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rossmickey(at)comcast.net
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 Posted: Tue Jun 16, 2015 9:34 am Post subject: What to put on the E-Bus? |
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I have been discussing this issue with some other builders off list and
decided to ask this esteem group. What do I put on my E-Bus?
I have a 40AMP B&C Alternator and a SD-8 backup basically wired as per
Z-8/13 with an E-Bus relay between the battery bus and E-Bus.
One option is to put everything you might need for safe flight and landing
on the E-Bus (such as landing lights and strobes) and only turn on what is
needed depending on the stage of flight (keeping the continuous load less
than the 8 amps being put out by the SD- .
The other is to just put on what is "essential" and then rely on being able
to flip the master switch to power the main to get at those "non-essential"
things that would be nice to have say for a night landing. The problem with
this is without an alternate feed from the E-Bus to the main bus, if the
battery contactor fails, all the items on the main bus are unavailable.
This was one of the reasons I was looking to install a cross feed between
the E-Bus and main bus but haven't installed such.
Right now, I am defining the minimum essentials as:
Electronic ignition
Advanced Flight System 5600 EFIS with GPS and AHARS
SL-30 Nav/Com
GRT Engine Monitoring
SL-70 Transponder
Dynon D-10 (for the blind encoder function)
My next level would be
Flaps
Nav Lights
Strobes
Landing Lights
Pitot Heat
The next level
GX-60 GPS/Com
M-200 CDI
Annunciator Control Unit
Last Level
TruTrak Sorcerer Autopilot
MX-20 Multi-Functional Display
Sl-15 Intercom/CD
Clock
Elevator Trim
Aileron Trim
Fuel Pump
Starter
Angle of Attack Indicator
Defrost Fan
Opinions are welcome.
Ross Mickey
N9PT
RV-6A
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kjashton(at)vnet.net
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| Posted: Tue Jun 16, 2015 11:20 am Post subject: What to put on the E-Bus? |
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I think you are overloading your E-bus. Let’s say you lose your alternator and b/u alternator at night in IMC. It might take 30 minutes or more to get down from altitude, find an airport and land. What do you need to power while doing that?
one mag or one electronic ignition already hot-wired to the battery with its own switch
a com radio (so you can declare an emergency)
cockpit flood lighting
minimum flight instruments
intercom
perhaps I’d put the transponder and GPS on the E-bus but keep them on only if necessary.
Maybe your battery is strong and can power more stuff for a longer time but what if it wasn’t fully charged? For me, I only put the things on the E-bus that I must have to land. I don’t need a transponder, engine monitor, strobes, landing lights, or flap motor. I would not want to risk turning on a landing light close in and have the e-bus items go black.
-Kent
Cozy IV N13AM
| Quote: | On Jun 16, 2015, at 1:33 PM, Ross Home <rossmickey(at)comcast.net> wrote:
I have been discussing this issue with some other builders off list and
decided to ask this esteem group. What do I put on my E-Bus?
|
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fvalarm(at)rapidnet.net
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| Posted: Tue Jun 16, 2015 12:59 pm Post subject: What to put on the E-Bus? |
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I consider the E-Bus as an Essential Bus. It's purpose is do allow bare
minimum equipment to run when turning off the main contactor (which also
takes electrical power) to CONSERVE your battery while you CONTINUE to
destination or a nearby airport when you have a failed alternator. Once you
are near the airport, you may turn on your main contactor allowing all such
things for landing.
Heavy loads such as landing lights, pitot heat, will max out your SD-8 all
by themselves.
I have the following on my E-Bus
One Nav/comm radio
One EFIS
One cabin/panel light (LED)
Engine monitor
Auto-pilot
With everything on, the steady state electrical load is less than the output
capacity of the SD-8, thereby saving the battery for end of flight.
Bevan
RV7A
40 amp Main Alt
8 amp backup alt
Garmin 396 has it's own internal backup battery
Dual P-mags powered from the main bus and they have their own internal
generators fro primary power once running.
I may add internal battery backup to EFIS in the future if needed.
--
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nuckolls.bob(at)aeroelect
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| Posted: Thu Jun 18, 2015 7:42 am Post subject: What to put on the E-Bus? |
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> On Jun 16, 2015, at 1:33 PM, Ross Home <rossmickey(at)comcast.net> wrote:
>
> --> AeroElectric-List message posted by: "Ross Home" <rossmickey(at)comcast.net>
>
> I have been discussing this issue with some other builders off list and
> decided to ask this esteem group. What do I put on my E-Bus?
