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TickTock
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The Anatomy of a Gid

Wed Oct 10, 2012 2:20 pm

I recently plotted gids versus time along side of energy versus time:

Image

Since the perturbations in the gid curve during a charge occur between 25 and 50 gids (which bounds the knee in the voltage vs charge curve), I am starting to believe that gids are nothing more than a linearized version of the voltage. I am guessing a polynomial is applied to the voltage, the coefficients of which are re-computed periodically to adjust for degradation. Makes sense, really, because with a lot of driving and regen cycles, integrating errors will start to accumulate. Voltage gives a more absolute measurement than trying to keep track of electrons as they move in and out of the battery. Not sure how useful this is - just, explains why is varies and may even explain why some people observe more energy per gid below 50 gids and others may not.

Herm
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Re: The Anatomy of a Gid

Wed Oct 10, 2012 3:12 pm

You probably are seeing the linearity of the voltage/charge curve of the battery pack, per Enginier he insists that each gid is 80Wh of energy or 22.5kWh usable for a new battery.. whether that makes it to the road depends on conditions and driving style. Its possible Nissan cheapened out and is just using a temperature/voltage table but supposedly a coulomb counter is involved. Have you tried adding a temperature correction as the pack heats up slowly during discharge?.. Voltage should be increasing (for a given SOC) as it heats up, minus the IR losses also.

Then again it could explain the overall goofyness.

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richard
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Re: The Anatomy of a Gid

Wed Oct 10, 2012 4:02 pm

Next on NOVA.. The Secret Life of Gids ;-)
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JimSouCal
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Re: The Anatomy of a Gid

Wed Oct 10, 2012 4:13 pm

I have been embarrassed to ask what is a "GID". My bet is it is buried in hundreds of legacy posts. So...

What is the definition and units, and relative formulas, that comprise a GID? I will go back ~30 years to elementary college physics from that and figure it out...

I do know that having 281 in your battery with a meter is a good sign...

Stoaty
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Re: The Anatomy of a Gid

Wed Oct 10, 2012 4:30 pm

Remember folks, the Wiki is your friend:

http://www.mynissanleaf.com/wiki/index. ... e=Glossary" onclick="window.open(this.href);return false;
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FairwoodRed
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Re: The Anatomy of a Gid

Wed Oct 10, 2012 4:40 pm

JimSouCal wrote:I have been embarrassed to ask what is a "GID". My bet is it is buried in hundreds of legacy posts. So...

What is the definition and units, and relative formulas, that comprise a GID? I will go back ~30 years to elementary college physics from that and figure it out...

I do know that having 281 in your battery with a meter is a good sign...
A GID is an arbitrary unit of measure that the community believes corresponds to battery pack state of charge. This unit was found by Gary Giddings by sniffing the cars CAN bus and it was named GID in his honor. Originally, 1 GID was thought to represent 80 watt hours. Lately, there has been questions on how exact that is under varying conditions.

So don’t bother with your physics books… :)

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GeekEV
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Re: The Anatomy of a Gid

Wed Oct 10, 2012 4:41 pm

Stoaty wrote:Remember folks, the Wiki is your friend:

http://www.mynissanleaf.com/wiki/index. ... e=Glossary" onclick="window.open(this.href);return false;
We have a Wiki? :lol: :lol: :lol:

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OrientExpress
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Re: The Anatomy of a Gid

Wed Oct 10, 2012 5:04 pm

So what is the description of the CAN Bus message that is used to derive the GID.

What device(s) in the LEAF generate the message, how do they generate the message, and what devices in the LEAF use the message and for what?
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TickTock
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Re: The Anatomy of a Gid

Wed Oct 10, 2012 6:55 pm

No one has confirmed for sure what the message is since the only people with access to the canbus definition are constrained by NDA. However, we are reasonably certain this message (5bc) is the "Charge Status Signal" described in the service manual transmitted from the EV/HEV to the TCU. We know it's units to be energy with nominal value of 80 watt_hours. It does not seem to be super accurate, though, with at least +/-10% variation. Despite this variation, it remains the best indicator of the available energy in the battery. None-the-less 10% error is a bit annoying when trying to figure out how many miles you have remaining. This is why we are trying to understand it better. In my chart I show that, for the simple scenario of a charge, I am able to much better compute the charge in the battery by monitoring the current and voltage into the battery and integrating the power over time. The reason I think the Leaf doesn't just do the same is this is much harder to do accurately when driving where charge moves in and out of the battery quite frequently - each time adding a little more error to the computation.

I have compiled everything I am aware of that we have reverse-engineered about the evcan and carcan busses here (don't forget to look at the tabs at the bottom of the spreadsheet).

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JimSouCal
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Re: The Anatomy of a Gid

Wed Oct 10, 2012 7:23 pm

Stoaty wrote:Remember folks, the Wiki is your friend:

http://www.mynissanleaf.com/wiki/index. ... e=Glossary" onclick="window.open(this.href);return false;
I did google search LEAF GID and my ROT was not so robust in clearing up any of my confusion.

Thanks for the pointer... This thread is revealing too, BTW. Thanks for that as well!

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