[NSRCA-dist8] Battery checkers

[Gordon Anderson]

Don't get me started on parallel charging!

G

Sent from my iPhone

> On Jul 31, 2015, at 5:15 PM, Patrick Harris via NSRCA-dist8 <nsrca-dist8 at lists.nsrca.org> wrote:
> 
> OMG...Jim...don't say "parallel charging' around Gordon....he'll have a fit! 😀
> 
> 
> 
>> On Fri, Jul 31, 2015 at 3:59 PM, James Hiller <jnhiller at earthlink.net> wrote:
>> Tried to fly today 17 MPH 101 degrees, this is getting old.
>> 
>> I use a free volt meter from HARBOR freight to check before flying to insure I'm not installing a used pack.
>> 
>> Before charging I check the voltage of each twin 5S pack to select packs with nearly the same voltage - usually within 2/10 V before parallel charging. I always charge at 1C. Takes about two beers to recharge a day's usage.
>> 
>> I monitor charge Mah, which is a total when parallel charging, that I average to a single battery to get a feel for per flight consumption.
>> 
>> Occasionally I'll charge individual batteries to try to negate the affects of parallel charging.
>> 
>> I've also noticed it takes longer to balance when the batteries are getting tired and I'll check the IR for weak cells ( IR Spread ).
>> 
>> I'm also not working the batteries very hard only gaining maybe 20 degrees over ambient.
>> 
>> Jim
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>> From: NSRCA-dist8 [mailto:nsrca-dist8-bounces at lists.nsrca.org] On Behalf Of Patrick Harris via NSRCA-dist8
>> Sent: Friday, July 31, 2015 3:32 PM
>> To: Gordon Anderson
>> Cc: AK, ID, MT, OR, WA, WY
>> Subject: Re: [NSRCA-dist8] Battery checkers
>> 
>>  
>> 
>> All very true. I pick up on average about 5 percent after my packs set awhile. I find the checker I use to be pretty close, but always about 5 to 10 percent off what the true level based on what I actually put back into them. 
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>> On Fri, Jul 31, 2015 at 3:25 PM, Gordon Anderson <gaa at owt.com> wrote:
>> 
>> Karl,
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>> Here is my 2 cents worth....
>> 
>> Predicting battery capacity from the open terminal voltage is not very accurate, I believe that is where this capacity prediction is coming from. I will bet if you let the batteries "rest" a few minutes after your flight and then check them again the capacity values will change. Battery chemistry is very non linear. I think the best predictor of battery health is the internal resistance, a lot of chargers will calculate and display this value. Keep an eye on trends, as the batteries age the internal resistance will increase and they will also get hotter during the flight and eventually start to puff up. The nice thing about monitoring IR is you can see if a cell is getting significantly different than the rest of the cells in the pack.
>> 
>> The best way to know the capacity you have taken from the pack is to use a data logger that is measuring voltage and current and then calculating the maHr usage. Even in this case you will have to put more back in than you took out, this is because of the IR that burns some up in heat and the fact that the process is not linear.
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>> --Gordon
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>> On Jul 31, 2015, at 12:11 PM, Karl Watts <karlwatt at sarmc.org> wrote:
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>> Do any of you guys or gals use battery checkers?  Are they reliable?  I have one that I use to check my batteries before and after I fly.  For my flight packs – 2 5000 mAh packs it consistently reads 97-99% and after flying 14-33%.  My confusion is when I take a pack that say reads 14% after flying and charge it I am only putting in about 3000 mAh.  Seems to me the battery checker should show 40% not 14%, I used 3000 mAh which is 60% of the pack.  Should I discard the battery checker?
>> 
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>> 
>> Karl
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>> 
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