Controlling a Trolling Motor

Discussion in 'General Electronics Chat' started by DRock, Jan 9, 2013.

  1. DRock

    Thread Starter Member

    May 7, 2011

    I want to use this 50A PWM DC Motor Controller from Sparkfun to control a 12V trolling motor:

    But I also need to be able to switch polarity on the fly because I might need to change directions suddenly. I use a DPDT switch right now with direct wires from the motor to the battery so it's either full on or full off and the switch seems to get pretty hot after running for a while...I don't think the switch is rated for high current. I am not exactly sure how many amps the motor draws but it's around 50-55 so do you guys think I will be able to run this combo for a couple hours while trolling some lures?

    If not can you recommend something I could build that would accomplish this?

  2. SPQR


    Nov 4, 2011
    Can you identify the trolling motor you use?
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    "Pretty hot" isn't a good thing with a switch as it is not supposed to do that at all! Plus here it is using up some of your precious battery power. You need both a switch and a Motor Controller rated more then the motor is to keep things safe, cool, and working for the long term.

    "How long" you can run depends on how much current you send to your motor, and how much your battery can store. For example, if you buy a 100 amp-hour marine deep discharge battery (hint hint get such a battery) you can only run a 50 amp motor for... oops, not 2 hours, somewhat less. You only get 100 amp-hours when you use it over 20 hours, or a 5 amp load. Besides, you don't want to use 100% of the energy in the battery or you will kill even a deep discharge battery.

    I would figure 1 hour of intermittent power from such a rig (100AH battery, 50A motor)... knowing I have some spare energy at the end should I have an emergency.

    It would really help to know how much current your motor takes. The first problem with telling how much current a trolling motor needs is you first have to put it in water to make that measurement.
  4. DRock

    Thread Starter Member

    May 7, 2011
    It's a 55lb thrust Minn Kota Endura C2 and I was told they make around 1A per pound of thrust so it's close to 55A. I don't think the 50A PWM I linked will work because I want to be able to go full throttle across the lake in my 10' boat which might take 15 minutes or so. I was thinking of water cooling it and then maybe it will work but if I can build one that could be a possibility also.

    Basically the stock speed controller broke and I would like to have the full 0%-100% speed range instead of 5 set speeds.

    I want to eventually install a water speed sensor and feed that back to the PICAXE to control the speed of the motor so that I can maintain a constant trolling speed.

    I am also having trouble sourcing a DPDT switch that I can use reliably at this current level...any recommendations?

  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Googling the current gets me numbers such as 1.1 to 1.3 for the factor for currrent from thrust. That's a max of 71.5 amps, and one expensive switch to do that.

    Doesn't this thing already come with a 5 speed reversing controller? Why don't you want to use that? If the location is poor... move it! The Minn Kota replacement switch is on EBay for under 30 bucks if you want to leave the handle intact (I would).

    It seems the speed control is made by energizing more or less of the motor windings... this is an excellent and efficient way to do it, better then any controller you could build.

    You could just extend the 4 wires from the motor to the new control station... using good connectors and wire of the same (or larger) gauge as inside the motor housing.

    From the C2 manual:

    • M1.GIF
      File size:
      11.3 KB