Date: May 18, 2005
From: "Robert L. Nuckolls, III"
Subject: Re: Full Charge on Battery?
>--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" >-->
>--> AeroElectric-List message posted by:
>I chanced apon this site. The suggestion that an Odyssey Battery may not
>be getting a full charge unless it receives a voltage of 14.7 volts is
>made. If true, this could be a problem for electrically dependent engines.
>Any clarification would be appreciated.
(update 12/11/05: I note that the controversial posting on the
Battery Tender website cited above has been pulled but here's the data
I posted that refuted Battery Tender's claims)
The 14.4 to 14.7 value is recommended for rapid recharge
of the battery . . . and probably assumes that the battery
was deeply discharged before the re-charge cycle begins.
The charging recommendations publication for Odyssey can
be found at . . .
. . . where we read that the fast recharge voltage
should not be sustained for more than 24 hours. They
recommend reduction to a "standby" charge value of
13.6 to 13.8 volts. A value that is consistent with
the rest of the lead-acid battery industry. One could
use the numbers on this chart for ANY lead-acid technology
except that I would say that you don't leave the fast-charge
level on for more than, say one tank of fuel duration
or much less than 24 hours. Any battery in an airplane
should be fully recharged in about one hour after
starting the engine. This is the reason for the "75%
rule" on alternator sizing in certified ships. If one
has used a max of 45A on a 60A machine to run the
airplane, you have 15A left over to quickly recharge
a deeply discharged battery. Boosting the voltage
to 14.7 increases the battery's willingness to accept
energy . . . but this level should not be maintained
Check out page 8 of . . .
and you see the same kinds of fast charge and float
voltage ranges. Same goes for Panasonic where on
page 3 of the same doucment we find 13.7 as a recommended
float charge and 14.7 as a recommended fast charge voltage
Bottom line is that ANY lead acid battery by ANY manufacturer
will ultimately achieve 100% charge at 13.8V at 25C. It'a all
a matter of how long you want to wait. If you're in a hurry,
then jack the voltage up a tad for a SHORT period of time to
speed up the recharge process. If your system is not endowed
with a automatic recharge/float voltage controller . . . well
shucks. Guess we'll have to compromise and set the critter up
for 14.2 and quit worrying about it. That's the lead-acid
set-point of choice for light aircraft since Duane Wallace
bolted the first batteries into the C-140/C-170 products nearly
60 years ago.
With respect to the writer's objections about "Pulse Current
Amps" take a peek at . . .
The graphical data for battery performance under various loads
is quite specific and yields factual engineering data. The
fact that Odyssey quantifies their batteries in a different manner
than some industry standards doesn't automatically mean that
their product is inferior or that the company is trying to
obscure any facts as to their product's performance.
Take a peek at . . .
. . . where we find the following definitions:
Cold Cranking Amps (CCA): "Discharge load measured in amps that a
fully charged battery at 0 F can deliver for 30 seconds
while maintaining its voltage above 7.2V"
Hmmm . . . Odyssey gives similar data but at 25C. Could it
be that the majority of Odyssey's customers use their
batteries as more mundane temperatures wherein the high
discharge rate performance data is more useful when plotted
at the higher temperatures? Don't know. But I doubt that
Odyssey believes they are competing with Die Hards and
boat batteries. And what's all this 7.2 volt stuff anyhow?
B&C has quantified their batteries for a 15 second dump
based on dragging the battery down to and holding it at
8.5 volts. This is easily accomplished with the tester that
both B&C and the 'Connection use in their shops. See . . .
Does that mean that B&C's marketing numbers are
bad or that they're trying to obscure any facts? No, I picked
that value 15 years ago because I didn't know of any starters
that would continue to crank an engine all the way down to
7.2 volts . . . And guess what? We DON'T do that test at
Reserve Capacity (RC): "Number of minutes a fully charged battery
at 80.F can be discharged at 25 amps until the voltage drops below
Well fooey, my e-bus runs only 5 amps . . . should I be bent
out of shape that Odyssey or any other manufacturer doesn't
give me a 5A value instead of the 25A value? Only if I'm
an ignorant consumer likely to make decisions based on a
particular manufacturer's marketing hype. If I'm a designer
who deals in engineering facts and data, then what ever data the
manufacturer supplies is GOOD data as long as it's accurate.
If I need ADDITIONAL data plotted in some other venue, then it's my
responsibility go get that data myself or request it from
the manufacturer. Most have much more data than they publish
and will supply it as needed.
Deltran's position on Odyssey products is not well researched.
It does not mirror any considered understanding of lead-acid
technology in general nor Odyssey's engineering and marketing
philosophies in particular.
The short answer is, "I'm not going to lose any sleep over it."
Bob . . .