Trolling Motor Interference

Ok, I have done a lot of searches and looked through different forums but I'm not finding what I am looking for. Here is my situation, Lowrance HDS Carbons front and rear, 24 v MotorGuide XI3 with Pinpoint GPS. I have 2 12 volt batteries run in parallel for the TM. Then I run 1 HDS off 1 battery and the other HDS of the other battery. The only transducer I have is on the back of the boat (which is a 16' Lund, all aluminum). As you can guess when I run the trolling motor I get interference on the graphs. I have read about using chokes, running a ground from the TM skeg to the battery, twisting power wires, shielding cables and have found some of these work and some don't. Now to my problem, If I take a wire and run it from the ground side of either battery to the hull of the boat, it clears up the interference on both graphs. I have read that this is a bad thing because it produces electrolysis and will destroy an aluminum boat. Is this true or is it ok to do. I don't understand why this simple connection clears up the interference on both graphs. Everything is run in a closed circuit, I'm not using the hull as a path for any of the circuits so I don't understand why hooking this wire from the negative battery to the hull would cause electrolysis. If anyone has any wisdom into this matter please spread the wealth. Thank you.

I would believe that the hull is grounded anyway. The outboard motor mounts directly to the hull. In my opinion it would be better to have the hull grounded. No difference in electrical potential therefore no chance in any galvanic action. To clarify I would ground or bond the hull to the negative side of the battery. I would not use the hull as a ground path back to the battery. I would still run both positive and negative wire to each device being powered.

I guess I left that part out. The outboard is pull start, no electrical start. Don't know if that figures in or not. But yes I am not using the hull as a path back to the batteries or for any of the electrical circuits. I just don't understand why grounding the battery to the hull clears up all the interference on the graphs from the TM. Thanks for your input.

It seems the hull is picking up interference from the trolling motor wires running thought it. It may be worth putting both graphs onto one battery. That would eliminate any difference in potential between the two graphs

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Originally Posted by goinfishin

Ok, I have done a lot of searches and looked through different forums but I'm not finding what I am looking for. Here is my situation, Lowrance HDS Carbons front and rear, 24 v MotorGuide XI3 with Pinpoint GPS. I have 2 12 volt batteries run in parallel for the TM. Then I run 1 HDS off 1 battery and the other HDS of the other battery. The only transducer I have is on the back of the boat (which is a 16' Lund, all aluminum). As you can guess when I run the trolling motor I get interference on the graphs. I have read about using chokes, running a ground from the TM skeg to the battery, twisting power wires, shielding cables and have found some of these work and some don't. Now to my problem, If I take a wire and run it from the ground side of either battery to the hull of the boat, it clears up the interference on both graphs. I have read that this is a bad thing because it produces electrolysis and will destroy an aluminum boat. Is this true or is it ok to do. I don't understand why this simple connection clears up the interference on both graphs. Everything is run in a closed circuit, I'm not using the hull as a path for any of the circuits so I don't understand why hooking this wire from the negative battery to the hull would cause electrolysis. If anyone has any wisdom into this matter please spread the wealth. Thank you.

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Well, I hear all kinda stuff about electrolysis. Keep your hull clean will help the most.

The motor is grounded to the hull via contact and bolts and also via the starter ground cable which connects to battery negative, thus tying the start battery negative to hull via the motor. The sacrificial anode should help electrolysis in this configuration. That is what it is for.

The ground returns should have a single point return, which is the motor ground via the start battery negative.

Any power ground that runs more than 1 foot length parallel to a signal lead is subject to crosstalk. Moving the rats nest sometimes fixes problems.
There is no known out the box cure for noise. Trial and error rules.




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Twisted wires and ferrite cores help enough innthe industrial world that we use the a lot to prevent cross talk on our control wires and circuits. Having one end of a sheilded cable grounded also helps plenty. If the tranducer cable has a sheild the head unit should have it grounded already from the factory. A fella could use a Dc to Dc converter. Run 24 volts to the converter step down will step it down to 12 volts and should clean it up also.

Independent battery to electronics and keep those wires as far away from trolling motor wiring as possible.
Just my opinion for sure!!
Chuck


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Quote:

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Originally Posted by Chuck Adams

Independent battery to electronics and keep those wires as far away from trolling motor wiring as possible.
Just my opinion for sure!!
Chuck


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That would definitely be the easiest thing to do.
I wonder if the interference is being induced on the transducer cable itself. That would be another area it could come from. We use and aluminized cable wrap /jacket on some of our robot control cables that run through areas of the machines to cut down the interference

Quote:

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Originally Posted by Chuck Adams

Independent battery to electronics and keep those wires as far away from trolling motor wiring as possible.
Just my opinion for sure!!
Chuck



Sent from my iPhone using Crappie.com Fishing mobile app

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This can also create problems. Unless the negative of the battery is referenced to the hull ground aka TM ground, you have an isolated power or floating power condition. This isolation is subject to stray rf.

IF you have a MK trolling motor with built in transducer, there is a ground wire via cable that connects to the head unit via the transducer connector. This small wire ties the isolated battery to the tm battery in this configuration. Expect noise.