Posts: 229
Threads: 57
Joined: Mar 2016
Reputation:
7
I currently monitor voltage and current in/out for my 3 battery banks and wondered if I could devise a Coulomb-counting battery monitor.
I was thinking of something in Node-red but thought Id ask if anyone has done it already
Its the algorithm I really need but if anyone has a NR flow or node that would be perfect
Thanks
Posts: 1,161
Threads: 98
Joined: Mar 2016
Reputation:
69
Complex stuff!! Think it would be better to save all the data in influxdb then do the calcs with SQL.
Posts: 8
Threads: 0
Joined: Dec 2020
Reputation:
0
Interesting paper. Off the cuff, the authors are thinking about new batteries and ignore battery capacity deteriorates with time and usage. Deterioration is different and known for different battery types like Lithium, Gel or Lead Acid. Deep cycle batteries are built better and deteriorate more slowly.
In my day job as an electrical engineer, I'd research this for a proper answer. These thoughts are factors that come to mind for the battery measurement task. I intend to do an actual algorythm for this in the next few months. I'm sure the smart battery chargers and solar controllers have remaining capacity in a battery figured out.
Coulomb counting couldn't be easier. An Amp is a Coulomb per sec or 6.241e18 electrons per sec. 100 AH batteries in theory are at 50% after 50 Amp draw for an hour. Hot batteries don't give as much, cold batteries (5Amps for 10 hours) give more. Capacity left in a battery could be calculated on the fly, or stored in a database and calced easily. Actual curves based on high or low draws could be considered.
Problem is, you don't know the AH capacity of your battery. You can measure how much gas you used, but your gas tank is probably smaller than you think. Amp hour capacity of batteries deteriorates with use, more so with most batteries if you run them down to zero a lot. There are accurate pulsed measurements of actual amp hour capacity, but that's overkill. For most uses, a battery that hits 66% of original AH capacity should be replaced as deterioration increases past there. Measuring voltage at a particular rate of discharge or better at no discharge somewhat indicates actual battery capacity deterioration. This measurement doesn't work if the battery has been recently under a charge from shore power or the alternator. I recall this is called a "surface" charge.
I'm looking at doing current measurement with a INA260 0.01 ohm shunt or a toroid with an ACS 712 or similar. The electrical isolation of the toroid seems better but then I'd need a ADC to measure voltage at the battery.
Another real world thought is to flag a low battery voltage after extended charge. Batteries fail by shorting out a cell when the plates touch.
