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Re: What is a "Gid"?

Posted: Wed Feb 08, 2012 9:21 pm
by surfingslovak
EVDRIVER wrote:I posted about these comments in the ev haters thread but there was not much attention. These are the worst comments I have ever seen related to EVs and in such a high number. Few people defended the dumb comments.
I'm under the impression that some of these comments are made for political reasons. This being an election year and all. I spent couple of days perusing and answering comments on that Yahoo article. The vitriol and negative sentiment against all things green is palpable. Same can be said of sites like Jalopnik and even boingboing. If this is reflective of the general mood in the electorate, then there might be much less political clout to address environmental issues in the near future.

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.

Most of the empirical data we have seen so far points to 70 to 75 Wh per gid. Our energy consumption data is derived from the energy economy gauge and the odometer, and it could be wrought with a systemic error. I tried to backcheck the models we came up with several times over the past few months, and I usually wound up with an error somewhere between 3 to 5%. I could never really put my finger on it.

One possible explanation would be drivetrain losses, which is what Gary referred to earlier, I believe. Do you think that these losses are baked into the energy economy figure? That would seem fairly logical to me. I believe that the coulombic efficiency of lithium-ion cells is very high, on the order of 99%. Where else could we lose energy?

Re: What is a "Gid"?

Posted: Wed Feb 08, 2012 9:35 pm
by Stoaty
Ingineer wrote:I typically see a full charge stop at 94-95% true SOC. My last charge to "100%" was actually to 94.591% SOC, and 22240 watt-hours, which is 271 "Gids".
Confirms my suspicion and info from another thread suggesting that an 80% charge is probably about 75% true SOC.

Re: What is a "Gid"?

Posted: Wed Feb 08, 2012 9:47 pm
by lukati
TonyWilliams wrote:
lukati wrote:
chris1howell wrote:I think the interesting question here for Ingineer is how did you know your SOC was 94.591%...?
Another interesting question would be the SOC value when car runs out of juice. Does it go to zero or not?
Obviously, the true battery SOC does not go to zero, as that would damage it. The Gid count goes to a very low single digit value (like 1 or 2).
Exactly. The gids go essentially to zero, which may indicate that they represent usable energy. If the SOC that is being broadcast by the ECU is not zero when the gids are zero, then that may tell us the "forbidden" charge in the battery that is protected by the BMS.

Re: What is a "Gid"?

Posted: Wed Feb 08, 2012 9:56 pm
by EVDRIVER
Nissan allows very aggressive cycling of the pack. I would not recommend frequent cycling to zero miles as there is not much left in the tank. Conversely, charging to 100% is 94% as mentioned.

Re: What is a "Gid"?

Posted: Wed Feb 08, 2012 10:08 pm
by TonyWilliams
lukati wrote:Exactly. The gids go essentially to zero, which may indicate that they represent usable energy.
Which gets to another issue. I don't think that the value of 281 Gid is the same as 140 Gid, or 1 Gid.

I suspect that 281 and 1 have similar, albeit smaller values than 140.

Re: What is a "Gid"?

Posted: Wed Feb 08, 2012 10:15 pm
by lukati
EVDRIVER wrote:Nissan allows very aggressive cycling of the pack. I would not recommend frequent cycling to zero miles as there is not much left in the tank. Conversely, charging to 100% is 94% as mentioned.
If 94.6% SOC is 22.2 kWh, then 100% SOC is 23.5 kWh, i.e. 0.5 kWh are missing. If they are at the bottom, then zero Gids should correspond to 2% SOC. You don't have to go all the way to zero Gids to determine whether the SOC goes to zero or not.

Re: What is a "Gid"?

Posted: Wed Feb 08, 2012 10:32 pm
by Ingineer
This is correct, I drove until VLB, then ran the heater until the main contactor opened. It was at about 2% SOC. I don't recall the watt-hours.

The 80 watt-hours per GID is an actual Nissan figure, it is not my "conclusion" or measurement. A typical full charge is 94-95% SOC.

-Phil

Re: What is a "Gid"?

Posted: Wed Feb 08, 2012 10:55 pm
by EVDrive
Nice Phil. You are making the average gas comsuming, terrorist funding, SUV loving American nervous enough to launch into a tyraid against cleaning up our filthy oil burning lives. At least we all have the guts to make a change for the better, support EV innovation and set a good example to our peers.

Don't let the stupid people with little forward thinking abilities and blurry vision distract you from the goal of leading our country to a clean fuel transportation future. There is hope for the average American; I used to drive an suv until I took it to the junkyard and traded up to Leaf. Woohoo.

Ingineer wrote:
GeekEV wrote:I'm sure we don't want to piss you off intentionally because then all we'll get is a lump of coal. :lol:

Everyone breathe!
Sorry if I'm a little hair-trigger, I've been dealing with the constant inundation of idiots emailing and calling me after the yahoo article surfaced. There are people really pissed about this, and I'm getting all kinds of haters and crackpots coming at me. It's truly a shame there is that much anti-EV sentiment!

-Phil

Re: What is a "Gid"?

Posted: Wed Feb 08, 2012 11:04 pm
by EVDrive
Phil, please put me on the RSVP list for the SOC meter upgrade. If you need some qa... I drive 100 miles a day to work and back and would be happy to provide qa services for free. Plus, I'm right next door to Berkeley. Pick me pick me. 8-)

Re: What is a "Gid"?

Posted: Thu Feb 09, 2012 12:51 am
by garygid
You can integrate current in and out for AmpHours, but must multiply amps by volts to get watts, and integrate to get watt hours.

Amp-Hours out can equal Ah in, but Wh into the battery will always be more than Wh out.

I am trying to represent usable "soc", not the absolute pack value. So, 281 Gids (presumably 100% usable) will only be 95% (+/-) of the "total" pack capacity.

If one's "100%-charging" achieves only 271 Gids, that is less than the 280 or 281 a full-capacity, well-balanced, normal-temperature "full" pack would occasionally produce, I suspect.

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If the LEAF's Gids are based primarily on Ah, there should be noticably MORE energy in the top half of the Gid range than in the bottom half.