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PWM for a high amp motor?

Discussion in 'Electronic Basics' started by Glenn Ashmore, Feb 15, 2005.

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  1. I have a 1500 watt 12VDC motor on the anchor windlass that I want to give
    all the power it needs. I also want to slow it down as the anchor comes
    onboard. I have built a little microcontroller program that counts the
    revolutions and calculates how much anchor rode is out. When the count gets
    less than 10' I want to start slowing the motor. The windlass has positive
    forward and reverse inputs and a single common so I assume the speed control
    should be on the low side. I figure adding a PWM routine to the PIC program
    would be the way to do it.

    The motor will draw about 120 amps under full load (which will be rare) and
    about 30 amps retrieving the last few feet of anchor anchor rode when the
    PWM will be required. I have a pile of IRFZ48V MOSFETS that are good to 72
    amps at 12 mOhms on resistance and wonder if they would be of use stacking 4
    of them in parallel. It also appears that some sort of diodes would be
    required accross the motor terminals to protect the MOSFETs from voltage
    spikes the current stops.

    The questions are, am I on the right track and if so, what do I use to drive
    the MOSFETs?

    --
    Glenn Ashmore

    I'm building a 45' cutter in strip/composite. Watch my progress (or lack
    there of) at: http://www.rutuonline.com
    Shameless Commercial Division: http://www.spade-anchor-us.com
     
  2. Rich Grise

    Rich Grise Guest

    Yes, it sounds like you're exactly on track, although this is kind of an
    advanced project to do from scratch, depending on how much experience you
    have with building stuff.

    Since you have 12V, all you need to drive the gates is something that can
    provide current to charge/discharge the gate capacitance as fast as
    possible. From what I've read, MOSFETs parallel really nice since Ron has
    a postiive tempco, or something like that. I haven't been keeping up with
    the latest chips and stuff, but I'm sure somebody's making something. Try,
    for example:
    http://www.google.com/search?q=mosfet+gate+drivers&btnG=Google+Search

    Good Luck!
    Rich
     
  3. cpemma

    cpemma Guest

    Download the kit instructions
    http://www.oatleyelectronics.com/kits/k098.html

    There's a 20A 12V circuit that looks upgradeable.
     
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