Voltage drop or something ?

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1

Hi !

I’m trying to build a battery capacities tester and I have some problems that you guys might help me explain.

If I measure my battery with no load or anything the voltmeter shows 1.2V but when I connect a 5ohm resistor to the battery and do the measure again its only show like 1.05V or something like that, why and how do I fix it ?

I need to measure it when it’s connected to the resistor so I can do the math and calculate the mAh on the battery.

Hope you understand anything of what I mean, btw the resistor and the voltmeter is in parallel if that matter.

2

have look at the circuit at this link:

http://www.discovercircuits.com/H-Corne … tester.htm

and by all means, do try and use google first in the future.

try: “battery load testing circuit”

3

The battery has internal resistance and when you draw current from it, the voltage measured at the battery terminals will drop.

The current I (Amperes) in the circuit is 1.05V/5Ohms.

The voltage drop across the internal resistance R is IR = 0.15V

The internal resistance is 0.15*5/1.05 = 0.71 Ohms.