Electric Stunt > Gettin all AMP'ed up!
Testing capacity of an older battery pack?
Ken Culbertson:
--- Quote from: TDM on October 21, 2020, 03:00:50 PM ---Put the next size bigger motor on the plane and all your problems will disappear.
--- End quote ---
y1 y1 y1 y1
Dennis Toth:
Lots of good thoughts. I think I will start by doing a full flight time ground run of each pack. The ground stalled load should be 15 -20 % higher than the in air load most of the time. I think this will see when it hits low voltage cut off (I do set it for soft cut-off). If we get past that with something let in the tank I will do flight test. As suggested keep it to safe maneuvers and work up slowly to more risky. I like the idea of doing the pattern in reverse as a test. Not sure if saving the $60 is worth this aggravation.
Best, DennisT
Mike Alimov:
--- Quote from: Dennis Toth on October 22, 2020, 03:47:04 PM ---Lots of good thoughts. I think I will start by doing a full flight time ground run [snip]
Best, DennisT
--- End quote ---
This is an almost sure way to kill your battery for good, and possibly fry your motor too (unless your setup has excessive headroom, like Dorin's). Ask me how i know.
Fred Underwood:
I'm not sure how you came up with that solution based on the suggestions. A ground load is not good test and will not cool the components, unless you have some cooling devised. It does not harm to run on the ground for a brief time to check that all wiring is intact and everything is working properly, but not to test capacity.
Running to low voltage is also not highly recommended. You might be ok with 3.5 under load, but 3.2v, often used for cutoff, will not help your batteries. If I recall correctly, my batteries didn't go below 3.7 during flying.
If the batteries have normal capacity, and no low/bad cells, fly the pattern in say 4 minutes and eliminate many level laps. Then try 4:30, and work your way up. A little trial and error with low risk will work.
Ken Culbertson:
--- Quote from: Dennis Toth on October 22, 2020, 03:47:04 PM ---Lots of good thoughts. I think I will start by doing a full flight time ground run of each pack. The ground stalled load should be 15 -20 % higher than the in air load most of the time. I think this will see when it hits low voltage cut off (I do set it for soft cut-off). If we get past that with something let in the tank I will do flight test. As suggested keep it to safe maneuvers and work up slowly to more risky. I like the idea of doing the pattern in reverse as a test. Not sure if saving the $60 is worth this aggravation.
Best, DennisT
--- End quote ---
DON'T DO IT unless you want to replace everything except the prop and timer. 5-10 seconds at full power to make sure it is working on the ground is fine but no more. I wish someone had gotten to me early and warned me to never do that.
Just like an IC stopping without warning electrics do it too. If you don't recognize a battery going south early enough the results are no different than an IC quitting. Watch the remaining capacity after a flight. A lot of savings can come from setting the cutoff as close as possible to the end of the pattern. I like 5 laps just in case I chicken out and want a go-around. If the remaining capacity starts to drop or one cell is dramatically lower than the others, retire the battery to test flights. As a battery starts to go south it will show signs in those last 5 laps first well before it craps out in a maneuver.
If you haven't done it, take an old battery and fly it till it quits. Only way to know what it feels like as it starts to slow down. If you know the warning signs you won't be doing cloverleafs or OH8's and getting killed. Nothing can prepare you for the broken wire/connection where it just stops. I have had a couple of those and not having the noise stop like it does on an IC deprived me of that half second to make an emergency move. Three bladed props wind milling don't fare well landing inverted!
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