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Old 01-23-2019, 01:53 PM
rv7charlie rv7charlie is offline
Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884

Originally Posted by mulde35d View Post

In response to Charlie's post, I appreciate the input on the start circuit. I originally had a fuse in line but after some conversations with a couple aircraft electrical engineers at work I pulled it since they convinced me it was pointless. I don't remember the conversation real well, but I am pretty sure it centered around the CB protects the wire from overheating due to pulling too much voltage. In the case of the 22 AWG starter wire if it were to accidentally ground out (the only time it would pull any voltage) then the bigger problem would be the active starter and not the 22 AWG wire heat. Hence no CB. Similar with the avionics relay, if the avionics master wire were to ground out it would simply close the relay, a pretty normal state. Hence no CB

I am curious, based on the comment about multiple failure points between the battery and avionics bus, how would one reduce those failure points while maintaining functionality and limiting complexity. Or is that simply the reality of the setup.
I hear you on the start circuit. I didn't mean to imply that it's actually wrong, but it is an 'unconventional' method of controlling the start circuit.

Sorry; I didn't study all the items on the main bus. My comment about the avionics bus assumed that it had all the critical avionics on it, so would need an alternate power feed. If the avionics bus is non-critical, then it's a non-issue.

On 2bat vs 2alt, I have only an engine bus and an airframe bus. Airframe bus is conventionally powered via the master contactor; the engine bus via a high current switch. Another high current switch is a cross-tie between the two buses. One alt feeds each bus. Adding a second battery to the 2alt system would be only slightly more complex, but add 15 lbs (or $400, if we're talking Lithium).

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