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Building a large 24V LiFePo4 bank on a boat

On a boat I would always keep some AGM for Engine Starting purposes Parallel them with the LFP batteries.

A AGM will almost always work. A LFP BMS might go up in smoke. Further your Alternators are designed charge lead, just parallel AGMs (doesn't need to be Huge) to your new battery bank - then you avoid most of the issues of destroying alternators.

There are some boat videos posted in this forum for Lead in Parallel to Lithium for Alternator charging applications. Just find the maximum charging voltage for your LFP bank and adjust your Alpha Pro regulator to that one. It's not the ideal voltage for AGM but close enough for them to be happy a long time.
That's exactly the plan. I have separate AGM banks (2P) for main engine starting, generator starting (all 24V) and 1 12V AGM for the wing/auxiliary engine. They will remain AGM and separated (all have own charger etc.).
The plan I'm talking about here is only concerning the "house" bank at present consisting of 6x 8D AGM.
 
Thank you for letting me join this forum. I have been impressed by the Youtube channel. I'm a Newbee in the LifePo4 world so bear with me if I ask stupid questions.

At the moment we have a quite traditional but well functioning setup in our boat: 24V and 220V board circuits. 24V house-battery bank of 2x3 200Ah AGM 8D batteries. Mastervolt charger 70A, Mastervolt inverter 3000W continouos, 150A alternators on main and auxilary engines, Northern Lights 16kW generator. Battery setups for engines and generator are totally separated from house bank.
2 Solar Frontier solar panels, total 340Wp that charge house-bank through Victron 35/150 MPPT.

As the AGM batteries are already quite old (>7 years) and I'd like to install much more solar panels (at least +3000Wp). I'm contemplating replacement of the AGM bank for a LifePo4 bank. In the same space as the 6 8D batteries I can store 64 3.2V 280Ah cells.

My plan is to:
- replace the present chargers and inverter for a much higher capacity (at least 200A charging and 8000W inverter capacity, probably with 2 Victron quattro units).
- organize the cells in 8 units of 8 parallel.
- install one 8S BMS that can handle at least 300A.
- install 10 350Wp extra solar panels through an extra Victron MPPT

My questions:
- what do you think of this? Any tips/tricks do's and don'ts?
- Is it OK to create the 8 units of 8 cells in parallel without any BMS and/or balancing device in the units?
- I would like a BMS 24V 8S of >300A with a separate charging connection (C-), not a common port. I cannot find any? Do you know of a quality BMS with these specs?

Hope to not have bored you silly with this long story and looking forward to some expert input!

Cheers, André
I have a question and please don’t take this personally. Why not use 48V since you are redoing your battery bank? I suppose you don’t want to redo all the equipment associated with it.
I realize it’s the same Watt Hours but it’s would be half the amperage and half the cost of copper wire.
 
I have a question and please don’t take this personally. Why not use 48V since you are redoing your battery bank? I suppose you don’t want to redo all the equipment associated with it.
I realize it’s the same Watt Hours but it’s would be half the amperage and half the cost of copper wire.
When I start taking the voltage of my battery bank personally, there is something seriously wrong :)
That said it's a very good question that I've been contemplating on for some time. However I think the hassle and introduction of more points of failure (of which you want as little as possible on a boat) with high amp converters has put me off...up till now...certainly in for some expert advice on this.
 
When I start taking the voltage of my battery bank personally, there is something seriously wrong :)
That said it's a very good question that I've been contemplating on for some time. However I think the hassle and introduction of more points of failure (of which you want as little as possible on a boat) with high amp converters has put me off...up till now...certainly in for some expert advice on this.
Actually it’s half the amperage. You shouldn’t have any more failure points than a 24v system.
 
I've been studying lithium battery systems non-stop for several weeks sitting here on the dock in Whangarei, New Zealand. My catamaran comes out of the water in 3 weeks for an electrical system upgrade. I've got to commit to a system design and specific equipment. My boat is 12VDC/120VAC and I want to add a parallel 240VAC system. I have 20 shiny new Eve cells and 6 400W panels in a storage unit and I need to do something with them!

