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Discussion Starter · #1 ·
Hello,

I am looking at using a Nissan Leaf Battery for my Project. the battery comes with 48 modules. I hope to configure a Pack at 7P7S. Is there an issue with putting 7 of these modules in parallel like this? Would I need any type of active balancing for this type of configuration?
Any help or response would be appreciated!
 

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I hope to configure a Pack at 7P7S. Is there an issue with putting 7 of these modules in parallel like this?
Since the module is a 2S2P combination of cells, the overall cell configuration would be 14S14P, for a nominal overall voltage of 52.5V... hopefully this is your intention. I don't know why you want such low voltage.

You would be one module short, of course; presumably you would buy one additional module.

Is there an issue with putting 7 of these modules in parallel like this?
No problem, you can parallel as many modules as you want if you're willing to fabricate appropriate bus bars or cables to connect them appropriately. You do need to connect the BMS tap terminals (the smaller one in the middle between the main terminals), not just the main terminals.

Would I need any type of active balancing for this type of configuration?
This has the same management needs as any other configuration, but the entire group of 7 modules is monitored and balanced as if it were just one module (two cells levels). With 7 modules in series you would need a 7-point (8 wires) BMS system. That would normally be an 8-point system with one input unused.
 

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This has the same management needs as any other configuration, but the entire group of 7 modules is monitored and balanced as if it were just one module (two cells levels). With 7 modules in series you would need a 7-point (8 wires) BMS system. That would normally be an 8-point system with one input unused.
I disagree. Each Nissan Leaf module (2s2p internally) should be treated as 2 cells, so you would have 14 cells in series. This is the reason the center tap is exposed (BMS purposes). So in addition to connecting each of the 7 center taps together for your 7p set of modules, you need a BMS wire on the center tap as well as the + and - taps, so that would be a 15 wire BMS.
 

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Discussion Starter · #6 ·
I disagree. Each Nissan Leaf module (2s2p internally) should be treated as 2 cells, so you would have 14 cells in series. This is the reason the center tap is exposed (BMS purposes). So in addition to connecting each of the 7 center taps together for your 7p set of modules, you need a BMS wire on the center tap as well as the + and - taps, so that would be a 15 wire BMS.
 

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I disagree. Each Nissan Leaf module (2s2p internally) should be treated as 2 cells, so you would have 14 cells in series. This is the reason the center tap is exposed (BMS purposes). So in addition to connecting each of the 7 center taps together for your 7p set of modules, you need a BMS wire on the center tap as well as the + and - taps, so that would be a 15 wire BMS.
Yes, sorry, I had explained that earlier and just put the wrong number in the final statement of the post.

GE11 is proposing to use, by coincidence, the same number of modules in parallel as in series, 7 x 7 for 49 modules in total. That's 7S (7P (2S 2P)), for an overall 14S 14P cell configuration as I had mentioned earlier in the post. Yes, that's a 14-point (15 wire) BMS.

The BMS requirement is not changed by the number of cells in parallel, although the balancing current needs to be suited to the capacity of the parallel cell group (an enormous 14 times 33.1 Ah or 463 Ah in this case).
 

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Since the module is a 2S2P combination of cells, the overall cell configuration would be 14S14P, for a nominal overall voltage of 52.5V... hopefully this is your intention. I don't know why you want such low voltage.
I am still wondering about this. Why only 52 volts?

You would be one module short, of course; presumably you would buy one additional module.
This is an awkward aspect of the 7x7 choice. Why not for instance, parallel modules in groups of 6 (instead of 7), and connect 8 (instead of 7) of those groups in series, for 48 modules (the number in a pack, not 49) in total, and an overall 16S 12P configuration, using a 16-point (17 wires) BMS?
The straightforward configuration choices for a full set of Leaf modules, without creating parallel strings:
  • 48 groups of 1 module = 48 modules with cells in 96S 2P configuration for 360 V nominal (stock Leaf)
  • 24 groups of 2 modules = 48 modules with cells in 48S 4P configuration for 180 V nominal
  • 12 groups of 4 modules = 48 modules with cells in 24S 8P configuration for 90 V nominal
  • 8 groups of 6 modules = 48 modules with cells in 16S 12P configuration for 60 V nominal
  • 6 groups of 8 modules = 48 modules with cells in 12S 16P configuration for 45 V nominal
  • 4 groups of 12 modules = 48 modules with cells in 8S 24P configuration for 30 V nominal
  • etc...
To minimize the size of cabling required and provide the greatest range of motor speed, the general approach would be to choose the highest voltage compatible with the controller and other devices. The controller also needs to handle the target maximum motor current, which is not the battery current and is not changed by the battery voltage.
 
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