AndyH
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Re: Actual LEAF Pack Capacity

Wed Feb 23, 2011 6:12 pm

Ingineer wrote:I would agree; "usable" capacity for the Leaf.

The battery manufacturer usually specifies Ah from 100% SOC down to a certain voltage per cell. On most Lithium Ion types this is 2vpc, but I would guess the usable capacity in the Leaf is not this low. So I suspect the dynamic calculations are to this as yet undermined number. Since I now have all the tools to monitor this, all I have to do is get in a Leaf, run the pack down and see where this occurs.

It's on my list! =)

-Phil
Cool! Inquiring geeks want to know!

Expect 3.0V for LiMn like LiCo. I understand that AESC lists LiMn2O4/spinel on their website, but Nissan's been working on/another variant with a bit higher max and nominal voltages. The BMS voltage reporting points seem to favor the slightly higher voltages. That's my guess, though...

Care to share how the car reports cell capacity? I'm surprised that it's aware of and reports total as opposed to 'consumer' capacity.

Thanks for this!
Andy

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Ingineer
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Re: Actual LEAF Pack Capacity

Wed Feb 23, 2011 6:37 pm

AndyH wrote:Cool! Inquiring geeks want to know!

Expect 3.0V for LiMn like LiCo. I understand that AESC lists LiMn2O4/spinel on their website, but Nissan's been working on/another variant with a bit higher max and nominal voltages. The BMS voltage reporting points seem to favor the slightly higher voltages. That's my guess, though...

Care to share how the car reports cell capacity? I'm surprised that it's aware of and reports total as opposed to 'consumer' capacity.

Thanks for this!
Andy
I think it reports usable capacity in Ah, not "total". This means down to whatever the Leaf considers LVCO.

I did not see any parameters to indicate any per-cell capacities are calculated or recorded. They do monitor each cell's voltage and there are 4 temperature probes. There are also quite a few parameters pertaining to capacity calculation, but they are all pertaining to the pack as a whole.

I suspect they monitor health at the per cell level simply by watching the voltage. If any one cell gets too far out of wack, you get a code, and the pack will go into reduced performance. The Battery ECU tells the rest of the car the maximum kW that can be drawn and put in at any given time, and this is what limits motoring and regen respectively. When I tested these, the car was at around 50% SOC and the pack reporting about 55 degrees F. The max out was at 110kW and the max in was at 30.34kW. I suspect 110kW is the maximum, because it was at 110kW even, whereas the max in parameter was an arbitrary value. This means at that particular time, regen or external charging would be limited to 30.34kW, but the car was not performance limited in drive.

All of this data is available over the primary CAN bus (EV), and each parameter seems to support a refresh frequency of at least 5hz. The Battery ECU alone has about 30 pages of parameters, with a lot of the pages consumed by the individual cell voltages, and there are also a lot of historical parameters. The ECU records at least a handful of different parameters for the last 8 events in a rolling buffer.

I will keep everyone posted next time I collect any juicy information of interest.

-Phil
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AndyH
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Re: Actual LEAF Pack Capacity

Wed Feb 23, 2011 7:49 pm

Ingineer wrote:
AndyH wrote:Cool! Inquiring geeks want to know!

Expect 3.0V for LiMn like LiCo. I understand that AESC lists LiMn2O4/spinel on their website, but Nissan's been working on/another variant with a bit higher max and nominal voltages. The BMS voltage reporting points seem to favor the slightly higher voltages. That's my guess, though...

Care to share how the car reports cell capacity? I'm surprised that it's aware of and reports total as opposed to 'consumer' capacity.

Thanks for this!
Andy
I think it reports usable capacity in Ah, not "total". This means down to whatever the Leaf considers LVCO.

I did not see any parameters to indicate any per-cell capacities are calculated or recorded. They do monitor each cell's voltage and there are 4 temperature probes. There are also quite a few parameters pertaining to capacity calculation, but they are all pertaining to the pack as a whole.

I suspect they monitor health at the per cell level simply by watching the voltage. If any one cell gets too far out of wack, you get a code, and the pack will go into reduced performance. The Battery ECU tells the rest of the car the maximum kW that can be drawn and put in at any given time, and this is what limits motoring and regen respectively. When I tested these, the car was at around 50% SOC and the pack reporting about 55 degrees F. The max out was at 110kW and the max in was at 30.34kW. I suspect 110kW is the maximum, because it was at 110kW even, whereas the max in parameter was an arbitrary value. This means at that particular time, regen or external charging would be limited to 30.34kW, but the car was not performance limited in drive.

All of this data is available over the primary CAN bus (EV), and each parameter seems to support a refresh frequency of at least 5hz. The Battery ECU alone has about 30 pages of parameters, with a lot of the pages consumed by the individual cell voltages, and there are also a lot of historical parameters. The ECU records at least a handful of different parameters for the last 8 events in a rolling buffer.

