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Author Topic: Testing capacity of an older battery pack?  (Read 1264 times)

Online Dennis Toth

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Testing capacity of an older battery pack?
« on: October 20, 2020, 03:31:32 PM »
Getting ready to start flying my electric Ringmaster and have to select some battery packs. I have several Thunder Power 4S-2200 packs that I was using in my Stuka but switched out to 2450 packs to be able to fly the full PA pattern as well as the OTS pattern (needed about 35 sec more for comfort). The packs were fine when I stopped using them and when I gave them a charge took a full charge. My question for the group is can we load test them on the ground somehow to have confidence they won't quite in the middle of the vertical eight when they get under stress?

Best,    DennisT

Offline John Rist

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Re: Testing capacity of an older battery pack?
« Reply #1 on: October 20, 2020, 06:10:05 PM »
Testing a LiPo on the ground is tricky.  Obviously if it is puffey  it is probably ready to retire.  Reading some articles it is suggested that measuring internal resistance is a way to check the health of a battery.  Low resistance is good high resistance is bad.   Supposedly some battery chargers can measure internal resistance.  At best it is difficult to measure internal resistance.  It is a very low value and takes good equipment to do it accurately.  What I am saying it that it can be done but it is not easy.   What I would suggests is fly the battery in the airplane.  Keep the flight safe.  Inside loops, wingovers, etc.   Stuff that will not kill the aircraft if the motor quits.  Things to look for is does the battery voltage get so low that the motor slows down.  IE the voltage gets so low that all of the voltage head room needed to maintain RPM regulation is gone.  If the motor felt strong for the hole flight make note of put back current it takes to fully recharge the battery.  It should be no more than 80% of battery capacity.  All this does not answer your question. Others may have an easy way to test battery capacity on the bench. But I don't know of any.

However I am using an KR timer.  If an airplane starts to slow down before the waring burp at end of flight I go to level flight.  When the RPMs drop a little more the KR timer turns off and I land safely.  The KR timer measures RPMs and when the RPMs falls a certain percentage below the set point the KR timer turns off.  For me there has always been plenty of time between motor slow down and KR timer shutdown to get the aircraft ready to land.  I have used plenty of crappy batteries that did not have enough capacity to finish a flight however because the way the KR timer handles thing I have never lost an Aircraft because of this problem.   D>K

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Offline Crist Rigotti

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Re: Testing capacity of an older battery pack?
« Reply #2 on: October 20, 2020, 06:21:14 PM »
Be sure the ESC is set on REDUCING the load an NOT on SHUT OFF.  Then if the battery starts to go out, the plane will just slow down and the motor will not stop.
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Offline Fred Underwood

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Re: Testing capacity of an older battery pack?
« Reply #3 on: October 20, 2020, 07:11:42 PM »
I watched a plane go to slow down mode because of low voltage in overhead flight toward the end of a flight.  It doesn't take much off peak rpm to lose line tension, and can be an unpleasant surprise.  I have "tested" batteries by by saving safe maneuvers toward the end of the flight, but that isn't a fool proof test as the load may not be as high as with overhead maneuvers.  IR is not a great way to follow the cells unless you have been watching the number of that battery on your equipment to see if it changes.  It can help if you find one cell significantly different.  That bad cell may low volt the pack.  I use a discharger with about 10 amp load and keep a cell checker on the pack to see if the cells are even under load.  If that seems ok, I fly the pack safely with recoverable maneuvers toward the end.  If the pack had normal capacity, even cell voltage under load, and normal IR for it, then it is likely safe.

When I data logged, I found that the average amp draw was about 20 amp for a 6S pack, and can be about double that in a hard draw maneuver, so that maneuver can discover low volt when you don't want to discover it.
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Offline TDM

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Re: Testing capacity of an older battery pack?
« Reply #4 on: October 21, 2020, 03:00:50 PM »
Put the next size bigger motor on the plane and all your problems will disappear.
Each goal you meet is a moment of happiness
Happiness is the harmony between what you think and what you do. Mahatma Gandhi

Online Ken Culbertson

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Re: Testing capacity of an older battery pack?
« Reply #5 on: October 21, 2020, 04:17:54 PM »
Put the next size bigger motor on the plane and all your problems will disappear.
y1 y1 y1 y1
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Online Dennis Toth

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Re: Testing capacity of an older battery pack?
« Reply #6 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

Offline Mike Alimov

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Re: Testing capacity of an older battery pack?
« Reply #7 on: October 22, 2020, 06:06:39 PM »
Lots of good thoughts. I think I will start by doing a full flight time ground run [snip]

Best,   DennisT

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.

Offline Fred Underwood

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Re: Testing capacity of an older battery pack?
« Reply #8 on: October 22, 2020, 06:50:33 PM »
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.
Fred
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Online Ken Culbertson

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Re: Testing capacity of an older battery pack?
« Reply #9 on: October 22, 2020, 09:29:14 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
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!

« Last Edit: October 22, 2020, 09:54:58 PM by Ken Culbertson »
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Offline John Rist

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Re: Testing capacity of an older battery pack?
« Reply #10 on: October 23, 2020, 07:09:01 AM »
Early on, in my venture into electric power, I fried a motor by trying for a full run on the ground.   We have things set up near the high limit of motor capacity to save weight.  I don't know how much harder a ground run pushes a motor.  But in most cases it is fetial.   n1  If you want to check out a timer's settings with a full run remove the prop or put on a small prop.   y1
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Online Dennis Toth

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Re: Testing capacity of an older battery pack?
« Reply #11 on: October 23, 2020, 02:11:29 PM »
Ok I got it. Plan "B" - 10 sec ground test to check rpm and current. If good, will do level flight test and check battery capacity. If good, will proceed to half OTS pattern test, then check capacity. If good, will do short (1lap between) OTS pattern, then check capacity. If good, fly full normal OTS pattern then check capacity. If any step is bad - buy new pack.

Best,    DennisT

Offline John Rist

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Re: Testing capacity of an older battery pack?
« Reply #12 on: October 24, 2020, 04:50:58 PM »
Ok I got it. Plan "B" - 10 sec ground test to check rpm and current. If good, will do level flight test and check battery capacity. If good, will proceed to half OTS pattern test, then check capacity. If good, will do short (1lap between) OTS pattern, then check capacity. If good, fly full normal OTS pattern then check capacity. If any step is bad - buy new pack.

Best,    DennisT
Great plan of attack!  y1
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