Building a large 24V LiFePo4 bank on a boat

[Mr.Bean2]

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

 

[grizzzman]

Yes you could. But for redundancy I would suggest at least two batteries and two BMS's ( Real important on a boat)

 

[Mr.Bean2]

Yes you could. But for redundancy I would suggest at least two batteries and two BMS's ( Real important on a boat)

Thanks,
Not sure I understand “2 batteries”? Do you mean creating 2 separate batteries consisting of 8 units of 4 parallel cells?
Then I end up with 2 BMS providing 24V each. How do I integrate these 2 batteries into one unit?

 

[MrM1]

Thanks,
Not sure I understand “2 batteries”? Do you mean creating 2 separate batteries consisting of 8 units of 4 parallel cells?
Then I end up with 2 BMS providing 24V each. How do I integrate these 2 batteries into one unit?

You use the term "Units"?? Do you mean series connected (+ to -). By 2 "batteries" @grizzzman probably means be 2 strings of 8 batteries in series then connected in parallel - a total of 16 cells. That would mean 2 BMS's, one on each string of 8 in an 8s2p (8 cells in series / both groups in parallel). This would create the redundancy. If one BMS or series string goes down, you still have a "battery".

at least 200A charging and 8000W inverter capacity

Question, can you build an array large enough to supply 200a charging?

- install one 8S BMS that can handle at least 300A.

That is a pretty tall order, but there are some. You might look at contactor type BMS's, but then you have another moving part subject to corrosion on a boat. Again, 2 series strings designed correctly could also allow for BMS's that are not so hi capacity because each series string carries only 1/2 the load. I know some do not like to design that way because if one string goes down you cannot run all your loads, but my thought there is, if I am only limping on 1 string, I'm not running all my loads anyway.

But with 2 strings, you can turn one off, or shut one down for repair and still have power.

- Is it OK to create the 8 units of 8 cells in parallel without any BMS and/or balancing device in the units?

N0. I do not think it is OK to ever run LFP cells with out a BMS. Still do not under stand what you mean by "8 units of 8 cells in parallel"?

 

[Mr.Bean2]

You use the term "Units"?? Do you mean series connected (+ to -). By 2 "batteries" @grizzzman probably means be 2 strings of 8 batteries in series then connected in parallel - a total of 16 cells. That would mean 2 BMS's, one on each string of 8 in an 8s2p (8 cells in series / both groups in parallel). This would create the redundancy. If one BMS or series string goes down, you still have a "battery".


Question, can you build an array large enough to supply 200a charging?


That is a pretty tall order, but there are some. You might look at contactor type BMS's, but then you have another moving part subject to corrosion on a boat. Again, 2 series strings designed correctly could also allow for BMS's that are not so hi capacity because each series string carries only 1/2 the load. I know some do not like to design that way because if one string goes down you cannot run all your loads, but my thought there is, if I am only limping on 1 string, I'm not running all my loads anyway.

But with 2 strings, you can turn one off, or shut one down for repair and still have power.


N0. I do not think it is OK to ever run LFP cells with out a BMS. Still do not under stand what you mean by "8 units of 8 cells in parallel"?

Thanks for bearing with me here. I want to use 64 cells of 3.2V 280Ah. To create 24V I need a series of 8 of these cells. Hence with 64 cells I can create 8 3.2V batteries (what I called units) of 8 cells in parallel. By putting these 8 batteries in series I create a 25.6V battery of 8x280=2140Ah. I think this is called 8P8S?

Not sure but I guessed that Grizzman was hinting at 2 times a 4P8S setup where you end up with 2 1070Ah 24V batteries with there own BMS. However I'm not sure if you can just put these 2 in parallel to create the 2140Ah again or there has to be a "master" BMS on top of the 2?

As I have several sources to charge the batteries I'm not aiming for 200A of charging capacity from the array alone. Depending on availability at any moment I can use shore power through the chargers, Generator power through the chargers, Alternator power (from the engines) directly and array power.

 

[MrM1]

I think the goal is to do some variation of 8s so that you end up with at least 2 separate 24v batteries that can then be paralleled via busbars. This would require 1 BMS for each 24v battery.

But keep in mind, in your original design, if you connect 8 in parallel, then connect 8 in series with only 1 BMS, each bms lead (x8) is monitoring 8 cells. Generally each lead monitors 1 or 2 cells. So it would be next to impossible in that config for the BMS to properly keep your 64 individual cells balanced. And you would not b able to monitor the health and voltage of each individual cell via the bms.

