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  1. #1
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    Default can you change polarity on motor???

    a brief history first...
    i bought an old johnson trolling motor on craigslist for about 50bucks... i its a bow mount... it had an old prop on it, so after a few crappy displays of 24lb performance, i decided maybe the prop needed changing.so i cut off the old fishing line i found around drive shaft... and put the new minn kota prop on ( i couldnt find any johnson props ) i had to modify the prop a little, it was easy... so i got the prop on and i noticed that the pitch on the prop was the opposite as the one that came with it and when i ran the motor that the wind the prop created was blowing the wrong way... i took it to the lake this way, and it was nearly impossible to use, i had to use both feet and could only turn with the motor off...

    so knowing all this brings me to my question...

    is it possible to change the polarity so that the blade spins the other way??? and if it is possible, will it damage the motor in any way???

    thanks
    zuke

  2. #2
    Commander ricksrster's Avatar
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    Default Re: can you change polarity on motor???

    Reversing the polarity should make it run backwards.
    "Many of the greatest sailors were pukers."--Thorfinn Skullsplitter

  3. #3
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    Default Re: can you change polarity on motor???

    so, this wont affect the long term perfomance at all???

    im just afraid it will somehow short circuit the motor, then ill be in a worse situation then before now...

  4. #4
    Commander ricksrster's Avatar
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    Default Re: can you change polarity on motor???

    If there are diodes in the circuit it could be damaged. If you have a wiring diagram for the motor, look for diodes. They will look like this --->l--- with the > filled in solid.
    "Many of the greatest sailors were pukers."--Thorfinn Skullsplitter

  5. #5
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    Default Re: can you change polarity on motor???

    Almost any newer (last 15 years) electrical device tends to have some polarity-sensitive solid state parts in it (perhaps just diodes as suggested). The obvious place is the speed control. I think it has been a long time since these were just simple rheostats. I would think it unlikely you could reverse the polarity unless the thing is really old. Of course a schematic would tell all.


  6. #6
    Lieutenant xtraham's Avatar
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    Default Re: can you change polarity on motor???

    could reverse the polarity at the motor itself if you want to dissasemble it, better to get the right prop..........

  7. #7
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    Default Re: can you change polarity on motor???

    as i said before, the motor is an old johnson trolling motor... i dont know the last time johnson made a trolling motor, but there is no replacement prop i can find...

    i will try an reverse the polarity today, ill let you know how it goes...


  8. #8
    Fleet Admiral jtexas's Avatar
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    Default Re: can you change polarity on motor???

    I hooked up my trolling batts bassackwards once...motorguide not sure of the year but the model was introduced in 2000...I was so confused for about a half hour...just couldn't get control of it thought somebody musta drugged my coffee... 8)

    my opinion, if it don't start a fire in the first 5 minutes, won't harm anything...I'm no engineer, rely on this at your peril, recharge your fire extenguisher, yada yada yada...

    oh yeah, forgot to mention...any body'd design a trolling motor with diodes that could be smoked by hooking a battery up backwards should be [fill in your favorite form of punishment here]...remember it's people like Bill Dance that have to use 'em!
    It's all about the tools.

    "If the ocean is glass flat and the sun is shining, you open up the special memory compartment of your brain and start recording the smells, sounds, sights and feelings." -- Philster

    "Poets talk about 'spots of time,' but it is really fishermen who experience eternity compressed into a moment. No one can tell what a spot of time is until suddenly the whole world is a fish and the fish is gone. I shall remember that son of a b**** forever." -- N. Maclean

  9. #9
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    Default Re: can you change polarity on motor???

    ok...

    so going off the last post, i switched the polarity ( put pos to neg and vise versa) i ran it for what felt like 5 minutes... no smoke, and no strange smells, and it seemed to work well, and this time the prop was spinning the same way...

    i am going to lake roosevelt on monday, so ill let you guys know how it goes...

    thanks for the help

    later
    zuke

  10. #10
    Commander ricksrster's Avatar
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    Default Re: can you change polarity on motor???

    I thought maybe they would use some modern type of circuitry in the speed control.
    "Many of the greatest sailors were pukers."--Thorfinn Skullsplitter

  11. #11
    Fleet Admiral Texasmark's Avatar
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    Default Re: can you change polarity on motor???

    If you are that inquisitive, just (disconnect power lines from the battery) remove the covers from the top of the motor and have a look around. While there, see how many wires go down to the motor.... If only 2 great.

