Grounding TM and Crank Battery to Eliminate Interference

[BassCatKev]

I've done a lot of research on this site regarding trolling motor electronics interference. I pretty much know all the things to check and try. I've screenshotted a ton of old posts so that I can go through an entire checklist. I also read where you only truly know if you have fixed the RFI by having your boat in the water to test the results since water is a grounding element. I want to have everything available with me next time I'm on the water.

If I want to ground my trolling motor battery to my crank battery I've read to use 18 gauge wire. So when people do this, do they literally just take some black wire and put ring terminals on both ends and hook from negative post of trolling motor battery to neg post of crank battery (my electronics are powered from crank battery)? I already know it needs to be the last (what most call it) battery in the tm series (the one the tm power wires run up front from). Does it have to be 18 gauge wire? I have some that I think is a little thicker.
My last of my trolling motor series batteries is very close to my cranking battery so I really just need to make it the length that reaches from post to post correct? In my case it may be something like 15 to 18 inches or less.
I thought I would try that before having to run a ground wire from say trolling motor transducer mount screw all the way back to the tm battery. Or the other one I read that said bow dash to tm battery. Those are long runs that I'd rather not do for I've never even fished wires before.
Thanks as always.

[TomP.]

I have always grounded the trolling motor skeg to my starting battery ground any ground wire under the front deck that goes to the starting battery will work. I have never knock on wood had any interference from my trolling motor doing it this way. Interesting I have never run across grounding trolling motor battery to starting battery.

[CatFan]

Is your TM US2? If so, any connection between the TM and cranking battery will create a lot of interference because it will blow the noise reduction circuit fuse in the TM head.

[rfdong]

Is your TM US2? If so, any connection between the TM and cranking battery will create a lot of interference because it will blow the noise reduction circuit fuse in the TM head.

so is ther any way to decrease using US2? Will grounding TM neg to Cranking neg take care of this?

[CatFan]

so is ther any way to decrease using US2? Will grounding TM neg to Cranking neg take care of this?

ANY connection will increase noise on US2. If you have interference on a US2 transducer, odds are good the fuse is blown.

[rfdong]

ANY connection will increase noise on US2. If you have interference on a US2 transducer, odds are good the fuse is blown.

Sorry to ask again Catfan but would the neg to neg ground wire solve this?

[CatFan]

Sorry to ask again Catfan but would the neg to neg ground wire solve this?

No, it would cause it. Benefits of the working noise reduction circuit are better than a ground connection.

[BassCatKev]

Is your TM US2? If so, any connection between the TM and cranking battery will create a lot of interference because it will blow the noise reduction circuit fuse in the TM head.

No sir I don't have the one with ducer built in. I believe that's what the US2 is.

[lpugh]

John I have read your posts for some time and I am impressed with your knowledge on the subjects. It appears you have deeper unstanding up electronics and batteries than I do and I belive that I am better than most with automotive and marine electrical systems.

The question I have for you is if not using the US2, would there be any disadvantage or harm to connecting the grounds together.
The reason I ask that is that I get a 2 to 300 mv reading between the grounds which to me means very small amount of current flow between the TM and the big motor when the TM is deployed. I did have a blown 3 amp fuse recently that I found no reason for and concluded it may have been caused by the battery charger or water intrusion getting the US2 wet. I did get about 200ma of current flow thru the 3 amp circuit when the TM is operating or on the battery charger. I also question if the motor case sections had a poor ground due to loose thru bolts if that would cause additional current thru the 3 amp fuse
I also know from saltwater salmon fishing that some fish are effected by this voltage in the water column via down rigger cables. I would appreciate your opinion on this

I do not have any interference issues at all on my graphs

[CatFan]

John I have read your posts for some time and I am impressed with your knowledge on the subjects. It appears you have deeper unstanding up electronics and batteries than I do and I belive that I am better than most with automotive and marine electrical systems.