 

[Cdkipp]

Your initial proposal is/was the most common way to build big packs. Now it is more common to break them up into more than one. Yes this does get you some redundancy but I think the most common reason for this is that most BMS units are mosfet based so they cannot handle the amperage you are talking about. One way to get around this is to switch to a BMS that uses relays and contactors rather than mosfet. https://www.aliexpress.com/item/100...sku_id":"12000022573215762","sceneId":"3339"}

 

[Cdkipp]

You would find the Ray Builds Cool Stuff you tube series interesting. He is a member here.

 

[Mr.Bean2]

You would find the Ray Builds Cool Stuff you tube series interesting. He is a member here.

Great stuff! Have been through most of his relevant videos. Still have a few questions that I hope this forum can help me with:

When I split my 64 3.2V cell battery up in a multiple I can go for 2, 4 or 8 batteries. Basically 8P8S or 2x 4P8S or 4x 2P8S or 8x 8S.
Let's for argument sake say I create 8 separate batteries of 24V with there own BMS. E.g. 8x the Overkill 24V 100A.
- Can I just put these 8 batteries in parallel into load/charge circuit?
- Can I draw 300A of this setup? In other words will the 300A be divided over the 8 batteries?
- Same for charging: can I put 200A of charging on this installation and will it distribute evenly over the 8 batteries?

Thanks, André

 

[MrM1]

Great stuff! Have been through most of his relevant videos. Still have a few questions that I hope this forum can help me with:

When I split my 64 3.2V cell battery up in a multiple I can go for 2, 4 or 8 batteries. Basically 8P8S or 2x 4P8S or 4x 2P8S or 8x 8S.
Let's for argument sake say I create 8 separate batteries of 24V with there own BMS. E.g. 8x the Overkill 24V 100A.
- Can I just put these 8 batteries in parallel into load/charge circuit?
- Can I draw 300A of this setup? In other words will the 300A be divided over the 8 batteries?
- Same for charging: can I put 200A of charging on this installation and will it distribute evenly over the 8 batteries?

Thanks, André

Yes. My only concern would be the 8 in parallel. In the lead acid days it was suggested not to exceed 4 in parallel. But with lfp and them not really needing to be charged to 100% almost daily it may not matter that much. Some one more experienced could answer about the 8 LFP in parallel

But if you built 8 in parallel, You'd want to make sure in your build that you were meticulous about things like cable length, crimping, terminal prep/cleaning and terminal "grease" (use something like No-Ox-ID A-Special)

 

[MrM1]

With 8 overkill 8s 100 amp BMSs 4 stings could completely go down or be disconnected for service and you'd still be able to draw 300 amps and charge at the 200 amps

 

[Cdkipp]

Great stuff! Have been through most of his relevant videos. Still have a few questions that I hope this forum can help me with:

When I split my 64 3.2V cell battery up in a multiple I can go for 2, 4 or 8 batteries. Basically 8P8S or 2x 4P8S or 4x 2P8S or 8x 8S.
Let's for argument sake say I create 8 separate batteries of 24V with there own BMS. E.g. 8x the Overkill 24V 100A.
- Can I just put these 8 batteries in parallel into load/charge circuit?
- Can I draw 300A of this setup? In other words will the 300A be divided over the 8 batteries?
- Same for charging: can I put 200A of charging on this installation and will it distribute evenly over the 8 batteries?

Thanks, André

 

[Rocketman]

For the bms - take a real close look at Batrium.

With the Batrium you could monitor and balance each of your 64 cells. It also has many relays for heating, cooling, allow to charge -( send this signal to the alternators), allow to discharge, plus it can connect via Canbus to the Victron Cerbo.

With such a large battery, I would probably make four “batteries” of 2p8s each and then monitor the 32 cells. Although you could setup the system as eight batteries of 8s.

 

[Rocketman]

One trick I found - before I made my big 2p4s 540ah battery for my RV, I made a small portable 50ah battery. I needed a small battery for one job - but I have found several others really good jobs for it too. The experience of making one battery really helped me when making the bigger battery.

I put power pole connectors and a light on the small battery - the light has been useful, I connected a water pump to the power pole connectors and I pump water into my rig. Pumping is easier than pouring. If you pour fuel - that could be another job.

