----- Original Message -----
Sent: Tuesday, June 22, 2010 7:39
AM
Subject: [LML] Re: Odyssey batteries with
very limited warranties
I'm with you completely Chris on the battery tender concept.
I've been using them on a VRLA Concorde battery that costs $1800.
I received more than 5 years life on the last battery. I maintain
the Legacy batteries on charge as well with a different make.
But testing is a different story and maintainers can't guarantee
capacity. Load testing is the only way to determine some faults.
My batteries failed under load in the Legacy but not on the ground. When
I pulled gear up everything died including my Avidynes. It took a lot
of investigation and help with B&C before we finally tracked it to a
problem with the Odyssey and they were replaced, I think they were 2-3 years
old. The starting amperage for the hydraulic pump caused the battery to
fail under load. My point was that for someone like Bob who wanted to
know his capacity, that test will give him a number and a trend each year.
But since you mention the discharge issue I have calculated some figures
and I am open to corrections and comments of course.
Assuming the PC925 discussed earlier, the 10-hour discharge rate capacity
is 27AH (2.7a for 10 hours). The 20 hour capacity is almost identical
at 28AH. The reserve capacity is 52 minutes at 25A discharge rate so you
have two bookends to use.
If an owner wanted to discharge at 25A and got 80% or more of the 52
minutes before voltage dropped to 10,5v then I would suggest that battery is
good.
If the test was performed at a more conservative C10 rate (2.7A) then the
battery would have to stay above 10v for at least 8 hours (80% of 10
hours).
Since Odyssey provides those high and low amperage benchmarks I believe
you can determine remaining capacity using a wide range of rates and keep
those batteries at long as they perform.
Paul
On 2010-06-21, at 6:39 PM, Chris Zavatson wrote:
Paul,
Changing the discharge rate during a capacity check
will alter the results Going higher in current will yield less
capacity while using less current will produce a higher capacity.
The battery has internal resistance that also uses up power (turns into
heat) during the discharge test. This loss is roughly a squared
function of the current, therefore changing the discharge current will alter
the results.
I highly recommend keeping batteries on a
maintainer while not in use. Once I started using these, my batteries
(Concorde 25XC) would retain over 90% capacity even after five years of
use. I can now replace them based on calendar time instead
of performance.
Chris Zavatson
N91CZ
360std
From: paul miller <paul@tbm700.com>
To: lml@lancaironline.net
Sent: Mon, June 21, 2010 5:20:51
AM
Subject: [LML] Re: Odyssey batteries with
very limited warranties
To avoid tossing a good battery you
can do a test similar to that used on our Concorde batteries.
Take the amp-hour rating (C1) and draw a load and measure the amps and
time down to the threshold of 10v or 20v depending on the battery. If
we can get 80% of the rated A-H capacity we keep it. But, we use a
normal discharge rate in the airplane, not a full draw at C1 as I think that
is unnecessary. So, maybe something like 20% of C1 discharging
through some lights for example or a rate that duplicates a discharge rate
in the airplane in your worst condition so that it will show up any faults
under load. Take a measurement every X minutes and get your capacity.
I'd do it on the bench out of the airplane and track the capacity
between annuals.
We previously tossed these expensive batteries
based on calendar life but we can now leave them on condition using these
tests.
Paul
On 2010-06-19, at 3:01 PM, Robert R Pastusek
wrote:
Just had two of my
four Odyssey PC680 batteries crap out after 2 years of service although an
identical set on the other buss are fine…
Robert,
I
have a similar setup in my IV-P and had planned to replace two of the four
batteries every two years, expecting them to last for four years…but I
never looked at the expected/advertised life; I was just following a
practice used for lead/acid batteries. Two of my batteries are coming up
on two years old; the other pair are coming up on four years, and I’d
planned to replace them during the condition inspection next month.
I’d appreciate your thoughts/experience on this.
Thanks,
Bob
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