On Sun, 11 Jan 2004 08:53:40 -0800, Jim Weir wrote:


I don't know about "toast", but I've got a theory...and am fleshing it out in a
3-part Kitplanes series right now...

With a fresh battery, a "trickle charger" that puts a small amount of current
into the battery and then "tricles down" as the battery voltage gets up to a
point does just fine.

However, as the battery ages and the internal resistance goes up, it requires a
higher and higher voltage from the trickle charger to bring itself up to what it
senses as "full charge". (I could snide comment about human males working the
same way, but I will refrain {;-) ) This higher voltage actually
overcharges the battery and forces the electrolyte out the spigots. (The mental
image fairly blushes...)

I'm working right now on a "cyclic" type of charger where the charger puts out a
full slug of current up to a precisely limited voltage (13.6 to be exact) and
then completely shuts itself off and lets the battery self-discharge itself down
to some much lower voltage (12.6 to be exact) and then repeats the cycle. The
folks at Concorde turned me on to this trick and they claim it is the ONLY way
to keep a recombinant gas battery happy. Seems to me it is the way to go with
flooded plate as well.

April, May, June 2004 Kitplanes columns.


Jim


I'd be hesitant in applying what Concorde says about the recombinant gas
batteries to other types of batteries, or even other manufacturers.

Living off the grid, and relying on FLA (flooded lead acid) batteries, I
have had a lot of experience in maintaining them. For the FLA batteries,
the manufacturers generally publish a recommended "float" voltage. So what
you need is a voltage limited charger.

For example, for my particular batteries, the recommended float voltage
(which is what you would use to keep a fully charged battery fully charged)
would be 2.20-2.23 volts per cell, or 13.2-13.4V for a nominal 12V battery.

A higher voltage would be used for charging (14.2-14.7V in my case).

At 13.2-13.4V, my batteries would not be overcharging, and the electrolyte
would not be leaking out.

And the numbers that apply to AGM or gas recombinant batteries are not the
same as what one would use for FLA batteries.

So for most FLA batteries, there should be no need to let them
self-discharge. But rather maintain them at the lowest voltage that will
maintain a full state of charge.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)