Leaf Gen1 Cells state of health- your opinion?

[Zapatero]

Hi,

i would like to have your opinion on the state of health of my battery cells:

I hava a Gen 1 Pack that has 24Kw/h of Energy. Today i drove it down 3.2 Volts on the lowest cell and 3.4 Volts on the highest cell.
When i have less volts in my pack i can see significant differences in the cell voltage. I think i should exchange the lowest cells!





Then i fully charged it on a public charging station to see how much kw fit into the car:





This is the result, the car was 100% charged when i unplugged it: 19,08 Kw/h





What do you think? Is this the capacity to expect from the Leaf cells or should it be better?

Cheers, Philip

[Kevin Sharpe]

What do you think? Is this the capacity to expect from the Leaf cells or should it be better?

What's the history of the battery? Has it been bottom balanced? Are you using the Nissan BMS or a third party system?

3.2V is very low and a 200mV difference between cells is huge. This is a useful guide;

[Zapatero]

I have an Orion BMS 2.
What exactly is bottom balancing? I'm not familiar with that.

Johannes told me that the information above is not quite correct. He uses the leaf BMS and told me that 3.5 Volts is 15% of charge.
Hopefully he will chime in on this!

[Kevin Sharpe]

I have an Orion BMS 2.

That could explain the differences between modules. I'd recommend parking your car outside until you understand what's happening.

I'd also suggest you read this post and ask yourself why we spend so much time encouraging people to use the OEM BMS;

https://www.patreon.com/posts/batman-41339476

What exactly is bottom balancing? I'm not familiar with that.

It's a big topic... start here;

http://evtv.me/2009/11/get-rid-of-those ... -circuits/

Johannes told me that the information above is not quite correct. He uses the leaf BMS and told me that 3.5 Volts is 15% of charge.
Hopefully he will chime in on this!

Each generation of Leaf module uses different chemistry and that might explain some differences. That said, it's critical you understand the battery limits if you are discharging down to 'zero' or below

[Zapatero]

That could explain the differences between modules. I'd recommend parking your car outside until you understand what's happening.

i was assuming that the difference is the result of the capacity. So the lowest cells are the weakest ones and should be replaced.

I'd also suggest you read this post and ask yourself why we spend so much time encouraging people to use the OEM BMS;
https://www.patreon.com/posts/batman-41339476

Unfortunately the information not public. But does it mean the LEAF BMS uses bottom balancing method?

It's a big topic... start here;

http://evtv.me/2009/11/get-rid-of-those ... -circuits/

I've read this and the orion BMS adressed this issue. It monitors the lowest and the highest cell and while discharging the lowest cell will be the bottom limit and while charging the highest cell will be the upper limit, so that the cells will not exceed their limits.
See Page 19 of the Manual:
https://www.orionbms.com/manuals/pdf/or ... manual.pdf

Each generation of Leaf module uses different chemistry and that might explain some differences. That said, it's critical you understand the battery limits if you are discharging down to 'zero' or below

3.5 Volt is where the discharge rapidly increases. But still doesn't mean that the cells cant be discharged a bit more? Of course this will not have a positive effect on the lifespan!

Johannes told me that 3.5 Volt on his BMS on the same Leaf cells like i have are still 15% of charge!

[Zapatero]

Have these informations been validated?
As i said, i have different informations from Johannes!

I would love to see some more data on this topic!

[Zapatero]

http://media3.ev-tv.me/DOEleaftest.pdf

Here's more different information


According to Kevins information i will now figure out where the balancing drift on the bottom end begins and try to set this as my low voltage.

Also i have to say that my car was in turtle mode (that i programmed into my ECU) way before. at 15% SOC i start derating the power to 50% and the lower the SOC gets the less power is available. I simply multiply Throtcur with 0.5 or less. at 5% SOC the throtcur is so low i can barely get up a hill.

[johu]

Yes, I had setup my inverter like in the DIY post cited above (low voltage limit 340V). That resulted in me getting stuck on the Autobahn while the BMS still reported 15% SoC. With the voltage limit disabled I could drive to the next charger just fine, the cell voltage was then 2.9V and the BMS still didn't report 0% but 8% or something.
Right now my car is sitting at 20,6% at an average cell voltage of 3754mV, min 3731mV, max 3773mV. This complies with the DIY post, so I assume the problem back then was that I had set up the inverter to IDLE voltage not loaded voltage. I will try to empty the battery today and report back.

Nissan Leaf BMS balances with only 10mA and I think they use a clever algorithm as they don't just balance cells with highest voltage.

[Zapatero]

What voltage did you set the inverter shutoff now?
It would be rerally interesting to get some of the Leaf BMS values while under load.

Thank you Johannes for answering this in thread!

@ Kevin Sharpe: I upped the voltage now quite a bit and will repeat the low discharge test and figure out where the drifting between the cells occurs.

Still i think i should replace some cells - just can't get my hands on the modules!!! so hard to find!

[johu]

Here is a log from today.
I start at 12.6% SOC and 3606mV average cell voltage (3543 mV minimum). At 8% I get the first power limit under full acceleration. At 7% there seems to be always a power limit. At 4% SoC the power limit dips down to 20kW. The minimum cell voltage is allowed to reach 2.5V
I finished the run at 5.9% SoC (regen...), maximum battery voltage 3307mV, minimum 3046mV. It looks like a large difference but down there a few 100mV doesn't map to much SoC difference.
The inverter voltage limit is set to 250V, DC switch voltage is 300V.
I didn't dare connecting the boost charger to 305V idle voltage Used the 3-phase buck one instead.

EDIT: one note on difference between BMS and inverter voltage: inverter voltage measurement isn't really linear, so it is just bang on around the point where it is calibrated (370V in my case).

[Zapatero]

Awesome information.

Can you turn the logging on the next time you do a long run? I would love to have more information from 100 % SoC to 20% SoC!
That's very very useful!

I finished the run at 5.9% SoC (regen...), maximum battery voltage 3307mV, minimum 3046mV. It looks like a large difference but down there a few 100mV doesn't map to much SoC difference.

So it seems like under the control of the Leaf BMS the cells are 200mv and more apart, too - just like with my Orion BMS 2

[johu]

That could explain the differences between modules. I'd recommend parking your car outside until you understand what's happening.

I'd also suggest you read this post and ask yourself why we spend so much time encouraging people to use the OEM BMS;

This forum is not the place to create more myths. Most people won't be able to access this Patreon post. While I also encourage the use of OEM BMSes I would not generally advise against third party ones if the situation requires it.
Anyway, I heard that Damien went to a rescue of a Tesla pack that caught fire because an Orion BMS did not stop the charger from charging. Why did this happen? I don't know. Could be bad parametrization or other misuse. Until the facts aren't clear it is not the time to jump to conclusions. Has this been covered in another topic - then I'm sorry to have not read it.
An open inverter board can blow up some inverters if not correctly parametrized. Is that an argument against using one?

EDIT: I did read through Jacks report on balancing and I always advised against simple top balancing. But part of his problem was incorrect use of the BMS (or maybe the BMS didn't offer this function). Of course you need to power limit and ultimately stop your car if ONE cell drops below a certain voltage. The Orion BMS in Zapateros car does that.
Balancing is NOT a safety function. If done correctly, the most it can do is get the maximum kWh from your pack.