Electric Trolling Motor - Battery Monitoring - 36V - Help?

[archjeb]

Hi Folks,

I've got an existing trolling motor with 3 group 31 AGM batteries wired in series to give me 36VDC to support a Minn Kota Ulterra. Its been working great, but the AGM batteries are starting to show some age. So I want to replace these with LiFePo4. But I'm trying to figure out my Battery Monitoring system out.

I have a Minn Kota MK345PCL charger which supports a Lithium charge profile. So I'm good there. I do NOT currently have the Shunt in place; but I want to buy that. Looking at the diagram I put together, you'll see the Victron SmartShunt I was looking at adding. I also was looking at the BattleBorn 100Ah batteries...because with the cylindrical cells, if there was a cell failure, I could continue to use but with the limited capacity till I get back home to replace it. Also, when camping, sometimes it gets below freezing in the Spring, so the low-temp charge disconnect is a plus. Finally, the build quality seems to very good; as I don't want to have a trip go short because of battery failure.

At any rate, the concern I have is with the shunt. I guess I can monitor the discharge rate with this configuration; but with 3 separate charge banks from the charger....the shunt will have no idea what charge is going into the battery.

For those of you that are using this kind of configuration, do you just reset discharge to 0 or set SOC to 100% and then just monitor the discharge?
Also, I want to disconnect everything from the batteries while charging so I don't have any parasitic discharge; I assume I can power the Smartshunt with the 36Vs on the switched side of my large 2 position switch (so its not powered when my 2 position switch is in the off position)? I'm not familiar with the Victron Shunts to know if you can configure them to auto-zero out everything on power-up?

Any better ideas or approaches with this setup that you suggest?





Thanks so much for any assistance or direction.

-J

 

[sunshine_eggo]

I have a Minn Kota MK345PCL charger which supports a Lithium charge profile. So I'm good there. I do NOT currently have the Shunt in place; but I want to buy that. Looking at the diagram I put together, you'll see the Victron SmartShunt I was looking at adding. I also was looking at the BattleBorn 100Ah batteries...because with the cylindrical cells, if there was a cell failure, I could continue to use but with the limited capacity till I get back home to replace it.

I don't follow the logic on this.

At any rate, the concern I have is with the shunt. I guess I can monitor the discharge rate with this configuration; but with 3 separate charge banks from the charger....the shunt will have no idea what charge is going into the battery.

You can give it reasonable info to sync to 100%. See last portion of post.

For those of you that are using this kind of configuration, do you just reset discharge to 0 or set SOC to 100% and then just monitor the discharge?
Also, I want to disconnect everything from the batteries while charging so I don't have any parasitic discharge; I assume I can power the Smartshunt with the 36Vs on the switched side of my large 2 position switch (so its not powered when my 2 position switch is in the off position)? I'm not familiar with the Victron Shunts to know if you can configure them to auto-zero out everything on power-up?

On power-up, they can be set to assume they're synched at 100% or report "--" since they don't know the SoC anymore.

You would power the shunt at the (+) terminal of the Bank 1 battery. It's power drain is minimal. Nothing beneficial to connecting/disconnecting.

Any better ideas or approaches with this setup that you suggest?

Best solution I see is to connect bank 3 (-) to the load side of the shunt instead of the battery terminal. The shunt can at least see the current passing into the last battery and use that singular charger as the fully charged trigger of the 3rd battery to sync the shunt to 100%.

Set shunt to 40.3V and 5%. Once it's above 40.3V AND the charge has dropped to < 5A, it will trigger the shunt to 100%. You might need to tweak the charged voltage for accuracy, but I suspect this will work without modification.

 

[archjeb]

Thank you for the detailed response. I appreciate it.

Regarding the cylinderical cells, I was basing that information from one of Will's videos @ the 4:42 mark:

I guess the BMS, if that failed I would be a sitting duck as that is still a single point of failure. But with a single cell failure it would only be reduced capacity. Where I'm going with this is, if I'm on a fishing trip I'd rather have some reduced capacity vs having no power and not being able to use my electric motor. But maybe I'm not being reasonable here on this particular corner case?

In the end I'm looking for what is reliable. The price tag on the lower cost units are appealing, but I'd hate for a trip to be cut short because of a battery failure.

 

[sunshine_eggo]

IMHO, the statement isn't correct. If a cell shorts, that shorted cell will drain the cells that are in parallel with it UNLESS all cells are fused, and the fuse to the shorted cell is popped.

Based on the spot welds connecting the cells to the nickel end plates, the cells are almost certainly not fused.

Regardless, Battleborn is a good battery.

 

[archjeb]

Thanks for the feedback.

I'm open to other batteries for marine electric trolling motor use. I'm just looking for whatever would be reliable. The Chins, Amperetime, etc all have an attractive price point; but reviews seem across the board. Plus, I'd really like to have cold-temp charge cutoff for the times I'm charging the boat batteries in the spring when the outside temp is below freezing at night - and the group 31 size batteries from these folks seem to not have that in their standard 100Ah LiFePo4 battery.

I'm stuck with Group 31 batteries because of the tight fit in the battery locker. A single large 36v 206Ah battery or multiple larger 12v batteries just will not fit with the shape of the battery locker. So 3 x group 31s (or 100Ah) batteries works perfectly.

I was open to the 100Ah SOK marine battery; but seemed like the Bluetooth interface was giving people some issues with some of the threads on this forum. And having 3 separate Battery Monitoring interfaces (internal per battery) appeared to be a little cumbersome. I like the idea of having a dedicated Victron display with remaining battery power to monitor while fishing.

Thank you.

-J

 

[KITROBASKIN]

So glad that a very capable member has contributed.
I am under-qualified to assist on a different thread the OP made about SOK batteries regarding these issues. Another consideration is whether it would be worth it for archjeb to get a couple Victron battery balancers, given that they will be in series. How worthwhile/advantageous would that expense be?

 

[AnarchyJet]

Considering the BattleBorns are over 2 times the cost of other options, you could buy 4 lower cost batteries and keep a spare. Or possibly fit 6 50ah LPF's in a 3S2P config for redundancy. Then a single battery failure would halve your capacity but keep you fishing.

 

[KITROBASKIN]

BattleBorn does not have Bluetooth. SOK can be purchased without Bluetooth for less $.
How many people with electric trolling motors have neither a shunt or battery balancers.

 

[archjeb]

Marine version of SOK 100Ah is Bluetooth.

As far as Shunts on trolling motor installs, its a mix out there. Seems like the hard core fisherman have Shunts because they need to know every detail to make sure their day does not get cut short. Especially the guys in tournaments.

Battery balancers; good question. When I called SOK and Battleborn and discussed charging options, they seemed pretty confident that with the multi-bank marine chargers with a Lithium profile, this will be fine and batteries would be balanced. BMS will take care of each battery since the charger delivers independant charge per bank.

Most folks are not using solar in this kind of deployment; its really a use and plug in and charge at the end of the day.

 

[eagleray]

I'm using Chins for a few different trolling motors. I have an old Terrova (same thrust as yours) but I haven't run it on the lake yet, just on the test bench. I'm in the desert so I got the cheapest one, but Chins does have a low-temp/bluetooth bells/whistles version for $500, which is still a steal compared to Battleborn. https://amzn.to/3m4JNx4