Uggh! Too many options = brain fog
Posted: Thu Apr 22, 2021 10:29 pm
I am in possession of a 2017 Leaf HV pack (out of a 2012), it has all the later parts, BMS etc. My initial plan was to use only 240v (10F, 20R), now I am thinking that going higher @ 320v (since all my relay parts are from the same vehicle and can handle it) would provide a more enjoyable vehicle.
Why this topic? I am completely overwhelmed with the BMS question. If I use the whole pack, split in two, it is academic. However, if the two packs become isolated during charge/discharge, the Leaf BMS is fried; so that path has a lot of risk
If I split the 320v into two equal halves (20F, 20R), I *could* charge them separately as well, eliminating some measure of complexity as I could use a standard US outlet of 120v. But that affects the weight balance F-R negatively (designed for about 30kg of "fuel" in the front, not 90kg :O) Best option is like 16F & 24R for weight balance. This makes reusing the Leaf BMS essentially impossible.
If I use a hardware solution that will ONLY protect the modules from over-voltage, I can split the pack any way I want, but.... the upper voltage limit would need to be carefully set. From reading everything I can find (here, DIYEV, P&S, Nissan etc) it seems like 4.5v is the absolute max charge voltage - the point at which damage can occur, so keeping lower than that is critical.
Then there is the question of temperature. Charge between 0C and 40C ONLY, stop discharge above 50C or so to avoid thermal run-away. Yea, that is simple for me to implement with hardware on both ends of the limit.
The LAST thing I want is dangerous, then unreliable, then short-lived, then messy, in order. Since I plan to only S L O W charge, that should be easily controlled with the Openinverter VCU to limit total pack voltage. Given the low current, individual module or cell shunts could easily be fitted and provide more than adequate safety. The idea is a 4.1v Zener and 470R resistor for each cell, or *maybe even one Z4.1 + 1000R and Z4.3 + 1000R in parallel per cell* and let the VCU handle the cut in-out voltage for the pack. I would also use snap-switches to enable the charge above 5C and cut everything off above about 50C.
Now for the question... How crazy am I?
Why this topic? I am completely overwhelmed with the BMS question. If I use the whole pack, split in two, it is academic. However, if the two packs become isolated during charge/discharge, the Leaf BMS is fried; so that path has a lot of risk
If I split the 320v into two equal halves (20F, 20R), I *could* charge them separately as well, eliminating some measure of complexity as I could use a standard US outlet of 120v. But that affects the weight balance F-R negatively (designed for about 30kg of "fuel" in the front, not 90kg :O) Best option is like 16F & 24R for weight balance. This makes reusing the Leaf BMS essentially impossible.
If I use a hardware solution that will ONLY protect the modules from over-voltage, I can split the pack any way I want, but.... the upper voltage limit would need to be carefully set. From reading everything I can find (here, DIYEV, P&S, Nissan etc) it seems like 4.5v is the absolute max charge voltage - the point at which damage can occur, so keeping lower than that is critical.
Then there is the question of temperature. Charge between 0C and 40C ONLY, stop discharge above 50C or so to avoid thermal run-away. Yea, that is simple for me to implement with hardware on both ends of the limit.
The LAST thing I want is dangerous, then unreliable, then short-lived, then messy, in order. Since I plan to only S L O W charge, that should be easily controlled with the Openinverter VCU to limit total pack voltage. Given the low current, individual module or cell shunts could easily be fitted and provide more than adequate safety. The idea is a 4.1v Zener and 470R resistor for each cell, or *maybe even one Z4.1 + 1000R and Z4.3 + 1000R in parallel per cell* and let the VCU handle the cut in-out voltage for the pack. I would also use snap-switches to enable the charge above 5C and cut everything off above about 50C.
Now for the question... How crazy am I?