# Why you should disconnect power to your trolling motor before charging



## Viking1 (May 23, 2010)

According to the Minn Kota owners manual you should not charge your battery while your trolling motor is attached. It seems they have added a wire to reduce interference with sonar and if you charge your battery with the TM connected it can short out the control module. Recently I did not unplug my TM while charging and guess what...just spent $250 getting the control module replaced. Below is the verbiage from the Minn Kota Owner's manual.

"Your Minn Kota trolling motor may be designed with an internal bonding wire to reduce sonar interference. Most alternator charging systems do not account for this bonding wire, and connect the negative posts of the trolling motor batteries to the negative posts of the crank/starting battery. These external connections can damage connected electronics and the electrical system of your trolling motor, voiding your warranty. Review your charger’s manual carefully or consult the manufacturer prior to use to ensure your charger is compatible." 

Hope this PSA helps you avoid problems!


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## Darkstar (Feb 2, 2017)

Just curious what amperage your charger was operating at? I just picked up a new powerdrive and am about to do the install.


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## bobber (Sep 29, 2015)

This has been a known problem since the first "digital" trollers were introduced 20 years ago. Took both Minnkota and Motorguide quite a while to acknowledge the potential problem, glad to see they are more upfront about it now.
Simple solution is a manual on/off circuit breaker between the battery(ies) and the troller. And remembering to use it before plugging in the charger.


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## LtShinysides (Dec 27, 2018)

bobber said:


> This has been a known problem since the first "digital" trollers were introduced 20 years ago. Took both Minnkota and Motorguide quite a while to acknowledge the potential problem, glad to see they are more upfront about it now.
> Simple solution is a manual on/off circuit breaker between the battery(ies) and the troller. And remembering to use it before plugging in the charger.


This. Don't ask how I know ...just make sure to get the right amp circuit breaker.


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## RaspberryPatch (Dec 17, 2016)

A circuit breaker functioning as a secondary switch to disconnect is good, but it is probable voltage and the cleanliness of the power that is harming the electronics.


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## firecat1981 (Nov 27, 2007)

So what do you do if you have an ACR and a GPS trolling motor? 

Sorry but their solution doesn't hold water for me. So the manufacturer wants me to disconnect my trolling motor, canceling out the GPS lock, every time I move spots? Or just never have the ability to charge your battery while running?


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## devrep (Feb 22, 2009)

"Your Minn Kota trolling motor may be designed with an internal bonding wire to reduce sonar interference. Most *alternator charging systems *do not account for this bonding wire, and connect the negative posts of the trolling motor batteries to the negative posts of the crank/starting battery. These external connections can damage connected electronics and the electrical system of your trolling motor, voiding your warranty. Review your charger’s manual carefully or consult the manufacturer prior to use to ensure your charger is compatible."


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## firecat1981 (Nov 27, 2007)

"Your Minn Kota trolling motor may be designed with an internal bonding wire to reduce sonar interference. *Most alternator charging systems do not account for this bonding wire, and connect the negative posts of the trolling motor batteries to the negative posts of the crank/starting battery. These external connections can damage connected electronics and the electrical system of your trolling motor*, voiding your warranty. Review your charger’s manual carefully or consult the manufacturer prior to use to ensure your charger is compatible." 

The way this reads, you should never charge with your alternator/stator, and only certain approved chargers will work. Just take out the bonding wire or isolate it better? Seems this shouldn't be an issue for a $1500 piece of equipment.


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## jimsmicro (Oct 29, 2013)

There's a big difference between how an alternator works and how a rectifier works. If MK is using the word "alternator" literally and correctly then most anybody with a true skiff doesn't have to worry about this at all because every small engine under like 150 horsepower is going to use a rectifier and not an alternator.


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## Darkstar (Feb 2, 2017)

firecat1981 said:


> So what do you do if you have an ACR and a GPS trolling motor?


Exactly what I plan to do using a blueseas mini add-a-battery plus kit. Hoping to charge the trolling motor battery while running. Does anyone else have a similar setup? Any issues I should know about? Charging from a Yamaha 70tlr.