BN: what ever you NEED for comfortable continuation of flight to your intended destination . . .
Maybe your battery is strong and can power more stuff for a longer time but what if it wasn't fully charged? For me, I only put the things on the E-bus that I must have to land. I don't need a transponder, engine monitor, strobes, landing lights, or flap motor. I would not want to risk turning on a landing light close in and have the e-bus items go black.
-Kent
BN: Various comments to this thread suggest that a review of the e-bus history might be useful.
I remember when the seeds of an idea for an 'endurance' bus germinated. . I was in a telephone conversation with a LongEz builder one evening about 1990. His anticipated use of the airplane was long distance travel over mountainous country. He lived in California and wanted to take trips back east. We were discussing flight system reliability, not just about his battery or alternator but the whole airplane. It was a comparative study designed to discover the weakest links (shortest endurance) in the system. The worst case scenario was deduced to be at altitude, a long way from concrete and maintenance-friendly facilities. The design goal was to put the sharp pencil to electrical demands for continued flight, battery only, to either intended destination or departure airport. A design goal for supporting en route demands for no less than 1/2 the fuel endurance . . . longer would be even better.
This was a time when the solid state transceivers and transponders were making good market penetration. We deduced that a 200W transponder consumed 20 watts average power if heavily interrogated, probably 10W or less over sparsely populated terrain. A comm transceiver in the receive mode was about 4w. Panel lighting could be whittled down to less than a watt. His turn coordinator demand was 6 watts. We deduced that after the low voltage warning light came on, the limited battery energy should be rationed out according to a carefully crafted and maintained, PLAN-B.
Engine endurance was limited to 4 hours by virtue of fuel aboard. We reasoned that COMFORTABLE battery-only endurance should not be less than 1/2 that value . . . and preferably more. Meeting this design goal depends heavily on two bits of knowledge. (1) Capacity of the battery in watt-seconds and (2) knowing the watt-seconds required to support en-route loads for the target endurance goals.
Gee . . . nobody told anyone about that kind of stuff in flight school . . .
The flight instructor syllabus was tailored to make us operators of airplanes, not system designers. Yeah, we knew about batteries from our experience with automobiles. But to consider the battery as a resource of energy with limited capabilities was not nearly so refined as our attitudes toward the OTHER energy source . . . tanks of fuel.
The e-bus was birthed from the knowledge that (1) it didn't take much energy to keep useful electro-whizzies alive and (2) enerby demands of a battery contactor were significant compared energy required to run a radio or light up the panel. So, the e-bus diode and alternate feed-path directly to the battery offered a way to PARTITION off the most useful devices such that low volts warning prompts reconfiguration of electrical loads by operation of two switches. The design goal being to KNOW how long the e-bus would stay up battery only . . . with enough energy left to run some lights and things during approach to landing. A typical e-bus load then was 2-3 amps tops.
25 years later, electrically dependent airplanes are growing in number. But the task of KNOWING what energy is needed to design and operated a failure-tolerant system hasn't changed. Depending on intended use of the airplane, goals for reducing risk by design and well conducted maintenance (the FAA calls is requirements for continued airworthiness), one still needs to add up the energy requirements, multiply by minutes of operation and then take steps to assure availability of thatn energy from some combination of engine driven power sources and batteries. Batteries evaluated as accurately as peering down the open filler cap on a fuel tank.
I will confess to the fact that early drawings for this Plan-B bus called it the 'emergency' bus. But as the concept evolved and new ideas were incorporated, it became obvious that the primary goal for the e-bus was to prevent an emergency situation from evolving . . . hence the renaming to 'endurance' bus: a calculated, planned and maintained Plan-B for failure-tolerant, comfortable continuation of flight with predictable performance.
I hope this helps our brothers understand why I get exercised when questions arise like, “How to I wire to support a 20-amp e-bus?”. The better question is, “Given the configuration of my airplane and it's intended use, which electro-whizzies should be feed from the E and battery busses . . . and how to craft and maintain XX minutes of endurance after loss of the primary alternator?” I understand why some questioners feel invaded or perhaps slighted when prospective counselors look past a question about wire gages and switch ratings to inquire into the life-story of the planned electrical system. Please understand that to offer such advice is like responding to: "How do I keep this soup tasting good . . . more basil or less sea-salt?". The useful answer to the question can only be offered by knowing what kind of soup you're cooking, what ingredients are on hand and in what proportions they are incorporated.
Bob . . . [quote][b]
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