I am measuring AA alkaline battery voltage with ADC and sending these values to my PC to plot the graph. Where I confused is when I connect 66 ohm to battery it's voltage dropping about 20mV. I thought it may be due to internal resistance, I calculated internal resistance from 20mV drop and 66ohm it gave me 1k ohm. I don't think the internal resistance of battery is 1k. I thought it's okay to ask it in here what causing to this drop.

 

hi ss,
Welcome toAAC,
Show us your calculations, you have made an error.
E

 

1.35V/66ohm=20mA. Drop is 25mV so resistance is 25mv/20ma=1.25 ohm.

 

Hello,

Did you calculate the voltage drop correctly?
I see 1.35 Volts with no load and 1.1 Volts with the 66 Ohms load, in your graph.

Bertus

 

1.35V/66ohm=20mA. Drop is 25mV so resistance is 25mv/20ma=1.25 ohm

hi,
Getting Closer.

1.35V/66ohm=20.4mA,
so how do you get Drop is 25mV .??
E


Update:
Double check the Onload voltage drop, 0.25V seems too high, unless the battery is very old.

 

hi,
Getting Closer.

1.35V/66ohm=20.4mA,
so how do get Drop is 25mV .??
E

we are measuring battery voltage with internal resistance drop so 250mV lost in the internal resistance? It's my fault I have done mistake when calculating internal resistance at first. İnternal resistance is 12.5 ohm by the way

 

Isn't it 12.5 ohm too high?

 

Isn't it 12.5 ohm too high?

Likely is for a new battery, but not for a used one.
Since the open-circuit battery voltage is about 1.35V, I estimate it's at least half discharged.

 

resistance drop so 250mV lost in the internal resistance

Hi ss,
I think you have made a simple typo in your reply, ie: 25mV post #6

E

 

Hi ss,
I think you have made a simple typo in your reply, ie: 25mV post #6

E

I thought this was the only thing I have written correctly in that post. I hope it's irony

 

hi ss,
No Problem.
If you have a few of that battery type on the bench, why not do an internal resistance check on each battery.?
E

 

A Duracell coppertop AA alkaline battery has a spec of 120 milli-ohms internal ompedance when new. Then one cell powering a 66 ohms load draws only 24.6mA and the voltage drop is 66 x 0.0246= 1.62milli-volts.

My new AA alkaline batteries measure 1.62V without a load. One useless battery in my garbage measures 1.33V. Your battery is also old garbage.

 

One useless battery in my garbage measures 1.33V.

Amazingly my AAA battery powered mouse will operate until the voltage drops below 1V.
So that's where all my batteries go to finish them off, from electronics that stop operating at a higher battery voltage.

 

1.35V/66ohm=20mA. Drop is 25mV so resistance is 25mv/2

I am measuring AA alkaline battery voltage with ADC and sending these values to my PC to plot the graph. Where I confused is when I connect 66 ohm to battery it's voltage dropping about 20mV. I thought it may be due to internal resistance, I calculated internal resistance from 20mV drop and 66ohm it gave me 1k ohm. I don't think the internal resistance of battery is 1k. I thought it's okay to ask it in here what causing to this drop.
View attachment 208505

According to this Graph the load current is: 1.1V / 66ohms = 16.83ma
The resistance causing the battery droop is: 0.25V / 0.01683A = 14.85ohms
I think the internal resistance of a battery goes up as it gets closer to being discharged.


View attachment 208514