ENIAC
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Re: 281 is not the maximum SOC value

Wed Nov 23, 2011 7:52 pm

Can you achieve 288 Gids on a Level 2 charge or only on a QC? Also, it feels like Gids are points along a curve, rather than along a straight line. So, simply dividing by 2.81 may not be the most accurate SOC calculation.
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DaveEV
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Re: 281 is not the maximum SOC value

Wed Nov 23, 2011 8:16 pm

DaveinOlyWA wrote:1) you overcharged the pack. a bit disappointed that QC would allow it.
Highly unlikely this happened if voltage never went above 395V.

jkirkebo
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Re: 281 is not the maximum SOC value

Thu Nov 24, 2011 5:54 am

DaveinOlyWA wrote:i think restarting a QC after 85% is a huge mistake. so what happened??
The charger stopped by itself. This is normal QC behaviour when you start from below 50% SOC. If you start from above 50% the charge process goes to 100%. Or in this case, 102.5% ;)

This should not be dangerous in any way, you are not required to stand by and watch the QC just because you started at 51%.

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Re: 281 is not the maximum SOC value

Thu Nov 24, 2011 7:27 am

jkirkebo wrote:
DaveinOlyWA wrote:i think restarting a QC after 85% is a huge mistake. so what happened??
The charger stopped by itself. This is normal QC behaviour when you start from below 50% SOC. If you start from above 50% the charge process goes to 100%. Or in this case, 102.5% ;)

This should not be dangerous in any way, you are not required to stand by and watch the QC just because you started at 51%.
the question was an attempt to determine possible reasons as to how 288 gids was obtained.

well i agree that QC being set to 80% is too conservative. i always felt that levels even at 95% was well within the safe limit.

but i was under the impression that the slightest amount of overcharging was detrimental. so 102.5% is a mistake in my book. maybe i am wrong. this chemistry is new. but the #1 reason for premature death in cellphone batteries is a combination of heat due to overcharging. that is why only "boost" charging is recommended for car chargers as they are not regulated.
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Danal
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Re: 281 is not the maximum SOC value

Thu Nov 24, 2011 7:49 am

DaveinOlyWA wrote:but i was under the impression that the slightest amount of overcharging was detrimental.
True when "over charge" is defined as "over voltage". GIDs are an unknown scale and to say that more than 281 gids = overcharge, when the pack voltage was 394.5 volts, dosen't line up. This voltage divides out to 4.109 per cell. The chemistry used in these packs is good to 4.2xx per cell, where there can be some debate about the last few digits. The state of charge was well under that voltage, and there is a 'balancer' in each cell (pair) to ensure no individual cell (pair) goes high.

The only caveat on all those voltages is that any given Lithium chemistry's max V goes down as temperature goes down. The voltages mentioned in the prior paragraph apply to 20C. Any good battery management system for a pack to be used outdoors leaves a little margin for "don't overcharge" conservatism, and leaves a little more margin for possible temp reductions (including after charge, but before use). Effectively, if charged to the proper max voltage for 20C and the temp falls, a Li battery is then overcharged.

Summarizing: Overcharge is defined by voltage, not GIDs, and the voltage reported was fine.



Put it another way: Up until this thread, it was thought that 281 Gids = 100.00% state of charge. Now that 288 has been seen, perhaps 281 = 97.56%.
Last edited by Danal on Thu Nov 24, 2011 7:59 am, edited 1 time in total.
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Danal
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Re: 281 is not the maximum SOC value

Thu Nov 24, 2011 7:59 am

It is not that quick charging above 80% is unsafe. It is that there is no advantage to a quick charger for that last 20%.

The charge algorithm for Li batteries calls for constant current, until the absolute voltage crosses a value that varies by chemistry. Then, constant voltage is used (and current naturally falls off) until the final "100% full" voltage is reached. In reality, most chargers terminate the CV phase when current falls below some fixed value, because as pack V increases, current decreases, and the gain of energy becomes so small the last minutes of charge are not worthwhile.

