Small LFP in // or one BIG ?

[nitrosails]

Hi!

I'm in the process of rebuilding a 43foot sailboat to sail around the world. We untie the line in 3 years.
I'll be installing LFP batteries.
What are the pro and cons between installing small lfp in // 12v 230ah * 2 or 3 in //, or one big 12v 700ah

thanks guys!

 

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[ianganderton]

At the end of the day any Lifepo4 battery is just a collection of cells whether they are arranged into several smaller lower Ah units or single big one. The number of cells is the same

What matters most to my mind is how the BMS manage the balancing of the cells along with the bigger loads you might want

It’s all about the way the bms’s are arranged

8.4kWh isn’t huge. Possible to draw quite large Amps out of a 700Ah battery though

 

[BobR]

Hi!

I'm in the process of rebuilding a 43foot sailboat to sail around the world. We untie the line in 3 years.
I'll be installing LFP batteries.
What are the pro and cons between installing small lfp in // 12v 230ah * 2 or 3 in //, or one big 12v 700ah

thanks guys!

You might want to read the articles at: https://nordkyndesign.com/featured-articles/
He recommends using smaller cells because the larger cell do not hold up structurally in the motions of a boat.

 

[BobR]

Hi!

I'm in the process of rebuilding a 43foot sailboat to sail around the world. We untie the line in 3 years.
I'll be installing LFP batteries.
What are the pro and cons between installing small lfp in // 12v 230ah * 2 or 3 in //, or one big 12v 700ah

thanks guys!

I'm using 230ah cells to build 2 24v batteries.

 

[nitrosails]

You might want to read the articles at: https://nordkyndesign.com/featured-articles/
He recommends using smaller cells because the larger cell do not hold up structurally in the motions of a boat.

Thanks for your reply

i found what he says :

Cell Sizes​

Single 3.2V prismatic LiFePO4 cells can nowadays be obtained in huge capacity, as high as 10000Ah. Commonly available cells range between 40Ah and maybe 1000Ah. It should be pointed out that the larger sizes are intended for stationary applications where no accelerations, vibrations or shocks are ever experienced.

A sales manager at Sinopoly I was talking to was adamant about using 100Ah or 200Ah cells only for assembling marine battery banks, with 100Ah being preferred and 200Ah acceptable. Large cells simply don’t have the structural strength-to-weight ratio required to be taken to sea on board small crafts and would exhibit shortened life due to internal mechanical damage arising from on-going vessel motion. It is common sense: as a cell becomes larger, its internal weight increases much faster than the rigidity and surface area of the casing and the casing is all what holds the plates together in a prismatic cell.

Failures have been reported on vessels equipped with 700Ah cells following ocean passages: some cells were suddenly found to be losing charge inexplicably, rendering the battery bank completely unmanageable and the matter ended in a complete write-off. All big-brand commercial marine lithium battery packs on the market today are built from cells no larger than 200Ah.



So i have my answer, better to put multiple 230Ah in //

 

[Steve_S]

I would think about safety, security & reliability.
1) If you have ONE huge Battery and something goes wrong, that's it, you only have the one. Remember Murphy's Laws Apply : "Anything that can go wrong will go wrong and at the worst possible time."
2) Paralleling 2 or more battery packs provides redundancy, they will share/split charge & load thereby reducing stress potential.
3) Keep It Simple & Serviceable (KISS), don't build a battery with Paralleled cells, stick to a simple Series Configuration.
4) Make sure all wiring and components are Marine Grade, so use tinned lugs, cables, etc., and properly crimped with high-grade shrink tube with adhesive !
5) When locating the battery assembly, make sure it is "high & dry" and the batteries are secured (water tight is best).

NOTE: BEFORE Purchasing cells, look at the Specs, particularly the physical size of the cells, they all vary depending on Manufacturer & AH Capacity. Know how much space you can allocate, not only for the cells but the BMS and the casing for each.
Special Note !! Do NOT use Very Large Cells ! they are intended more for static placement like a home ESS and not for mobile (especially rough) use. IF you are DIY'ing the batteries, then have a "spare BMS", fuses etc on hand (see murphy's laws). You can buy Battery Boxes or build your own but the ABS Plastic Boxes are likely most suitable for Marine use, see link below for example.


