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## Viking1 (May 23, 2010)

Darkstar said:


> Just curious what amperage your charger was operating at? I just picked up a new powerdrive and am about to do the install.


I have a computerized charger that analyzes the battery and adjusts the amperage based on what's best for the battery. It also has something built into it that keeps the battery from building up sulfides. Once the battery is charged it automatically trickle charges it to keep it from discharging. Just my 2 cents, spend the extra money to get the automatic chargers.


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## Viking1 (May 23, 2010)

RaspberryPatch said:


> A circuit breaker functioning as a secondary switch to disconnect is good, but it is probable voltage and the cleanliness of the power that is harming the electronics.


Cleanliness of power is not the issue with my set up. The trolling motor is attached directly to a deep cycle battery. All connections are coated with dielectric grease and there is no corrosion. I have always had a 50 amp circuit breaker located on the positive terminal. The gas motor on the boat is manual pull start so there is no charge going to the motor while I am running. To be fair to Minn Kota the trolling motor is 10 years old, only after forgetting to unplug my TM while charging (sometimes I just push the circuit breaker sometimes I just unplug the TM) did I have the problem with the control module. After this happened I just read the owners manual and saw the warning and just passed it on.


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## firecat1981 (Nov 27, 2007)

Your trolling motor was 10 years old? Charging was not your issue assuming you used it on a regular basis. Old age was imho. Trolling motors are disposable technology these days, just like laptops, cellphones..... I would say the average life span is under 7 years on most, shorter on saltwater models.


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## Viking1 (May 23, 2010)

firecat1981 said:


> Your trolling motor was 10 years old? Charging was not your issue assuming you used it on a regular basis. Old age was imho. Trolling motors are disposable technology these days, just like laptops, cellphones..... I would say the average life span is under 7 years on most, shorter on saltwater models.


There is no way to know for sure what caused my failure but the only thing different was that I charged the battery with the TM plug in without the circuit breaker turned off. After reading the Minn Kota owners manual I became aware of the issue with the bonding wire and thought that could be the reason for the failure. I usually get about 10 years out of a TM before it dies. The MotorGuide on my Pathfinder is 12 years old and still going strong. I just make sure to wash them with fresh water, repaint housing when paint wears off and lube wire connections with dielectric grease.


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## Guvner (Jun 19, 2013)

Darkstar said:


> Exactly what I plan to do using a blueseas mini add-a-battery plus kit. Hoping to charge the trolling motor battery while running. Does anyone else have a similar setup? Any issues I should know about? Charging from a Yamaha 70tlr.


Charging from a 70TLR won't give you much excess power to charge your troller battery, even when your starting battery is fully charged. The alternator only puts out 17amps and the ACR would only take that once your starter battery is fully topped and not drawing any current.

So even a run at full WOT would at best put 17 amp hours back into your troller.

Depends on the runs you make, but for me it wasn't worth the time and money to put it on my skiff.


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## Darkstar (Feb 2, 2017)

I figured it wouldn't be a whole lot but a little is better than none. I just got a great deal on the unit and it is incorporated into a 10 amp onboard charger.


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## Tautog166 (Jul 7, 2018)

firecat1981 said:


> So what do you do if you have an ACR and a GPS trolling motor?
> 
> Sorry but their solution doesn't hold water for me. So the manufacturer wants me to disconnect my trolling motor, canceling out the GPS lock, every time I move spots? Or just never have the ability to charge your battery while running?


Maybe an email to the manufacturer would clarify this. It’s a non issue for people running their trolling motor off a dedicated battery. Just have to remember to unplug or switch the circuit off. 

How much run time are you realistically expecting with one battery on the whole boat? Running tm, bait tank, electronics, and starting the motor.


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## firecat1981 (Nov 27, 2007)

Walter Lee said:


> Maybe an email to the manufacturer would clarify this. It’s a non issue for people running their trolling motor off a dedicated battery. Just have to remember to unplug or switch the circuit off.
> 
> How much run time are you realistically expecting with one battery on the whole boat? Running tm, bait tank, electronics, and starting the motor.