I will keep everyone posted next time I collect any juicy information of interest.

-Phil
Thanks Phil. This sounds exactly as documented in the service manual. The battery controller tracks voltages, current in/out, and voltage drop, but also measures cell (actually, parallel group) internal resistance and uses that to determine the degradation factor.

Consult III?

Herm
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Re: Actual LEAF Pack Capacity

Wed Feb 23, 2011 8:26 pm

With this we have all the data needed to track pack degradation long term... you may have to capture a few 100% cycles to generate a report, not necessarily down to turtle mode. We could also generate our own SOC display for those that want to know to the second decimal point.

I would love to see some temperature data after the car has been soaking in the sun all day long.

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Ingineer
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Re: Actual LEAF Pack Capacity

Wed Feb 23, 2011 8:56 pm

AndyH wrote:Thanks Phil. This sounds exactly as documented in the service manual. The battery controller tracks voltages, current in/out, and voltage drop, but also measures cell (actually, parallel group) internal resistance and uses that to determine the degradation factor.

Consult III?
Correct, the Internal resistance was in there. There's also an amperage reading for all cells.

(just kidding! ;-) )

The runtime shows Consult 4, but on the screen it shows Consult III+. There is a new interface that's special as well. The setup is not backwards compatible (yet), and costs $7K. (not kidding!)
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AndyH
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Re: Actual LEAF Pack Capacity

Thu Mar 10, 2011 9:51 am

Carcus wrote: Ok. Thanks.


And from what I've read, the degradation won't necessarily be linear? I'm thinking the drop from 80% to 60% will happen quicker than the drop from 100% to 80% ?
The most accurate answer is probably "it depends". ;) I think it'll be more linear than not, though.

Here are two degradation charts. PSI makes very good quality LiFePO4, while Moli are very good quality LiMn2O4. LiFePO4 tends to gain capacity over the first 75-150 cycles before dropping. I don't know if LiMn has a similar 'break in'.

Image

Image

bowthom
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Re: Actual LEAF Pack Capacity

Thu Mar 10, 2011 11:06 am

Great info, so instead of 10% at the ends of the charge discharge curves they are using 6%.
24kWh / .88 = 27.27kWh total pack (100%) capacity. 80% (extended life mode) of 88% = 70% of total pack capacity and is one of the industry norms when testing cycle life. The 80% extended life should obtain 4000 cycle life which means if you used 80% every day it would deliver 11.95 years and 240K ~ 320K miles. For those of you charging to 80% and 100% at times. Just use the ratio of 80% to 100% charge times to figure where you will land between these to figures.

10.95 yrs 80% charge (extended life mode)
|
|
|
6.8 yrs 100% charge

So if you charge to 100% half of the time, your expected life would be 8.9 years if you are using all the capacity. If not then it is not a full cycle and life is extended. You can see how predicting capacity life and warrantee period is sketchy at best. Your driving habits and range needs dictate the battery life and Nissan has no control over the outcome.

I love having hard numbers. What we need now is the cycle life of the battery when charging / discharging to the 6% limits (88% user capacity). My figures above assume 2500 cycles but that may be optimistic (it was based on std 10% limits) so it could go as low as 2000 cycles (5.5 yrs) at 6%.

More numbers please :D
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AndyH
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Re: Actual LEAF Pack Capacity

Thu Mar 10, 2011 11:12 am

bowthom wrote:More numbers please :D
42! :lol:

ENIAC
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Re: Actual LEAF Pack Capacity

Thu Mar 10, 2011 11:13 am

Interesting data AndyH. Now I'm wondering if charging to 80% every night is the best strategy. Seems like if you want to extend the battery life, you should reduce the charging cycles. Charging to 100% every other night would actually work for me. Would that strategy be better than charging to 80% every night?

So AndyH, based on all this data, your personal experience, and you driving needs, what is your charging strategy going to be? I really appreciate your maintenance tips in another thread here.
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DaveinOlyWA
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Re: Actual LEAF Pack Capacity

Thu Mar 10, 2011 2:09 pm

ENIAC wrote:Interesting data AndyH. Now I'm wondering if charging to 80% every night is the best strategy. Seems like if you want to extend the battery life, you should reduce the charging cycles. Charging to 100% every other night would actually work for me. Would that strategy be better than charging to 80% every night?
no it would not. a charge cycle is a replenishment of 100% of the NEW battery's capacity.

iow, 4-25% charges equals a single charge cycle.

other than that. i dont appear to be getting a 24 kwh usable capacity. it seems to be more around 21½-22. should i be concerned?
2011 SL; 44,598 mi, 87% SOH. 2013 S; 44,840 mi, 91% SOH. 2016 S30; 29,413 mi, 99% SOH. 2018 S; 25,185 mi, SOH 92.23%. 2019 S Plus; 412 mi, 99.72% SOH
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