Grade-A Matched & Batched cells with test report from EVE from this link suggested.

1pcs Eve 230ah Lifepo4 (lfp) 3.2v Cells Battery (new Version,Fully Matched And Batched)--genuine Grade A - Buy Eve,Lifepo4,Rechargeable Battery Product on Alibaba.com

1pcs Eve 230ah Lifepo4 (lfp) 3.2v Cells Battery (new Version,Fully Matched And Batched)--genuine Grade A - Buy Eve,Lifepo4,Rechargeable Battery Product on Alibaba.com

www.alibaba.com

ABS Waterproof Box:
https://www.alibaba.com/product-det...terproof-Battery-Box-Case_1600553604483.html?

Suggested BMS: JK(jikong) 2A Active Balance Smart BMS for 4-8S 12V PN: JK-B2A4S20P

A resource to download which you will find handy on Battery Assembly and more:

Luyuan Tech Basic Lifepo4 Guide

This document was posted to the forum by Amy from Shenzhen Luyuan and written by Steve S. It was meant to be posted as a resource. Below is her description of the resource: Dear all friends in the forum, This file in the attachment was...

diysolarforum.com

Hope it helps, Good Luck.

 

[wholybee]

We really need more information before this can be answered. What loads are you planning to have? Electric cooking, A/C, or just small loads like lights and instruments? You should work up an an energy budget worksheet.

For your question, there are pros and cons. The most reliable is a 4s (4 series) configuration with cells as large as you need. I have seen cells as large as 400Ah. If you need larger than that, or if space doesn't allow the large 400Ah cells, then you will need some sort of parallel configuration. Or, you might choose a parallel configuration for some redundancy, that if one fails you can use the other as a backup.

There are 2 parallel configurations. Series first, or Parallel first. With Series first, you are making multiple complete batteries, each with it's own BMS. It is more complicated, has the potential for issues with eddy currents, more points of failure, but has redundancy so if there is a minor failure you have a backup. With parallel first, its much simpler, a single BMS, but no redundancy in a failure.

You could also do multiple banks, where they are not paralleled together, but you can switch from one to another.

Because it is a boat, you also should make yourself aware of ABYC E-13, which if you follow to the letter rules out nearly all drop-ins and nearly all FET based BMS's. If you intend to insure your boat, adherence to E-13 is basically mandatory.

 

[BobR]

Hi!

I'm in the process of rebuilding a 43foot sailboat to sail around the world. We untie the line in 3 years.
I'll be installing LFP batteries.
What are the pro and cons between installing small lfp in // 12v 230ah * 2 or 3 in //, or one big 12v 700ah

thanks guys!

there is also some good info here: https://www.custommarineproducts.com/system-design.html

 

[Samsonite801]

Hi!

I'm in the process of rebuilding a 43foot sailboat to sail around the world. We untie the line in 3 years.
I'll be installing LFP batteries.
What are the pro and cons between installing small lfp in // 12v 230ah * 2 or 3 in //, or one big 12v 700ah

thanks guys!

Just FYI, I have 1680 Ah (six 12v 4s 280 Ah cells, six OverKill 120a BMS's)...

My rule is to have available the best possible redundancy, and a setup where the max amperage potential of battery is available for use as well (for me it's 720a continuous if needed).

Each 12v battery having their own thing going on, it's easy to take one out of the loop (with individual breakers on each 12v battery) troubleshoot a cell failure (or any problem), since each cell belongs to a BMS sense voltage, I can read any voltage of any cell using the phone app (I renamed all my BMS in the bluetooth app to show proper number for easy identification).

I can log into any of the 6 BMS's and see individual battery SoC, or with the Victron BMV-712 battery monitor / shunt, I can read entire pack SoC...

It costs a bit more for 6 BMS's and six breakers, etc, but it opens up doors for higher current use later if I find I needed more capacity down the line. Also means that the load is distributed across six packs, so each one is barely breaking a sweat, even when I peg my load draw to maximums (so it should help the longevity of the BMS MOSFETs, as they will run much cooler throughout their service life).

I am extremely happy with the layout I chose, now being in perfect operation since Spring.