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Topic: Measuring the capacity of a battery using ACS712 current sensor ! help ! (Read 1 time) previous topic - next topic

johnerrington

I found the link
https://www.analog.com/en/products/power-management/battery-management/coulomb-counter.html

however there is no further useful information.


Quote
You need at least 22 bits of analog conversion
which gives 0.000024 % accuracy - I dont see why.

If the battery is rated in Ah I dont see why "coulomb counting"  (coulomb = 1 amp second) cant give a reasonable result, which is all you can expect ...

without exhaustive data on the individual battery (discharge curves at different tempertures, different currents, battery degredation etc).

And as MarkT says
Quote
You'll probably want to use the battery voltage as well, to reliably detect the onset of full discharge as the coulomb-counting isn't highly accurate.
Of course the issue with coulomb counting is you need to record the charge drawn from the battery provided it is at full capacity when you start integrating (coulomb counting); and how do you know its INITIAL state of charge?
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MarkT

I found the link
https://www.analog.com/en/products/power-management/battery-management/coulomb-counter.html

however there is no further useful information.

Quote
You need at least 22 bits of analog conversion
which gives 0.000024 % accuracy - I dont see why.

That's for high dynamic range when the load varies.
Many devices alternate between high current and low current modes (active v. sleep mode).  The
active current might be 100mA, the sleep current 5uA.  If you want 1% accuracy for both cases
thats 21 bits or so...

However there's an easier way - use a diode shunt to give a logarithmic voltage reading representing
the current, makes for great dynamic range at the expense of accuracy (but estimating battery
capacity is a rough and ready thing anyway).  10-bit ADC is probably good enough then.

The main downside to using a diode in this way is that temperature correction may be needed for
reasonable performance as diode forward voltages depend on temperature as well as current.
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