Alkaline battery voltage drop with load

Thread Starter

ssonel1

Joined Feb 24, 2020
15
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.
1590847110424.png
 

Attachments

bertus

Joined Apr 5, 2008
20,538
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
 

ericgibbs

Joined Jan 29, 2010
10,042
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.
 

Thread Starter

ssonel1

Joined Feb 24, 2020
15
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
 
Last edited:

Audioguru again

Joined Oct 21, 2019
1,492
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.
 

mglucas

Joined Feb 3, 2012
1
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
 
Top