Easy Battery Internal Resistance Measurement Tagged with: Battery, Hall of Fame, Internal Resistance, Measurement, Tips, Video Tuesday, June 19th, 2012 09:47 am GMT -6 Tuesday, June 19th, 2012 09:47 am GMT -6Tuesday, June 19th, 2012 09:47 am GMT -6 Quick and easy directions for manually measuring the internal resistance of a battery pack. Share this: Recommend on Facebook Share on Google+ Tweet about it Tell a friend Related posts: LiPo Battery Care Tips Tip: Is your Model Airplane Nose Heavy? Tip: Understanding Battery Internal Resistance Puffed RC Battery Pack? Upgrading to a Bigger RC Battery Pack Best and Worst Places To Be When Flying Motor I0 and Rm Constants Motor Voltage Constant Kv Epoxy Gluing Tips for Model Airplanes Model Aircraft BEC Guide Real Review: Hobby King Battery Monitor Programming an RC Speed Control, Part 1 Logging In... Add Comment Register Profile cancel Sign in with Twitter Sign in with Facebook or Name EmailNot published Website Comment Sure! Also send me the free email newsletter. 7 Replies 7 Comments 0 Tweets 0 Facebook 0 Pingbacks Last reply was Tuesday, July 10th, 2012 02:12 pm GMT -6 Carlos View <abbr class='timeago' title='2012-06-20 15:15:16Z'>Wednesday, June 20th, 2012 09:15 am GMT -6</abbr> Voltage (volts) / Resistance (ohms) = Current (amps). Voltage (volts) * Current (amps) = Power (watts). You need to match the resistance and power capacity (watts) of the power resistor to the number of cells. For three cells, you could get away with using a 10 watt 15 ohm power resistor. Ohms of between 10 and 20 are probably good. pmullen View <abbr class='timeago' title='2012-06-22 21:08:11Z'>Friday, June 22nd, 2012 03:08 pm GMT -6</abbr> Good video. You mention several equations. Are they written out somewhere? Carlosreplied: View <abbr class='timeago' title='2012-06-22 21:23:41Z'>Friday, June 22nd, 2012 03:23 pm GMT -6</abbr> No, but they are really simple: internal resistance = (voltage drop under load) * (load resistance in ohms) / (no load battery voltage) maximum safe battery load in amps = 0.10 * (3 volts) * (number of cells) / (battery internal resistance) Mark Harrison View <abbr class='timeago' title='2012-06-24 21:22:19Z'>Sunday, June 24th, 2012 03:22 pm GMT -6</abbr> What kind of power resistors are you using? What kind would be suitable for 2S, 3S LiPo cells? Carlosreplied: View <abbr class='timeago' title='2012-06-24 22:32:33Z'>Sunday, June 24th, 2012 04:32 pm GMT -6</abbr> Hi. I did not say in the video which resistor to get because it all depends on what you can find. I just uploaded a simple spreadsheet to help with the calculations (link below). I’m also including links to two Radio Shack resistors that offer workable solutions for 3S and 4S. The lower the resistance (ohms) the better, because the voltage drop is higher and easier to measure. Hope this helps! http://rcadvisor.com/wp-content/my-files/p/battery-internal-resistance.xls Radio Shack, 25 ohm, 10 watt resistor http://bit.ly/PXEyG3 Radio Shack, 10 ohm, 50 watt resistor http://bit.ly/Mu11ry Jim Taylor View <abbr class='timeago' title='2012-07-10 20:01:12Z'>Tuesday, July 10th, 2012 02:01 pm GMT -6</abbr> Thank you! I’ve been wanting to know how to do this, and I found your instructions easy to follow. After measuring all my LiPos as you describe, I found I could use an AstorFlight Whattmeter to do the measurement (and confirm the results). Carlosreplied: View <abbr class='timeago' title='2012-07-10 20:12:26Z'>Tuesday, July 10th, 2012 02:12 pm GMT -6</abbr> I’m glad you found the video useful. The only real challenge is finding a resistor that won’t burn up with a low enough resistance so that the voltage drop is easily measurable. Hope that made sense! Once you have the right resistor and soldered the connector, it only takes a few seconds to test a battery pack.