My first thought was to put in a 16S 48VDC bank and a large inverter and just design around that. That would allow me to ditch my humoungous diesel genset and add high-output alternators to the main diesels. Then I started to realize I'd never find a 48V alternator to charge that bank....and the selection of 48VDC marine grade equipment is very limited. Since my boat has a huge quantity of legacy 12VDC loads, I need to put in a 4S 12VDC lithium bank and ensure it's care and feeding. After a week I abandoned the 48VDC bank and started planning around two parallel 24VDC banks, each with a FET-based BMS. It seemed to be so sensible to have a self-balancing BMS that could separately regulate charging and discharging. Much more refined and civilized than an emergency-disconnect-or-die BMS with a contactor.

At the end of the day I had to face the simple fact that I have a 12VDC boat. 12VDC is critical for communications, raising the anchor, refrigeration, desalinating water. The 12VDC system deserves the highest standard of care. And the market offers up far more 12VDC equipment with worldwide availability. 12 Volt wiring, inverters and chargers are bigger and heavier but 12VDC high-output alternators are half the cost. Avoiding a separate DC system with associated bus bars, disconnects, and fusing also saves me time, space, and money. I will install one big honking 12VDC LFP bank.

My 12VDC LFP bank will be configured as one 5P4S bank with a contactor-based BMS. In my opinion, paralleling FET-based BMS units gets to be a hairball. Would these multiple battery systems, each with their own state-of-charge calc all dance in lock-step forever? And what prevents circulating currents between them? Everybody's in charge and nobody's in charge of the charging sources. In my case that's two diesel alternators, a diesel genset powered charger, 120VAC shore power, 240VAC shore power, and three solar controllers.

My off-grid home floats in saltwater, breathes salt air, and it's often hundreds of miles from anywhere. I can't have my critical power running through equipment that doesn't have proven reliability in the marine environment. I'm all for Chinese-designed electronics and electrical equipment for low cost, land based applications. On my boat, only my Sunpower solar panels come from China. That's not true actually. I do have a number of Alibaba USB chargers, flashlights, and other LED widgets - but they're mostly all dead or dying of corrosion.

I now need to chose between the few over-priced, barely customizable BMS products with established presence in marine. I'm holding out hope for something that will exchange more than just "charge enable" contacts with Victron and Wakespeed systems.
 
Actually it’s half the amperage. You shouldn’t have any more failure points than a 24v system.
The boat is entirely 24V DC based with a few 12V exceptions that are fed with some DC/DC converters. When I make my housebank 48V I guess I need to "sandwich" it between high Amp DC/DC converters. These introduce points of failure. I'm afrai I'm talking from experience here as our Cummins electronic common rail diesel has been randomly stalling for the best part of a year without anybody being able to find the problem. Very long story short it was a 24/12V DC converter between the engine management (24V) and the dashboard instruments (12V)...because of this flacky converter the engine every few days or so thought I switched it off...not a nice experience in the middle of the ocean and certainly not while maneuvering in close quarters :-(
 
I've been studying lithium battery systems non-stop for several weeks sitting here on the dock in Whangarei, New Zealand. My catamaran comes out of the water in 3 weeks for an electrical system upgrade. I've got to commit to a system design and specific equipment. My boat is 12VDC/120VAC and I want to add a parallel 240VAC system. I have 20 shiny new Eve cells and 6 400W panels in a storage unit and I need to do something with them!

My first thought was to put in a 16S 48VDC bank and a large inverter and just design around that. That would allow me to ditch my humoungous diesel genset and add high-output alternators to the main diesels. Then I started to realize I'd never find a 48V alternator to charge that bank....and the selection of 48VDC marine grade equipment is very limited. Since my boat has a huge quantity of legacy 12VDC loads, I need to put in a 4S 12VDC lithium bank and ensure it's care and feeding. After a week I abandoned the 48VDC bank and started planning around two parallel 24VDC banks, each with a FET-based BMS. It seemed to be so sensible to have a self-balancing BMS that could separately regulate charging and discharging. Much more refined and civilized than an emergency-disconnect-or-die BMS with a contactor.

At the end of the day I had to face the simple fact that I have a 12VDC boat. 12VDC is critical for communications, raising the anchor, refrigeration, desalinating water. The 12VDC system deserves the highest standard of care. And the market offers up far more 12VDC equipment with worldwide availability. 12 Volt wiring, inverters and chargers are bigger and heavier but 12VDC high-output alternators are half the cost. Avoiding a separate DC system with associated bus bars, disconnects, and fusing also saves me time, space, and money. I will install one big honking 12VDC LFP bank.