An ACR set up uses 2 batteries, seperate circuits that are charged by the ACR one at a time and can be combined in an emergency to start the motor using power from both.

But to answer I get about 4 hours of medium run time on my trolling motor now, with the livewell and lights running off the same, and only battery. I still have enough juice to crank the motor.


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## Darkstar (Feb 2, 2017)

Walter Lee said:


> Maybe an email to the manufacturer would clarify this.


That is on my to do list. When I get an answer I’ll post the details.


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## Darkstar (Feb 2, 2017)

I’ve emailed both Minn Kota and Blue Sea Systems. We’ll see what they have to say.


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## Viking1 (May 23, 2010)

I did not know what an ACR was so I got this link when I Googled it: https://www.bluesea.com/support/articles/1366/Automatic_Charging_Relay_[ACR]_Explained

I always learn something new from this forum thanks to the posters that brought it up.


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## Darkstar (Feb 2, 2017)

I received a reply from both Minn Kota and Blue Sea Systems

Minn Kota

Question:
I am installing a new powerdrive 55 ipilot and also have a 7605 blue Seas add-a-battery plus system with an ACR. Will charging the trolling motor battery via the ACR cause damage to the trolling motor if it’s plugged in? Is this ACR compatible with the internal bonding wire?

Answer:
Thanks for contacting Minn-Kota. Do you have some more info on that system so we can answer you better? 
(Sent Link to Blue Seas Product Page)
Thanks for the info. That should work just fine. Sorry just have never heard of that.

That reply doesn't inspire a lot of confidence!!!

Blue Seas Systems

Question:
Installing a new trolling motor and 7605 and am concerned about damage to the trolling motor from the ACR. The following is from the trolling motor manual. Does the 7605 operate in this manner?

Your Minn Kota trolling motor is designed with an internal bonding wire to reduce sonar interference. Most alternator charging systems do not account for this bonding wire, and connect the negative posts of the trolling motor batteries to the negative posts of the crank/starting battery. These external connections can damage connected electronics and the electrical system of your trolling motor, voiding your warranty. Review your charger’s manual carefully or consult the manufacturer prior to use to ensure your charger is compatible.

Answer:
This is the first time I've heard of this issue. The 7605 does require that the start battery and the House/Aux/Trolling battery have a common negative connection. Which according to Minn Kota, may damage the trolling motor. I can't say much, other than for the 7605 to work, you will have to wire it in a way which will void the warranty on the Minn Kota trolling motor.

I find this a little odd, because standard practice for a boat is to have all battery negatives tied together, so its a bit weird that they don't want you to do that.


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## Darkstar (Feb 2, 2017)

Anyone else out there using an ACR to charge their dedicated trolling battery?


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## Imago (Aug 9, 2018)

Typical Humminbird (from a Solix 10 and Ulterra owner). What they say doesn't really make sense; as the people at Blue Sea pointed out. They don't seem to understand their own equipment, and their only concern is to absolve themselves of responsibility. That's the corporate world for you.

I was thinking of combining the circuits for my trolling motor and my starter battery. I had one starter battery run flat as I wasn't charging the battery, but relying on the 'alternator' when it was running. They drain quite quickly when not being used as the motor draws significant current even when 'off'. My boat manufacturer (Baycraft) hadn't installed a cut off switch so the only way to disconnect the motor was to uncouple the terminals. I was advised (by Blue Sea) to keep the 2 systems separate. This seems to confirm that's good advice. In the end I installed a separate charger for the starter battery and a master switch to cut off any drain on the battery. No trouble so far.

I did look at the 'mini add a battery'. but I understand it needs an additional battery. This seemed like too much weight for an 18' skiff.

Modern electronics and batteries are both very complex. Whilst most skiff electrics are ridiculously crude. Not a good combination. The idea that one should be manually uncoupling motors on modern (high expensive) boats is quite ridiculous and yet probably common. It just shows the problems with the marine industry.


