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Old 03-29-2018, 07:20 AM
Nihon_Ni's Avatar
Nihon_Ni Nihon_Ni is offline
Join Date: Jun 2011
Location: Fredericksburg, VA
Posts: 244

Originally Posted by Mich48041 View Post
The downloaded Power Point drawing is much easier to read.
Flip the E-Bus-relay diode over so that the arrow points towards positive.
It will blow the fuse (or itself) the way it is now.

Originally Posted by Mich48041 View Post
You might consider using a 2 or 3 amp circuit breaker instead of that 5 amp fuse
on the ground side of the aux alternator relay. Sometimes alternator output voltage
is unstable and momentarily bounces above the over-voltage module set point.
It might be desired to reset the breaker. If the aux alt voltage continues to be too
high due to aux regulator failure, just turn on some more electrical loads.
If the load on the aux alternator is at its maximum capability, then increasing the
load even more will decrease the voltage output.
Bob's design had a 2A CB there, but I was trying to avoid a round trip to the CB console. I suppose I could mount a CB somewhere other than the CB console since I wouldn't reset it in flight if it popped anyhow, and I don't need the CB as an alternate switch; or I could use a CB switch instead.

I haven't had time to consider relocating my CBs from the F-865 Console to somewhere on the panel, but I have 8 hours in the thinking machine (airliner) tomorrow, so hopefully I can work through those decisions/implications.
Rob K
RV-8 under construction as of Sep 30, 2012
Tail kit completed on Feb 8, 2012 (180 hrs)
Wing kit mostly completed, fuselage under construction as of March 6, 2014 (750 hrs)
Paid up for 2018

Last edited by Nihon_Ni : 03-29-2018 at 07:23 AM.
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Old 03-29-2018, 06:12 PM
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johnbright johnbright is offline
Join Date: Aug 2010
Location: Newport News, Va
Posts: 151
Default Alternator field circuit breaker

Originally Posted by Nihon_Ni View Post
... was trying to avoid a round trip to the CB console... I wouldn't reset it in flight if it popped... I could use a CB switch instead.
B and C Aero, that's basically Bob Nuckols, regulator installation instructions say:
  • Use KLIXON or Mechanical Products circuit breakers... avoid combination switch-circuit breakers for reliability reasons.
  • A panel location within the pilot's field of vision and reach is recommended.

I didn't find a source at the moment but as I recall it is Bob Nuckols and the reality is that the crowbar fires falsely on occasion so you want 1) Not a fuse but a resettable device... a circuit breaker. 2) Easy access to the circuit breaker in flight.
John Bright, RV-6A 25088, at FWF
O-360, 8.5:1, vert sump, SDSEFI EM-5
Dual alt, single batt. Wiring and IP CAD files here
Newport News, Va
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Old 03-29-2018, 09:24 PM
rv7charlie rv7charlie is offline
Join Date: May 2006
Location: Pocahontas MS
Posts: 2,679

What John said. You want a really short time constant for OV protection to protect your avionics, which can lead to occasional nuisance trips. The one breaker you'd want to try resetting (once) while in flight. It's detailed in the book.

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Old 04-16-2018, 06:50 PM
Nihon_Ni's Avatar
Nihon_Ni Nihon_Ni is offline
Join Date: Jun 2011
Location: Fredericksburg, VA
Posts: 244
Default I think I've reached a solution!

I wanted to post an update to my design. I really appreciate all the help folks have given me with my design, and all the time they have spent to review my architecture and offer input. Special thanks to Joe and Carl, who sent me tons of info in email and helped me figure all this out.

I contacted EMag and got an answer to my dilemma about where to put the P-mags:

The P-mags should be put on the main bus because we only require a battery for starting. After 800 RPM or so we switch to running off our internal generator and do not require an external source. In the event of an internal generator failure we would switch back to the external power (main bus). Be sure to do the minimum cut-out test to see where the ignitions drop off and note it so in the event of an alternator failure you wont run the risk of the having to low of RPM for our ignitions to continue sparking.

If you do put us on the battery directly you run the chance of leaving us on and draining your battery.
With that advice, I've once again removed the battery bus and put the P-mags back on the main bus.

I also posted my design on Matronics and got some additional feedback, including a few comments from Bob Nuckolls himself.

Joe pointed out that I had the voltage regulator wired incorrectly, and I realized I had switched part numbers from the generic Ford regulator on the Z-13 to the LRC3 on the Z12, but hadn't updated the icon or wiring. Bob Nuckolls also gave me some advice to remove a redundant crowbar on the master switch because it's included in the LR3C.

