[Test-Equipment] "Conductance" battery checker

[Brooke Clarke]

Hi Ray:

There is a correlation between the equivalent circuit of a battery and 
it's state of charge.  The older battery chemistries like Lead Acid or 
Carbon Zinc were fairly easy to test but the newer chemistries like 
Ni-Cad, Ni-MH or any of the Li types are much harder to test because 
they have much lower values of internal resistance.  It's possible to 
use a capacitor ESR meter to test batteries with an easy modification to 
protect the meter from the battery voltage.
http://www.prc68.com/I/BatTst.shtml#EVB
The HP 4328A Milliohmmeter can be used to directly measure the internal 
resistance of batteries up to 150 Volts.
http://www.prc68.com/I/HP4328A.shtml
Note is uses an AC signal rather than trying to measure a DC voltage drop.

Since batteries work by chemistry the time required for the reaction can 
be on the order of seconds (Magneasium batteries like the BA-4386/PRC-25 
need a heavy load applied for a number of seconds to activate).  This 
implies that testing them with signals that are on the order of 
milliseconds may not be as good as using a load that lasts for some 
seconds.  The equivalent circuit will contain a ladder topology where 
there are large capacitors causing long time constants to see deep into 
the chemistry.

There's a state of charge tester that's designed specifically to test 
LiSO2 chemistry batteries.  As far as I know it's the only way to test 
these batteries that does not involve actually draining the battery 
while counting coulombs.
http://www.prc68.com/I/SOC.shtml

Have Fun,

Brooke Clarke
http://www.PRC68.com


Raymond LaRue wrote:
> Looking for information on designing and building a battery
> "conductance" tester.  In an extended web search, I see a couple
> companies that sell small 6 and 12 volt conductance testers.
>
> They apparently inject a small AC voltage into a battery on or off line,
> in a non-intrusive way.  Calibration data is developed by profiles from
> testing good batteries.  The resultant voltage and current phase
> differentials are processed and utilized to give an indication of
> remaining battery capacity.
>
> The commercial testers available are not very expensive, but those found
> on line give little detail about how they operate and they appear not to
> quite meet my needs, as I would like to try this technique by composite
> testing of a series of SLA batteries.
>
> I am prone to try building one if helpful info were available.
>
> Does anyone have any experience with such, or have design info for
> building a battery conductance tester?
>
> Thank you for your attention.
> 73,
> Ray, W4BYG
> Cleveland, TN
>
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