Hi there people
We are in the process of getting the Certificate of
Airworthiness for our Glasair powered by Renesis 4 port.
Our AP is questioning the electrical system and wondering if
we should have redundant supplies in case of electrical
system failure.
Can any of you make comments on risk or preferred systems.
Our setup has one automotive 40amp alternator and two HC20
(PC680 equivalent) paralleled (two batteries are used due to
physical location) and mounted in tail for W&B and to
keep cool.
My planning was:
1. Keep battery cool
2. Replace every two years
3. Battery Failure modes:
Open circuit cell - Alternator and second battery do
the job (No indication that one battery has failed)
Short Circuit cell - Battery voltage drops and
overcharges ??
4. Alternator failure modes:
Open Circuit - Low current and Low voltage alarm
with 30min electrical reserve capacity
Short Circuit - Charge circuit fuse blows then same
as open circuit
I understood that a shorted cell was very low risk in AGM’s
if not overheated.
I thought creating redundancy may introduce other failure
modes.
Appreciate any feedback.
Steve
Hi
Steve,
Are
you signed up for the Matronics Aeroelectric List, and do
you have a copy of the Aeroelectric Connection book? If
not, then stop, do not pass go, and do both. Those issues
are pretty well hashed out there.
Now
to specifics. Have you done a load analysis for your
plane? If not, you might be a bit surprised at how much
current can get sucked up by modern homebuilts, especially
running automotive style injection. FWIW, 55-60 amp
alternators are available for very little money (at least
here in the USA) and likely will weigh no more than your
40A model. The higher output models will be running a lot
farther from their max output (think heat).
Failure
modes: I'd agree that properly maintained, the battery is
one of the least likely things to have a catastrophic
failure. Alternators, not so much, though modern ones are
pretty tough. You left out one failure mode: overvoltage
due to regulator failure. That is the one that presents
the biggest risk, because it can take out everything
electrical in the a/c. There are simple protections for
it, which result in the same plan B as your other failure
modes: get on the ground within 30 minutes. Some have
tested battery life in VFR a/c using Tracy's engine
controller & minimal airframe electrical loads, &
saw around 35-40 minutes life with a PC-680 size SLA
battery.
More
later; time for breakfast.
Charlie