[Letux-kernel] battery state of charge formula

H. Nikolaus Schaller hns at goldelico.com
Sun Jun 5 08:20:25 CEST 2016


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 construction 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.

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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