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'[PIC:] Ideas For Reading A Battery (was ADC Source'
2004\05\27@130837 by Bob Axtell

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Mr Pefhany is right on. The battery needs to be read under load to
determine its internal resistance.

What I usually do is to measure the battery under load. In one product
with 4 AA Alkaline cells, I did the measurement 4 times / day:

1. Normally the ADC is turned off, and no battery divider is in place.

2. At the time to take the samples, I:

   A. Place the battery divider into the circuit, and turn on the ADC.
I then take two samples, average, and store the values.

 {It is more accurate if there is a few minutes between steps A and B.}

    B. I then place a 100mA resistor load across the nominally 6V
battery. I quickly take two samples, average, store, then disconnect the
heavy load quickly. I am under load for about 10mS.

    C. I take everything back to normal.

    D. I then analyse the value without the load and with the load; if
    the two readings are different by more than 15%, the battery is now
flat. I usually consider the min. voltage as well under load.


--Bob


Spehro Pefhany wrote:

{Quote hidden}

Replier: Most attachments rejected
      --------------
        Bob Axtell
PIC Hardware & Firmware Dev
  http://beam.to/baxtell
      1-520-219-2363




--

Replier: Most attachments rejected
      --------------
        Bob Axtell
PIC Hardware & Firmware Dev
  http://beam.to/baxtell
      1-520-219-2363

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