Need PWM ctlr for 12VDC Motor

Discussion in 'The Projects Forum' started by Jack_K, Aug 22, 2012.

  1. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    I need to control the speed of a 12 VDC motor on a fishing boat. The speed will be determined by the resistance of a pot connected to the "gas" pedal. The motor draws as much as 50 amps I'm told.

    I assume a PWM controller would be the best way to go? I've searched the archives but haven't found what I need.

    A schematic and some explanation of the circuit is what I'd like.

    Anybody up for this?

    Thanks,
    Jack
    P.S. This is a personal project.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I'd say you are not looking well enough!
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    50 amps huh? You might need to supersize your order or you could end up with fries as well.

    :D
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Yup ! Way over there!!
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    http://www.cfnet.net/tm/

    The gentleman there is using a 'Chinese Electric Scooter PWM speed controller' for his trolling motor.

    Perhaps you should check this out for your needs. Maybe even just to purchase and examine for ideas.
     
  6. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    Any suggestions?
     
  7. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    That's an interesting post. However, I'd like to build my own. That's why I asked for help and maybe a schematic or two.

    Thanks,
    Jack
     
  8. wayneh

    Expert

    Sep 9, 2010
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    PWM is definitely the approach you want, and the schematic is theoretically not all that complicated. The problem is the power rating, which requires special parts and mechanical solutions to dissipate heat, eg. big heat sinks.

    I'm wondering what the REAL draw is for your motor. I mean, it might draw 50A when you start at full speed from a dead stop, or if it fouls with weeds or sand or whatever. But under normal operation where you want speed control, it's probably far less.

    That makes me wonder if there couldn't be some sort of kick-in, kick-out relay where the PWM circuit would be bypassed if the current load gets too high. PWM control would only kick in when amps fall below, say, 10A.

    I have no idea how practical this is to implement. Just a wild idea.
     
  9. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    I agree that the startup or stall current is probably the max of 50 amps. The spec said 50 amps maximum, no explanation.

    The running current is prpbably more likely 20-30 amps.
     
  10. wayneh

    Expert

    Sep 9, 2010
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    Hmmm, well at my level of expertise (not so much), 30A might as well be 300.

    You might benefit from reading this thread.
     
  11. Jack_K

    Thread Starter Active Member

    May 13, 2009
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    Thanks. I had already read that thread. I had even considered using a one-shot like the 74LS123 or newer variants.

    That's still not what I'm looking for though.

    Jack
     
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