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  #11  
Old 08-02-2019, 02:22 PM
erich weaver's Avatar
erich weaver erich weaver is offline
 
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Originally Posted by DanH View Post
I think it is. The whole point was quick, predetermined load shedding. Most installs have gone far astray from that simple concept. We have builders who think "essential" includes a wet bar and a massage chair

A lot depends on if you plan externally powered engine systems (EI and/or EFI), and VRF vs IFR avionics.
Im not following what the criticism of the Nuckoll's E-bus architecture is. Its what I have (Z-13/8), along with P-mags and a two-screen EFIS. Im VFR and using AFP fuel injection (no EFI), and a single battery, dual alternator, although Im not sure what all that has to do with using an E-bus or not. Can you elaborate for a simple minded kind of guy like me?

thanks

Erich
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  #12  
Old 08-02-2019, 02:37 PM
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Carl Froehlich Carl Froehlich is online now
 
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Quote:
Originally Posted by erich weaver View Post
Im not following what the criticism of the Nuckoll's E-bus architecture is. Its what I have (Z-13/8), along with P-mags and a two-screen EFIS. Im VFR and using AFP fuel injection (no EFI), and a single battery, dual alternator, although Im not sure what all that has to do with using an E-bus or not. Can you elaborate for a simple minded kind of guy like me?

thanks

Erich
For VFR with pMags this is not as critical. For IFR with dual glass panels these single battery designs typically produce single point failure risks (note - the second alternator mitigates the one risk that is most likely but has a low impact, but not the less likely with higher impact risks).

Many ways to mitigate, like adding a covey of backup batteries (not my preference).

Carl
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  #13  
Old 08-02-2019, 03:15 PM
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Quote:
Originally Posted by erich weaver View Post
Im not following what the criticism of the Nuckoll's E-bus architecture is.
It's not criticism Erich, at least not by me. I merely think we're moving past it.

Try this. The E-bus is load shedding architecture based on a vacuum pump, single wet battery, and one alternator. Flip a switch, quickly knock off everything but a radio and some basic nav. Gyros to stay upright, analog airspeed, etc.

Today we have battery technology which is improving every day, in both capacity and reduced weight. Alternators are small and light compared to the past monsters, so it's easier to justify two of them.

Aircraft electrical design is migrating to dual independent bus power for EI and/or EFI. It will soon be the standard, even on the certified side. Those are loads we can't shed. And of course everything in the panel is electric, no gyros. Load shedding is no longer a real option, but it doesn't matter. Given the available capacity we can install, there is no real need for it.
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  #14  
Old 08-02-2019, 04:01 PM
rapid_ascent rapid_ascent is offline
 
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I donít think itís such a problem with fuses in series if you take some precautions. Itís true that in the event of a dead short the current could be much higher that the fuse rating for a short amount of time. Often shorts are not dead shorts though but low impedance shorts.

I think in the situation that you have the worst case you have is a dead short on one of your sub-circuits takes out the upstream fuse. So you lose your interior light or your clock power in that event. Not really a big deal. You could make the wire from the battery larger and use a larger fuse for the feeder fuse. That is probably what I would do. Having an unprotected wire is never a good idea. You could use a time lag fuse for the feeder fuse and that might help too. The alternative of have a hot glowing wire until it melts through in one spot isnít a good alternative in my mind for a fault condition.
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  #15  
Old 08-02-2019, 04:04 PM
Finley Atherton Finley Atherton is offline
 
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IMHO no need for an E-bus. Most avionics have an ON/OFF switch. If necessary add extra dedicated switches for other avionics/components that you may want to load shed if the alternator fails.
Might take an extra second or two to load shed than with an E-bus setup but is that really a problem?

Canít say I am keen on an Avionics bus and single avionics switch - switch fails and you lose your avionics. I have a single bus with switches on all avionics. Takes a couple of seconds to switch everything ON or OFF but one of the reasons I built a plane is because I love gadgets including switches.
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  #16  
Old 08-02-2019, 07:38 PM
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Quote:
Originally Posted by Carl Froehlich View Post
For VFR with pMags this is not as critical. For IFR with dual glass panels these single battery designs typically produce single point failure risks (note - the second alternator mitigates the one risk that is most likely but has a low impact, but not the less likely with higher impact risks).

Many ways to mitigate, like adding a covey of backup batteries (not my preference).

Carl
Thanks for the email Carl, I'm digesting as we speak. Looks like a very redundant system despite many relays.

Quote:
Originally Posted by DanH View Post
It's not criticism Erich, at least not by me. I merely think we're moving past it.

Try this. The E-bus is load shedding architecture based on a vacuum pump, single wet battery, and one alternator. Flip a switch, quickly knock off everything but a radio and some basic nav. Gyros to stay upright, analog airspeed, etc.

Today we have battery technology which is improving every day, in both capacity and reduced weight. Alternators are small and light compared to the past monsters, so it's easier to justify two of them.

Aircraft electrical design is migrating to dual independent bus power for EI and/or EFI. It will soon be the standard, even on the certified side. Those are loads we can't shed. And of course everything in the panel is electric, no gyros. Load shedding is no longer a real option, but it doesn't matter. Given the available capacity we can install, there is no real need for it.
Dan would you happen to have any schematics or basic sketches of what the dual independent bus architecture would look like?

Quote:
Originally Posted by rapid_ascent View Post
I donít think itís such a problem with fuses in series if you take some precautions. Itís true that in the event of a dead short the current could be much higher that the fuse rating for a short amount of time. Often shorts are not dead shorts though but low impedance shorts.

