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nuckolls.bob(at)aeroelect
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 Posted: Tue Feb 18, 2020 6:03 am Post subject: Always Hot Power to Injectors and Ignition Coils |
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At 05:10 AM 2/17/2020, you wrote:
| Quote: | Sorry, still not able to post directly.
A couple of questions. How will you do a “mag check” if the coils are always powered? |
You don't do a mag check on things that are not
mags . . . If you've got a coil misbehaving
the engine will let you know about it without
any sort of preflight check.
| Quote: |
Does anyone have any experience with the somewhat pricey but seemingly reliable and well built Gigavac MX series contactors? I realize they aren’t available on the aviation aisle at NAPA, but I can always carry a spare. |
What brings to a notion that you
need such a beast? And if 'seemingly
reliable' why would you carry a spare?
| Quote: | | Lastly, what software are you guys using to draw your very nice electrical schematics? I’m looking for something that doesn’t have a steep learning curve that an old guy can pick up reasonably quickly. |
AutoCAD and it's contemporary competitors
will open, edit, create and print files
with the .dwg format.
All of my drawings along with the symbols
library are downloadable from the website.
About any version of TurboCAD off eBay
will work for you. Here's one good
example
https://tinyurl.com/upvbr3f
there are numerous tutorials on TurboCAD
available from the same website.
Bob . . .
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mmayfield
Joined: 09 Oct 2009
Posts: 40
Location: NSW Central Coast, Australia
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| Posted: Tue Feb 18, 2020 2:17 pm Post subject: Re: Always Hot Power to Injectors and Ignition Coils |
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[quote="nuckolls.bob(at)aeroelect"]At 05:10 AM 2/17/2020, you wrote:
| Quote: |
You don't do a mag check on things that are not
mags . . . If you've got a coil misbehaving
the engine will let you know about it without
any sort of preflight check.
Bob . . . |
You certainly do.
But let's not call it a "mag check". Let's call it an "ignition check". For all intents and purposes there's no obvious difference to the naked eye.
So on my dual EI aircraft that check is specified by the electronic ignition manufacturer along with the maximum rpm drop. The purpose is not only to check that the spark is getting to all the plugs on the operative ignition (a problem which can be masked when both systems are on), but also that the electronic ignition warning system is functioning correctly. Switching each one off in turn effectively simulates a "failure" of the ignition unit.
I once foolishly overlooked this check, took off, and it turned out both plugs on one of my 9 cylinders were fouled (which would've been detected had I done it properly). At full power and 150 litres/hour takeoff fuel flow, the unburned fuel was being pumped through that cylinder and expelled into the hot exhaust where it ignited causing a massive bang and large sheet of flame to be expelled very shortly after takeoff. Coinciding with this "after-fire" was a large back pressure created through the engine which cause a temporary dramatic and rather eye-watering power loss.
This occurred repeatedly (with a large power loss each time, followed by recovery) until I pulled the power back when it settled a bit. I did the tightest circuit pattern I've ever done in my life. Spectators on the ground thought I was going to crash - they could hear each "bang!" accompanied by the big sheet of flame out of the exhaust.
So yeah.... you do an ignition check, which looks and feels identical to a "mag check" with electronic ignition units. 
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cofford
Joined: 01 Jan 2018
Posts: 9
Location: Puget Sound, WA
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| Posted: Tue Feb 18, 2020 8:06 pm Post subject: Re: Always Hot Power to Injectors and Ignition Coils |
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In my setup, the ignition check is done at runup using the ignition select switch. A 1-1 switch is used to ground a pin on each ECU which disables the ignition for that ECU. Normal operation is in the center position, with neither pin connected to ground. This is verified through RPM drop, and could be wired to discrete inputs on the EFIS for display. The ECU controlling the fuel injectors (switched ground) is done in a similar manner, except that one ECU is disabled during flight, and a 1-3 switch is used.
Just as a disclaimer, I'm not flying yet, so this is all per the installation manual and my understanding of the system operation.
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