Resistor

[Mikey59]

I'm wanting to test some aa and aaa batteries for there internal resistance and believe I can do this using a resistor along with a multimeter.the question is,which size resistor do I need?

 

[AnalogKid]

Do some research to find the approximate internal resistance values and peak output currents for your batteries. If you attach an external resistor equal to the internal ESR (equivalent series resistance), the measured output voltage should decrease by 50% (Ohm's Law). For other rations of unloaded-to-loaded voltages, Ohm's Law will give you the ESR. Use Joule's Law to estimate the power dissipated in the external resistance, and buy one with at least twice that power rating.

Note that this kind of testing will discharge the battery very quickly. Also, the battery ESR changes with load current. Consider testing the batteries at 1/10th their rated peak current, a much more representative load.

ak

 

[Mikey59]

Do some research to find the approximate internal resistance values and peak output currents for your batteries. If you attach an external resistor equal to the internal ESR (equivalent series resistance), the measured output voltage should decrease by 50% (Ohm's Law). For other rations of unloaded-to-loaded voltages, Ohm's Law will give you the ESR. Use Joule's Law to estimate the power dissipated in the external resistance, and buy one with at least twice that power rating.

Note that this kind of testing will discharge the battery very quickly. Also, the battery ESR changes with load current. Consider testing the batteries at 1/10th their rated peak current, a much more representative load.

ak

I do I ac

 

[Mikey59]

Just found this,even though the gold and black battery reads good in open circuit it doesn't when testing for internal resistance.hes using a 110 ohms but does not say what wattage it is.im no expert on electronics but does 110 ohms sound too high

 

[dorke]

110 ohm (or about) is fine for "small" batteries like the ones shown in the video.

 

[Audioguru]

When it has powered the smoke detector for 1 year the 9V alkaline battery in it measures close to 9V but its internal resistance has become so high that it cannot supply much current. The smoke detector blinks the LED every 10 minutes and during the blink it measures the battery voltage to see if the battery needs replacing because it must provide plenty of current to make a loud alarm if it detects smoke.