My 12VDC LFP bank will be configured as one 5P4S bank with a contactor-based BMS. In my opinion, paralleling FET-based BMS units gets to be a hairball. Would these multiple battery systems, each with their own state-of-charge calc all dance in lock-step forever? And what prevents circulating currents between them? Everybody's in charge and nobody's in charge of the charging sources. In my case that's two diesel alternators, a diesel genset powered charger, 120VAC shore power, 240VAC shore power, and three solar controllers.

My off-grid home floats in saltwater, breathes salt air, and it's often hundreds of miles from anywhere. I can't have my critical power running through equipment that doesn't have proven reliability in the marine environment. I'm all for Chinese-designed electronics and electrical equipment for low cost, land based applications. On my boat, only my Sunpower solar panels come from China. That's not true actually. I do have a number of Alibaba USB chargers, flashlights, and other LED widgets - but they're mostly all dead or dying of corrosion.

I now need to chose between the few over-priced, barely customizable BMS products with established presence in marine. I'm holding out hope for something that will exchange more than just "charge enable" contacts with Victron and Wakespeed systems.
Thanks very much for your elaborate description of your "journey". Very interested with what configuration you will end up and your experiences! Do you already have an idea on how to regulate the alternator charging of the LiPo bank?
 
I now need to chose between the few over-priced, barely customizable BMS products with established presence in marine. I'm holding out hope for something that will exchange more than just "charge enable" contacts with Victron and Wakespeed systems.

There are a fair number of third party BMSs that will integrate with Victron (and thus wakespeed) through an additional driver for Venus OS (running on a Raspberry Pi and/or the Cerbo GX, as I recall). The Victron Communit link is here: https://community.victronenergy.com...nusos-driver-for-serial-connected-bms-av.html

Personally, I'm going with a REC Active BMS, as it will do the job nicely and will integrate via CAN Bus out of the box.
 
I have three 24volt LiFePO4 batteries built, operating and cycling on solar PV panels. two of them are in a 2P8S configuration. and the third one is a 4P8S configuration.

I use an Electrodacus SBMS0 for each of them. there is no need for big relays and MOSFETs as the other BMS systems use.

you parallel the 4 cells 1st so you have 8 sets of cells in parallel.
then you connect each set of 4 (already paralleled) in series to get your 24volt battery.
the correct way is to label it as4P8S.

the Electrodacus SBMS0 balances each set of 4 cells and monitors it without any problems. so what I am trying to say is the Electrodacus will monitor each set of 4 cells to charge them up to 3.55 volts each set of 4 paralleled cells.
the Electrodacus prevent you from overcharging the cells and balances them while charging.

although supposedly you could do an 8P8S configuration, I truly think 2 of the 4P8S would be the better way to go; and each would be 1120 A each at 24 volts but actually 25.6 volts nominal (3.2x 8 =25.6 volts).

my batteries typically run from 27 volts to 27.6 volts. when fully charged.
you only want to top balance them at the 1st use to 3.65 volts and should not need to do that again.
the LIfePO4 do not want/need to be charged to 3.65 volts for normal use and long life.

the LiFePo4 is charged slowly on solar at a .2c rate or so normally.
I am presently assembling the 4th LiFePO4 battery with 32 EVE280K cells that are solar rated for 6000 cycles.
3.2volt x 280Ah/cell x 32cells = 28,672 Wh potential capacity per 32 cell battery.

once again it will be a 4P8S battery build configuration.
hope this helps you.

you are never going to pull 1120 amps at 24 volts. more like not even 250 amps but the larger capacity batteries give you a longer run time for cloudy weather.
 
Thanks very much for your elaborate description of your "journey". Very interested with what configuration you will end up and your experiences! Do you already have an idea on how to regulate the alternator charging of the LiPo bank?
I'm going to retain the 55A alternators and AGM starting batteries on both main diesels. These both charge the house bank through diode isolators. If I do nothing, the new lithium house bank will quickly suck the life out of the alternators. In my current haulout I'm installing a current limiting solution to protect the alternators. They are Renogy 20A DC to DC battery chargers. These inexpensive products work with LFP. They have a digital "charge enable" input meant to be connected to the ignition switch and a separate digital input which cuts the charging current by 50%. I'll wire the charge enable so that it can be interupted by the BMS.

After living with the new systems for a season I'll make the final decision on removing my genset. At that time I'll bolt a serpentine belt pulley to the front face of the flywheel and add a second high-output alternator to each engine. I'll probably buy my alternator from Mechman and use a Wakespeed regulator which will be under the command of the BMS - hopefully through a robust data link.
 
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