I think in the situation that you have the worst case you have is a dead short on one of your sub-circuits takes out the upstream fuse. So you lose your interior light or your clock power in that event. Not really a big deal. You could make the wire from the battery larger and use a larger fuse for the feeder fuse. That is probably what I would do. Having an unprotected wire is never a good idea. You could use a time lag fuse for the feeder fuse and that might help too. The alternative of have a hot glowing wire until it melts through in one spot isnít a good alternative in my mind for a fault condition.
Thanks for the good feedback and ideas Ray.

Quote:
Originally Posted by Finley Atherton View Post
IMHO no need for an E-bus. Most avionics have an ON/OFF switch. If necessary add extra dedicated switches for other avionics/components that you may want to load shed if the alternator fails.
Might take an extra second or two to load shed than with an E-bus setup but is that really a problem?

Canít say I am keen on an Avionics bus and single avionics switch - switch fails and you lose your avionics. I have a single bus with switches on all avionics. Takes a couple of seconds to switch everything ON or OFF but one of the reasons I built a plane is because I love gadgets including switches.
Fin
9A IFR
Australia.
Interesting approach Fin, thanks for the ideas. I'm now in the process of rethinking my buses.
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  #17  
Old 08-02-2019, 09:02 PM
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Ok, just throwing ideas out there. I like what Carl has sent me as I sure as heck can't find any single point failure modes. However, does anyone see any in this drawing? This is a modified Z-19 (I still need to add a battery bus but no big deal, mainly seeing if there are any single point failures)

-If you lose your alternator you still have two batteries feeding both buses. (also: alternator I'm going with has it's own overvoltage protection)

-If you lose your main battery and/or contactor you still have alternator and aux battery feeding both buses

-If you lose your aux battery and/or contactor you still have main battery and alternator feeding both buses.

Am I missing something here on a redundancy perspective?

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  #18  
Old 08-02-2019, 10:07 PM
Bicyclops Bicyclops is offline
 
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Default Possible smoke alert

If you activate the Bus 2 alternate feed relay without closing either of the battery contactors, you'll be backfeeding Bus 1 through an un-fused 16 awg wire. Not sure that's up to the possible loads. It sure wouldn't carry the starter.

If I remember right, 'Lectric Bob has a diode and a thinner wire where you show the 6 gage interconnect wire in order to feed the E-Buss without backfeeding the main bus. The whole purpose of Bob's alternate feed is to be able to quickly shed the lighting and other heavy loads and to run the E-bus without the ~1A draw of a contactor once the alternator fails. You've already got redundant feeds to both the busses. You don't need a way to smoke a wire by inadvertently throwing switches in the wrong sequence. At the very least, fuse that wire at the battery. Speaking of which, the way it's drawn, you might wind up trying to charge Batt 2 through that 16 gage wire with a certain combination of switch positions.

Ed Holyoke
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  #19  
Old 08-02-2019, 11:41 PM
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jcarne jcarne is offline
 
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Quote:
Originally Posted by Bicyclops View Post
If you activate the Bus 2 alternate feed relay without closing either of the battery contactors, you'll be backfeeding Bus 1 through an un-fused 16 awg wire. Not sure that's up to the possible loads. It sure wouldn't carry the starter.

If I remember right, 'Lectric Bob has a diode and a thinner wire where you show the 6 gage interconnect wire in order to feed the E-Buss without backfeeding the main bus. The whole purpose of Bob's alternate feed is to be able to quickly shed the lighting and other heavy loads and to run the E-bus without the ~1A draw of a contactor once the alternator fails. You've already got redundant feeds to both the busses. You don't need a way to smoke a wire by inadvertently throwing switches in the wrong sequence. At the very least, fuse that wire at the battery. Speaking of which, the way it's drawn, you might wind up trying to charge Batt 2 through that 16 gage wire with a certain combination of switch positions.

Ed Holyoke
Ed, awesome feedback! Your memory is correct, Bob shows a diode with a 16awg wire between the two buses. At this point I'm trying to avoid the E-bus setup as I would rather be able to get power to anything I want. My thinking is, two batteries should give me more than enough juice to get where I need to in an IFR situation (especially considering the EFIS has it's own back up battery) and I can load shed/select what I want manually. I understand workload in a situation like this may be higher but I can't imagine myself turning the landing lights on when I know power is limited. haha

So here is revision 2 based on your feedback. After thinking about what you said it does seem like the bus 2 bypass relay was pointless in my case. I sent a 6awg wire direct to the buses now. I also deleted the copper bar between the two battery contactors since the aux battery will likely be in the cabin of the plane towards the back somewhere (this may change wire gauge but I need to look into that). The only downside I see at this point is that like you said if the alternator fails I will have to have the current draw from the two contactors to keep the batteries online. The only single point failure I see at this point is the wire going from bus 1 to bus 2. However, I would imagine that failure EXTREMELY unlikely especially if I make it out of copper bar. Also, if that connection fails it only takes out bus 2.

Let me know if I am missing something else. Thanks again for all your help everyone, keep it comin!

P.S. Don't pay any attention to anything coming off of the buses. I haven't changed that yet.

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Last edited by jcarne : 08-03-2019 at 12:04 AM.
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  #20  
Old 08-03-2019, 06:53 AM
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Jereme,

You're moving things around on existing diagrams without much big picture oversight. Asking folks to vet this diagram is something akin to click bait. We can spend time with it, but to what end?

Start with basics. Will you have engine electrical loads? That would EI, and/or EFI with the required electric pumps.
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