Electronics > Power/Renewable Energy/EV's
Nissan leaf 16v battery floating and inverting questions
badjob:
So I got 2 leaf modules to replace my lead acid in the solar setup and they are phenomenal. Unfortunately, I've now run into the issue that most good inverter manufacturers cut off at under 16V. |O Anyone know of a pure sine wave that will run at up to 16.4v?
I have a cheap inverter that doesn't seem to cut off but it's modified sine wave. Only 500w which is right where I like it. Yesterday I blew some caps on it but that was an easy fix. Still chooching along but it makes some power supplies whine.
If such a thing doesn't exist, what are my other options? Can I modify the over voltage cutoff easily? Some kind of step down?
The second question relates to charging. I asked all the solar guys but they weren't the nicest. I use an EPever MPPT that doesn't turn off float. I'm only charging the battery to 16.2v which is 4.05v per cell (80%). Some information says to float at 4.0V, some says to float way below where you are charged. Will Prowse, the youtube solar guy says to float at .1 below where you charge and then go back to boost at .3 below that. Nobody has an answer backed by any science.
When I charged the thing up and used 3.9v per cell, all charging stopped (good) but then my loads were taken up by the battery instead of the panels. 4.0 was slightly better but I saw some .5 amps tickling the battery for a while longer which I'd rather not have and it still took a while to start using the solar instead of the battery. I might try the prowse suggestion today.
If the floating isn't going to overcharge my battery, will it have any other negative effects? After all this thing will take 65A+ in both directions. Can such tiny currents .5A at most degrade it? :-//
NiHaoMike:
Could the MPPT be programmed to just hold the voltage at 4V/cell? Standard lithium charges to 4.2V/cell and settles back to about 4.15V/cell so a constant 4.1V/cell is OK. Nissan Leaf batteries are LiMn which charge to 4.1V/cell, so 4V/cell should similarly be OK. Maybe stick to 3.9V/cell to be conservative.
Have you considered hacking your cheap inverter to increase the duty cycle, then adding a LC filter on the output? Or go straight to DC. That boosts efficiency when using it to operate electronics. You can also connect the HVDC to a VFD and then get fancy V/Hz control for motor loads, at a fraction of the price of ready made solutions.
badjob:
I thought the leaf batteries went to 4.2v per cell just like other lithium. Everywhere says that is their max but I have never seen a datasheet in the wild. Like 4.16 was 99%. You might know better than me though. Anyways, with this profile I am hitting 4.04 per cell max, my solar puts out 7A at best. Perhaps I will back it off all by .1V? Want to be in the 80-85% range, not fully charged.
I'm all open to modifying the inverter and have a bunch of scraps lying around. I'll start searching to see if anyone has done something similar, too lacking knowledge to come up with it on my own.
This is what I have: https://www.amazon.com/Boost-Truck-Automotive-Power-Inverter/dp/B0051PULH6
As for DC/DC stuff I use buck and boost converters for whatever I can, some stuff is not really adaptable. The most useful part of this system is charging my radios and 18650s right now and that's all DC/DC.
Must say though, these batteries rock. They ran my corded drill and didn't lose much charge at all. Compared to lead acid was definitely worth it if they don't degrade. Thinking of doubling up on capacity even.
This and the seller is where I got 4.2 from : https://www.summet.com/blog/2015/10/31/how-to-build-a-16-volt-battery-module-from-six-nissan-leaf-cells/
john61ct:
LiNiCoAlO2 (NCA) or (more likely IMO) LiNiMnCoO2 (NMC) was the Leaf chemistry for 2014 and earlier, depends on who you believe
Apparently Lithium-Manganese, LiMn2O4 aka LMO (IMR?) afterwards.
afaic 4.2V is the "danger do not exceed" maximum for charging voltage.
Stopping anywhere near 4.1V, say 4.11V, is very very close to full capacity, much safer (boom bad!) and more conducive to longevity. As is charging at a low rate, say 0.2-3C
I recommend using a current-limiting charger with adjustable voltage setpoints and ideally allowing for a CC-Only stop-charge, or at least one where holding the Absorb/CV stage can be reduced to a pretty short mimimum.
Ideally allowing Float to be set to None, otherwise maybe set to 3.6V or so to carry concurrent loads, should be well below resting voltage after fully charged.
badjob:
So then I'm doing good but maybe closer to 90 than 80%. The absorb is supposed to be 10 minutes only, the lowest. In practice I think it runs longer. But this isn't a plug-in charger, its a solar charge controller. I only have the options I have. Ones with all of these abilities will cost more than the batteries.
I'll take another vote for float far below charging voltage. I kind of did this previously, but then the controller draws from the battery only and ignores the solar until the voltage drops to that level. I am in luck though, because I can't even reach .2c.
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