If you are getting a sudden jump in voltage after a couple of minutes, I
would have a look at the field coils and bridge rectifier in the alternator
I have seen simmilar in the past, where you would get a constant discharge
until such time as there was enough residual field in the alternator
to kick it into charging. You could speed up the kick over to charging by
running higher RPM from start (not ideal for reasons of wear) in this
instance
it was a defective diode in the bridge rectifier. As for the noise, likely
as you say, a noisy component in the reg being amped by the firewall, which
shuts up
once its up to temp.
craig
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com]On Behalf Of Richard Lamprey
Sent: Tuesday, 15 January 2008 10:44 AM
To: europa-list@matronics.com
Subject: Europa-List: Rotax 912 electronic noise
Can anyone shed light on an strange noise that emanates from my engine on
startup? The engine is a basic 912UL, with about 520 hours on it. The
noise is an electronic note, almost flutelike, around G in pitch. After
startup, and idle at about 2200 RPM, you hear this noise through the
firewall, loud enough for a passenger to comment. With increasing RPM, it
doesn't increase much in pitch, just slightly, and therefore I think it must
somehow be related to the alternator output, or possible the voltage
regulator (Ducati); and not related to any noisy bearings in anything.
You cannot detect this noise if you stand close to the running engine,
with the cowling off. It seems that the firewall acts as a resonating
surface to amplify it to inside the cockpit.
The noise goes for about 5 minutes during warm-up, then quite suddenly it
completely disappears, usually at about the time of taxying out. All
through this startup, the engine runs smoothly, and temperatures and
pressures behave normally. The big spike-protecting capacitor charges up,
and after a minute or two from startup, the voltmeter shows a switch from 12
volt (not charging) to 14 volt (charging), All quite normal, and seemingly
unrelated to the noise.
This noise didn't happen when the engine was new. It began after about
300 hours of engine time. It is particularly noticeable after sometime
without engine operation, say 2 weeks or longer.
Any ideas on this mystery noise gratefully received!
Richard Lamprey
Europa Classic, 5Y-LRY
Nairobi, Kenya
5:39 PM
|