I've moved the starter switch from a CB to a fuse. I had it on a CB so that I could pull it in the event the starter ever hung up. After considering it anew, I realized I could get the same result by just turning off the master, and I'd be a lot more apt to find the master switch that I use on every flight, than find the starter CB. I also moved the LV Warning line to the fuse block, so now I have 8 CBs total: Main Alt Fld, Aux Alt Fld, L Ign, R Ign, AP Servos, Auto Pilot, Com2, Transponder. (The last two are there so I can reduce the load on my E-Bus if needed during an alternator failure, and I'm still thinking about moving them to a fuse and using a switch instead.)

I also removed the alternator's fuselink between Main Bus 2 and the Alt Fld CB. Having two fuselinks in series, as I did at one point in my design, doesn't give me the protection I thought it would. I now have fuselinks between the Bus 1s and Bus 2s. After some more thought I've moved the CBs to the right side of the instrument panel, which reduced the wire run to about 18" from the fuse blocks of Bus 1 (both Main and Essential), so I've kept the fuselink to protect those two wire runs.

I moved the trim and fuel gauge power to the E-Bus. Someone suggested that the power they consumed was a good trade off for having that information on the E-Bus, and upon further thought I agreed with that suggestion.

I also changed the inline fuse from the SD-8 to the 30A that Bob recommends in his Z-13/8. I'm not sure how I got a different value for that fuse, but someone pointed it out to me.

I removed the current limiter between the battery contactor and Main Bus 1 upon advice that a second current limiter was just introducing additional points of failure without any added protection.

I removed the OV light and will use the G3X annunciator for that function.

I've been reading through the G3X install manual to check for inputs from my electrical architecture to its monitoring devices. I changed the shunt on the SD-8 circuit to the part number called out by that manual.

Right now I still have three advisory lights in my design (battery fault, aux alt warn, and starter engaged). I'm not sure if I'll use all of those or use the G3X annunciator instead.

I think that's a round up of all the changes I've made since the last post on this thread.

I'm sure there will be more changes as I start building the electrical system, but I think this plan is solid enough to start installation.

I saw many builders suggest planning everything out before you start installing a single wire, and I took that advice to heart. I probably spent waaaay more time on this subject than most people do. I'm a slow builder, and I'm okay with that. Although my electrical journey was probably overkill for a lot of people, it's what I needed to get an understanding of the airplane I'm building.

I still have a few decisions to make. Namely, the EarthX battery. I reviewed the RV-8 accident last fall and have been giving that a lot of thought. I haven't made up my mind yet, but I feel comfortable moving forward with that decision still tentative.

Dan and Carl pointed out that I had been fixated on a main alternator failure as the most likely electrical causality, which it is not. Having just completed my PMP certification, I took a page out of my textbook and did a risk analysis of various electrical failures (components, failed connections, shorts of every wire, etc.). It's still a work in progress.

One of the main things I learned is you can't just take good ideas from one design and incorporate them into another design without thoroughly understanding the implications/functions of each component, which I do not. I've read Bob's book more than twice and spent way too many hours working with my plan, and I'm still a novice. Thanks again to everyone who helped further my education.

I'm looking forward to FINALLY installing my first wire!
Rob K
RV-8 under construction as of Sep 30, 2012
Tail kit completed on Feb 8, 2012 (180 hrs)
Wing kit mostly completed, fuselage under construction as of March 6, 2014 (750 hrs)
Paid up for 2018

Last edited by Nihon_Ni : 04-19-2018 at 06:35 PM.
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Old 04-20-2018, 08:46 AM
444TX 444TX is offline
Join Date: Dec 2005
Posts: 97

Nice diagram and load charts.

I have been watching your system design progress and most of the problems I had seen have been addressed. I have a few ideas, not that they must be followed.

1. SD-8 alternator. You might call B&C. The regulator needs good cooling to achieve maximum available output. Under the cowling may be too hot for the best results.

2. The main alternator current limiter is too small. Most alternators easily put out more than advertised current. Recommend 70 amp.

3.The Auxiliary Alternator warning light will always be on with the switch turned off. Unless you plan to leave on, the solution would be a double throw switch that would also turn off the light circuit when not being used. A warning light on all the time would be a nuisance.

4. The 20 gauge essential buss jumper is too small for a continuous 15 amp load of more than 2 seconds. I would recommend a 14 or 16 gauge jumper with no protection. Same for the 22 gauge main buss jumper. Protection is unnecessary, especially if a very short run.

5. The 30 amp inline fuse for the E-buss alternate feed relay is just adequate for full load. Would put a 40 amp with the wire size used or would recommend a 40 amp current limiter. (same thing different package)

6. The main alternator and auxiliary field breakers should be easily accessible and identifiable by feel.

7. Recommend all Honeywell TL quality and/or type switches. The Carlin can give problems, especially on inductive loads. Fast-on are nice, but a quality switch is more important.

