Nice work with lots of planning. There may be a few gotchas though.
1. BATTERY BUS (SWITCHED). If you are forced to shut of the master in flight you have no power to the bus and lose fuel pump and electronic ignition #1.
Yes, absolutely true. My thinking was that the loss of the master (and/or both alternators) it was time to get on the ground. The fuel pump is backup for the engine driven pump during take off and climb. Not required to get safely on the ground when power is limited to battery. The same for EI #1. EI #2 will get me on the ground. Would I really want to run 2 electronic ignitions when power is limited to what is in the battery? I think this is sound reasoning, but am open to others thoughts.
2. If switching the E-BUS switch from VPX to battery there may be a momentary open that would reset some of the avionics. If done in IFR or an emergency this would not be good. At least test for problems.
The only time I would switch the E-buss on is if both alternators went down or the master relay craped out. Power would already be dead. (I would still have the G5 as it has it's own battery backup.) At that point it is intended to be a fast easy way to unload non-critical items with a single switch.
Garmin allows two power feeds into each instrument separated by internal diodes. Power feed to the instruments is power in #1 through the master/VPX, and power in #2 through the E-buss. You can see that in the pin outs for the critical instrument diagrams. There is no cross talk between the power feeds.
Powering the E-buss all of the time is possible. However, since I have Avionics #1 and the E-buss on the same switch (DP/ST) leaving the E-buss on all of the time is not possible as currently wired. I will think on that one for a while to see if there is a better alternative.
3. Might take the E-BUS backup power feed off the fuse and use the fuse box input stud with a fuse link. Would not use one fuse for so much important stuff. Have seen fuses melt and fuse connections get hot and distorted.
This comment/question has me really thinking. I have the blade fuse in the rear behind the rear bulkhead. If I used a resettable breaker on the IP I could at least bring back some power if the breaker tripped. It would really be a bad day if I lost both alternators and then popped the E-buss. All I would have left at that point is the G5 and no EI ...... that needs some rethinking!!
I had been considering that I needed to move at least one of the ignitions to a direct battery feed based on reading the Light Speed Ignition installation manual. The ignitions are one thing I do not have wired yet since I haven't purchased the engine. So easy to change.
Thank you for your comment!
4. 7 SWITCHES. Three are down on and four are up on. The aircraft standard is all down for off and up for on. I see what you may be doing and it is you who is flying your design, but non standard can cause confusion issues when emergency decisions are made. Would recommend consistency.
Here is the thought process. (Page 19 of the power point is the switch group in question) In the normal run/cruse condition all switches are up. The bottom row is all on, the top row is all off. They are rocker switches that show red when down, so in normal run no red shows. If any switch is pushed to the down position, it is an abnormal situation and red shows on the top of the switch. i.e. boost fuel pump on is down (showing red) reminding me to turn it off as appropriate.
Again, my logic tells me this is simple and appropriate. As always I am open to other thoughts.
5. I would remove the G5 from any external bus inputs to keep true independence. A single point failure could take out the entire set of Garmin flight instruments. I know that the Garmin experts say it can/will not happen, but do you want to bet your life on it flying IFR. True independent redundancy would be preferred.
The G5 connection to the system is through the CAN buss. Physical damage to the CAN buss wiring/daisy chain can take the buss down. However communication is based on packets of info being transmitted with appropriate headers. The loss of the CAN buss or corrupt information on the buss have no effect on other buss devices. This is the same buss technology that has been used in automobiles for about 50 years.
MY larger concern is that by taking the G5 off the buss you loose all of the backup functions available from the G5 which are GPS, AHRS, and auto pilot functionality.
A single large diagram of all the power circuits may find other small potential problem areas. A lot is riding on the VPX. Hope it is reliable and glitch free.
I don't disagree here on the VPX. I would really be bummed if ever had to rip it out and reconfigure to a conventional power system.
I do like what I have, and think I have a reasonably well thought out implementation plan. I like the flexibility and diagnostic capability and think it a good trade off. I also like solid state components.
I appreciate the comment on one large diagram. The (virtual) paper I have been working with, as well as my evolving thought processes led to several smaller diagrams. What is important is that I can find and identify every wire from the diagrams. In the spread sheet, I also listed what is on each buss so I can see the overview there.
One last comment: I am close to a finished plan for my specific aircraft, but am always open to thoughtful feedback. Usual disclaimers, I do not suggest this is appropriate in whole or part for anyone else's project. I will be testing and looking for issues before and well into flying. I will try to follow up in this thread over time.
George