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Gene's Tips #4

Checking your Batteries


     In preparing for the new flying season, I'm checking batteries in my fleet.  Nothing worse than having a $20.00 (bad/weak) battery causing a crash.  


     I use a couple of tools.  First I give the battery a nice slow overnight charge.  That means a 12-16 hour charge at approximately 100-120 mah.  Then using a Hanger 9 digital variable load voltmeter set to add a 500mah load under test, I check the voltage.  A typical good fresh charged 4 cell nimh battery will show ~5.5V fully charged and it will drop to ~5.2V under load.  A 5 cell nimh battery will show ~7.1V fully charged and it will drop to ~6.7V under load. If the voltage is lower, I then will plug the battery into my SIRIUS peak charger ( or any other good peak charger set to around 500mah) and peak charge the pack and re assess with my digital volt meter as before.  The last check is to take the fully charged battery pack and cycle it to see how many mah you get.


     In my tests I found the 5 cell pack in my AVA was dropping to ~6.4V under load. That wasn't too bad but when I cycled the 1600mah battery it was only producing 900mah.   Surprisingly the pack was just barely two years old!  It was tossed.  My other 5 cell 1600mah pack from the same manufacture cycled at over 1300 mah and it's 4 years old.  I had already decided to replace this pack just due to the age but I would be confident using his pack for a while longer.


     Also don't forget to check your pack before the first flight and maybe check after 3 flights to see how it is holding up.  I won't fly with a 4 cell battery that drops below 4.8V under load.  My cutoff for a 6 cell battery is 6V.


     See you at the field!


     Gene T.