ripple4
Well-known member
New leaf owner here. lurked quite a bit. i gathered up pieces for an idea around the web and wanted to float an idea to see if i was missing something, what could go wrong and try to get ideas on how to work around any potential issues. I was looking at 32ah 3.7v pouch cells and found that it may be possible to make a leaf battery for less than Nissan is selling for. Alibaba has got 3.7v 32ah pouches for $27/each which times 192 is $5200 + shipping. assuming no volume discount. these cells advertise 3000 cycles, which is more than 9 years of life.
https://www.alibaba.com/product-detail/3-7v-80156240-32Ah-Lithium-polymer_60741109055.html?spm=a2700.8592591.0.0.23a910a9o1UCd1
After watching some YouTube about dissembling a 4-cell unit the pouch tab design looks to be unique on the Nissan cells, both side to side and in protrusion from the cell. Also the internal black plastic supports for the cells might not be reusable since the internal connection would need to be in different places. But with ABS plastic and 3D printing a new end cap could be made with new bus bars resistance welded to the generic cell tabs and locate the buss bar connection lugs in the correct spots for the leaf pack wiring. or the cell ends could be wired to connection points and then encapsulated in epoxy with mounting holes that are cast in.
Going further, if one was going to make a clean sheet cell format, since the Nissan cells are ~52mm thick then one could stack 6x 8.5mm pouchs into the same thickness. then it would not be space prohibitive to upgrade from the 2p2s cell arrangement to a 3p2s arrangement and still fit in the stock battery case. also one of the biggest complaints i read is battery cooling. i suggest that since cells are slightly thinner without the aluminum cans and various air gaps, it would be possible to install copper heat conduction sheets every second cell layer and tie the ends opposite of the buss bars with a fluid heat transfer block. the heat transfer fluid i would use something like mineral oil or low viscosity transformer oil, in case it ever leaked. and then plumb each of the 48 heat transfer blocks to a liquid/liquid heat exchanger that connects to the leafs gylcol coolant system. coolant pipes run back to the charger on '11 and '12 cars so teeing into those would be the plan.
proposed layout:
https://ibb.co/e7dk2K
if that was not enough to soak in, they have pouch cells that go up to 50ah in close to the same size format, which would push the stock 22.1kw cars up to 35.5kw in the 192 cell 2p2s. but with 288 cells in a 3p2s arrangement then pack capacity would be 51.8kw, still fitting into the stock battery case and with active temperature management.
Lastly, looking at videos of people who put in G2 cells into old G1 cars, they seem to say that the cars original BMS will not immediately allow the extra capacity, but over time it will learn to use it and give extra miles on the range meter. (http://www.mynissanleaf.com/viewtopic.php?f=30&t=24732&start=10) so in principle with enough time, the courage to open the traction pack, re-engineer what hundreds of very very smart professionals perfected, might save some money and/or give capabilities not previously possible. it maybe possible to create a battery after Nissan stops supporting the car at the end of the day. Do the experts see problems here? what could go wrong with each step and how could it be worked around? i personally dislike newbie post with grand plans, and if i'm not missing anything i was going to get 6x 50ah cells and make one battery unit cell and attempt to test it, like seeing how fast it can charge without overheating with the cooling sheets. what the real capacity would be of the 50ah 3p2s unit cell within the limits of the BMS voltage cut offs. etc.
opening up pack to get to unit cells
https://www.youtube.com/watch?v=0dBjPwJ_Qaw
opeing up unit cells and looking at pouch cells
https://www.youtube.com/watch?v=WcqaAz1vjlo
https://www.alibaba.com/product-detail/3-7v-80156240-32Ah-Lithium-polymer_60741109055.html?spm=a2700.8592591.0.0.23a910a9o1UCd1
After watching some YouTube about dissembling a 4-cell unit the pouch tab design looks to be unique on the Nissan cells, both side to side and in protrusion from the cell. Also the internal black plastic supports for the cells might not be reusable since the internal connection would need to be in different places. But with ABS plastic and 3D printing a new end cap could be made with new bus bars resistance welded to the generic cell tabs and locate the buss bar connection lugs in the correct spots for the leaf pack wiring. or the cell ends could be wired to connection points and then encapsulated in epoxy with mounting holes that are cast in.
Going further, if one was going to make a clean sheet cell format, since the Nissan cells are ~52mm thick then one could stack 6x 8.5mm pouchs into the same thickness. then it would not be space prohibitive to upgrade from the 2p2s cell arrangement to a 3p2s arrangement and still fit in the stock battery case. also one of the biggest complaints i read is battery cooling. i suggest that since cells are slightly thinner without the aluminum cans and various air gaps, it would be possible to install copper heat conduction sheets every second cell layer and tie the ends opposite of the buss bars with a fluid heat transfer block. the heat transfer fluid i would use something like mineral oil or low viscosity transformer oil, in case it ever leaked. and then plumb each of the 48 heat transfer blocks to a liquid/liquid heat exchanger that connects to the leafs gylcol coolant system. coolant pipes run back to the charger on '11 and '12 cars so teeing into those would be the plan.
proposed layout:
https://ibb.co/e7dk2K
if that was not enough to soak in, they have pouch cells that go up to 50ah in close to the same size format, which would push the stock 22.1kw cars up to 35.5kw in the 192 cell 2p2s. but with 288 cells in a 3p2s arrangement then pack capacity would be 51.8kw, still fitting into the stock battery case and with active temperature management.
Lastly, looking at videos of people who put in G2 cells into old G1 cars, they seem to say that the cars original BMS will not immediately allow the extra capacity, but over time it will learn to use it and give extra miles on the range meter. (http://www.mynissanleaf.com/viewtopic.php?f=30&t=24732&start=10) so in principle with enough time, the courage to open the traction pack, re-engineer what hundreds of very very smart professionals perfected, might save some money and/or give capabilities not previously possible. it maybe possible to create a battery after Nissan stops supporting the car at the end of the day. Do the experts see problems here? what could go wrong with each step and how could it be worked around? i personally dislike newbie post with grand plans, and if i'm not missing anything i was going to get 6x 50ah cells and make one battery unit cell and attempt to test it, like seeing how fast it can charge without overheating with the cooling sheets. what the real capacity would be of the 50ah 3p2s unit cell within the limits of the BMS voltage cut offs. etc.
opening up pack to get to unit cells
https://www.youtube.com/watch?v=0dBjPwJ_Qaw
opeing up unit cells and looking at pouch cells
https://www.youtube.com/watch?v=WcqaAz1vjlo