Extra Battery, How to Integrate with 24kWh Traction Battery?

[mux]

Those specs... well, don't use them. No way those are lithium polymer, no way they're high voltage chemistry, no way that you can safely discharge to 2.5V and get rated cell life. That last point is moot anyway obv, as the Leaf will cut them off at 3.2V/cell anyway.

Well, I guess it's time to run the wiring now! Sounds like you're getting an extended Leaf in the near future.

[jkenny23]

Don't hold your breath, I'm moving to another state in a little over a month and have no garage (and no free time) now, so the actual installation won't be for at least that long. I do however plan to fully test all 12 modules (somewhat necessary since they weren't able to give me matched modules from a single pack), and will keep them in my trunk to see how living with the extra ~180 lbs and reduced trunk volume is. Currently I get between 4.1-4.7 mi/kWH depending on weather and percent of highway driving/driving with passenger.

I'm well aware I can't use the full voltage range of the cell, it was just an added bonus that they're technically rated for 4.3V, which means at only 4.03-4.11V charged these cells should last a very long time. I expect the real pack usable capacity will only be around 5-7 kWH. I'll run my same "4.11V vs. 4.3V" discharge test that I had done previously, this time on a 4.35V rated Sanyo 18650, to get a better idea of what I might expect.

[arnis]

Those specs... well, don't use them. No way those are lithium polymer, no way they're high voltage chemistry, no way that you can safely discharge to 2.5V and get rated cell life. That last point is moot anyway obv, as the Leaf will cut them off at 3.2V/cell anyway.

Well, I guess it's time to run the wiring now! Sounds like you're getting an extended Leaf in the near future.

Leaf cutoff is around 2.6V. And it is absolutely safe to discharge down to 2.6V with no "excessive" degradation.
I do that constantly and I have one of the best surviving Leaf battery packs on this planet

[mux]

Those specs... well, don't use them. No way those are lithium polymer, no way they're high voltage chemistry, no way that you can safely discharge to 2.5V and get rated cell life. That last point is moot anyway obv, as the Leaf will cut them off at 3.2V/cell anyway.

Well, I guess it's time to run the wiring now! Sounds like you're getting an extended Leaf in the near future.

Leaf cutoff is around 2.6V. And it is absolutely safe to discharge down to 2.6V with no "excessive" degradation.
I do that constantly and I have one of the best surviving Leaf battery packs on this planet

It... is? Oh, you mean on the '13-'17 Leaf! The '11-12 Leaf has a 3.2V cutoff (with turtle coming on at 3.22V)

[arnis]

Maybe it depends on degradation levels?

[mux]

No, cutoff is hardcoded and completely dependent on battery chemistry. LMO/LCO batteries are always cut off well above 3V, because there is basically no charge under 3.5V. NCA on the other hand (the 'Lizard' and beyond battery chem) is usually cut off between 2.5 and 2.75V and still has quite a decent chunk of charge left under 3.5V.

[jkenny23]

Well my pallet of very well protected/packed batteries arrived today, only opened one up so far to check. Main battery terminals are on the smallest side of the battery, there's channels for airflow through it for active thermal management if needed, and there's a 10-pin balancing connector (no BMS on the battery module itself), with a little fuse block for the balancing connector on the side. Will start testing these modules next week:



I also got my Leaf module today (newer type, 500WH). I made up a couple cables to connect it to my 10A battery tester, and re-wired my other battery current/voltage monitor so I will be able to check the split of current between the Leaf module and the "extender pack" which is starting with the Boston Power Swing 5300 cells in 2s2p:



Should be able to start that test cycle tomorrow and have it run through the weekend. At only 5A charge and 10A discharge it will take around 15h for charging and 7.5h for discharging.

[mux]

Don't want to spoil an otherwise nice post, but you shouldn't have gotten the new Leaf module, unless your car has the same type. They only used LMOs in the '11-12, after then they quickly shifted to aluminum-based and those have very different discharge curves.

[jkenny23]

Don't want to spoil an otherwise nice post, but you shouldn't have gotten the new Leaf module, unless your car has the same type. They only used LMOs in the '11-12, after then they quickly shifted to aluminum-based and those have very different discharge curves.

Is that true even for the 24kWH "lizard" pack? Info here suggests it kept the same LMO cathode but changed electrolyte: https://pushevs.com/2018/03/20/nissan-l ... batteries/

[mux]

Yup, the Lizards are not LMO. They're already relatively high-cobalt NCAs. Totally different chemistry.

Edit: meh, it's a lot more nuanced than that technically. The LMOs of first were heavily aluminumized LMOs to deal with the high discharge current. The lizards are probably manganese-cobalt-aluminum hybrids. You can't just change the electrolyte to deal with heat issues, the degradation is just as much due to electrode materials. That being said, all I have to go on is discharge curves, I haven't done any chemical analysis on them.

Regardless, you'll see more capacity down between 2.75-3.5V in a Lizard battery. It's not as pronounced as the difference with modern '16-'17 NMCs, but it's a decent enough difference that it's probably not a good analogue for the early LMOs.