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ceengland7(at)gmail.com
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 Posted: Fri Feb 14, 2020 11:35 am Post subject: Always hot power for fuel injectors and ignition coils |
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On 2/14/2020 12:49 PM, cofford wrote:
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Hi everyone,
I'm currently planning the electrical architecture for my RV-8 with EFII and I've been following the recent discussions of fuel injector power with great interest. Does anyone connect the positive side of the injectors and coils to the always-hot battery bus and leave them powered all the time, or are they generally always switched?
I'm leaning towards a dual-feed bus with diode-protected feeds from the main contactor and a relay on an aux battery. I'll post a schematic when I get done drawing it.
Thanks,
Casey
My opinion is that there's a difference between powering engine
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components directly from a (unfortunately named) 'battery bus' and
leaving them always hot.
My *engine bus* is fed from the battery, by a fusible link-protected
feeder, *through a high current switch*. It also has a secondary
(backup) switched feed from the main a/c bus. All the engine components
are fed from this engine bus.
This is *not* my always-hot battery bus.
If you start feeding multiple components with always-hot feeds, it's
likely to get very difficult to keep track of what's hot & what's not
when working on the plane. It also makes it impossible to make
everything 'cold' for an emergency landing.
As has been discussed here recently, with proper installation, the only
way (at least at the type of odds of a wing failure) an entire bus can
go down is a failure of the switching mechanism, which is why there are
two feeds to the bus.
FWIW,
Charlie
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cofford
Joined: 01 Jan 2018
Posts: 9
Location: Puget Sound, WA
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| Posted: Sat Feb 15, 2020 3:17 pm Post subject: Re: Always hot power for fuel injectors and ignition coils |
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Thanks Charlie, agree with your reasoning and I am heading towards a similar solution, though perhaps with a relay at the battery instead of a high-current switch. Just wanted to make sure that I wasn't missing something.
Thanks,
Casey
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ceengland7(at)gmail.com
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| Posted: Sat Feb 15, 2020 3:47 pm Post subject: Always hot power for fuel injectors and ignition coils |
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On Sat, Feb 15, 2020 at 5:25 PM cofford <cofford(at)gmail.com (cofford(at)gmail.com)> wrote:
| Quote: | --> AeroElectric-List message posted by: "cofford" <cofford(at)gmail.com (cofford(at)gmail.com)>
Thanks Charlie, agree with your reasoning and I am heading towards a similar solution, though perhaps with a relay at the battery instead of a high-current switch. Just wanted to make sure that I wasn't missing something.
Thanks,
Casey |
I considered another relay, but decided to use the switch since I found one with the current capability, and it eliminated a set of contacts (control for the relay), a coil, and multiple termination points connecting the control to the relay. Given the redundant feeds, probably not worth worrying about.
Charlie
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ceengland7(at)gmail.com
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| Posted: Sun Feb 16, 2020 8:28 pm Post subject: Always hot power for fuel injectors and ignition coils |
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On 2/16/2020 9:34 PM, Robert L. Nuckolls, III wrote:
| Quote: | At 09:04 PM 2/16/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "cofford" <cofford(at)gmail.com> (cofford(at)gmail.com)
Hi Bob,
Thanks for your thoughts. I plan on mounting my battery on the firewall, and the engine fuse block on the cabin side, near the battery and pass-through. The relay would be mounted to the battery box. I was not planning on adding any circuit protection devices to the engine bus relay feed. |
Why the relay? Why not run all those engine
feeds off the main bus? That way, if the engine
is running, all the other stuff is running too . . .
and vice versa.
Then your task is simpler. Keep the main bus
hot . . . a goal that has been successfully
achieved on thousands of airplanes for
a long time.
Bob . . . |
I'll take a swat at it. 'Ingrained habits/training'.
From a purely functional standpoint, sure, but...
We've spent our whole flying careers expecting the engine control (mag switches) to be independent from airframe electrical control. I might be a minority of one, but it seems to me that even if I'm intimately familiar with my plane's unusual switchology characteristics, someone else likely won't be. And in the (admittedly rare) case of the legendary 'smoke in the cockpit' scenario, we've all been trained to make the electrical system 'cold' first, then try to work our way back to restoring power, if we can. By having the much more elaborate switchology of an electronically controlled engine on an independent bus, we can hopefully avoid having 'muscle memory' cause a problem, instead of solving one.
The guys who've been flying alternative engines for years are much more reluctant to allow someone else to fly their planes, and a big driving factor is that engine operation is so different in many of the installations. When we add electronic fuel injection to a traditional engine, it really has become an 'alternative engine' as far as operational issues are concerned.
Charlie
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user9253
Joined: 28 Mar 2008
Posts: 1924
Location: Riley TWP Michigan
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| Posted: Mon Feb 17, 2020 6:10 am Post subject: Re: Always hot power for fuel injectors and ignition coils |
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Charlie, you are not a minority of one. I am on your side. The master switch
should shut off all electrical power except to the engine. The engine bus
should be supplied by two current paths. The pilot should have the ability to
shut off all sources of electrical power as close to the sources as possible.
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