    If you don't see any electronic (other than switches) goodies under the cowl you should be good to go.

    Wouldn't think there would be any kind of rectifier. 2 reasons. Current too high, would generate considerable heat, and reversing polarity hurts nothing with a dc motor.

    Reversing polarity is "how you reverse" a dc motor. And if you are concerned about shorting something out, measure to the metallic case of the motor (ground) from each wire coming up from the motor....may have to disconnect them from where they are currently attached too get an accurate reading. They should be isolated. If not it won't work because your motor case will be sitting at 12v when you reverse the wires. But, as I said, if you have 2 wires coming up you're probably ok. I wouldn't think that the designer would rely on the physical parts to make the return path for current to the motor....doesn't make good design sense.

    Then the only question is, did they ground the case to the battery - terminal.....but you don't care.

    If the 2 wires going to the motor are isolated from ground, just reverse them where they connect to whatever they connect to. Everything else can remain the same including leaving your + and - wires to the battery on the same terminals as they were previously.

    Mark
    If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

  12. #12
    Fleet Admiral jtexas's Avatar
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    Default Re: can you change polarity on motor???

    Motorguide 5-speed foot controls (and most minnkotas I think) with have 4 wires going to the motor...3 from the speed dial plus the ground wire directly from the plug. They get 4 speeds from two of the wires via an arrangement of resistors, and hi-speed from the third.
    Just talking about pre-electronic-controls era motors. I got this from schematics at mikesreelrepair.com - they've got minn-kota and MG, sorry no Johnson. But I doubt the technology is all that different.

    I have no experience with the newer fly-by-wire motors with electronics...but I sure hope they are designing some idiot-proofing into them.

    I disassembled my foot contol and cleaned and sanded every contact point...surprising improvement in performance.
    It's all about the tools.

    "If the ocean is glass flat and the sun is shining, you open up the special memory compartment of your brain and start recording the smells, sounds, sights and feelings." -- Philster

    "Poets talk about 'spots of time,' but it is really fishermen who experience eternity compressed into a moment. No one can tell what a spot of time is until suddenly the whole world is a fish and the fish is gone. I shall remember that son of a b**** forever." -- N. Maclean

  13. #13
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    Default Re: can you change polarity on motor???

    Quote Originally Posted by zuke1
    ok...

    so going off the last post, i switched the polarity ( put pos to neg and vise versa) i ran it for what felt like 5 minutes... no smoke, and no strange smells, and it seemed to work well, and this time the prop was spinning the same way...

    i am going to lake roosevelt on monday, so ill let you guys know how it goes...

    thanks for the help

    later
    zuke
    Two things to note; It's too late now but for future reference, it may not be a good thing to run the motor out of the water for extended periods. They often rely on the water for cooling the motor.

    As mentioned, make sure you verify that any exposed metal surfaces do not have +12 VDc on them now. Years ago, they took shortcuts and the entire assembly may not have been insulated. Reversing polarity may put +12v batt power on the metal shaft etc. Just a precaution...

  14. #14
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    Default Re: can you change polarity on motor???

    I have an old "Monkey Ward" 3 speed electric from the 60's. This type just uses a 3 position switch with resistors and a rocker switch to reverse polarity. Many times I inadvertantly hooked up the battery clips backwards and had 3 speeds in reverse and1 forward with no ill effects. However, at all times, the battery was isolated from the aluminum boat hull. I can see the possibility of a short circuit happening if I had the battery minus connected to the hull through other devices.
    In my case, as a portable unit w/battery, it worked out fine!

    CD

  15. #15
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    Default Re: can you change polarity on motor???

    Why not just find one online that fits it right and save your self some time and effort by not messing the whole thing up and never using it again.

    http://www.youngprops.com/johnson.htm

  16. #16
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    Default Re: can you change polarity on motor???

    ok... took it to lake pleasant az today.. the motor did really well, and felt much more powerful than before... it did seem to drain the battery a little faster though...

    so, i still need a new trolling motor though...

    well, thanks for all the help...

    zuke out...


  17. #17
    Fleet Admiral Texasmark's Avatar
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    Default Re: can you change polarity on motor???

    Well dude, if it did better than before, it obviously drained your battery more than before since it must have been sucking more amps to get the power to do more than before. No brag, just fact. 8)

    Mark
    If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

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