[Ovmsdev] Storing Calibration Data

phil hochstetler phil.hochstetler at gmail.com
Tue May 3 12:34:24 HKT 2016


On Mon, May 2, 2016 at 10:52 AM, Tom Saxton <tom at idleloop.com> wrote:

> Hi Phil,
> That's why I was careful to specify 24 kWh in my comments.
> It would be great to get your numbers into the Plug In America Leaf
> survey. You can be the first 30 kWh owner to contribute.
> http://www.pluginamerica.org/surveys/batteries/leaf/survey.php
>     Tom
> On May 2, 2016, at 10:25 AM, phil hochstetler <phil.hochstetler at gmail.com>
> wrote:
> One more twist is that 2016 models (SV and SL) have the 30kWh battery (not
> the 24).  Lots more gids so going to a gid based scheme is good as long as
> you don't think 281 is the max number of gids.  My 2016 Leaf SL will charge
> to 363 gids.
> Phil H.
> On Mon, May 2, 2016 at 9:02 AM, Tom Saxton <tom at idleloop.com> wrote:
>> As a 2011 Leaf owner, I'd rather have a number that shows an estimate of
>> how much energy is available in the pack rather than a percentage of a
>> constantly-varying pack capacity. 100% means one thing when you have a new
>> full pack in the summer and something else entirely in the winter after
>> losing 2 capacity bars. A remaining energy estimate is an easy number to
>> compute, just use gids or gids divided by gids for a nominal new pack (281
>> for a 24 kWh pack).
>> For compatibility with Gary Gidding's original SOC meter, use (100 * gids
>> / 281), done in integer math so it truncates instead of rounds.
>> It's arguably more intuitive to express the pack energy as miles, but
>> such a range estimate is always going to be wonky. The car can know how
>> you've driven recently, but can't know how you're going to drive. If you've
>> got lots of charge (the most common case) you can drive however you like.
>> If you're low on the charge, the case that matters the most, you want to
>> know how much energy is the pack to inform your driving decisions. Can I
>> make it if I turn off the HVAC? Do I need to get off the freeway and drive
>> lower speed highways? Can I make it to that next charging station, or do I
>> need to look for less traditional charging (an outlet at a 7-11, etc.)?
>> For that, I need an energy number, not an SOC number based on a varying
>> pack capacity, and not a range estimate based on how I have been driving. A
>> true, unadulterated energy number.
>> One could express the energy number as gids or kWh, but those are pretty
>> nerdy numbers. A more intuitive approach is to use the EPA (or NEDC) range
>> estimate for a full, new, nominal pack and scale from there. For the 24 kWh
>> Leaf, the EPA rating is 84 miles, so to calculate rated miles remaining in
>> the pack use (84 * gids / 281).
>> Just like a range estimate based on your recent driving, the rated range
>> won't tell you how many miles you'll get, but you can easily develop
>> intuition. In moderate weather, at a steady highway speed (55 to 60 mph) on
>> level road, you can get mile-for-mile. At steady 40 mph, you can get even
>> better. Cold weather, higher speeds and climbing elevation will all reduce
>> your range, and you'll build up intuition for that.
>> The rated ranged also gives drivers a standard number they can compare
>> with other drivers who likely have different driving style and conditions.
>> Building that intuition from a SOC percent based on changing capacity or
>> a range estimate based on recent driving is much more difficult.
>> OVMS has support for both a rated range (called ideal range because
>> that's what the Roadster called that calculation) and estimated range based
>> on recent driving.
>> That just leaves the question of how to compute the SOC percentage, and I
>> personally prefer current energy divided by the original pack capacity
>> rather than the degraded pack capacity. As I lose capacity, I want that
>> number fully visible in the SOC I see after a charge.
>> We've lost one capacity bar in our Leaf. When we do a full charge, we see
>> 79.0% on the Gid meter and when we do an "80%" charge we see 66.9%. As
>> those numbers change, I know how to adjust my expectations and my driving
>> so I don't get surprised.
>>    Tom
>> On 5/2/16, 3:51 AM, "Tom Parker" <ovmsdev-bounces at lists.teslaclub.hk on
>> behalf of tom at carrott.org> wrote:
>> >Hi,
>> >
>> >The Leaf's range estimate is pretty wonky as it's strongly influenced by
>> >your recent consumption. A much better range estimate is obtained from
>> >the current gids (approximately the kWh stored in the battery) and a
>> >Wh/km value. The Gen 2 Leaf is a little more efficient and I'm guessing
>> >people might want to adjust the value, so this efficiency probably
>> >shouldn't be hard coded into the firmware.
>> >
>> >I'm currently using the gids value to calculate state of charge, based
>> >on the maximum gids that the car can hold (as the battery degrades it
>> >can't store so many gids, so the SOC calculation needs to know this. I'm
>> >currently using the largest gids value seen since startup. Every period,
>> >I set the maximum gids to the largest I've seen in the period (currently
>> >60 days) to allow the maximum gids to sink as the battery degrades.
>> >
>> >I've since found the BMS's state of charge field and may abandon this
>> >complex gids based SOC and use whatever the Lithium Battery Controller
>> >thinks the state of charge is. The car also knows it's Wh/km (it's
>> >displayed on the dashboard) so if I could locate that data in the CAN
>> >bus, I could replace the hard coded efficiency with something based off
>> >that.
>> >
>> >In the meantime, I'd like to store both the efficiency and the maximum
>> >gids in parameters so they're visible to the user and they can be
>> changed.
>> >
>> >Is it safe to use Parameter 0x14 and 0x15 (20 and 21 in the app) to
>> >store calibration data? These parameters don't seem to be defined or
>> >used and the android app will let you modify them.
>> >
>> >Thanks.
>> >_______________________________________________
>> >OvmsDev mailing list
>> >OvmsDev at lists.teslaclub.hk
>> >http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
>> >
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