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BMS Limitations?  

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krumholz
(@krumholz)
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01/12/2017 12:17 am  

Is there any limit on how many cells I can add in parallel to one of your 48v bms's? fyi - I'm working with 845 cells and would like to build 5 - 48v batteries (13s13p).

Bonus question: would you bestow any kind of a volume discount for that type of a setup?


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garolittle
(@garolittle)
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01/12/2017 9:59 am  

Excellent question. I have the same question so let’s wait for a response together.  


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krumholz
(@krumholz)
Street cred = 10 mAh
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Posts: 4
01/12/2017 11:16 am  

I should have specified that I'll be getting kits and bms's for all of the batteries. It's also looking like I'll be getting closer to 1000 batteries, so 20 kits and maybe 4 or 8 bms's.


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Micah (Vruzend Rep)
(@admin)
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02/12/2017 11:13 am  

Theoretically no, there is not a limit to the number of cells that can be put in parallel when using our BMSs. When the cells are in parallel, they basically act like 1 big cell, so all the BMS "senses" is 1 big cell. However, the main practical limitation just becomes the balancing time. If your pack does get out of balance over time and the BMS starts balancing it, the low balancing current means larger parallel groups takes longer to balance. This usually isn't an issue, but theoretically if you had 100 cells in parallel, that could take days or more to balance if severely out of balance.

However, for that and many other reasons, its better to build a few packs and put the packs in parallel, than just parallel hundreds of cells in a single pack.

For something around 20 kits I do believe we can work in a discount for you - though I can only speak for the USA operations. If you are ordering from outside the US, I can check with the international order center for you regarding volume discounts.


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krumholz
(@krumholz)
Street cred = 10 mAh
Joined:5 months  ago
Posts: 4
07/12/2017 11:42 am  

I think I'll start by making a small initial order so we can test out the diy battery process and then move on to making a bigger order once we know that will work for us.

With the 30 amp maximum rated discharge current on the 48v bms, is that figured by using the C rate of the batteries or the battery capacity? For instance, if I have a 13s10p pack with batteries at 2600 mAh, the pack would be 26ah but would I need to know the  C rate to figure out whether I could discharge at the 30 amp limit? How do I locate the C rate of the batteries?


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krumholz
(@krumholz)
Street cred = 10 mAh
Joined:5 months  ago
Posts: 4
07/12/2017 3:07 pm  

Ordered some laptop batteries from ebay and thought I was getting 9 2600mAh cells based on the laptop battery packaging but when I tore the casing off, the batteries were 1800mAh. Other than taking a 30% hit on capacity, is there a downside to building a 48v with these?


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