The question I have for you is if not using the US2, would there be any disadvantage or harm to connecting the grounds together.
The reason I ask that is that I get a 2 to 300 mv reading between the grounds which to me means very small amount of current flow between the TM and the big motor when the TM is deployed. I did have a blown 3 amp fuse recently that I found no reason for and concluded it may have been caused by the battery charger or water intrusion getting the US2 wet. I did get about 200ma of current flow thru the 3 amp circuit when the TM is operating or on the battery charger. I also question if the motor case sections had a poor ground due to loose thru bolts if that would cause additional current thru the 3 amp fuse
I also know from saltwater salmon fishing that some fish are effected by this voltage in the water column via down rigger cables. I would appreciate your opinion on this

I do not have any interference issues at all on my graphs

The only disadvantage would be the risk of shorting a battery In the event you need to jump start from a TM battery. The one with the shared ground attached is fine, but Murphy will have somebody connect to the wrong one. I like to see the wire connecting them have about a 3A fuse in it as a backup.

[Bradrodfish]

Guys
You all need to pay attention to Catfan's recommendations. He is correct about increasing noise. The potential of electrolysis also exist in grounding the Troll motor batteries and cranking batteries. Please also note that all Late model Minn Kota troll motors have internal grounds. Not just the US2 ones. Check your fuse if you have one. It is in the head.

[BassCatKev]

I have read all the posts and as the OP I do not have the Universal tm with ducer inside. I have a 83/200 tm mount ducer. I don't even know if grounding crank and tm batteries will even be what eliminates my RFI. I just want to understand this tm/crank ground option.
Just a piece of wire with 2 rings neg post to neg post?
1 amp fuse or 3 amp fuse? What gauge wire?
Do any of you feel that this whole topic should be the last option or not an option at all to eliminate rfi?


I have thousands invested in this and I'm going to learn all options to make them work correctly. If this grounding shouldn't be done at all please let me know.
I'm holding back other questions regarding fuse in tm head and other things since my OP was specific to making this wire.
Thanks

[TomP.]

I am using my SI transducer mounted to my trolling motor and grounding the trolling motor case to the starting battery ground has worked on getting rid of interference on every trolling motor I have put on my boat. Many times what happens is the ground inside the trolling motor is not adequate. It is just what has worked for me and many others.

[lpugh]

Thanks John,
I have read several articles on interference that have mentioned that additional grounds can in fact increase interference and I get, as it also increase the wire run lengths which can also increase interference IE: a bigger antennae
I guess like most things its a compromise

[ifishinxs]

I am using my SI transducer mounted to my trolling motor and grounding the trolling motor case to the starting battery ground has worked on getting rid of interference on every trolling motor I have put on my boat. Many times what happens is the ground inside the trolling motor is not adequate. It is just what has worked for me and many others.

It worked well for me when I had a Minnkota Maxuum..I have zero issues with the Ultrex.

[TomP.]

What I think makes the big difference is wrapping the ground wire around the external transducer wire and acting as RF shield.

[BassCatKev]

Regarding my op... If I end up wanting to try eliminating my rfi issue by grounding tm battery to crank battery, I simply take the wire I just rigged in pic below and connect to the neg posts of each battery......correct? Wire in pic is either 16 or 18 gauge

[grout-scout]

Regarding my op... If I end up wanting to try eliminating my rfi issue by grounding tm battery to crank battery, I simply take the wire I just rigged in pic below and connect to the neg posts of each battery......correct? Wire in pic is either 16 or 18 gauge

Don’t do it, you can eat up your motors.

[BassCatKev]

I read a thread about this but after much discussion it ended up being an improperly wired tm battery series and/or an older model charging system. I know it's asking a lot but check out post #8. I think you were part of this thread as well. Maybe it's still not a good thing to do. If you are absolutely certain or want me to verify anything in my specific system please say so. I'm hoping one of the pros on here (That may be you) can tell me DEFINITIVELY if this is a viable option or not. If I wasted 2 ring terminals and a piece of wire so be it.
http://www.bbcboards.net/showthread....r+wire+routing

[Rip Bass]

Regarding my op... If I end up wanting to try eliminating my rfi issue by grounding tm battery to crank battery, I simply take the wire I just rigged in pic below and connect to the neg posts of each battery......correct? Wire in pic is either 16 or 18 gauge

You can use that wire but I would definitely use an in line fuse,3a. Grounding the batteries together can cause electrolysis but it won’t hurt to try it long enough to see if it stops the interference. If it does cause electrolysis, you should see it in a few hours of use.Some guys have fixed interference with ferrite rings,something else to try if you haven’t.