DIYbanter - View Single Post - What is the proper way to test alkaline batteries?

mike[_22_]

On 9/24/2017 12:29 PM, wrote:
On Sunday, 24 September 2017 19:32:47 UTC+1, John-Del wrote:
On Sunday, September 24, 2017 at 5:34:07 AM UTC-4, mike wrote:
On 9/22/2017 6:06 AM, wrote:
On Thursday, September 21, 2017 at 7:46:39 AM UTC-4, John-Del wrote:
On Thursday, September 21, 2017 at 3:35:43 AM UTC-4, GS wrote:
Phil Allison wrote:
GS wrote:

--------------------
Phil Allison

** The ESR of a cell or battery is a good guide to its condition.

A fresh AA alkaline measures 0.1 ohms or lower while a tired one
measures 1 ohm or greater, a fresh 9V measures under 1 ohm. Along with a
voltage test you have enough info to match or discard used cells.

.... Phil

What's a good way to do that ?

** Do what ?

Test ESR or correlate it with open cct cell voltage?

.... Phil

ESR.

Greg

IIRC, you take the open circuit voltage and write it down.

You take a voltage reading under a known fixed load and write that down.

You plug those two voltage readings along with the load resistance

value into a formula (that I can't recall) and you get the internal
resistance of the battery.

Which voltage do you use?
When you apply the load, the voltage starts to drop.
So, which voltage along that curve do you use?
And when you "let go", the voltage won't return to the original level.
Note that the voltage at the instant you apply the load won't be available
unless you use a scope, or some otherwise accurate sampling to measure it.

Great in theory, but not nearly so simple in practice.

If you're applying a load suitable enough to cause a constant drift of voltage or the OC voltage doesn't return to pre test state, the load is too high for the battery in question or the battery is shot. Old School battery testers used to use a switch to select which resistor to load down the battery in question, AA, AAA, C, etc., while displaying the battery voltage on the meter. The only time I saw the meter drift downward was if selecting a D battery test for a AAA for instance.

If your battery voltage is drifting down, its ESR is drifting up. If you want to know what state it's in after the test you'd use the last voltage reading. But there's no point, if it's dropping noticeably either it's had its day or the test load is too high.

NT

Do the math.
How much current do you apply?
How much voltage represents 0.1 ohm of ESR?
Compare that to the change of voltage over a second when you apply
that current to a brand new battery.
The battery model is more than a resistor in series with a fixed voltage
source.
Maybe someone here can supply the actual model of a battery that represents
the voltage over time for a given current as a function of recent
history of the battery load.

The only way I got usable ESR results for matching cells was to apply a
square wave switching
from one non-zero load to a different non-zero load and measuring
the amplitude of the square wave...always using the same frequency
of square wave.
The devil is in the details.