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It's entirely possible that a battery can deliver
80% rated capacity at C/5 but not be able to deliver starting
current.
Testing needs to be done both ways and if capacity
is met, there should be no problem continuing that batterie's use.
Self discharge of lead batteries is about 5% /
month at 20ºC. A float charger that gives about 2ma-3ma is all that's needed for
a 30AH battery.
A battery maintainer that gives a 2A charge and
drops to trickle when the battery gets up to 13.5 - 14V and kicks in again if
the battery gets down to 12V will do nicely also so long as the trickle charge
is not too high.
Wolfgang
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Chris, et al,
I use Battery Tenders (BT) on all SLA batteries if there will be
extended periods of disuse, including the airplane. I have a
B&C battery (may be an Odyssey) from 1998 (before the BC110 reversed
the anode/cathode position) that still powers the start motor on a
generator. My tractor battery (used for mowing and snow
removal) has been maintained for years on a BT when not in use.
My motorcycle sits unused through the winter months - the battery is from
2000) and spends those cold months on a BT - it still works. I have
made use of discarded B&C batteries all over the place - used for
raising my airplane on electric jacks, used for winching it in, etc.
They continue to be usable if maintained with a BT from time to
time. I do not temp fate - the aircraft battery (B&C) is often
replaced every 3 or 4 years depending on how I have misused it.
Pre-flight requires checking both the main battery and the EI backup
battery for VDC levels and trends.
A battery expert (usually an older person) will tell you that this is
nuts - they just haven't experienced a well made SLA battery with
pads and their reliability - if kept charged/maintained. Of course,
that's just my observation.
Grayhawk
In a message dated 6/21/2010 5:39:52 P.M. Central Daylight Time,
chris_zavatson@yahoo.com writes:
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 |
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