![]() ![]() You do bring out a weak point in my post and that is that I did no go in much – nothing actually – of the following calculations and that if you want to get correct voltages and mAh capacity you have to do it in Excel or similar. Also, I just want to be able to compare batteries with this “PEPs” value and as long as the same computer is used this is very “comparable” between different batteries. Without compensation for this possible variation of the reference voltage this did not seem to me to be the easiest/best choice so I settled for the simpler assumption that the USB 5V was “good enough”. The 1.1 V reference has roughly +- 10% variation (according to the datasheet) which translates to a 4.5 V to 5.5 V swing on the USB port. ![]() Using the built-in voltage reference is very handy, but I use it mostly when I drive the Arduino from more unstable sources than a computer USB. Also note that a NEW Battery Capacity Tester with a more general focus for all kinds of batteries can be found here!Īs usual if anything goes wrong or gets broken by using this information I am sorry – but all the decisions are yours! ![]() After saving this to your disk rename the extension to “.ino”. NOTE: Right click on the link and select “Save target as…” Due to limitations with WordPress this Arduino source code file has been given the extension “.doc”. Here is a link to the Arduino program: Batter圜apacityTester Note that under other (“laboratory”) conditions these batteries can give other mAh capacities – but as I do it the same way in all my tests you can compare the results between the batteries that I test. MAh My testing method also gives the capacity in mAh under the above “simulated real world picture-taking” conditions. (This goes well with my Canon S95 that signals empty battery at that voltage.) Cut off voltage is 3.0 V for Li-ion batteries so that is where I stopped the tests. Running through the whole test takes about 3 hours per battery. The circuit takes into account the resistance of the MOSFET transistor used – just below 0.4 ohm – but it lowers the load a little bit. PEPs This 16 second 5.6 ohm load followed by a 16 second rest period just had to have a name so I called it Photoman Equivalent Picture samples (PEPs) – cool eh? □ NOTE that this is not real pictures taken but gives a good enough approximation – especially for comparing camera batteries!. More to read about battery measurement in the CIPA document – but be warned it is very technical! Initially I wanted to follow a “real” standard like the CIPA one – but it was much to complicated for me and would involve far too much manual work. The load in this case is around 2.5 watts so use an appropriate resistor – with higher rating unless you want it to get very hot! □ I also decided to let the battery “catch its breath” for 16 seconds between each “picture” – again mimicking ( very oversimplified) the real world behaviour while keeping the testing time down. Settled for a more standard resistor of 5.6 ohm. That ideally translated to a 5.2 ohm resistor giving around 500 mA load for 16 seconds each. I wanted the load to mimic the actual taking of pictures by applying the load for a number of shorter times – like taking pictures.įor the 3.7 V Li-ion batteries on test here I decided that, as the battery according to Canon should give about 300 pictures, I would apply the load in around 300 short intervals. The circuit I decided on can handle the three most common batteries: 1.2 V NiMh, 3.7 and 7.4 V Li-ion by changing the load resistor. I just copy it from there to Excel and do the calculations and graphics in Excel.Īfter some consideration about the measurement process I decided to try to approximate the real world picture-taking – but I also wanted a repeatable and reasonable easy and quick way of comparing different batteries. Someone was! □ (Interested in the Arduino program!) Link at the bottom of this post! The program outputs measurements to the serial monitor. (If anyone is interested I can put up the Arduino program that controls it.) I have used this on my tests of camera batteries – check them out! To automate the testing of camera batteries and to make the tests repeatable I came up with a small circuit controlled by a Arduino microcontroller – you can see the battery capacity tester circuit on the left. See the new, more general, improved and still simplified version of the New Battery Capacity Tester here ! NOTE! This Arduino Battery Capacity Tester has been updated! ![]()
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