Testing Batteries - Manual and Automated
February 2012 Page 27
Each year I like to test my ship's batteries and replace those that do not have enough individual capacity to last 3 hours at a 1A load. But how can the average pilot perform a reasonable "real world" test with easily obtainable equipment?
See the Excel spreadsheets linked below and this Soaring magazine article for an explanation of the testing that I perform and the simple test rig that I use, along with Excel templates for gathering the data and then graphing the results.
There are three versions of the spreadsheet;
2x16 LCD Display
240x320 Color TFT Touch Display
Taking hours to manually collect battery test readings can be BORING! Lets try to automate the testing! You will be surprised how inexpensive this system is to build.
I use an inexpensive Arduino Duemilanove single board computer along with a display shield and a few other components to automate the testing. This record the battery readings over time when connected to our test load. Readings can be manually captured but are also sent to the serial port and then captured on the Arduino development software's serial port monitoring facility. More information can be found at the Arduino developers web site.
As pictured above there are two different displays I have used (with separate code):
Because the Arduino's analog inputs have a absolute maximum voltage limit of 5Vdc I had to convert the 12Vdc battery voltage to something that the Arduino could handle. To do this I built a simple resistive voltage "divider" to protect the inputs from a battery voltage which can easily exceed 14Vdc when fully charged. The divider is made from a 22KΩ and 10KΩ resistor (nominal values) creating a lower input voltage by a ratio of 1:3.2 [10/(22+10)]. Thus to protect against an absolute maximum battery voltage of 15Vdc the divider will convert this to a quite safe 4.7Vdc input voltage to the Arduino. If your battery input is greater than 16Vdc (5Vdc x 3.2) then the voltage divider will need to be modified. See this web site for an explanation of, and calculator for, voltage dividers. For the best accuracy of the battery voltage measurements the divider's resistors' actual values (versus nominal values) need to be carefully measured and those values entered into the Arduino code.
An optional addition is a simple piezo electric buzzer connected to a digital output to chirp at each reading and then to produce an alarm at the end of the testing to tell you to disconnect the battery from the big 12Ω resistive load. These components, along with battery connection jacks, are mounted onto an Arduino breadboard shield (see the pictures) place between the Arduino and the display to create a very compact and neat package.
Arduino Code - My latest Arduino software packages for each display type can be found here. After you open Arduino code packages you will find full build instructions in the comments area near the top of each listing.
Aruduino Hardware and Components - All required Arduino hardware and the associated parts will cost between $20-$40 on eBay, Amazon, Banggood, AliExpress, Mouser, and other electronic component outlets. More hardware specifications can be found in the comment fields of the Arduino code list.