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Nissan Leaf 24v Bank [need guiadance]
#1
Hello World!.

Before I start, thanks for this wonderful database of knowledge, I did try to search for anything regarding Nissan leaf 24v config before posting but was unable to find anything that answers my questions. 


I'm currently using a "hybrid" system at my home, it's pretty small.

x2 355W Paneles ( 2 more on the way)
x2 12v AGM  110A at 24v
The inverter is an old Trace SW4024 that connects me to the grid if my batteries are low and charge them while the load is power from the grid.

I'm buying Nissan Leaf G1 Modules ( 6) to build a 24v Battery.


Here are my questions:

BMS: I don't like what's on eBay on the cheap side but can't afford batrium so I'm on the middle. I saw the chargery BMS8T and decided to go with that one as 3 Nissan Modules comes to a 6S config. Is this BMS a good choice?

Bank Configuration:  if I go with only 3 modules for a 24v 6s battery configuration comes easy to mind  (connect in series) and the BMS connection seems simple enough.

since I'm buying 6 of them I'm starting to get confused about how should I configure them, I could go for 3 pack of 2 modules in series and then parallel them to get my target. but is it healthy for the batteries? and how should I connect the BMS in this case?.



I appreciate your input.

PS: i just notice the mistake in the post name. sorry!

Regards from The Dominican Republic.
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#2
Moved as thread is about battery build, not progress of powerwall/pack.

any configuration is really healthy, per se. The unhealthy part comes in with if you connect them in such a way that a section in the series string has a different overall capacity to another section. So, lets say you go with 6s (6 packs, we'll say). Then if pack 2, for example, has a different capacity than any other pack by more than about 3% of the whole. This will make the BMS work far harder than it should.
If pack design is 20 Ah, then 3% would be 0.6 Ah. This would be about 20.6 Ah on the high end, and 19.4 Ah on the low end. Even this could be too much for some systems. The goal with pack design (regardless of what or how many makes up a pack) all packs in the series need to be as close to the same capacity.
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#3
(12-11-2019, 06:00 PM)Korishan Wrote: Moved as thread is about battery build, not progress of powerwall/pack.

any configuration is really healthy, per se. The unhealthy part comes in with if you connect them in such a way that a section in the series string has a different overall capacity to another section. So, lets say you go with 6s (6 packs, we'll say). Then if pack 2, for example, has a different capacity than any other pack by more than about 3% of the whole. This will make the BMS work far harder than it should.
If pack design is 20 Ah, then 3% would be 0.6 Ah. This would be about 20.6 Ah on the high end, and 19.4 Ah on the low end. Even this could be too much for some systems. The goal with pack design (regardless of what or how many makes up a pack) all packs in the series need to be as close to the same capacity.

Thanks, wasn't considering that part, ill keep it in mind.

So then What about the BMS placing os this battery config? if I parallel 2 modules (4 cells) will be considered as 2 cells by the BMS?

Regards.
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#4
Any packs/cells that are connected in parallel, the BMS will electrically see it as 1. So you could parallel 10 skids if you wanted, and the BMS would only see it as one. Though, the more you add in parallel, the more the balance portion has to work if there's any imbalance. More parallel = more capacity = more time to keep it in check. So you need to make sure you size your bms to your packs.
But, really, the balancing portion should be minimal if the packs are sized correctly with each other. If packs are continually needing balancing done quite often, then there are failing/weak cells in that section that should be addressed. Being that these cells are in a skid, it'd be hard to replace a few cells. So you have to future proof yourself as best as you can by sizing the bms to handle more than you would normally with a pack that's easier to work on.
Proceed with caution. Knowledge is Power! Literally! Cool 
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#5
(12-11-2019, 06:58 PM)Korishan Wrote: Any packs/cells that are connected in parallel, the BMS will electrically see it as 1. So you could parallel 10 skids if you wanted, and the BMS would only see it as one. Though, the more you add in parallel, the more the balance portion has to work if there's any imbalance. More parallel = more capacity = more time to keep it in check. So you need to make sure you size your bms to your packs.
But, really, the balancing portion should be minimal if the packs are sized correctly with each other. If packs are continually needing balancing done quite often, then there are failing/weak cells in that section that should be addressed. Being that these cells are in a skid, it'd be hard to replace a few cells. So you have to future proof yourself as best as you can by sizing the bms to handle more than you would normally with a pack that's easier to work on.


so if understand correctly this what i came up with (se attache img).

Thanks for your time.

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#6
I'm not familiar with the wiring configuration of EV battery skids.
What's the polarity of the Green bars you have there?

Normally, a BMS will have absolute Pos and absolute Neg. Then a wire connection in between each pack in the string (so where Pos and Neg meet).
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#7
The nissan leaf modules come with 2 cells inside and from what i could research from videos online, 1st cell goes in the middle terminal second cell on the pos, an so.
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#8
Ahhh, ok. So yeah, then your wiring would be correct.
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#9
So Nox, did your diagram work?  What BMS did you use for this?
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#10
Photo 
(09-16-2020, 03:24 AM)gathman Wrote: So Nox, did your diagram work?  What BMS did you use for this?

Yes, i used a Chargery BMS.

If you need better visual clarification of how to connect your BMS to the cells check this one out. (cant remember where i found it, sorry to the creator of this diagram)

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