coulomb wrote: ↑
Sun Oct 13, 2019 3:33 am
Lothsahn wrote: ↑
Sat Oct 12, 2019 11:18 pm
By high, I meant 75% (as shown in the picture). The slope of the curve is rather flat there--especially compared to the bottom 10% of the battery.
Ah. The last 10% is "off the cliff", which I assume we (and Nissan) are staying away from.
Between 10 and 50 Ah, the voltage changes .3V, but that covers 72% of the capacity of the battery.
Actually, I read 0.5V (2.5 divisions of 0.2V each). That's about 0.5/3.65*100% = 14% of nominal voltage. I would not call that "flat". I agree that is it flat relative to the cliff, but I assume that the cliff is off-limits. Am I wrong assuming that the cliff is off-limits?
Ah crud. I misread 3.9 as 3.7. You are right. .5V.
That said, you and I are saying the same thing with different terms.
What I call flat, you're calling not flat. I think the primary reason is I was trying to illustrate that when at VLBW/Turtle in a Leaf, the voltage differences are huge (because you are off the cliff), whereas when it's charged, they're not. On the other hand, your experience is with other chemistries and potentially power regulators (where a .5V difference is significant). In short: Large = off cliff, Small=the normal section of the curve between cliff and 4.1V.
The assumption that Nissan is staying away from "off the cliff" is a good one, but unfortunately, not correct. To maximize range, Nissan does in fact allow cells to go quite low--here's a few posts on turtle voltage, seeing 3.2V and potentially even lower:
Keep in mind that those posts are about the 24kWh Leaf, which has a different voltage curve than the one we've been looking at for the 40 kWh cells:
https://qnovo.com/wp-content/uploads/20 ... harge2.gif
(you can see the cliff starts at 3.4-3.6V, depending on current draw)
This is why it's critical to immediately charge the leaf if you ever get to VLBW or Turtle--you've already started down the cliff, and it's not good to leave the cells at that low SOC for long.