which point the battery is already 90+% depleted and the engine won't
run for more than a couple of minutes. I believe I have my alarms set
for about 12.8 volts. As Ron mentioned, Bob Knuckols at aeroelectric.com
is the trusted authority. Some of the EAA info is very inaccurate. By
the time a battery is noticeably poor at starting an engine, it has long
since lost much of its reserve capacity to supply energy after an
alternator fails.
10 volts is a bit high for fuel pump pressure dropping considering
automotive electronics must start an engine down to about 8 volts to
cater to cranking in winter with a soggy battery. Doesn't matter though
as battery is about 99% DEAD at 10 volts under moderate/light load. Also
most computers extend the injector on time to cater to low voltage
situations.
I have seen several flooded cell batteries suddenly fail open circuit
but the alternator usually keeps running fine until a heavy sudden load
is applied. Often means you don't even notice until the next time you
try to start the engine (or move the landing gear). Flooded batteries
tend to have a short storage life if not topped up regularly or put on a
battery maintainer to hold the storage at around 13.6 volts.
I have seen a few AGM (odysey type Absorbed Glass Mat) batteries fail
but they all had been fully discharged for some reason and they could
not be recharged. Their other annoying feature is that they don't
tolerate over charging well and have a short life if the charging
voltage is high. They have a long storage life but one must be cognizant
of small current drains to electronics for any battery if they are left
connected but unused for months at a time. Regulators, alternators,
computers, etc. all tend to draw standby current.
Ken
ray.mason@dcsol.com wrote:
My subie powered rebel initially came with one high pressure pump. After the
HP pump in my daughters car failed and having a problem with air getting into
my line I redesigned my fuel system for two pumps on separate switches and
made sure they were below the header tank. I only have one battery, an
odyssey. I can't remember ever hearing of a battery just dying so IMO one is
enough. My pumps will not provide enough pressure when the voltage drops
to below 10V. I have had a Alt wiring failure and noticed the flag on my elec
gyro came down, so that is an additional warning you can use and make sure
you land before the voltage gets to low.
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