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nuckollsr(at)cox.net
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 Posted: Sat Feb 24, 2007 7:40 pm Post subject: Shielded wires with modern ignition systems . . . |
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At 09:26 PM 2/24/2007 -0500, you wrote:
| Quote: |
The ROTAX 912ULS wiring diagram (with electron mags) shows shielded wire
for the ignition with a ground at both ends. I assume this diagram
should be followed?
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Hmmmm . . . I'd recommend you ground at the engine end
only and use the shields to provide ground for the mag
switches. Nonetheless, there are thousands of airplanes
flying wired "per instructions" that function fine but
with a non-zero risk of problems with ground loops.
Bob . . .
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nuckollsr(at)cox.net
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| Posted: Sun Feb 25, 2007 7:21 am Post subject: Shielded wires with modern ignition systems . . . |
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At 10:52 PM 2/24/2007 -0800, you wrote:
| Quote: |
The Jabiru mags are not "electronic ignition" as commonly classified. they
do have a transistor switch inside.
Although shielding the P lead is not necessary, best practice is to run in
shielded lead, ground the shield at mag end to a spare thread hole (on the
alternator statorplate will do). At the mag switch end, the shield is
connected to the gnd terminal of the switch, but not connected to the
airframe here.
during running, there are over 200v of spikes on these lines. Refer to the
files section on Yahoo Jabiru/engines group, "radio noise" , look for
jab.coil primary - a photo of the trace on the P lead.
http://groups.yahoo.com/group/jabiruengines/files/Radio%20noise/
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Excellent data sir! Thank you. I'm disappointed to hear about
it though . . . you would think that a company so obviously
dedicated to the use of modern machining and manufacturing
techniques would go a step further with their ignition system.
Having said that, I'll have to acknowledge that their decisions
may well have been based on a considered trade off between
cost and performance . . . and using shielded ignition control
leads has been a standard practice in aviation since the first
radio went into an airplane perhaps 95 years ago!
Okay, based on expanded knowledge offered by our brother Ralph,
we know that optimal wiring for the engine is POORLY explained on
page 10 of the Jabiru 3300 installation manual. Ralph
correctly cites the need for shielded wire and I concur
with the techniques he suggested above.
Bob . . .
----------------------------------------
( IF one aspires to be "world class", )
( what ever you do must be exercised )
( EVERY day . . . )
( R. L. Nuckolls III )
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