Lithium Polymer internal resistance meter determines battery life

in Lithium Ion, project logs by DP | 4 comments

Here’s a project that let’s you measure the internal resistance of Lithium Polymer batteries. It measures the total current as the battery discharges through a 1 Ohm resistor. From the known voltage and the discharge current the internal resistance can calculated.

This device can be used to measure the internal resistance of Lithium Polymer batteries used in electric RC models. The power consumption of these models is quite high, and the batteries wear out in 100-200 recharge cycle. The internal resistance is a good measurement of the age of the batteries. New cells are below 5mohm, and the ones at the end of their life are above 20mohms. It also depends on the original quality.

Via Hacked Gadgets.

This entry was posted in Lithium Ion, project logs and tagged , , .

Comments

  1. it was said on hackaday that the internal resistance was not related to battery health.

    what you you think about that ? I’m unsure.

    And I’m not sure it’s wise to short batteries on a 1-ohm load…

  2. Winston says:

    Or, you could just buy one. Earlier versions of this US$16 unit got bad reviews because they were wired incorrectly:

    http://www.hobbyking.com/hobbyking/store/__22412__Turnigy_Mega_Checker_4_in_1_Battery_Checker_Monitor.html

    • Winston says:

      Just found this comment about the above meter and it’s not good:

      “that particular meter is not very useful in assessing internal resistance as it measures exclusively through the balance leads. Given this, the resistance of the connector and balance wires are included in the measurement and these are variable and can be much greater than the internal resistance of the cells themselves”

  3. Daniel Black says:

    Li Ion is 4.2V fully charged which at 1 ohm will give max 4.2A current which doesn’t sound like a problem for the crazy high power batteries that RC hobby people use. A lot of those will push several hundred watts continually!

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