[NSRCA-dist8] Battery checkers

[Patrick Harris]

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.

On Fri, Jul 31, 2015 at 3:25 PM, Gordon Anderson <gaa at owt.com> wrote:

> Karl,
>
> 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.
>
> --Gordon
>
>
>
>
>
> On Jul 31, 2015, at 12:11 PM, Karl Watts <karlwatt at sarmc.org> wrote:
>
>
> 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?
>
> Karl
>
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