Originally Posted by smoothoperator
The ESS of a Tesla requires much more management and is incompatible with the Karma thermal system. The engineering cost to put such 18650 batteries in a Karma enclosure, along with the thermal systems that would need to be installed/engineered would be astronomical. The whole car would need to be re-engineered. This along with the new BMS and custom engineering and integration work needed to implement a completely different battery chemistry make it cost prohibitive to go that route. It would cost millions. From my experience it is best to use battery technology that is closest to what the car was designed for. We are talking about off the shelf modules used in other cars vs custom engineering a small form factor battery that Tesla has poured many hundreds of millions into perfecting. Heck even Rimac uses these A123 batteries and they are an extremely lean performance EV company that does most everything in house.
you don't want to use Tesla approach. Among other reasons, check out YouTube videos of LiCo fires.
What we are doing is junking the gasoline side altogether and fitting Enerdel batteries into the original pack and the spaces that are cleared in the front. A quick photo of our project below. You can see a native pack on the right.
Replacing cells in the main pack might seem simple but it isn't. Couple of reasons:
1. Central BMS expects certain signals from the cell-level BMS boards. So you want to keep the same BMS electronics. This means you need the same cell count. This means that you are now constrained on the AH per cell. This means that you might not be able to realize any gain in pack size after all as cells come in very discreet capacity levels
2. cell-level BMS will be designed to fit the module that's in the car now. It won't fit (physically) on anything else.
3. If there is any difference between the chemistry used in the car and chemistry you are using, BMS will not be happy and may result in you not being able to utilize full capacity of your new battery
4. You would be lucky to achieve 50% space utilization of that 260 liters. Connectors, cables, cooling, BMS, cell hardware, etc. Datasheet for A123 cells used in Fisker
. You will notice that at the cell level, these have ~250WH/liter density. If you could utilize 100% of 260 liters available, you would have a 65kwhr pack. That would be nice. There is a reason why it's not 65kwhrs...
My [well informed] assessment is that it will be very hard to achieve anything beyond 25kWHr usable in the native pack space without going to dangerous chemistries such as Tesla's.