[Letux-kernel] battery state of charge formula

H. Nikolaus Schaller hns at goldelico.com
Sun Jun 5 09:02:04 CEST 2016


Hi Marek,

> Am 05.06.2016 um 08:27 schrieb Belisko Marek <marek.belisko at gmail.com>:
> 
> On Sun, Jun 5, 2016 at 8:25 AM, H. Nikolaus Schaller <hns at goldelico.com> wrote:
>> 
>>> Am 05.06.2016 um 08:20 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
>>> 
>>> Hi Marek,
>>> 
>>> I did a quick research and google came up with some interesting results.
>>> 
>>> a) http://www.hindawi.com/journals/isrn/2013/953792/
>>> 
>>> b) http://www.mpoweruk.com/soc.htm
>>> 
>>> "Practical SOC Estimation
>>> Alternatively the performance characteristics of a typical sample cell (or cells) can be measured and the results used as a template to represent the performance of the rest of the population. Basing the cell performance estimates on look up tables constructed from measured data from actual cells is much simpler than carrying out theoretical estimates since it automatically takes account of most if not all the factors affecting the SOC. Look up tables are stepwise approximations of the performance response curves which represent the cell discharge performance as a function of temperature, discharge rate or other parameters. See example above. The necessary look up tables are developed from laboratory measurements under controlled conditions. The process of gathering the data and constructing the look up table is called cell characterisation and only needs to be carried out once, however a new data set or look up table must be produced for each cell chemistry variant and cell const
> r
>> uc
>>> tion used."
>>> 
>>> => exactly what we had done / proposed in non-DT driver
>>> 
>>> c) http://liionbms.com/php/wp_soc_estimate.php
>>> 
>>> d) http://www.mdpi.com/1996-1073/8/8/7854/pdf
>>> 
>>> e) http://www.mdpi.com/1996-1073/7/5/3004/pdf
>>> 
>>> f) finally I found "our" formula (which appears to circulate around RC model communities and practitioneers):
>>> 
>>> 2006:
>>> 
>>> http://www.candlepowerforums.com/vb/showthread.php?115871-Li-Ion-State-of-Charge-and-Voltage-Measurements&s=d700f18111fc9a99aaa214274cdc41ff&p=2440539&viewfull=1#post2440539
>>> 
>>> 2008:
>>> 
>>> http://www.rcgroups.com/forums/showpost.php?p=9276188&postcount=9
>>> http://www.rcgroups.com/forums/showthread.php?t=827602&page=2
>>> 
>>> The 2006 message was the oldest one I could find on the net: (google search "0.1966 Square Root 0.0387 1.4523 3.7835" before 2006)
>>> I think we should add proper attribution in our commit message - and perhaps do a little more research if we can find a source for citation, i.e. the "inventor" of the formula.
>> 
>> Here is some other hint where it comes from:
>> 
>> http://www.candlepowerforums.com/vb/showthread.php?357487-How-long-to-charge-a-new-batteries-(14500-and-18650)&p=4163950&viewfull=1#post4163950
> I found also this:
> http://www.candlepowerforums.com/vb/showthread.php?345795-Estimating-remaning-capacity-in-LiIon-batteries

yes, that are real curves.

>> 
>> "I believe the formula came from a Sanyo publication a few years back. ... Tom"
>> 
>> "Tom = Silver Fox" appears to be a "guru" on that forum.

After having breakfast I think we should simply make the formula work...

I forgot to copy it:

State of Charge % = 100 (0.1966 + SquareRoot(0.0387 - 1.4523 (3.7835 - Vresting))

echo "scale=2 ; (0.1966+sqrt(0.0387-(1.4523*(3.7835-$1))))*100" | bc

using my pocket calculator (didn't check if I have bc installed) it should say 39.33% for 3.7835V
and 99.88% for 4.2V

BR,
Nikolaus

>> 
>>> 
>>> Something like:
>>> Proposed-To-Use-By: Pavel Machek
>>> Invented-By: unknown (before 2006)
>>> Published-By: <http://www.candlepowerforums.com/vb/showthread.php?115871-Li-Ion-State-of-Charge-and-Voltage-Measurements#post2440539>
>>> 
>>> BR,
>>> Nikolaus
>>> 
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>> 
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> 
> BR,
> 
> marek
> 
> -- 
> as simple and primitive as possible
> -------------------------------------------------
> Marek Belisko - OPEN-NANDRA
> Freelance Developer
> 
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