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Old 2017-10-20
MichaelLevy MichaelLevy is offline
Non-WIMAC Member
First Name: Michael
Last Name: Levy
MAAC Number: 15553
WIMAC WINGS: Solo Planes
 
Join Date: Oct 2009
Posts: 313
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Another reason why it's good to know the IR of you battery before flight. Suppose you are using an old 4S battery, still flyable but not too trustable with a just measured IR of .010, .012, .010 and 30 ohm respectively. You've flown it before with no problem. You take off and very soon after, the power starts to drop rapidly. In cases like this my standard protocol was to find the closest open place to land cut power to preserve whatever is left for a final flair, hoping to limit the damage. This is the wrong response when dealing with a suspected IR issue because in fact there is a lot of power left in the battery, but you are basically flying on 3 cells instead of 4 and have quite some time to fly. The best response, even counter intuitive, is to gun the throttle, using maximum available power and get into a better final approach.

I had a similar experience with a fully charged 6s batt on one of my jets. Had initially plenty of power, immediately did one touch and go after take-off and lost power on the second take-off. In this particular case, when I brought the battery home and recharged it, the weak cell had a IR of .075 ohm, up from about .028 ohm before the flight! That cell was totally finished. So yes, things can deteriorate quickly once the IR starts to climb abnormally in one cell.

Last edited by MichaelLevy; 2017-10-20 at 03:50 PM.
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