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## Tautog166 (Jul 7, 2018)

I agree, “That should work just fine” does not inspire much confidence.

I guess you have to pick your poison and take your chances. Will minn Kota honor their warranty from their reply? Would they ever know if you had the Blu Seas system if you did blow your tm?

As long as I have a dedicated tm circuit, I’ll just disconnect before I plug in the charger.


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## Finn Maccumhail (Apr 9, 2010)

Just to clarify, this only applies if your trolling motor and GPS are on the same battery/circuit, right?


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## Darkstar (Feb 2, 2017)

I don't interpret it that way but I may be wrong. My plan is to have a start/house battery and a dedicated trolling battery. I have sent another email to Minn Kota asking for clarification regarding the warranty. We'll see what they say.


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## Finn Maccumhail (Apr 9, 2010)

Darkstar said:


> I don't interpret it that way but I may be wrong. My plan is to have a start/house battery and a dedicated trolling battery. I have sent another email to Minn Kota asking for clarification regarding the warranty. We'll see what they say.


That seems wrong but I'm not an expert.

My panga has two TM batteries and a dedicated charger and they're not connected to anything else. They're located under the forward casting deck. Then the cranking battery which is connected to the main switch powers the power pole, trim tabs, lights, radio, GPS, and starts the big motor are on their own system with the single battery under the rear deck.


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## Cam (Apr 5, 2017)

Engineer specs are often not reality. I suspect if there was a problem with people using chargers on their TM banks we would see a lot of TM failures due to this since it is so commonly done by so many people.


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## bobber (Sep 29, 2015)

Mike at Master Repair warned me of of this issue many years ago when the Dual Pro charger feeding wet cells was the standard. He didn't state a technical reason just advised to disconnect the troller when recharging. Since he does have a smidgen of experience with troller systems I've followed that advice since. Never had a headboard burn out.
Coincidence? Superstition? Scientific fact?
Dunno don't care. Not changing now.


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## Bamatami (Jun 24, 2019)

Viking1 said:


> According to the Minn Kota owners manual you should not charge your battery while your trolling motor is attached. It seems they have added a wire to reduce interference with sonar and if you charge your battery with the TM connected it can short out the control module. Recently I did not unplug my TM while charging and guess what...just spent $250 getting the control module replaced. Below is the verbiage from the Minn Kota Owner's manual.
> 
> "Your Minn Kota trolling motor may be designed with an internal bonding wire to reduce sonar interference. Most alternator charging systems do not account for this bonding wire, and connect the negative posts of the trolling motor batteries to the negative posts of the crank/starting battery. These external connections can damage connected electronics and the electrical system of your trolling motor, voiding your warranty. Review your charger’s manual carefully or consult the manufacturer prior to use to ensure your charger is compatible."
> 
> Hope this PSA helps you avoid problems!


I just bought a new Minn Kota TM and I was doing research on a charger. I read the above in the manual and had concerns about not using their brand of charger. They do recommend only using a MK charger that apparently would not interfere with this bonding wire in the TM. I thought they just wanted us to purchase their chargers and scare us, but after seeing Viking's post upon doing further research, I'm not going to risk it. So, I should be fine if I disconnect my TM before charging the battery, right?

And, one final stupid question...please don't beat me up! If the TM uses a 12V *30ah* battery, could I use a 12V *35ah* instead? Thanks!


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## prinjm6 (May 13, 2015)

After damaging my Xi5 control board by charging with out disconnecting from battery, it has kept me from purchasing a "On the run" charging system or going lithium with OTR.


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## flyclimber (May 22, 2016)

Bamatami said:


> If the TM uses a 12V *30ah* battery, could I use a 12V *35ah* instead? Thanks!


Should be fine 35ah is a larger capacity. The only thing to be aware of would be the discharge capacity, you want to make sure the battery can output it. May be worth a call to the manufacture of the TM for guidance.


