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Re: What is a "Gid"?

Posted: Thu Feb 09, 2012 1:20 am
by Ingineer
Gary,

It's watt-hours, not amp-hours. There is a separate amp-hour calculation.

Because you aren't watching SOC, but watt-hours, expect it to go down over time as the battery ages.

-Phil

Re: What is a "Gid"?

Posted: Thu Feb 09, 2012 1:24 am
by lenny
BTW, somewhat off topic, but is "gid" an acronym or shorthand for something?

Re: What is a "Gid"?

Posted: Thu Feb 09, 2012 1:34 am
by gbarry42
Somewhat on topic, the 'gid' is the number shown on garygid's SOC meter.

Re: What is a "Gid"?

Posted: Thu Feb 09, 2012 1:50 am
by garygid
Yes, some folks started calling the "unknown-units" value (0 to 281) a "Gid" after my "garygid" forum handle. Then, the "soc" Meter might be a Gid-Meter.

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If the Gids are essentially 80 watt-hours each, why are the top 20 or so "always" used up so much quicker than those in the center of the range?

What is "counted" to make the value increase during charging?

What is "counted" to decrease the value during driving?

If it is ONLY watt-hours in/out of the battery, each charge/discharge cycle would have a net gain of perhaps 800 Wh (10 Gid), right?

So, there must be an "adjustment" somewhere for higher pack voltage when charging, and the lower voltage when discharging.

Presumably, the voltage (and history) of the 96 cell-pairs must be considered when charging near the top and discharging bear the end.

----
Yes, it appears that the VCM uses the Gids to calculate the Fuel bars (there are at least two sets).

What is used to create the Capacity Bars, and create the Battery Temperature Bars?

Re: What is a "Gid"?

Posted: Thu Feb 09, 2012 5:43 am
by TickTock
garygid wrote: If the Gids are essentially 80 watt-hours each, why are the top 20 or so "always" used up so much quicker than those in the center of the range?
This is indeed a curious observation that the upper gids are used up faster. If you look at the graphs early in this thread, it is clear that (at least during charging), the unit value of 1 gid in wh is pretty consistent over the entire range (ignoring the noise, the graphs are very linear). Data doesn't support the observation of gids being less energy at the top of the scale.

It must be the weight of all those extra electrons in the full battery <wink> :)

Re: What is a "Gid"?

Posted: Thu Feb 09, 2012 6:00 am
by Ingineer
As I explained in the post before, this is coulomb counting but it is accomplished with a "drifty" hall-effect device, so it is periodically corrected by watching temperature/voltage etc.

Nissan calls it stored watt-hours.

At the BayLEAFs/Nissan meeting, Hidetoshi Kadota, Nissan's Chief Vehicle Engineer for the Leaf, explained this is one reason they decided not to show the public these numbers. Both SOC and watt-hours can suddenly jump without warning if the battery ECU corrects it's coulomb counting.

Either way, I can assure you what you are calling SOC, Nissan is calling stored watt-hours.

-Phil

Re: What is a "Gid"?

Posted: Thu Feb 09, 2012 6:43 am
by lukati
Given the fact that battery voltage is a non-linear function of SOC and inherently difficult to determine under load, it is probably not surprising that Gids should be non-linear as well, particularly at the two extremes where non-linearity is highest. If you can't trust your Hall probe (and your cell voltage), than you have to fudge your numbers to make it work.

For me the important information coming from Phil's data is the fact that the BMS protects only 2% capacity at the bottom and ~5% at the top. Unlike the Prius NiMH battery that Toyota won't let you abuse, your use pattern on the LEAF will truly affect the longevity of the pack. We knew that going in, now we have the numbers to prove it.

Re: What is a "Gid"?

Posted: Thu Feb 09, 2012 7:31 am
by Herm
lukati wrote: For me the important information coming from Phil's data is the fact that the BMS protects only 2% capacity at the bottom and ~5% at the top. Unlike the Prius NiMH battery that Toyota won't let you abuse, your use pattern on the LEAF will truly affect the longevity of the pack. We knew that going in, now we have the numbers to prove it.
Nissan seems to be confident on the durability of the batteries.. hopefully they dont pull a Honda and reprogram the limits after 3 years to reduce battery degradation.

It appears we finally have our fine grained battery wear meter..

Re: What is a "Gid"?

Posted: Thu Feb 09, 2012 7:44 am
by Stoaty
lukati wrote:For me the important information coming from Phil's data is the fact that the BMS protects only 2% capacity at the bottom and ~5% at the top. Unlike the Prius NiMH battery that Toyota won't let you abuse, your use pattern on the LEAF will truly affect the longevity of the pack. We knew that going in, now we have the numbers to prove it.
The 5% at the top doesn't surprise me, but I am stunned by the 2% at the bottom. These numbers just reinforce that I want to continue using the middle 60% most of the time for maximum battery longevity. Of course, we won't know exactly how much difference the usage pattern makes for a few years until Leafs start dropping like, well, Leafs. :o

Re: What is a "Gid"?

Posted: Thu Feb 09, 2012 7:47 am
by DaveinOlyWA
More typical is 18-21.5-ish kWh, depending largely on temperature. For example, I drive 100 miles, and average 4.8 miles/kWh, that infers 100/4.8=20.8kWh.
what varies by temperature? i am getting same "conflict" so have been tracking when i lose bars, the temp (via dash) and GID reading. it does have some drift to it. despite having a few days in the 50's its still a bit early to expect that on a regular basis but will see if numbers drift from temp changes.

There is some non-linearity, true, but it's still a lot better than the 12 bars on the dash. The graph below shows the non-linearity better, I think. I plotted the energy into the battery versus time and gids vs time during the same 100% charge. You can see that the energy into the battery is a very linear constant rate (as expected), but the gids do vary a little - particularly at the low end.
i see lower GIDs restored quicker but attribute a lot of that to less accuracy reading GIDs when pack is low and also less accuracy when pack is high. look at it like an analog gas gauge when the needle moves slowly when full or near empty and quickly in the middle. it should move at the same rate all the way thru when driving constantly? i frequently will gain GIDs when parking, sometimes as much as 9. the biggest gain did happen during a time of rapid temperature rise due to transitioning from cloudy morning to full Sun in afternoon.

But back to the topic of gids. If I recall correctly, we started discussing it last summer, and the thread carried over to this year. My original suggestion was 75 Wh per gid, which was pretty speculative at the time. If a gid really was 80 Wh, then we might have overestimated the amount of energy left in the battery after turtle. Evnow did couple of really nice plots and this table for usable battery capacity. TickTock presented very interesting plots as well, I will try to find and link to them.
the only thing we really know is what the car tells us so its battery bars, temp bars efficiency gauge and odometer.

there is something that is putting a slight skew onto these numbers that is varying from driver to driver. is it DC conversion errors caused by feeding different systems? gauges, 12 volt battery, etc?

most seem to be tied closely to temperatures as i have seen and i eliminated climate control completely on my tests and it still showed a reduced battery capacity so not only was my efficiency bad, my pack had less to give.

lead acid is affected by temperature much more than Li. could it be a significant diffference when temps are in the 20's and 40's? keeping in mind the battery is much smaller and its ambient temperature would very closely match OAT?

as far as GID i went to 8 on my test and that was with only 5 power circles remaining. based on how fast GIDs were dropping on the gauge, (they do slow down at the end) verses the rate of "circle loss" i might have been lucky enough to get to 6 ?