Electrolysis on trolling motor & outboard prop

[ICALDUX]

Hello all,
I recently installed a new HUMMINBIRD HELIX 12 at my console. I ran an independent wire from cranking battery to unit. I put inline fuse at cranking battery positive connection. I’m also installing a HELIX 9 at the bow which I’m waiting on still. I have an 24V 80 lb Ultrex with built in US2 transducer. Seeing that I am installing a transducer to trolling motor for MEGA DI I disconnected transducer wire in trolling motor head. I also found 3A fuse blown at head and replaced. There’s no other changes to boat or wiring. Would I have caused the issue by disconnecting US2 transducer? I believe there’s a ground loop in it but wouldn’t that be if it were attached to a graph? The ground cable at my outboard is good. I’ve got a 2017 Ranger Z518. I also noticed that my trolling motor wires come in and land on different batteries. Positive comes from trolling motor goes through breaker then lands on positive of rear battery(closest to transom). Negative comes from trolling motor & lands on negative of forward battery (closest to passenger seat). Also there is a negative cable going from negative of rear battery going to negative of cranking battery. Any help is much appreciated & thank you in advance for any help.

[CatFan]

Also there is a negative cable going from negative of rear battery going to negative of cranking battery.

This is why the 3A fuse was blown and will blow again as soon as everything is powered up. It's also on the wrong battery which is why you have the electrolysis. Just remove the jumper between the cranking battery and TM battery and you should resolve the problem. If you have a jump start system, the jumper needs to be moved to the battery with the TM negative on it.

[ICALDUX]

This is why the 3A fuse was blown and will blow again as soon as everything is powered up. It's also on the wrong battery which is why you have the electrolysis. Just remove the jumper between the cranking battery and TM battery and you should resolve the problem. If you have a jump start system, the jumper needs to be moved to the battery with the TM negative on it.

CatFan, thank you very much for the response. I do have a factory installed jump switch. I replaced the fuse yesterday as I was reading about interference and read about a 3A fuse that could cause interference if blown. I was on the water today and when pulling up the trolling motor to leave the first spot I noticed the electrolysis. For the hell of it I checked the 3A fuse and it was still good. I went ahead & put the boat back on the trailer & came home. I did find that the TM batteries were wired incorrectly. The negative from cranking battery was going to negative on battery #2 which the TM positive wire lands on. So I moved that over to the #1 battery which the TM negative lands on. Also after changing the wires I checked the 3A fuse & it’s still good. Can you think of why this may have happened like that. With the blown fuse and wired incorrectly I never had an issue. I replaced the fuse & first trip out I have electrolysis. Is it because the fuse is in the ground loop? I’m at a loss. Again thank you for your response & any insight.

[CatFan]

CatFan, thank you very much for the response. I do have a factory installed jump switch. I replaced the fuse yesterday as I was reading about interference and read about a 3A fuse that could cause interference if blown. I was on the water today and when pulling up the trolling motor to leave the first spot I noticed the electrolysis. For the hell of it I checked the 3A fuse and it was still good. I went ahead & put the boat back on the trailer & came home. I did find that the TM batteries were wired incorrectly. The negative from cranking battery was going to negative on battery #2 which the TM positive wire lands on. So I moved that over to the #1 battery which the TM negative lands on. Also after changing the wires I checked the 3A fuse & it’s still good. Can you think of why this may have happened like that. With the blown fuse and wired incorrectly I never had an issue. I replaced the fuse & first trip out I have electrolysis. Is it because the fuse is in the ground loop? I’m at a loss. Again thank you for your response & any insight.

Your TM lower unit was 12V below the outboard lower unit, so current would flow between them when in the water. The fuse shouldn't have affected it.

[wmitch2]

Your TM lower unit was 12V below the outboard lower unit, so current would flow between them when in the water. The fuse shouldn't have affected it.

So, what does the fuse protect ? And what is affected when it is blown ?? I found mine had blown, replaced it, but couldn't tell anything different.

[PJ-Rohlf]

So, what does the fuse protect ? And what is affected when it is blown ?? I found mine had blown, replaced it, but couldn't tell anything different.

I may be wrong but I believe it has something to do with the universal sonar transducer power.

[ICALDUX]

So, what does the fuse protect ? And what is affected when it is blown ?? I found mine had blown, replaced it, but couldn't tell anything different.

My understanding is that it is a “bonding loop” if blown sometimes it will cause interference with the electronics displays. I’m not even sure how long it had been blown. But I was getting interference with my graph at the bow when I stepped on trolling motor switch. It was like a spike each time I applied power. That is gone now. I just hope correcting the cable wiring at TM batteries solves electrolysis problem.

[Lou r Pitcher]

So, what does the fuse protect ? And what is affected when it is blown ?? I found mine had blown, replaced it, but couldn't tell anything different.

If we consider below using a training technique called hole flow theory where current flows from + positive to the (-) negative terminal......

A trolling motor at full speed may use 50 or so battery amps which would after they turn the motor would flow through the trolling motor power circuit to return to the (-) trolling motor battery connection.

If the wire or connection on the trolling motor battery circuit was ever broken,corroded or just not be 0 ohms, the 60 amps will flow along the least resistive path to reach the trolling motor battery they came from. With US2 trolling motors, that could be through the transducers shield, then through the sonar unit, then though its unfused black power wire to reach the cranking battery negative connection which in some boat setups has been bridged (bonded) over to the trolling motor battery negative post.

No way that a delicate transducer shield, the sonar interna lwiring and sonar power wiring can flow the heavy trolling motor amps. So the sonar graph circuit would overheat/melt if it were not for a small amp protection fuse used in the the trolling motor.

If the fuse blows, no overheat occurs, but the US2 sonar circuits in bonded trolling motor battery/cranking battery boats no longer have the 'Faraday shielding' effect of the lower trolling units metal housing, The motor and lower unit with the open fuse behaves as an unshielded RF antenna sending unwanted interference into the US2 circuit and your sonar display.

[E-rude_Dude]

I guess I’ve been lucky. I’ve never had interference issues with the 4 boats I’ve owned. My current tin boat has a MG TM with HB graphs too.

[Lou r Pitcher]

I guess I’ve been lucky. I’ve never had interference issues with the 4 boats I’ve owned. My current tin boat has a MG TM with HB graphs too.

That luckiness may be because your cranking batteriywas never bonded over to your trolling motor batteries or you used an ext transducer and left your US2 circuit unconnected.

[wmitch2]

That luckiness may be because your cranking batteriywas never bonded over to your trolling motor batteries or you used an ext transducer and left your US2 circuit unconnected.

That must be it for me, as I don't use the US2.