[Ovmsdev] OVMS Leaf Support

[Tom Saxton]

There are three interesting values related to SOC on the Leaf.

Gids: Discovered by Gary Giddings, each Gid represents 80 Wh of energy
currently in the battery pack. A nominal new packs reads 281 Gids on a full
charge and the car stops going at about 6 Gids. 80*(281-6) = 22 kWh of
usable charge. Gary Giddings' original SOC meter calculated

SOC  = Gids/281 

So that gives an SOC in energy units like the Roadster's ideal miles, except
that the car dies at about 2% SOC. Also, the Gid measurement is temperature
dependent, understates charge in hot weather and overstates it in cold
weather. The value is not directly readable from the primary CAN bus, but
folks have figured out how to query it from there. The implied precision of
the measurement is 1/281 = 0.36%, but the accuracy is much worse than that.
It's typically shown to 0.1%.

Ah: The car's estimate of the pack's capacity in Ah was found on the main
bus. As I understand things, it correlates well with Gids but there isn't an
accepted standard nominal new pack Ah value. The Leaf Spy app lets users set
their Ah value from which another SOC percent is computed, rendering those
values unique to each car and thus useless for things like battery capacity
studies.

True SOC: This is a horrible name for the high precision value that drives
the SOC bars in the Leaf. (It's a byte value, so not quite 0.1% precision.)
The giant problem with this value is that it's relative to the pack's
current estimated pack capacity. So, even after your pack has lost 30% of
its capacity, it still charges to 100% of that, shows all 12 SOC bars on the
dash and "True SOC" still runs up to 100.0.

Personally, I would want OVMS to show:

SOC % = Gids/281
SOC Energy = Gids (like ideal miles in the Roadster)
Pack Ah treated as CAC is in the Roadster

Many, perhaps a majority, of Leaf owners will want to see the "True SOC"
because they don't realize how stupid that is until they lose a capacity bar
and realize that SOC still goes to 100% even though that doesn't mean the
same thing it did when the car was new, so any intuition they've acquired
about how much charge it takes to drive from A to B has to be constantly
adjusted.

   Tom

From:  Mark Webb-Johnson <mark at webb-johnson.net>
Reply-To:  OVMS Developers <ovmsdev at lists.teslaclub.hk>
Date:  Tuesday, October 15, 2013 10:33 PM
To:  OVMS Developers <ovmsdev at lists.teslaclub.hk>
Subject:  Re: [Ovmsdev] OVMS Leaf Support

My biggest confusion at the moment is SOC% in the Leaf. There is a lot of
talk about gids, etc, but I've never gone into it too deeply.



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