Just got back from our second weekend seminar gig of 1998 in
Manassas, VA. Dee and I got home about 1:00 a.m. today
and I had 600 pieces of e-mail to sort through! This is
a thread formed of comments from several listers on the
same topic but possibly from or more than one list . . . .
Yep . . . two extra volts is indeed one way to kill 'em dead.
>I purchased a new Concord sealed battery (X25) for my RV6A and it
>died after one year of use. I think the reason was I had my voltage
>regulator set to high. Initially, I adjusted Vans voltage regulator
>to about 13.6 volts ( which may have been to high for that
>battery ? ), however, over the years time my charging voltage
>crept upward until it reached about 14.5 volts. I kept lazily
>putting off getting under the panel to readjust it. I noticed
>the battery getting weaker every time I went out to the airport,
>until it was at 8 volts this week.
>What should I set that the voltage charging rate to so I don't
>fry my new battery ?
13.2 was NOT too high; 14.5 was not terribly abusive for short flights
but probably too high for extended cross country travel (see below).
-----------------
>I installed a new sealed liquid battery recently. With my old battery my
>system would charge at 14.4 to 14.8 volts. I installed the new battery (the
>only change) and now I'm charging from 14.6 to 15.5 volts! Could it be the
>combination of a new battery and the cold Wx (it was 30 degrees Sunday).
Possibly but I doubt it. Depending on your regulator, it MIGHT be
temperature compensated for battery charging requirements. In any
case 14.4 to 14.8 was too high for about any choice of battery
technology.
--------------------------
>> My notes of wisdom collected from the List indicate that RG batteries
>> should be charged at 14.4 to 14.8 v. >>
>
>I don't know where you got your info, but RG batteries should be charged
at no
>more than 2.35V per cell (6 in your 12V battery = 14.1V). So says the RG
tech
>experts at Battery Man magazine.
A possible source of "elevated charge voltage requirements" for the
RG batteries may have started with B&C some years back. The literature
from B&C's manufacturer of RG batteries was recommending a higher
bus voltage for short cycle ops like 1-4 hours per week in an airplane.
If one wanted to use an RG battery in a continuous float mode (like
standby power in an uninterruptable power supply or emergency lighting)
the classic lead-acid 13.8 volts at room temperature numbers applied.
Early recommendations for Concord agreed. About two years after B&C
won their STC on the RG battery and several years after Concord came
out with their early entries into GA battery sizes (they were
building RG battereies for bigger airplanes for some time), Skip
Koss of Concord showed me data at OSH demonstrating that their RG
products would achieve 100% of recycle recharge in airplane service
with the classic 13.8V figure.
This is a recommendation from one manufacturer of sealed lead
acid batteries that may illustrate the source of confusion . . .
"Cycle Applications: Limit initial current to 0.20C (C is the nominal
A.H. capacity of the battery). Charge until battery voltage
(under charge) reaches 2.45 per cell at 68 degrees F (20 deg.C).
Hold at 2.45 volts per cell until current drops to approximately
0.01C ampere. Battery is fully charged under these conditions, and
change to float voltage."
Interpretation of this paragraph is as follows: Suppose you have
a 17 a.h. battery with unknown state of charge (you've not flown
in several weeks and you just used it to crank a fussy engine).
You can RAPIDLY stuff energy back into this battery by setting
the charge voltage at 14.7 volts (2.45 x 6 cells) and holding
it there until current going into the battery drops to .17
amps (17 a.h. x .01C) whereupon you REDUCE bus voltage to
the appropriate "float" value.
"Float of Stand-By Service: Hold battery across constant voltage
source of 2.25 to 2.30 volts per cell continuously. When held at
this voltage, the battery will seek its own current level and maintain
itself in a fully charged condition."
This paragraph says that if you want to maintain a battery on
a constant voltage bus for periods of time AFTER 100% recharge
has been achieved, then the bus voltage should be between
13.5 (2.25 x 6) and 13.8 (2.3 x 6) volts. Of course these values
are 68F/20C temperature values.
Sooooooo . . . if you do a lot of short flights, 14.7 is good,
long flights 13.8 is better. Obviously, the NEXT generation
voltage requlators should be getting "smart" to the extent that
they not only accomodate a battery for its temperature MODULATES
bus voltage appropriately to take care of both the short flight
and long flight scenario.
Since this product does not yet exist . . . may I recommend that
the 14.0-14.2 volts is a good compromise . . . in any case,
CONTINUOUS bus voltage operations above this value are not healty
for any battery . . . thing is, for wet ones, you can replace
lost water . . for sealed batteries, once cooked always cooked.
I didn't ask Skip about how much TIME it took to get a Concord
battery back to 100% at the "float" voltage level . . . obviously
it will be LONGER than a the "cycle" level but lacking means
for dynamic control of voltage during each recharge cycle, to
err on the side of minimum smoke is good policy . . .
Bob . . .
AeroElectric Connection
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