Need explanation about Nissan Leaf charging process

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Lorand_91

Member
Joined
Oct 10, 2024
Messages
11
Location
Virginia
Hi!

So, since batteries generally need a higher voltage to charge than they are rated for, how does it work when we are only providing 120V and 240V (lvl1 and lvl2)?
What happens when we plug a lvl1 or lvl2 charger into a Nissan Leaf?
Does the car step up the voltage to the 360V needed to charge the battery?
Is there a built-in converter that handles this process?
 
Hi!

So, since batteries generally need a higher voltage to charge than they are rated for, how does it work when we are only providing 120V and 240V (lvl1 and lvl2)?
What happens when we plug a lvl1 or lvl2 charger into a Nissan Leaf?
Does the car step up the voltage to the 360V needed to charge the battery?
Is there a built-in converter that handles this process?
Yes, the Nissan Leaf has a built-in charger that steps up the voltage when you plug it into a Level 1 (120V) or Level 2 (240V) charger. It converts the AC voltage to a higher DC voltage, around 360V, which is what the battery needs to charge. So even though you're providing lower voltages, the car's charger handles the conversion to ensure the battery gets the power it needs. Awesome right!
 
Interesting topic! I'd like to know a bit more detail :) I think the battery is composed of lots of smaller stacks (moduls) of cells arranged in parallel? And these stacks are in series to get a total of 360 V (nominal)? Does the charger actually make sure every individual cell is charged, or is it only checking every stack? Or (I hope not) only the total voltage of the pack?

Also when the state of charge nears 100%, the charger will do a "balancing" round. I guess the charger stops, then the shunts turn on where needed to move energy from more charged modules to less charged ones (or are the shunts always on during charging?), the charger waits a bit, then it charges a bit more, and do that 3 or 4 times? Is that right?
 
Interesting topic! I'd like to know a bit more detail :) I think the battery is composed of lots of smaller stacks (moduls) of cells arranged in parallel? And these stacks are in series to get a total of 360 V (nominal)? Does the charger actually make sure every individual cell is charged, or is it only checking every stack? Or (I hope not) only the total voltage of the pack?

Also when the state of charge nears 100%, the charger will do a "balancing" round. I guess the charger stops, then the shunts turn on where needed to move energy from more charged modules to less charged ones (or are the shunts always on during charging?), the charger waits a bit, then it charges a bit more, and do that 3 or 4 times? Is that right?
 
I individually monitor my circuit breaker panel and the Leaf will begin to taper the charge current as it nears 100%. It will go from around 1450 watts down to around 600 watts, then pause for about 5 minutes, and do a short tapering charge 3 times. I'm not sure how the BMS is working, but as far as power draw, it does use power until the 3rd short charge is complete.
 
Hi!

So, since batteries generally need a higher voltage to charge than they are rated for, how does it work when we are only providing 120V and 240V (lvl1 and lvl2)?
What happens when we plug a lvl1 or lvl2 charger into a Nissan Leaf?
Does the car step up the voltage to the 360V needed to charge the battery?
Is there a built-in converter that handles this process?
If you're interested in details, purchase Leaf Spy Pro and an OBDII adapter and you can look at the voltage on all 96 cells that make up the battery pack. There's lots of threads on using Leaf Spy.
 
Ok, now I am more confident on this topic. Thanks guys!
@Steve52, maybe I will look. It was more a question out of worry. I don't know exactly what made me ask it, haha!
I will go through the threads then. I appreciate it!
 
I think the battery is composed of lots of smaller stacks (moduls) of cells arranged in parallel? And these stacks are in series to get a total of 360 V (nominal)?

Physically, there are 48 modules in series. Each module consists of 4 cells in 2P2S, meaning put 2 cells in parallel, and put 2 of those pairs in series. Each cell is about 4v; each module is about 8v; the whole pack is about 380v at full charge.

The system sees all of this as 96 cells. (Technically each of those logical cells is made up of 2 physical pouch cells in parallel, but is a single cell for all the electronics and software. Two 30Wh cells in parallel are completely indistinguishable from one 60Wh cell.)

Does the charger actually make sure every individual cell is charged, or is it only checking every stack? Or (I hope not) only the total voltage of the pack?
There are two separate devices in play, the charger and the BMS (battery management system). The BMS is inside the pack, and the charger is under the hood, outside of the pack. The BMS does all the work of managing each individual cell. The charger only provides the total voltage.

Also when the state of charge nears 100%, the charger will do a "balancing" round. I guess the charger stops, then the shunts turn on where needed to move energy from more charged modules to less charged ones (or are the shunts always on during charging?), the charger waits a bit, then it charges a bit more, and do that 3 or 4 times? Is that right?

Yes, with the clarification that the BMS inside the pack is the one that is managing those shunts to balance the individual cells.

And yes, the BMS is frequently rebalancing when the pack is active, whether driving or charging or sitting at a stop light. (Nissan has not published the exact criteria for exactly how or when it decides to rebalance any given cells.)
 
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Excellent! Thank you!

I also found this to complement your information: https://www.orionbms.com/manuals/pdf/nissan_leaf_modules.pdf

Nissan provides a center tap on each module to allow the BMS to discretely measure each of
the 2 internal cells in series

So the BMS monitors the 3.7v of two cells that are in parallel. Neat.

If there are 48 modules, and the system sees 96 cells, and in leaf spy the balancing between the cells looks like it is paired (one blue bar, one red, one blue, one red, etc.), is it faire to assume the shunts are fixed between the two pairs of each of the 48 modules? Or is it on a grid and cell #43 could balance with, say, #2?

This post seems to suggest the LBC (BMS?) can pair any two of the 96 cells: https://mynissanleaf.com/threads/always-shunting.15627/post-350041
 
If there are 48 modules, and the system sees 96 cells, and in leaf spy the balancing between the cells looks like it is paired (one blue bar, one red, one blue, one red, etc.), is it faire to assume the shunts are fixed between the two pairs of each of the 48 modules? Or is it on a grid and cell #43 could balance with, say, #2?

This post seems to suggest the LBC (BMS?) can pair any two of the 96 cells: https://mynissanleaf.com/threads/always-shunting.15627/post-350041
No, there is no pairing. They aren't shunts that move electricity from one cell to another cell. They are simply resistors that burn off extra voltage from any cell that needs it. Watch LeafSpy for a while and you'll see that there are often many more, or many less, than half red or blue. They are not paired off. Red is a cell being bled off, blue is not.

Yes, the LBC (leaf battery controller) is the BMS.
 
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