 

[Cdkipp]

One trick I found - before I made my big 2p4s 540ah battery for my RV, I made a small portable 50ah battery. I needed a small battery for one job - but I have found several others really good jobs for it too. The experience of making one battery really helped me when making the bigger battery.

I put power pole connectors and a light on the small battery - the light has been useful, I connected a water pump to the power pole connectors and I pump water into my rig. Pumping is easier than pouring. If you pour fuel - that could be another job.

RVer also. I use my Norco jump pack for these odd jobs but I am working on a small lifepo4 pack now. I agree these come in handy in all types of situations you would not expect especially when you are away from civilization or in an emergency.

 

[jwelter99]

I do marine systems like this for a living.

I would take your 64 cells and organize them into 2 * 24V batteries with 8s4p topology.

Then parallel these, with appropriate fusing, to feed your "house" bus.

I urge you to not use FET based BMS's for this. Use a BMS that can control external contactors for your emergency disable. FET based BMS do not integrate well into these existing environments and have a habit of failing closed which is a danger. Using a contactor based BMS you can set it up to handle your full charge/discharge requirements per battery - which should be your target.

REC and Orion are the best choices. Batrium can work but a bit too hobbyist for a marine environment.

 

[svsagres]

I do marine systems like this for a living.

I would take your 64 cells and organize them into 2 * 24V batteries with 8s4p topology.

Then parallel these, with appropriate fusing, to feed your "house" bus.

I urge you to not use FET based BMS's for this. Use a BMS that can control external contactors for your emergency disable. FET based BMS do not integrate well into these existing environments and have a habit of failing closed which is a danger. Using a contactor based BMS you can set it up to handle your full charge/discharge requirements per battery - which should be your target.

REC and Orion are the best choices. Batrium can work but a bit too hobbyist for a marine environment.

Definitely agree. I’m building a (much) smaller system on my sailboat, but am still going with the REC Active BMS. When things are working properly, I want it all integrated so that the contactors/relays never fire. BMS, Alternator, and Inverter/charger all communicating so that the battery State is maintained, and nothing gets shut off cold.

At the same time I’m also working in manual overrides, so I can get home if I need it. (I’ll actually probably just have a little lead acid starting battery and ability to flip core safety electronics to it).

 

[rmarsh3309]

Andre, I'm in the design phase of a nearly identical system on my catamaran. I'm looking to protect a 2P8S assembly of 280AH cells and I'm leaning towards a contactor-based protection system. I don't see how I can have my various charging sources orchestrate if I don't have a single monolithic battery. Where are you heading with your design?

 

[Mr.Bean2]

Andre, I'm in the design phase of a nearly identical system on my catamaran. I'm looking to protect a 2P8S assembly of 280AH cells and I'm leaning towards a contactor-based protection system. I don't see how I can have my various charging sources orchestrate if I don't have a single monolithic battery. Where are you heading with your design?

I'm certainly not as far as you. I'm only studying the possibilities this far. My AGM's are still doing a good job...but I expect them to go bad within a year or 2. After looking at some more channels on the subject (digital mermaid, off grid garage etc.) I think I will go for 4P8S. Hence building 4 seperate 24V batteries with there own BMS, main switch etc. and paralleling them into the circuit. I think I will also opt for contactor based switching. I want to be able to switch of the charging without switching of the load side. I still have to dive into the alternator charging. I have 2 large 110A, 24V Mastervolt alternators on the main and auxilary engine through Alpha Pro regulators...however I need a way to regulate these for charging a large LiPo bank while not destroying the alternators nor the batteries.
Of course very curious for the way you're going forward. Lots of luck!

 

[eXodus]

I'm certainly not as far as you. I'm only studying the possibilities this far. My AGM's are still doing a good job...but I expect them to go bad within a year or 2. After looking at some more channels on the subject (digital mermaid, off grid garage etc.) I think I will go for 4P8S. Hence building 4 seperate 24V batteries with there own BMS, main switch etc. and paralleling them into the circuit. I think I will also opt for contactor based switching. I want to be able to switch of the charging without switching of the load side. I still have to dive into the alternator charging. I have 2 large 110A, 24V Mastervolt alternators on the main and auxilary engine through Alpha Pro regulators...however I need a way to regulate these for charging a large LiPo bank while not destroying the alternators nor the batteries.
Of course very curious for the way you're going forward. Lots of luck!

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.