>Date: Sun, 26 Dec 2004 17:14:48 -0600
>From: "Robert Samuels" <[EMAIL PROTECTED]>
>To: soaring@airage.com
>Subject: Re: [RCSE] dead battery question
>Message-ID: <[EMAIL PROTECTED]>
>
>Twice i've had single cells in a pack become dead. That is, the cell(s) in
>question had no voltage. On the advice from a local battery supplier I
>"shocked" the cell(s) by touching the leads from a 12 volt battery to the
>bad cell for an instant. It caused some sparks when I touched the positive
>to positive and negative to negative. It appears to have revived the cells
>and the packs now function normally and have run through charge/dicharge
>cycles showing full capapcity. Immediately after the "shock" the
>previously
>dead cell had a no load voltage reading of 1.2 volts. Remember, the
?touching of leads was for an instant only. I offer this story for
?information only and have no idea if it is good advice. But it worked for
>me.
>
>Robert Samuels..........St. Louis
Robert;
Here is what is happening to the cell that has gone dead. A small
"whisker" grows across the dielectric and causes the battery to become
shorted. By touching 12v across the battery actually burns the whisker and
makes the battery "alive" again. The problem here is that once this occurs
with a battery then the chances of that battery going dead in the future is
quite high.
I would become very leery about a battery pack that looses a cell.
Chances are all of the batteries in the pack are from the same batch during
manufacturing. If one goes dead then the chances are that the others may
develop problems as well. You may want to rethink the way you maintain your
batteries. Here is something that I do that has provided me great success
over many years of flying. The first thing is you need to have a good,
accurate battery charger as well as a good, accurate battery cycler.
Here is what I do. When ever I get a new battery back I charge &
cycle it 3 times. After the third time I determine the true battery
capacity based upon the time in which it took the battery to become drained
and my discharge rate. EVERY battery I own I write the date & new, actual
battery capacity on it. I use a sharpy marker to do this so it doesn't wear
off. Through out the flying season as I recharge the battery I will cycle
down. I do this every few months, just to make sure the battery is in good
shape. I also make note of the real capacity of the battery. If I loose
10% or more of the battery capacity I no longer use the battery. I may keep
it for bench work but I will never put it back into a plane or transmitter.
I simply go out and replace the battery.
When charging the battery I always use a C/10 charge rate for
overnight charging. This is safe charge rate and will cause the least
amount of damage if left on for more than 10 - 12 hours. I don't recommend
leaving the batteries on for longer or the battery will heat up and cause
damage to the internal battery structure if done to many times.
I'm sure there are others out there that may have a more refined
approach for battery maintenance, but this works for me. I can honestly say
that I have not had a battery failure in over 20 years of flying. I adapted
this maintenance practice after I crashed one of my old time favorite power
planes back in the mid 80's. There is too much to risk when dealing with
questionable batteries. I know when I go to the field I am flying with a
set of batteries that I know exactly what condition they are in.
Happy New Year.
Kurt
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