[Ovmsdev] Battery capacity metrics (for the Leaf, and in general)

Robin O'Leary ovmsdev at caederus.org
Sun Feb 24 21:08:07 HKT 2019

On Sun, Feb 24, 2019 at 05:34:21AM +0000, Anko Hanse wrote:
> I had been searching for a way to directly get the battery capacity from
> the can bus, but had not found one. Hence my search for alternatives
> via the VIN.
> Even if I do a google now on 'leaf can bus 59e' I don't get useful
> hits. And no finds in the canmsgs google docs either...  Makes me
> wonder what docs you have access to...

I have no documentation; everything is speculation, based on many forum
discussions and my own observations of the car I own (a 2015 UK-built
24kWh Acenta), so it is quite possible that my conclusions are wrong,
or don't apply to other models.  I would like others to check whether
the value in 0x59e is a useful measure of capacity for them before we
adopt it as a standard.

> As for the web-interface, we might want to still display the detected
> battery capacity there, just not as a changeable setting but as
> readonly info.

Yes, although these are two different things, which may both be useful
for different purposes.  Unlike the fixed value of max_gids, the battery
energy capacity metric varies over time: as well as a general decrease
due to battery age, it also has short-term up and down swings as the BMS
recalibrates after charging.  Some people don't like this "randomness",
and prefer to see calculations relative to a fixed base-line.  There is
something to be said for both approaches.

As for the config page, for now, I would suggest structuring it so that
the switches for the preferred SOC and SOH display metrics are paired
with conditional settings for the corresponding full-scale value, maybe
something like:

	SOC display:				{xnl.soc.newcar}
	.	(*) from dashboard display	{=false}
	.	( ) relative to fixed value:	{=true}
	.	.	[	] (GID=80kWh)	{xnl.maxGids}
	SOH display:				{xnl.soh.newcar}
	.	(*) from dashboard display	{=false}
	.	( ) relative to fixed value:	{=true}
	.	.	[	] (amp.hour)	{xnl.newCarAh}
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