Allow battery voltage range of less than 1V

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Currently the battery voltage range can not be made smaller than 1V.  For 
instance if the low voltage is 9.4V then the high voltage must be at least 
10.4V.  The problem is that LiFe packs operate in a narrower range of voltages. 
 For instance the 3S pack I use in my Taranis and 9x has a range of about 9.4V 
to 10V.  Currently it is impossible to make the battery meter accurate because 
of the 1V minimum.

Of course a fresh LiFe pack might be charged to 10.8V but it drops to 10V or 
less within seconds then remains at around 9.9V until the pack is almost fully 
discharged and the voltage starts to drop below 9.9.  This is the nature of 
LiFe packs, it would be nice if the battery meter could be made more accurate 
by using a narrower voltage range.

Original issue reported on code.google.com by coderi...@gmail.com on 26 Jul 2013 at 6:29

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this is the typical discharge curve of a lifepo4 battery also consider we are 
discharging at 0.2A
http://www.avdweb.nl/Article_files/Solarbike/Batteries/LiFePO4-discharge-charact
eristics.jpg

You can select 3.1 per cell as minimum and 10.3V as maximum and you will be in 
the linear part of the curve.
The keypoint here is that you are discharging at fractions of C.
But anyway a narrow range does not disturb anyone.

Original comment by romolo.m...@gmail.com on 26 Jul 2013 at 6:47

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Yes that curve looks correct.

I'm basing my requirements on the fact that I discharge to approximately 80% 
capacity of the pack which is ~3.1V per cell with 80% mAh going back in on 
charge (actual measurements here).  In this case I would use a range of 9.4V to 
9.9V to make the battery meter accurate.

Using a maximum of 10.3V is no good because the battery is essentially never at 
that high of a voltage.  Like I said, you may charge to 10.8V but once put in 
the radio and powered on it will drop to 9.9V within seconds.  10.3V is way too 
high and will make the meter half empty within seconds.

In any case, like you said, allowing a narrower range should not hurt anything.

Original comment by coderi...@gmail.com on 26 Jul 2013 at 6:56

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Fixed on SVN. Will be in next (minor) release.

Original comment by bson...@gmail.com on 26 Jul 2013 at 7:51

• Changed state: Fixed

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This works really well now, thanks!

Original comment by coderi...@gmail.com on 26 Jul 2013 at 11:53

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Has this been fixed in OpenTx2?

Original comment by spastr...@gmail.com on 9 Oct 2014 at 2:45