Custom EV PWM Motor Controller Help

Discussion in 'General Electronics Chat' started by Iyik, Oct 3, 2012.

  1. Iyik

    Thread Starter New Member

    Oct 3, 2012
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    Hey there, this is my first post on these forums, I have recently decided to make a an EV, I will go get a real cheap old sport car and then do an EV but I am trying to plan money beforehand. My biggest issue right now is a Motor Controller, after doing a bit of research I decided that with the (minimal) experience I have I may be able to make one myself. So I've been trying to figure out where to even start to power a 96-144v motor @ 200amps (550 for 2 mins). I THINK I need a MOSFET driver hooked up to about 8x 130amp MOSFETS (figured that from ReVolt) for the controller itself though I'm sure it is much more complicated than just that. Another question I have is how these controllers work. It seems like the supply input is a massive 144v that is then immediately stepped down to 12v for the MOSFET driver which puts out another 12v @ ~15amps....so how does that translate to 144v @ 550amps at the motor?

    EDIT: Could I realistically do this on a very basic circuit consisting of basically the supply input 144v, a 12v control input from the Pot Box (from pedal/accelerator) and hooked up to a single very large MOSFET with no driver or microchips or anything crazy?? Like say....400a or 500a output?
     
    Last edited: Oct 3, 2012
  2. crutschow

    Expert

    Mar 14, 2008
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    The MOSFET requires 10V on the gate to switch, but the voltage it switches at the drain is 144V.

    The control of such large power is typically done with PWM for good efficiency. Otherwise you dissipate a huge amount of heat in the control transistors.

    No offense, but I believe this is a little more than you should attempt with your level of understanding, unless you have a large budget to replace the many transistors you are likely to blow. :rolleyes:
     
  3. Iyik

    Thread Starter New Member

    Oct 3, 2012
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    I agree it is a little more than I should attempt, nonetheless I would rather attempt this than buy a 1,800$ Motor Controller..

    Anyway I have seen many circuits for smaller motors and videos and so forth just basically using the input of 12v or so directly into a MOSFET with the control coming from a little potentiometer and putting out ~10amps or so to the motor and seems to work flawlessly, no microchips or MOSFET drivers. Even saw one for an ICE starter motor. SO, basically what I'm asking is; is something like that possible for 144v and a much higher amperage since it is still the same basic principle no matter the size of the motor (right?)??
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,019
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    Scaling up the design from a 10A controller is rather like scaling up a balsa wood model airplane to build a 747. Scaling doesn't work that way.

    With a small motor you can tolerate the power loss in a simple series linear controller. But you are talking about 144V X 550A = 79KW. Ignoring the fact that your efficiency would go to heck, the linear controller could be dissipating at least 1/4 of that or about 20KW. The heat sink to dissipate 20KW would be humungous.

    So you need to do PWM to minimize dissipation and get good efficiency (you are interested in maximum range before the battery dies, aren't you?). That requires a PWM controller, a bunch of heavy duty MOSFETs, and a high-current MOSFET driver to rapidly switch the large capacitance of the MOSFET gates to minimize switching losses.

    Suggest you try to find a design for such a high power controller somewhere and copy that. By the time you are through I wouldn't be supprised if it cost you more than the $1800 for the manufactured controller.

    Good luck.
     
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