8. Have no provision to power up the avionics prior to engine start. Would be nice for IFR. Set up radios, check ATIS, insert flight plan, call for clearance, etc.. A small/medium Lithium could be used.

9. I would not use a Lithium for the main battery, especially IFR all electric plane. Time will tell. (I'm sure to start a fire storm for that suggestion)

10. Would recommend a Honeywell double throw switch for the avionics switch. (extra contact area). Why the diode, unnecessary voltage drop and can control current with the avionics switch. Breaker switches can be problematic. Does the avionics switch circuit between the busses need protection? You could put a 14 gauge fuse link on each end, but I would not bother.

11. Would run the strobes through a breaker rather than a fuse. Have seen multiple strobe fuses melted. This is documented, but not fully explained.

12. You have fuses for the GTN650. There is no way to reboot the radio. This is done with the breakers. Suggest easily accessible, small breaker panel with the necessary breakers.

You have the diagrams, now for the install. Be sure and use high quality connectors. Be careful of chafing areas and protect well. With the large number of connections a Daniels crimper, used red/blue crimper, tefzel strippers would be worth the investment, but not necessary with verification of proper results. Get the proper solder sleeves. Work on perfecting your techniques. Follow techniques in the manuals. The install is only as good as the harness and connection quality.

Looks like you are on the right path. Hope I am helping and not being too critical.

George Meketa
RV8, 16 years
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Old Yesterday, 06:39 AM
Mich48041 Mich48041 is offline
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,577

1. Yes, heat is an enemy of electronics.
2. A 60 amp ANL current limiter will conduct 70+ amp indefinitely without blowing. Read Bob Nuckolls' post:
3. Using a double pole switch is a good idea. One half of it can disable the aux alternator warning lamp.
4. The E-Bus jumper is 16 AWG. The #20 is a fuselink. It will conduct more than 50 amps before it melts. See this chart:
The main bus jumper is 18 AWG (not labled). The 22 AWG fuselink will melt if current exceeds 40 amps.
7. Yes, switches that use rivets as conductors (through plastic) are prone to fail.
8. There is a TCW 3 AH battery to prevent brownout during engine cranking.
9. Lots of aircraft use a Lithium battery including Van's new version of the RV-12 But who knows? I plan to keep my Odyssey PC680.
10. The diode is necessary to block starter current if the builder or future pilot inadvertently leaves the E-Bus switches turned on. The diode will also block reverse main bus current if the battery contactor fails or if the pilot turns on the E-Bus before turning on the master switch.
Joe Gores
RV-12 Flying
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Old Yesterday, 11:10 PM
444TX 444TX is offline
Join Date: Dec 2005
Posts: 97

I will attempt to explain

2. When designing an electrical system one normally uses manufacturer supplied specs to provide the necessary data required to make informed choices. In choosing the current limiter size there are multiple selection factors, with current value being only one. For temperature the standard fuse re-rating is -25% for temperatures over 25C. That means that your 60 amp fuse would now be de-rated to 45 amps under the hot cowling. We have a 4 gauge B-lead cable that is capable of handling more than 80 amps (125 amp free air)(333 amps wire melting point from Joe's supplied chart) under the worst conditions being protected by a 60 amp current limiter. I stand by recommending a higher than 60 amp current limiter (80 is what is available). Not that the 60 will not work, maybe. I will disagree with Bob K. on this one. Do what you want.

4. The small gauged fuse link buss jumpers are without doubt too small for the application. At times there are reasons to design a circuit with high voltage drop, minimum wire size and tight overload protection, but this is not the place. The max E-bus amp load is 15 amps. A 16 gauge wire is rated at 12.5 amps (free air) and a 20 gauge at 7.5 (free air). The buses are powered by an unprotected 10 gauge cable. The #1 and #2 E-buses are likely next to one another requiring a short jumper that has no realistic chance of a short. I will up my recommendation to a 14 gauge or larger jumper. Same for the main bus jumper.

8. I still highly recommended an E-bus battery to power up the avionics, including the radio. The brown out battery does not provide this function. I assume, with this panel, the plan is to fly IFR. With all the items requiring boot up and set up time this is a feature that is closer to being required than just nice to have. My 8 (IFR) has a E-bus battery (lithium) that is the first thing turned on every flight when entering the plane.

10. The diode is a band-aid for a design flaw. Why would you want to drop voltage to the E-bus under all normal conditions. The switch wiring flow could easily be designed in a way to have the diode isolate the E-bus only when using the Alternate E-bus switch. If left alone at least monitor main bus voltage with the EFIS and not just E-bus voltage.

These changes are not that difficult.

I will work on suggestions for Rob's "How Do I Get Electrical Experience" thread. Design is the hard part, now just need to work on techniques.

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