# Tesla style DIY replacement Leaf battery help

#### PES2000nz

##### 1 µW
Apologies in advance as I am new to the forum and only have rudimentary electronics knowledge. I have searched this excellent forum and google and have not found the answers I require so reluctantly have decided to post in seek of help.

I would like to build a Tesla style DIY replacement Nissan Leaf battery using 18650 cells that is liquid cooled. I understand that the Gen 1 Leaf uses 48 modules each of 4 cells at 3.75V and 32.5Ah each. The module is a 2S2P arrangement. So total system is 360V with 23.4kWh.
The motor is 80kW so I calculated the current required would be around 220A based on 360V.

So if I use the LG HG2 18650 cell 3.7V/3Ah/20A:
Module = 22 cells in parallel 3.7V/66Ah/440A
Pack = 12 modules in series 44.4V/66Ah/440A
System = 8 packs in series 355.2V/66Ah/440A
Total 23.4kWh 355.2V 440A

Are my calculations correct as I cannot find the motor current specifications and am uncertain about the requirements of continuous vs max current requirements and whether current requirement will be less as the motor is three phase.

Once again my apologies for what is probably elementary mathematics for most forum users.

Phase current will differ from battery current (it can be greater) but the kW drawn from the battery remains the same.

It's a hell of an undertaking to make a well engineered (safe, reliable) battery from that many cells. I couldn't advise you of the best route, but I'd take a good look at repurposing existing OEM automotive battery modules as a potentially easier alternative.

Thank you for taking the time to reply.
Can I assume that the 80kW motor will not require more than 220A (plus some efficiency losses). Is a battery pack with greater current i.e 440A in this case compatible with the motor if it only requires 220A.
If I am to start looking for compatible OE batteries then I need the same specs i.e. 360V and 220A. Most batteries/packs have voltage and capacity listed but I struggle to find the current.

Yes, 80kW of power delivered to the motor with a 360V battery should require approx. 222A (it will be a little more due to controller losses of a few percent).

I don't know enough about the Leaf as to whether the motor power is 80kW input maximum or if there is a higher momentary peak-rating.

The maximum current output of batteries is often stated as "C" rather than a figure in amps. It's just a multiple of the cell capacity. So a 10C 5Ah cell is good for 50A. If memory serves the standard Leaf cells are rated at 10C.

Your math is correct, but the leaf doesn't charge above 4.1v for cell longevity reasons, so you'd need to add around another 10% to meet the original spec. Why 18650 replacement? Do you have an end of life gen 1 pack?

I would suggest looking at other used EV batteries, like Chevy Volt or whatever is available.

If you have an older Leaf, the batteries pretty much sucked on those but the newer ones are better, so a pack from a newer one might make a lot of things easier.

I have 14 leaf modules in my golf cart - from a 2014 Leaf that had 300 miles on it. Had them three years with great results. Problem is finding them.

Yes my poor leaf's battery pack is degrading rapidly. All the 2nd hand Leaf's in New Zealand are imported from mainly Japan or the UK and are not covered under any form of warranty and Nissan are not providing any support. Replacement batteries are not available nor are any used cells whether Leaf or Volt hence the interest in 18650 cells. Realistically it is probably cheaper just to buy another 2nd hand leaf But I thought I would do the due diligence on such a project.
Am I correct that higher rated current for the pack (440A vs 222A required) is not an issue.

I'm looking to do some thing similar with some iMiEVs here in Perth, but a few Nissan Leafs are in the same boat now.
Try to use the existing BMS wiring looms and so on, so that there's minimal interruption to the current system. And a Liquid cooled battery is quite feasible wit the Leaf packs - heaps of spare room once you use a high energy density cell.

440A is no problem, in fact it's better for the battery as it's less stressed due to not being asked to deliver its maximum rated current

PES2000nz said:
Yes my poor leaf's battery pack is degrading rapidly. All the 2nd hand Leaf's in New Zealand are imported from mainly Japan or the UK and are not covered under any form of warranty and Nissan are not providing any support. Replacement batteries are not available nor are any used cells whether Leaf or Volt hence the interest in 18650 cells. Realistically it is probably cheaper just to buy another 2nd hand leaf But I thought I would do the due diligence on such a project.
Am I correct that higher rated current for the pack (440A vs 222A required) is not an issue.

I sent you a pm, I happen to have an early leaf pack in excellent condition with low km. I bought a wrecked leaf for the drivetrain

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