What specifications do I need on my motor speed controller?

Discussion in 'General Electronics Chat' started by hspalm, Jul 2, 2010.

  1. hspalm

    Thread Starter Active Member

    Feb 17, 2010
    201
    8
    Hi
    I want to buy a PWM controller for a 24v DC motor I took off an electrical lawnmower. It's stall current is 136A and the motor is rated 300W.
    I suspect that when the motor is propelling me and a kick-scooter (http://shopzone.no/images/sparkesykkel standard.jpg) the current will peak around this value when accelerating from 0 km/h? So I need to buy a PWM controller that exceeds this value, right? Would I be better of bying one complete, or building one? I have made small PWM motor controller with microcontrollers, but I don't know the best way to amp up the power this much... Is it as simple as one or maybe two linked in an array of the IRL1004?
    Datasheet:
    http://www.irf.com/product-info/datasheets/data/irl1004.pdf

    Thanks in advance, I really appreciate all the help you have given me in my earlier threads.
     
    Last edited: Jul 3, 2010
  2. hspalm

    Thread Starter Active Member

    Feb 17, 2010
    201
    8
    Ok, so I have drawn an example circuit so you may correct me, and/or add components I should use in my circuit.

    http://www.hpstuff.no/bilgalleri/motorcontrol.JPG

    I will also be adding a fan witch draws the heat from a big heatsink that the transistor is mounted on.

    edit: Should I be using a current limiting resistor between uC and gate on mosfet? In case something fails.
     
  3. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    Yes, yes you should.

    As for the scooter and your 136A stall current, You may want to make this a 'power assist' motor.

    Starting from 0 will cause quite a few problems. If you get going with your foot, then use the motor to keep your speed up, you will have less battery issues.

    You will need a huge battery to get this thing going from 0, and it will die rather quickly.

    You will also need some sort of gearbox to increase torque and reduce the motors RPMs.
     
  4. hspalm

    Thread Starter Active Member

    Feb 17, 2010
    201
    8
    Thank you for your reply. The motor is fitted with a gearbox with a pretty big ratio, but i do not have the specifications for it. On the lawnmover the end shaft of the gearbox was again geared down with a ratio of about 1:6 (guessed by looking at it). the lawnmover specifications can be viewed at gardena.com, model number 380 EC. This is a technical drawing:
    http://www.gardena.com/RES/resources/xviews_pdf/04028-20.pdf

    I will try to measure the rpm of the end shaft later, to see if it needs some extra gearing down. The speed we want is around walking speed ++. If we use the method of kickstarting the scooter with our legs, maybe we won't need a speed controller after all?
     
  5. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
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    Thats what I was getting at.

    You should set the speed with gearing. That way you need only a on/off switch.

    A momentary thumb button would do. You want to use momentary just incase you fall off, you want it to stop. A unmanned scooter wreaking havoc on traffic can get you arrested these days. ;)
     
  6. hspalm

    Thread Starter Active Member

    Feb 17, 2010
    201
    8
    Great idea, thanks!
     
  7. retched

    AAC Fanatic!

    Dec 5, 2009
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    Glad I could help.
     
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