Question
I’m looking at buying a hell of a lot of 18650 cells and connecting them together for a large battery system for the build. I heard from the youtuber jehu garcia that cooling isn’t really necessary on batteries if their discharge stays at 1c (which i think is one amp per hour). I’m looking at around 4500 battery cells to make a ~70-80kw battery. The continuous power rating of the motor i’m looking at is 69kw. I put into the conversion calculator the voltage of the batteries and the discharge rate at max motor power (69kw). Am i doing this wrong? Can i just say that if i’m drawing 70kw from a 70kw battery that’s 1 amp or as i got almost 17,000 amps from the calculator does that mean i’m running the batteries at 4 times their rating when i’m maxing out the motor (that doesn’t seem right)?
Reply
moltenmetal
Absolutely DO NOT make your own battery pack out of 18650s. That would be, frankly, a completely idiotic move.
Also refrain from purchasing what I purchased, which were LiFePO4 prismatic cells. They are selling for virtually the same cost today as I bought mine for back in 2014. You can in contrast buy a Chevy Volt pack, complete from a wrecker, for 1/4 as much money. Those cells have a higher power to weight ratio by a lot, come with a BMS that other people have already hacked/cracked so you can make use of it, comes in nice “bricks” of 24-48 V that you can recombine into new series/parallel arrangements that best suit whatever motor/inverter you end up using etc.
DO NOT attempt to run any conversion without a BMS. A BMS, with at minimum an alarm trip on high and low voltage on every cell (or every group of cells in parallel) is minimally necessary safety equipment for working with Li ion high energy density cells. If you go without a BMS, expect to have a fire, because YOU will end up being the BMS and the likelihood that one day you screw up is very high indeed.
As to re-purposing OEM EV motors/transaxles and inverters- it can be done. It’s not for the faint of heart, and it doesn’t go well in all types of vehicle.
I’m not familiar with drivetrains or suspension arrangements in sprinter vans so will leave it to others to comment.
A trip to www.diyelectriccar.com would be more useful to you than a trip to YouTube in my opinion, as someone who did his own conversion and who is about to undertake another.