/I'm not sure how robust a battery of this type
/will be in this application. I was under the
/impression these batteries were more suitable
/for back-up and low current demands rather than
/regular engine starting. They are also a bit
/fussy about being correctly recharged.
A very large market for sealed lead acids
is battery backup for uninterruptable power
supplies for computers. Of course they're
very popular for a lot of emergency power
situations such as exit lighting, etc. The
little versions are showing up in everything
from camcorders to cellphones. There was some
mythology floating around for some time that
all sealed batteries were "fragile" while in
fact, this was a carryover from people's experiences
with gel cells . . . which are indeed easier to
damage from overcharge than their flooded cousins.
Some general notes on life . . . . Consider
that a lead-acid battery that is cycled off the
top 5% or so of capacity will transfer many
more watt-seconds over it's lifetime than if it's
cycled down to 50% of capacity per cycle. This
is one reason why subtle changes in construction
and chemistry are necessary for a battery are
needed for deep cycle operation in golf carts, etc.
Let's compare two battery scenarios using
identical chemistry. Suppose we need 200 amps
for 5 seconds to crank up the engine. This
works out to 12,000 watt-seconds of energy
pulled from the chemistry. Consider that a
10 a.h. battery will deliver about 400,000
watt-seconds while a 24 a.h. battery will pump
out 950,000 watt-seconds. Cranking the same
engine from the two batteries pulls them down
3 percent and 1.2 percent respectively.
Now, in spite of the fact that BOTH batteries
are initially capable of doing the same job
when new, the smaller battery is being cycled
2.5 times deeper than the big guy. So, in spite
of the fact that both are properly maintained
AFTER the engine starts, the smaller battery
can be EXPECTED to degrade faster from use.
With respect to general robustness, the RG
batteries I certified onto single engine
airplanes had NO practical current limit for
recharge . . . meaning that you could put them
on a constant voltage bus with a pair of
400 amp starter generators and not fear for
their health. I also demonstrated the ability
of two, 22-pound, 24 a.h. batteries to start
a Beech C-90 (PT6 engines). Now, in this
application, they probably wouldn't last as
long as the larger battery they replaced
because of the cycle depth (it takes
about 60,000 watt-seconds to start a C-90)
but then, the RG batteries were 1/20th the price
of the ni-cads they replaced. We're still wondering
if we should do some cost of ownership studies to
see if they're a practical subsititute
When someone expresses some dis-satsifaction in the
way an RG battery performs, I am primed to ask if
they replaced with the SAME or SMALLER capacity,
whether the battery was subject to total depletion
followed by storage (battery master left on for
two weeks . . . REALLY hard on a battery) and is the
bus voltage where it belongs (13.8 to 14.2 tops).
Initially, Concord asked that their RG products be
maintained at 14.6 volts . . . about 0.4 volts higher
than "normal". At OSH last year, Skip Koss showed me
test data which indicated that the RG battery charged
at the nominal 13.8 volts contained no less engergy
than one charged at 14.6 . . . .
By-in-large, I find no reason to consider the RG
batteries as more "fussy" or "fragile" than any other
technology of lead-acid battery. If one wishes to
take advantage of their enhanced cranking capabilities
and put in a LIGHTER battery of less capacity, then
reduced service life should be EXPECTED . . . but
considering that it's probably lower in cost too, the
cost-of-ownership for keeping the battery servicable is
probably close to a wash. The most useful thing you can
do to extend battery life is keep the engine tuned up
and deduce the technique for reduced cranking TIME.
Electronic ignition is a BIG plus . . . these
engines start in a few blades if there's fuel . . . so
look at primer systems and best technique for use. How
many people consider fuel sytems operations when trying
to optimize battery life? (da leg bone's connected to the
thigh bone . . . da thigh bone's connected to the . . .
well you all know how it goes).
Regards,
Bob . . .
AeroElectric Connection
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(o o)
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