Arduino - State of Charge - auxiliary battery monitor

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Conroe

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Advocate II

Hi all,
Been fiddling with Arduino boards for a while on and off, and I'm wanting to develop a monitor for my Cranking and Auxiliary battery banks, and perhaps the solar panel, but primarily for the Auxiliary. I'll measure voltages on all three, and measure current flow on the negative of my Auxiliary Batteries.

That will all be nice and easy to monitor, but this week I've been looking in to whats involved in estimating a battery's State of Charge, and it seems to be a minefield of PHDs. I would love to be able to estimate the AUX battery's State of Charge, and based on current use, estimate how long it can be run before reaching a safe state, such as 50%. Coulomb Counting seems like a reasonable technique, except that as overlanders, we rarely know when our battery is fully charged. A heap of googling comes up with buzz words like "peukert's equation" and "kalman factors", but in a number of PHD papers that I've browsed over, there seems to be little in the way of an implementable equation. I don't need incredible accuracy, I'd just love to be able to keep an eye on the system, and have a better solution than Terminal Voltage, while under load. I've been out of Uni for 4 years and am a bit out of touch with some of the mathematics.

Has anyone tried tackling something like this and found a reasonably useable accuracy?
 

Conroe

Rank II

Advocate II

Found some helpful info on the owner's manual for the Enerdrive battery monitor. The user inputs the battery capacity and the float voltage. It seems that their unit either auto-synchronises when the terminal voltage sits at float voltage for 4 minutes or more, or you can manually synchronise it when you know the battery is fully charged. From here I suppose they measure current draw with respect to time and just Coulomb Count down. Looking at spec sheets such as the Fullriver DC120 it seems that the float voltage is specified there. I could include Peukert's Law to account for changing capacity with respect to current draw, and factor in the terminal voltage to get a reasonable estimate.

http://www.enerdrive.com.au/wp-content/uploads/Enerdrive-eLITE-Manual-Rev5-print.pdf

http://www.fullriver.com/products/admin/upfile/DC120-12B.pdf
 
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