steve murray
Well Known Member
I have been flying my RV8 with Subaru 6 cylinder engine conversion for about 10 years and just under 700 hours. Thought it was time to perform another battery capacity test as my ignition is 100% dependent on electrical power. My configuration is two Odyssey PC625 batteries. I have the ability to completely isolate the batteries for catastrophic electrical failures but for this test I wanted to simulate normal flying conditions with an alternator failure. Using my normal operations the batteries are managed via an EXP Bus.
Test conditions. Outside temp was 79F. Alternator turned off for entire duration of the tests. I tried to make the test somewhat worse case by adding a bunch of loads that I would likely be shed in real alternator failure. The electrical load was two LED landing\taxi lights, 4 Amp heater blower running, Grand Rapids EIS and EFIS running, MT electric prop control, both electric high pressure fuel pumps running and all the power used by fuel injectors, ECU, etc.. Prop RPM was around 800 -1000 RPM so engine RPM was around 2,000. I
Test Results: The first item to fade was the MT Prop controller which began indicating a failure mode at about 11.3 volts. In this condition, the prop stays at same pitch. I was able to manually cycle the pitch at this point by taking the controller out of Automatic mode , and using the ?manual? toggle switch I did not check this capability later on, so not sure how long I would have the ability to manually adjust the pitch.
I did have some data collection issues as below 10 volts at the EIS and EFIS started to drop out (this was my data collection source using the EFIS to log data). I am assuming the noise in the data (constant up\down by ? volt ) is a result of the Exp Bus switching between batteries but I am uncertain. Next time I think I will hook up the voltmeter directly to the batteries and obtain data in that manner vs. using EIS\EFIS.
Happy to see, the engine was running fine down below 10 volts after about 65 minutes. The two PC625 batteries are a 5 years old. I think I will try to repeat this test every year or so. For planning purposes, I will try to be on the ground in 30 minutes after alternator failure as I may only be using one battery if I am forced to go to the backup bus architecture.
Would appreciate the input of others in regards to the difference in electrical load of the injectors when running the engine on the ground at 1,000 RPM vs cruise RPM of about 4,400 RPM?