Large battery bank design question


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coolwaterxii

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Jul 20, 2021
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2
Hi all,

I talked to Batrium about going about a battery bank with a Sol-Ark inverter(s) where it can draw 200-400A continuous, 1000A surge/peak. He strongly recommends to keep it simple and doing a 8P16S 48v @ 2480Ah capacity should be fine.

The question that I now have is how to arrange the batteries and avoid multi-string. I'm sure this has been done before, but I want to make sure since I don't see 8x 310Ah cells in parallel in the site. So what do you all think? I tried to make sure that the busbar is at opposite ends and same length to help out with even distribution of electricity across battery cells.

Any suggestion is greatly appreciated.

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OffGridInTheCity

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Dec 15, 2018
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2,033
A question and a comment.

Question:
You say/show 8p and comment that it's 2480ah @ 48v. That would be 2480ah per 'p'. 2480ah/8 = 310ah per cell. Is each cell 310ah? - sounds like a different ah than I've commonly seen so I wanted to double check. This question bears heavily on the comment :)

Comment in reference to this - https://support.batrium.com/article/91-cell-monitor-pack-design-considerations - ".... We recommend 200-300Ah, it is subjective as others have used them on 800-1000Ah..... At 1000Ah will take 5 weeks, for some this is acceptable but we do not think it is ideal...".

If your cells are 100ah, then 8p would be 800ah on each 's'. That's near the top end of what Batrium can balance effectively with mons.
If your cells are 200ah, then 8p would be 1600ah on each 's' - the max that Batrium recommends is 1000ah.
If your cells are 310ah, then 8p is 2480ah as you wrote above - this is clearly too big for Batrium.

Suggest breaking you battery up into to multiple parallel batteries to bring the max 'cell size' down to something Batrium can balance reasonably well.

Note: I have 84 (lithium-ion) packs @ 260ah each arranged in 6 parallels batteries of 14s. So each mon balances 260ah. From this experience, I can easily see 520ah balance or even more - but 2480ah per 'cell' balance would definitely be a stretch!
 

coolwaterxii

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Jul 20, 2021
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Yes, it's a CATL 3.2v 310Ah prismatic LiFePo4 battery. It's advertised at 310Ah but they said expect 300ish. Others on diysolarforum are reporting between 299-300Ah; so pretty close to what sales is telling me.

I did talk to Jaron at Batrium about this last night, and he said it should be no problem as he has seen customers with this big of a battery bank. It might take longer if the batteries were unbalanced before hooking up the BMS. I'm planning to balance the batteries before assembling this, so this might not be a problem.

Maybe what I'll end up doing is to buy two Batrium K9 mons, assemble in one battery pack. If Batrium is having a hard time balancing, or there's an issue, then fall back to breaking it up to two.
 

OffGridInTheCity

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Dec 15, 2018
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2,033
Maybe what I'll end up doing is to buy two Batrium K9 mons, assemble in one battery pack. If Batrium is having a hard time balancing, or there's an issue, then fall back to breaking it up to two.
The K9(s) are not a strong as the mons... and per their own documentation its 5 weeks for 1000ah with mons and you have over twice that + a less strong balance with K9s. While I agree that regular (or alot of) balance should not be needed once you're initially balanced, it doesn't square with my experience with Batrium or their documentation. Seems like a bit of oversell to me :)

To be clear - I do recommend Batrium. If you go with the new Watchmon Core - it can do K9s or Mons. If the K9s don't do it, you can retrofit some mons and you can even have mutliple mons per cell.. so you'll have options without having to re-do the actual battery.

I'll be interested to see how this works for you - please let us know :)
 
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