LiFePo4 for Marine 36volt Electric Trolling Motor

[archjeb]

Hi Folks. New member here.

I'm seriously looking at changing my AGM Group 31 batteries I've had wired in series (3 x 12) for a 36volt MinnKota Trolling motor.
It works well; but the weight of the 3 batteries (71# a piece) is over 200#'s and sometimes when trolling with wind, I end up running the batteries down to 25%.

I've had these AGM batteries for several years and I'm starting to see a little age on these as they don't last as long as they use to when on the boat all day fishing/trolling. So I'm looking at replacing them in the near future. I figure I'll go LiFePO4 so I get a bigger discharge cycle and reclaim some weight with lighter batteries.


The new SOK Marine 100Ah looks like a good fit as it is actually dimensionally a little bit smaller than my existing FullRiver AGM (DC115-12) batteries.

The storage compartment can only hold (maximum space) of 3 group 31 batteries. So that is why I'm looking at the 100Ah batteries and not the bigger marine battery that they make.


So my questions:

1. Has anyone torn apart the new SOK 100Ah marine battery? I assume its watertight with the plastic case...so any water splashing (specifically salt water) will not harm it. Does it have wire jumpers for interconnecting the cells? Or is it a copper bus bars?

2. I have a 3 bank Minn Kota Charger (MK3300) that does 10Amps per bank. Any concerns about using this charger for these LiFePo4 batteries?
Do I need to equilize the charge on these batteries before use? Or can I let the Minn Kota charger deal with it since it is a 3 bank charger and would charge each battery as needed?

Thanks!

 

[Substrate]

2. I have a 3 bank Minn Kota Charger (MK3300) that does 10Amps per bank. Any concerns about using this charger for these LiFePo4 batteries?

NO. As nifty as it looks, that is designed for lead-acid. It may have damaging desulfation pulse, but a quick look reveals it has temp-comp (good for lead-acid), but not for LFP. Lead-acid chargers also sometimes have specialty charge steps that tend to extend the absorb too long etc etc. Save the Minnkota for your backup-agm bank only.

With an LFP designed charger, it is usually recommended to charge them individually upon receipt prior to placing them into normal series / parallel service. ESPECIALLY since you are looking to install them in series for your application.

SOK may have additional details to consider, and possibly be needed to maintain any sort of warranty.

 

[archjeb]

Hi Substrate,

Thanks for the reply. Ok, I'm not against a whole-sale replacement of battery bank and charger; I can re-purpose these for other projects.

Any recommendations for an on-board Marine charger for 3 banks of LFP batteries?
A quick Google search showed this charger...but I don't see any reviews

3 Bank Lithium Marine Battery Charger

This is a 3 Bank Lithium Marine Battery Charger perfect for charging 12v LiFePO4 batteries. This charger has built in low voltage cut off charging activation with a push of a button. This means when you run your lithium batteries all the way down they will reach what is called low voltage cut...

hardcorefishandgame.com

Thanks.

 

[Substrate]

I'll admit my ignorance in the area of multi-bank chargers, so I can't comment on your choice.

I was thinking of the latest NOCO GenPRO10X3 3-bank charger with LiFePO4 support (has auto memory once you make the initial chemistry setting change to LFP)

But would that be ok with SOK using a multibank charger? I'm pretty sure if the batts are torn down and charged in isolation, but if left the batts series connected and you tapped across all three with the bank charger, would that confuse or trick the SOK bms?

Another possibility is to just get a single 12v LFP charger for an initial commissioning individually, and then rely on a 36v charger in normal use?

I'm ignorant here, so be SURE to get a more knowlegeable answer from others or perhaps make sure this is ok with SOK first.

 

[archjeb]

I'll reach out to SOK and ask them. Interestingly, when I look at Minn Kota's data sheet for the charger I have...it says it supports LiFePO4 batteries.
From their datasheet:
"""Supported Battery Types: 12v AGM, 12v Flooded Lead Acid, 12v Lithium LiFePO4"""

 

[SignatureSolarJames]

there are 36v waterproof options out there with 36v chargers

 

[archjeb]

there are 36v waterproof options out there with 36v chargers

You talking a single 36v battery pack? My issue is...space. I have a battery locker that can only fit 3 x group 31 batteries lined up in a single direction.
This is in the floor with Starboard / HDPE box & cover (Picture is with the cover removed). You'll notice that I can't just pull the forward battery out. I have to remove the center battery to get that forward battery out. So its cramped.




On a different note, I found this charger that looks promising for a 3 bank option.

3 Bank Lithium Marine Waterproof Battery Charger

This is a 3 Bank Lithium Marine Battery Charger perfect for charging 12v LiFePO4 batteries. This charger has built in low voltage cut off charging activation with a push of a button. This means when you run your lithium batteries all the way down they will reach what is called low voltage cut...

www.monstermarinelithium.com

Anyone have any experience using these as far as reliability?

 

[SignatureSolarJames]

You talking a single 36v battery pack? My issue is...space. I have a battery locker that can only fit 3 x group 31 batteries lined up in a single direction.
This is in the floor with Starboard / HDPE box & cover (Picture is with the cover removed). You'll notice that I can't just pull the forward battery out. I have to remove the center battery to get that forward battery out. So its cramped.


View attachment 116764

On a different note, I found this charger that looks promising for a 3 bank option.

3 Bank Lithium Marine Waterproof Battery Charger

This is a 3 Bank Lithium Marine Battery Charger perfect for charging 12v LiFePO4 batteries. This charger has built in low voltage cut off charging activation with a push of a button. This means when you run your lithium batteries all the way down they will reach what is called low voltage cut...

www.monstermarinelithium.com

Anyone have any experience using these as far as reliability?

36v is a lot smaller than 3x 12v

 

[archjeb]

The 36volt ones I'm seeing in the 100Ah range are too tall. They are about an 1" taller than standard or my existing AGM group 31s. That is the issue I have for the finite space.

I only have 8.66" of height available. Ionic for example is 9.5" high and that is only for a single 50Ah.

 

[Substrate]

I'll reach out to SOK and ask them. Interestingly, when I look at Minn Kota's data sheet for the charger I have...it says it supports LiFePO4 batteries.
From their datasheet:
"""Supported Battery Types: 12v AGM, 12v Flooded Lead Acid, 12v Lithium LiFePO4"""

Ah, ok the search I did for your MK3300 showed support for only flooded, agm, and gel, so maybe it was an older model.

Appears that they support LiFePO4 quite well now.

I see some handy tips like this:

https://minnkota-help.johnsonoutdoors.com/hc/en-us/sections/4412903178775-Battery-Selection-and-Information

But again - this is from a guy with absolutely zero multi-bank experience. Glad you are getting info from others.