I've been running an Odyssey PC 625 battery cranking my 0320 Lycoming for
several years. Cranke the think at 20 degrees in Canada. The only problem
was that I had to add some lead wts in the battery box to keep the c.g.
where it was.
Stu Fields
"Rob Cherney" wrote in message
...
On Sat, 30 Aug 2003 23:32:20 GMT, (Badwater
Bill) wrote:

Another goofy thing about the Odyssey is that you can't recharge it
using a trickle charger. Less than 1.25 Amps won't put all the energy
back into the battery. You have to use a 10 Amp charger to get back
to full energy.

From their data, it looks like the charge efficiency sharply decreases
below 0.1C (1C = rated A-h @ 10h discharge rate). This is 1.6A for
your battery. Note that this only applies to a fully discharged
battery.

Anybody know the chemistry behind that? I don't get
it. Lead peroxide is lead peroxide. When you drive the sulfate off
the lead atom and reattach an oxygen, what the hell difference does it
make how fast you do it (high Amps)?

Hawker doesn't say specifically, but reading between the lines it
looks like it could be a function of the small amount of tin that's
added to the lead in the plates. This is done to increase service
life for deep-discharge applications. Don't ask me about tin
chemistry, though. I'm an electronics weenie.

The only thing I can think of is
that the battery itself has an internal resistance of 7 Ohms so the
higher the current, the higher the temperature of the battery itself.
And, as you all know, for every 10 degrees Centigrade, the chemical
reactivity rate coefficient doubles.

Two things:

The internal resistance is 7 milliohms.

The primary aging mechanism for these batteries is corrosion of the
positive electrode grid. For this particular mechanism, the reaction
doubles every 8 °C, not 10° C as one would expect.

So, the rate constant will be
higher for the charge cycle on a hot battery. They say you can
completely recharge this baby in 2 hours if you use 10 Amps. I'm
thinking that it heats up...that's why!

Yep, and that's not unique to this particular battery.

Actually, Odyssey says the battery can be recharged in as little as 20
minutes, assuming you have a charger that's beefy enough (3.5C= 56 A).
At this rate, the internal temperature will rise about 20 °C and will
peak about the time charging current starts decreasing (assumes the
recommended voltage-limited constant-current charging).

For a 2-hour charge, the expected temperature rise will be only about
10 °C.

By the way, my information came from http://www.hepi.com/papers.htm.
I pretty sure the Odyssey battery is an evolution of the Cyclon and
Genesis batteries that are mentioned in the papers.

Lastly...

I did a lot of research on batteries and settled on the Odyssey when a
replacement was needed for Long-EZ N271J. I put a PC-925 (27 A-h) in
her back in February. So far, so good.


Rob-
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Robert Cherney e-mail: rcherney(at)comcast(dot)net