Alternator size

[efwd]

Hi Victor
I hesitate to reply, in fact I have written this reply three times. The reason, I don't have the calculations to refer too and as with many of us, electrical was not my favorite. Anyhow, for what it's worth I have everything on your list except the tail light but I do have aft facing white lights on both wing tip position lights. Some of our numbers don't match such as the trim motor. I calculated my amps (but I don't have the data here at home) then, while at the Kitfox Factory, I spoke with Judd. On his advise, I am not running any addtl alternators. My 912iS electrical system is operating all those items on your list. I do have the backup battery as Justin mentioned but I have no reason to believe it has ever kicked in to keep the PFD or MFD screens on. Im running the VPS as well and I have a mechanical Master switch. I run a lot of stuff on startup too. Landing lights, strobe, position lights, Radio, Transponder, both PFD and MFD etc etc.

[VictorV]

Hi Victor
I hesitate to reply, in fact I have written this reply three times. The reason, I don't have the calculations to refer too and as with many of us, electrical was not my favorite. Anyhow, for what it's worth I have everything on your list except the tail light but I do have aft facing white lights on both wing tip position lights. Some of our numbers don't match such as the trim motor. I calculated my amps (but I don't have the data here at home) then, while at the Kitfox Factory, I spoke with Judd. On his advise, I am not running any addtl alternators. My 912iS electrical system is operating all those items on your list. I do have the backup battery as Justin mentioned but I have no reason to believe it has ever kicked in to keep the PFD or MFD screens on. Im running the VPS as well and I have a mechanical Master switch. I run a lot of stuff on startup too. Landing lights, strobe, position lights, Radio, Transponder, both PFD and MFD etc etc.

Thanks for the info. So it looks like you turn everything on before you hit the start button? I think it's
not obvious when the battery backup kicks in to keep your avionics alive during start. You could verify
by disabling the battery backup and measuring the voltage at the avionics power terminal during
start to see what it does and then turn the backup battery on and see if it's different. Not sure that will
work though since there are 2 power inputs to each avionics device.

One important difference between the 912is you have and the 914 I am planning to use is that the 912is has
2 internal alternators. One is 16 amps and the other is 30 amps. The 914 only has a single 18 amp alternator
which is pretty wimpy considering the engine needs 8 amps to run and the radio can use up to 7.5 amps
during transmit.

Victor