Animesh said:
Can I measure the internal resistance of a freshly charged battery by
directly using a Multimeter. Or it will damage my Multimeter.
Thanks
This will wipe out an analog meter in a big hurry. A digital multimeter
is probably protected against such an event, but it will not give you an
accurate measurement.
If you have the continuous current draw specification for your battery,
divide the measured voltage by that value to get a comfortable design value.
The internal resistance of a battery can be found experimentally by
measuring its unloaded voltage (Vu), then loading it with a resistor
that is small enough to cause the battery voltage (Vl) to sag and and
dividing the difference between them by the load current(Il). (Vu-Vl)/Il
To get good resolution the load resistance should be about three times
the estimated internal resistance. The manufacturer's web page or data
sheet or someone with experience with the type of battery you have can
probably tell you how much current it can deliver. From that you can
approximate the internal resistance and pick your load resistor.
Remember that unless your battery is very small, the load resistor will
dissipate a great deal of power, so select one with an appropriate rating.
This method is dangerous for large batteries (like car batteries)
because the amount of current needed to cause the voltage to sag can be
enormous (hundreds of amps). The battery may also be damaged if the load
is connected for more than a few seconds.
I have done this many times with bench power supplies. I have never
tried it with a battery. You should definitely get a second opinion WRT
safety and potential battery damage before you try it.
EI