Reply part 1
Thanks for the feedback, everybody. Let's see if the forum's new multi-quote feature works...
My only thought as I looked through it is that you might not be happy with the size of your aux battery.
I think you're right, Paul - after I built my aux battery box the other day, I wasn't terribly happy with the location and size I picked. I've now found a different battery (Panasonic high discharge rate job designed for backup power supplies) that I'm going to mount in a different spot. It's supposed to be able to run my worst case 4A load for 40+ minutes, which is better.
I noticed the "double" fusing (60A and 40A E) on the Alternator and Battery main lines. Is this normal?
There are other unprotected lines in the system. Just curious why you chose the Alternator fusing at that location.
The intent of the "double" current limiters is to protect the battery, two different ways: one saves the day if the alternator develops a catastrophic short, and the other one protects the battery if a short develops in the approximately two-foot-long, fat wire that penetrates the firewall and runs to the main bus fuse block. I could have used a single current limiter instead of two, but a faulted alternator would have also taken the main battery offline with that configuration.
By virtue of the nature of aircraft electrical systems, there are in fact a few unprotected wires. I've tried to note all of these with an asterisk, denoting that they should be constructed in such a way that they're as short as possible. If you see a wire that doesn't have a fuse, circuit breaker, or fusible link upstream and that doesn't have an asterisk on it, please tell me so I can fix my mistake!
Your design looks very complete, and although really not that complex, a considerable amount of extra weight? (that's a question not assumption)
That's certainly a fair criticism. Believe me, I drew some way more elaborate designs before I settled on this one.
Although the number of extra schematic symbols seems excessive, I don't feel like there's an unacceptable amount of extra weight added. Fuse blocks and relays are pretty light, and my aux battery weighs about 5 lbs. There isn't any extra heavy-gauge wire since all the aux bus currents are low. I need to lose about 5 lbs anyway, so there's where I'll get the payload back!
Just a comment - I believe an airplane should be flyable with a total loss of electrical power, from either or both systems. I assume you have appropriate back up instrumentation in case both fail.
Absolutely.
Is this an electrical system for a RV or a Boeing 737?
Another fair comment!
I'm still looking at it, but do you have to throw 5 switches as normal procedures? 3 Master/Bat switches (Buss 1, Buss 2, Aux Bat), plus an electronic ignition switch and mag switch? Nothing wrong with this, but my comment / suggestion is add check-list/procedures for normal, non-normal and supplemental operations to the system description.
Sorry, I should have been more descriptive of my thinking here. Yes, there are three power switches, and two ignition toggles. I have added an aux bus master switch, but I have combined the functions of an E-bus alt feed switch and an aux alternator field switch into the Bus 2 Master switch. So really, I think I have the same number of switches as a typical Z-12 or Z-13 design. I just went back to the book to make sure and it seems like the same number to me.
I tried to make normal operation be as simple and carefree as can be: Turn on all three master switches, turn on the ignitions, crank up, make sure all the red lights are out, and go flying. And good input on the checklist: I always try to remember that I may not always be the PIC in this ship, so as the designer I have a responsibility to make the operation of the system clear to those who'll fly it other than me. Part of this is good "switchology" and labeling, and another big part is constructing clear checklists that spell everything out.
Are there critical pilot (switch) actions? Meaning, can throwing or not throwing a switch, out of sequence or not at all, cause a problem? In other words, can the pilot do something to really screw-up a perfectly good electical system?
I hope not - I've tried to think through all the possibilities. You can't do any damage if you move any of the bus master switches in the "wrong" sequence, since there shouldn't be anything order-dependent. Let me know though if you spot anything suspicious. And actually you could accidentally leave both the Bus 2 Master and Aux Batt Master switches completely off, and still go flying - you wouldn't have the aux battery or standby alternator online, and the E-bus alt feed path would be open, but all your stuff would come on and be powered by the main alternator. No different from a much simpler system, really - I'm trying to think in layers after all.
Of course if you left the Bus 1 Master switch off, it wouldn't crank when you pushed the starter button, so you'd probably know something was up if you did that!
What if you leave the electronic ignition switch on (even with masters 1, 2 & aux off)? Will it drain battery'(s)? If yes, what do you have help you not forget? (By the way I have this issue since the EI is hard wired to the battery.)
Oh George, why do you tempt me... yes, it would run down the battery. So just for you, I designed a circuit that will warn me if I turn all the airplane power off but leave the ignition turned on.
(see below for update)
Tell you why I say this. An example, a very popular jet airliner has an electrical system switch that normally should never be touched, unless a check-list calls for it, only for a non-normal condition. However unknown to a crew (may be the engineers did not think of it either) this switch can disable the whole planes electical system, after a period of time, with some what subtle warnings, especially if they're ignored. No one knew this could happen, and this plane model was in service for many years, before this crew figured out a way to cleverly (carelessly?) defeat all the protection with one switch.
That's sobering. But that's exactly why I wanted to put my drawings up for criticism... to force myself to think about how to avoid that kind of trap. I think I've got a way to warn the pilot of just about anything bad that could happen, either by component failure or pilot action, but I guess you never know.
I also noticed the double fuse for the 60A alternator.
Yah, see above and look closely at the schematic, and I think you'll see the intent. Or maybe not, let me know if it still looks unnecessary.
I'll save this and if I ever have an all electric IFR RV, I'll steal and copy your ideas.
You and everyone else are welcome to it!
Since the forum places a limit on the length of a single post, this will be continued in part 2...
