On Wed, Oct 15, 2014 at 6:07 AM, Justin Richards <justin.richards@gmail.com=
>
wrote:

> Experimenting to determine internal resistance of a battery using O/C
> voltage and Loaded Voltages and and currents is proving to be problematic=
..
>
> The questions that arise are:
>
> 1. Should you discharge a little just to take the surface charge off befo=
re
> doing the tests. (I am doing this about 5 secs then remove for 5 secs the=
n
> begin the experiement)
>
> 2. How long after the load is applied should the measurements be taken. (=
I
> try to take measurements as soon as possible)
>
> 3. Can a series of voltage and current measurements be taken over time to
> help better model the internal resistance.
>
> 4. Should a low or high value resistor be used. (I am using 149.1 ohms an=
d
> 15.4ohms)
>
> Test at 149.1 ohms
> O/CV 12.91 C/CV 12.89V C/CC 0.086A =3D ~ 0.23 ohms
>
> test at 15.4 ohms
> O/CV 12.86 C/CV  12.65V  C/CC 0.819A =3D ~ 0.24 ohms
>
> I am considering using the impedance measurement trick I was taught at TA=
FE
> using a low level AC waveform  and matching the volt drop across the
> battery and variable resistor, then measuring the variable resistors DC
> resistance.
>
>
Justin, I've seen a few 16 channel charger/discharger/impedance analyzer
for Ni-Cd batteries. Even SLA are different from NI-Cd, one of the biggest
problem of SLA being the gel drying and impedance increasing over time, the
basic measurement principle remains the same.

Discharge the battery to a resistor and measure the dU/dI after a few
charging cycles. The impedance value will change. The value of the resistor
is usually chosen for the battery rated current.

Take as many samples you can from the complete charge to near the complete
discharge and see the impedance variation.

best,
Vasile
--=20
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