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## hipshot (Sep 29, 2018)

I’m not real sharp on electronics, so I don’t know how relevant this is. Back i the 80s when I bought my bass boat the common knowledge was that you always unplug the TM when charging. I installed an onboard charger that had an isolator which wold allow the outboard to charge the house battery when running, then switch the charging to the TM batteries once the house battery was full. Obviously, I did not unplug the TM every time I cranked the outboard. The system never caused me any problems, but


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## hipshot (Sep 29, 2018)

I always unplugged the TM when plugged in to 110 volts. Don’t know why this last part was omitted from the above post,

Technology jacking with me again......


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## Dustin1 (Feb 11, 2007)

I've been running an Xi5 Pinpoint with a charge-on-the-run system for almost three years on my Shadowcast without a single issue. The system incorporates a simple Blue Seas ACR. Even with the relatively small charging amperage output of the engine (~15 A), I get enough charging to allow me to fish for days in the Glades. I don't have any additional loads on my trolling motor battery.


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## Darkstar (Feb 2, 2017)

After multiple conversations with Minn Kota they indicated the Blue Sea DC charging system was fine for use with their trolling motors. For AC systems, out of an abundance of caution, I would unplug the trolling motor.


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## Bamatami (Jun 24, 2019)

prinjm6 said:


> After damaging my Xi5 control board by charging with out disconnecting from battery, it has kept me from purchasing a "On the run" charging system or going lithium with OTR.


I wasn't planning on an "on the run" charging system. I hadn't really thought about it at all actually. I was just going to go to Harbor Freight and buy a charger. Then I read tonight from Minn Kota about using only their chargers with their trolling motors. When I researched it, I found this forum and this discussion and I appreciate the help!


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## Bamatami (Jun 24, 2019)

Darkstar said:


> After multiple conversations with Minn Kota they indicated the Blue Sea DC charging system was fine for use with their trolling motors. For AC systems, out of an abundance of caution, I would unplug the trolling motor.


That's what I'll definitely do! I appreciate all of the input and suggestions!


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## jay.bush1434 (Dec 27, 2014)

My TM batteries are completely separate from my starting/house battery. The onboard Powermania charger is only wired to the 2 Odyssey PC1200’s which power my Ulterra. The starting/house battery is tied into the charging system from the engine. When I charge the TM batteries, I disconnect the plug on the deck but I do that more so to let it dry out and help prevent corrosion than any electrical issues. I also rarely leave my TM on the boat when it is hanging in the cradle behind the house.


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## Viking1 (May 23, 2010)

If the TM uses a 12V [B said:


> 30ah[/B] battery, could I use a 12V *35ah* instead? Thanks!


You need to match the voltage (V) number which is 12V in this case. The "ah"stands for amp hours which is a measure of how long your battery will last based on how much electricity your trolling motor draws in a period of time. Most manufactures will give a recommendation on the minimum ah battery you should buy based on the lb thrust trolling motor you have. If you look at your trolling motor specs online you should be able to find out how many watts it will use in an hour then you can use this formula to determine how long the the battery will last V(amps) = Watts. For a rough estimate with a 35AH battery you will get around an hour and a half of use with a 30 to a 40 lb thrust trolling motor. On my 55 lb thrust Rip Tide I can get up to 3 days of use with a Group 27 battery which on average has between 85 and 105 AH. There are a lot of variables on how much time you will get based on wind, current and if your TM uses digital or analog technology.


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## steve49 (May 24, 2021)

I have 2 batteries that are in paralell, meaning they are together putting out a total of 12 volts. I installed a 30 amp switch to a 60 amp relay that turns power on to the TM. When I run the Tohatsu outboard the switch to the TM is switched off, as it also is during battery charge at home. This has isolated the TM itself, but allows the batts to charge during outboard run time. What I question is that this "bonding wire" is said to be on the negative side. Can this be explained to me. Do I need to isolate the TM negative side also? So far after 3 months I have had no problem. I did learn the hard way on my old TM to disconnect the TM during charging as I had to replace the pedal control board which was a $100. bill


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