It’s been a while so here’s a progress update:
Swapping Generation 2 (G2) cells into a Generation 1 (G1) Nissan Leaf project update.
We swapped the G2 cells into our original G1 case. We kept the wiring, busbars etc from the G2 intact but kept the temp sensors, relays and other non-cell stuff of the G1. Our initial assumption that the Battery Management Computer (BMS) sense leads would be identically wired in both generations was proved wrong when we connected the G1 BMS computer to the G2 loom and, “Let the smoke out”, i.e. burnt some electronics in the BMS.
Lesson 1: Don’t make assumptions when a couple of quick tests can provide data.
This was a big problem because it seems that the car will only talk to the BMS it is programmed to. Only Nissan can re-program it and they are not keen on helping. Some research and help from good guys both here on MNL (I’m not going to explain that acronym!) and other places led us to believe that the ID of the BMS is held on one chip, IC9. This chip is fairly easy to move with good hobby solder and de-solder equipment.
We obtained another G1 BMS and set off to try again.
First we swapped the bus bars and sense leads from the G1 cells onto the G2 cells. This wasn’t too bad because the leads are all held nicely in place by the insulators. With some power tools (set to lowest torque) and a decent height workbench it was a quick process. We kept the metalwork structure of the G2 cells and this meant a little modification to the main (rear) cell bank. There’s a bar which goes right across the pack on the G2 which when combined with G1 conductors would perfectly short-out the 200V, 12kWh bank. So we cut down it rather than starting an impressive fire-this was a literal hack using a hacksaw!
Next we de-soldered the all-important chip, IC9, backed up its contents with an EPROM flasher/reader, then soldered it onto our replacement G1 BMS. This all went smoothly.
Bringing the rebuilt cells and BMS together in the G1 case all seemed good. Lid bolted down, battery bolted into car, connections made, park-lock override fuses and 12V reconnected, power button, hmmm. Not good...
We had battery health bars showing but no state of charge (fuel gauge equivalent) and no range, just ---. Leaf spy showed pack voltage OK and SOC at about 40% which is what we expected. However it had no individual cell data. Some head scratching, a realisation and a few choice curses later I realised I hadn’t put the busbar connecting the two smaller cell banks in.
Lesson 2: Check your work before testing it.
Off with the 12V and connectors, down with the battery, off with the case, in with the busbar, on with the case, up with the battery, on with the leads and 12V, on with the power button, same result. Its late now and we’re at high mistake risk so tidy up, go home and think.
Three possibilities spring to mind:
1. We fried another BMS. With that busbar out the power may have tried to go through the BMS instead. We’re not sure we heard the isolating relays clunk and so we’re not sure any power has even tried to get through.
2. We messed up on the restart procedure.
3. Something wasn’t right with the new BMS and what we did to it. Firmware issues? Changing IC9 isn’t the magic bullet?
We have our feelers out for anothernother BMS but are not sure what exactly to investigate if this isn’t the cause. We are however enjoying the process. We are learning lots.
Any ideas and theories will be gratefully received and considered