Internal resistance of a battery

[jak9]

hello friends,
i am calculating internal resistance of a car battery during the charging phase. When the car is moving the alternator keeps on charging the battery if the output voltage of the alternator is greater than the battery voltage. Basically to proceed with this i have input of continuous voltage and current which is measured at the battery terminals. These signals are in phase but have ripples and that means its a pure resistive circuit. So the voltage divide by the current has to give the internal resistance value. If we consider an open circuit in which the internal resistance would be calculated as,
Ri=Voc-Vterminal/Ibatt
but when i have to calculate the battery internal resistance during its charging phase then how i amply this formula because in this case i have voltage and current signal which are measured at its terminal and its going to be a closed circuit and also what about the ripples? So should i directly divide Vbatt/Ibatt to get internal resistance or something else?
The other thing is the voltage and current has ac component that is some ripples so how to consider these ripples to get internal resistance?
thanks

 

[IanP]

It may be very difficult to directly measure the internal resistance of a battery during the charging phase ..
Some instruments use so called Large Pulse Resistance measurement, that is they connect a big load to a battery for a very short period of time, say, 1ms ..
By measuring voltage drop and current one can then estimate the internal resistance ..
See attached drawing ..

IanP
:wink:

 

[jak9]

well after going through lots of literature i conclude that during charging of a battery the terminal voltage is bigger than cell emf so the internal resistance of a cell causes the terminal voltage to change because of voltage drop across it so the internal resistance of a cell during charging would be
Ri=Vterminal-Emf/I
and the circuit would consist of only one resistance and a capacitor(electrochemical double layer capacitor) in series
i hope i succeed with this assumption
if you have any views or suggestions about this then please let me know

---------- Post added at 18:23 ---------- Previous post was at 18:22 ----------

@IanP...thanks for you suggestion but what you are saying is DC load test which i have already implemented during the cranking phase that is when the car is started and i got correct Ri for that but during charging phase its bit difficult so i used the above defined assumption and i hope its correct