.

    Luck .......... ^_^
     
  3. raleighnut

    raleighnut Guru

    Location:
    On 3 Wheels
    I think that's with a 3 phase brushless 'Hall Effect' motor.
     
  4. Tigerbiten

    Tigerbiten Veteran

    I think it works for all motors.
    Electronic tutorial on PWM & Motors -> http://www.electronics-tutorials.ws/blog/pulse-width-modulation.html
    From the tutorial ......
     
    NickNick and raleighnut like this.
  5. PhilDawson8270

    PhilDawson8270 Veteran

    The easiest way would be to use an off shelf electronic speed control unit
     
    keithmac likes this.
  6. QFour

    QFour Regular

    Location:
    Nottingham
    The OP is studying Electrical Engineering don't think the University would appreciate an off the shelf conversion.

    Everything you are trying to do has already been done many years ago. They have certainly moved on from DC Brushed motors and Lead Acid batteries. If all you are doing is fitting a motor to a frame with a cog to drive the chain just fit a big switch between the batteries and the motor. You will not be able to control the speed unless you use either fit a very large variable resistor in the circuit which will heat up like an electric fire or a modulating controller something like you get on model railways where power is supplied as a variable square wave.

    If it's a DC Motor just connect one 12v battery up and see what happens. If it's a bit slow try two in series. Still to slow use Three. Not many DC 36V motors out there probably 12v. Simple to find out amperage with a meter. Alternatively just connect a battery up and time how long it take to flatten it,

    Good luck with your project
     
    Last edited: 21 Nov 2017
    raleighnut likes this.
  7. PhilDawson8270

    PhilDawson8270 Veteran

    They wouldn’t appreciate somebody wasting their home reinventing an off the shelf solution. Particularly without good reason or benefit.

    Making bespoke versions when off the shelf stuff Works is seriously poor engineering.
     
    raleighnut likes this.
  8. raleighnut

    raleighnut Guru

    Location:
    On 3 Wheels
    Yep,
    Yep it's not like he's wound the Armature on the motor himself.
     
    PhilDawson8270 likes this.
  9. Paul Bromley

    Paul Bromley Active Member

    Location:
    Stoke on Trent
    Ned Mohan is a good source of all things power electronic. His books are usually regarded as the reference source
     
  10. subaqua

    subaqua Guru

    Location:
    Leytonstone
    Last time I checked 3no 12Volt batteries in parallel still gave 12V just lasted a lot longer .....
     
  11. QFour

    QFour Regular

    Location:
    Nottingham
    Ohhhhh .. Senior Moment ..


    View: https://www.youtube.com/watch?v=pIC3oiddJM0


    This guy has come up with a brilliant way of controlling the motor. Magnet on one pedal and a read switch on the frame. Provides power to the motor every time the pedal goes by the read switch. The faster you pedal the faster the motor goes. You are in effect generating a DC Square wave.
     
    Last edited: 21 Nov 2017
    NickNick likes this.
  12. keithmac

    keithmac Über Member

    Ebikes come with various motor control strategies, either crank motion (hall effect sensors) or crank torque sensors to decide on and off state for the motor.

    They all use wheel speed feedback (remeber you are limited to 15.5mpg), having a bike triggered by the throttle only is technically illegal iirc, it has to be done by pedalling.

    Have a good look round the ebike forums, the normal now is 36v or 48v lithium ion battery packs at least 15ah.

    If you can design a programmable controller which can be reflashed it would be a good start, I would say writing the software would take more time than wiring the hardware to get a usable SAFE ebike out of the other end.

    To be honest with what you are starting with you might not get a satifactory outcome, weight is a big factor on how useable a cycle is. My Gtech comes in around 16kg (36v motor, LiOn battery pack).
     
    PhilDawson8270 and NickNick like this.
  13. raleighnut

    raleighnut Guru

    Location:
    On 3 Wheels
    The throttle only option is now illegal, good job it wasn't when I built my trike (and Maz's Dawes)
     
    keithmac likes this.
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