Looks like you have a well thought out
system.
Only question is will battery present
low enough resistance to blow the fuse in the B+ lead in case of
over voltage, thus preventing damaging voltage to reach EC,
injectors and spark igniters?
I think best option is having external
voltage regulator that can be crowbarred with an OVP module and a
big diode in series with the B+ lead in case of alternator short.
Sorry to hear of your mishap Finn, glad your Ok.
Much appreciate your reflection and to revaluate my own risk
I agonised over the electrical risk / failure modes. Opting
to ‘kiss' and not seek full redundancy.
Your experience brings a sober reconsideration of my
assumptions and decisions which I’m trying to recollect and
would value others critique.
My system:
#
Single automotive Alternator - Fused B-lead - NO Over-voltage
Crowbar circuit
#
Twin 25Ah batteries connected via dual battery isolator switch
Off / A / B / BOTH.
#
Engine Power through Primary SPST switch with backup SPST
upstream of current shunt
#
Primary and Backup Fuel Pumps with automatic backup activation
on low fuel pressure
#
Engine Fuel pumps fed from Header/ReserveTank. Header fed via
single wing tank via Primary and Backup transfer pumps
#
EC2 redundant ECU's
#
Armoured CAS wiring
#
‘Audible' EFIS Alarms for Volts, Amps, Fuel Pressure, Transfer
Fuel Flow, Fuel Level, Gear etc.
Pre Flight Testing
Before
Engine Start
#
Measure individual battery volts while 2 x main 25Ah batteries
disconnected (Isolator switch in Off position) via EFIS on its
own battery backup delta V < 0.3v if OK then switch isolator
to Both
After
Engine Start
#
Check Alternator Charging Both A, B and back to Both batteries.
#
Test Both Primary and Backup Engine Power Switches
#
Test Engine Fuel Pumps - Switch Off Main Pump to test auto
activation of backup, reset/arm
#
Test Fuel Transfer Pumps - Switch Off Main Transfer Pump to test
auto activation of backup, reset/arm
#
Test ECU B and Coils
After
Engine shut down
#
Turn battery Isolator Switch to Off position and note Battery
delta V before turning Off EFIS
My Key Failure mode consideration / assumptions
Alternator
-
Short
Circuit (Low risk but catastrophic) must be protected against
via fuse
Over
Voltage (Low risk) - EFIS Alarm - On reflection perhaps I ought
include a Crow Bar but it does introduce complexity/danger
Batteries
-
Open
Circuit (Significant risk) - Solution - two batteries tied
together reducing chances of failure and protects should failure
occur
Shorted
Cell (Low risk) - Outcome ???? Battery fire - Halon
extinguisher
Testing
before and after flight picks up failure and lowers risk
Keep
Batteries away fro heat and vibration
Second
battery provides more air time in case of Alternator failure
though introduces significant weight
Crank
Angle Sensor -
Failure
is catastrophic so armour and attention added
Power
Switching -
Failure
(High risk) therefore backup required
No
Relays as they introduce complexity
Key Questions
Crow
Bar on Alternator?
Should
I have gone with AeroElectriic circuit with Backup Buss etc. ?
Appreciate peoples thoughts.
Steve Izett - Perth Western Australia
Glasair Super II RG
Renesis 4 port EC2 EM3 RD1C Prop MTV 7 Elec
Steve Izett.