Anyway, the CC to CV transition occurs at about 80% (very very roughly). Once transitioned into Constant Voltage mode... all chargers run at the same speed

Well, almost the same speed. Given that the LEAF has a 3.3kW charger and really should have more... there is still some advantage to a QC, even in the last 20%, for a LEAF.


But, in the general case, where the Li pack has some capacity "C", and the charger is capable of doing the Constant Current phase at 1C or above... in those scenarios, a 1C charger vs. a 2C (or more) charger will reduce the Constant Current phase's wall clock time. However, a 1C or 2C or more charger all take about the same wall clock to complete the Constant Voltage phase.
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jkirkebo
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Re: 281 is not the maximum SOC value

Thu Nov 24, 2011 9:15 am

ENIAC wrote:Can you achieve 288 Gids on a Level 2 charge or only on a QC? Also, it feels like Gids are points along a curve, rather than along a straight line. So, simply dividing by 2.81 may not be the most accurate SOC calculation.
I have never seen more than 272 on a 100% charge because I have only done one two times and both times with pre-heat. Pre-heating a 100% charged cars seem to actually lower the gids, contrary to on a 80% charged car.

I will test L2 to 100% without pre-heat this weekend, both days. Or more correctly, I will check the gid value before starting pre-heating.

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Re: 281 is not the maximum SOC value

Thu Nov 24, 2011 9:23 am

Danal wrote:It is not that quick charging above 80% is unsafe. It is that there is no advantage to a quick charger for that last 20%.

The charge algorithm for Li batteries calls for constant current, until the absolute voltage crosses a value that varies by chemistry. Then, constant voltage is used (and current naturally falls off) until the final "100% full" voltage is reached. In reality, most chargers terminate the CV phase when current falls below some fixed value, because as pack V increases, current decreases, and the gain of energy becomes so small the last minutes of charge are not worthwhile.

Anyway, the CC to CV transition occurs at about 80% (very very roughly). Once transitioned into Constant Voltage mode... all chargers run at the same speed

Well, almost the same speed. Given that the LEAF has a 3.3kW charger and really should have more... there is still some advantage to a QC, even in the last 20%, for a LEAF.
I noted down the different power levels from the quick charger.

22-45% - 46kW.
60% - 35kW
68% - 30kW
75% - 25kW
80% - 20kW
86% - 15kW
93% - 10kW
96% - 8kW
98% - 6kW
100% - 4.8kW
102.5% - 2kW

Thus the QC is advantageous up to even 100% because of the 3.3kW charger, just as you wrote. With a 6.6kW charger, and considering the small amount of energy in the upper 10%, I'd say QC up to around 90% makes sense.

I also wrote down the percentages gained in 10 minute segments:

22% to 48% = 26%/10 min
48->71=23
71->85=14
85->94=9
94->99=5

CV-mode was reached much lower than 80%, though I failed to recorde the precise value. My guess is around 65%.

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Re: 281 is not the maximum SOC value

Thu Nov 24, 2011 9:59 am

Good work, nice data, doing QC on a 2012 model, right?

The "GIDs" is a value in one of the EV-CAN messages, first identified by "turbo2ltr". He found that the 2011 LEAF uses this value to derive the Fuel Bars. Thus, this appears to be a higher-resolution "fuel" gauge, not linear, not "SOC", but more than just a value derived from ONLY the Pack Voltage.

Our "SOC-Meter" shows the "raw" value (some started calling it a "GID"). It also shows the "GID" value as a percentage of 281 (the highest value known at the time) for convenience in visualizing an answer to the "How full is my e-tank?" question.

We still know nothing about how this value is derived, but it generally goes up when charging (or doing Regen), and down while driving.

Important driving milestones appear to be pegged to "GIDs":
LBW: just below 18%
VLBW: just below 9%
Turtle: near 4 (GIDs or %?)

If you have the Logging Port on your SOC-Meter, a CAN-Do log of the EV-CAN bus during a full QC session would be great to publish for others to examine and investigate.

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Re: 281 is not the maximum SOC value

Thu Nov 24, 2011 10:12 am

Danal wrote:It is not that quick charging above 80% is unsafe. It is that there is no advantage to a quick charger for that last 20%.
Other than the part where it only takes 25 minutes to charge that last 20%. :D
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