LeftieBiker wrote:I was originally going by the post below, in which a Russian claims, in a video, to have swapped a 30kwh pack into a 24kwh Leaf - he claims it didn't work initially, but then did work when the 30kwh controller (I assume the LBC) was swapped as well. After that I think I got turned around by the discussion of the 40 to 30 swap. I apologize for the confusion. It should be noted, though, that using 30kwh packs in 24kwh Leafs does seem to be possible, with the bonus of getting to use the extra capacity.
First post on this page:
Bkvszomorito managed to get the 30 kWh pack to work in the 24 kWh Leaf because he swapped the LBC AND VCM. This will only work on 3/2013+ model Leaf's (not 2011/2012, nor apparently 2/2013 or earlier). Bkvszomorito used a 3/2013 Leaf. However, if you do this, the intelligent key immobilizer will trigger and then you will have to tow the leaf to a dealer re-activate your keys before the car can be driven.
bkvszomorito wrote:I have swapped the VCM (engine control) electronic controller and the battery pack, and it works perfectly, without any issue.
If your car is produced before 02.2013, unfortunately the VCM is not compatible, so it should not be easy to do the retrofit.
(The above quote is from a PM)
In terms of a straight cell swap from a 30->24, it appears the reference voltages are extremely similar between 40 & 30, but NOT between 30 & 24. Here's a link to the voltage graphs:
https://pushevs.com/2018/01/29/2018-nis ... eal-specs/
If you notice, both cells are fully charged at 4.2V, which means that putting a 30 or 40 kWh cells in a 24 kWh BMS will NOT overcharge them (my earlier post was incorrect and I will edit it to reflect this). However, the voltage where the rapid dropoff starts is 3.6V for the 24 kWh cells but only 3.3V for the 40 kWh cells. This means that a 24 kWh BMS (unless reprogrammed, which I'm not aware of anyone successfully doing) will show VLBW at 3.6V per cell. However, if using 30 or 40 kWh cells, 3.6V is only halfway through the discharge curve, meaning that you still have half the battery capacity remaining.
I think turtle typically kicks on around 3.0V per cell, so the car won't actually turtle, but it will just be a very confused car that can drive 80 miles at VLBW.
Because the voltage curves match between 30 & 40, this problem doesn't exist. Therefore, one should be able to simply do a 40->30 cell swap and have everything work (except range indication). However, bkvszomorito found that after doing such a swap, he had issues where the car was not fully utilizing the battery. It was charging only to 97% and turtling at 22%, leaving exactly 25% of the range (10kWh). So it appears that the 30 kWh BMS is somehow either hardcoded to 30 kWh (either intentionally or to fix the BMS range estimation issue) or the internal resistance of the 40 kWh cells is different enough to trigger strange behavior. The BMS that bkvszomorito used does have the firmware update for the 30 kWh range estimation.
This means that a 40->30 cell swap is possible, but only 30 kWh range will be available, and unfortunately, the reserved range appears to be near the bottom end of the battery. It would be ideal if the BMS only charged the battery to 75%, but alas, that's not how it appears to work. Nonetheless, the 40 kWh would have a lower DoD on each drive, so theoretically, it should last somewhat longer.
Hopefully this helps anyone who reads this, planning to do dissimilar cell swaps.