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Rotax 912 electronic noise

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lamprey(at)infocom.co.ug
Guest

Posted: Mon Jan 14, 2008 5:47 am Post subject: 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

  

  

   [quote][b]

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m.j.gregory(at)talk21.com
Guest

Posted: Mon Jan 14, 2008 9:42 am Post subject: Rotax 912 electronic noise

Richard,  

   

Anything related to the alternator output would vary with the RPM, but it wouldn't surprise me if the Ducati regulator was doing something mysterious.  A vibration within the regulator attached to the firewall would allow the firewall to act as a sounding board as you suggest.  

   

If it can be done safely, you might be able to see if the regulator is involved by getting someone to press their hand on it while the engine is running.  If this damps the vibration (or the hand can feel the buzz) then this could confirm it.  Alternatively, you might temporarily detach the regulator from the firewall (but make sure it is still properly grounded) and see if the resonance is still there.  Ducati regulators are not known for their longevity, especially if they get hot in service (go on, tell us it's hot in Kenya!).  Many regulators had been replaced after 300 hours or less.    

   

I am not sure how normal is your delay of a minute or two before the voltage rises from 12 to 14.  The regulator ought to provide full charging voltage immediately the alternator is up to speed, unless there is a discharged battery drawing a heavy current that drags the voltage down; even then, I would expect the voltage to rise slowly as the battery charges rather than jump suddenly, assuming you are not switching any major electrical loads at the time.  

   

I defer to Gilles Thesee regarding the internal workings of the regulator and what might cause it to act in this way, if indeed it is the culprit.  

   

Mike Gregory        

  

From: owner-europa-list-server(at)matronics.com [mailto:owner-europa-list-server(at)matronics.com] On Behalf Of Richard Lamprey

 Sent: 15 January 2008 00:44

 To: europa-list(at)matronics.com

 Subject: 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  

    

   

  [quote] [b]

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craigb(at)onthenet.com.au
Guest

Posted: Tue Jan 15, 2008 2:50 am Post subject: Rotax 912 electronic noise

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

 [quote]   --

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lamprey(at)infocom.co.ug
Guest

Posted: Wed Jan 16, 2008 6:35 am Post subject: Rotax 912 electronic noise

Thanks Craig and Mike for your inputs.  I have  limited knowledge of electrics, but my thoughts about the sudden jump from 12 V  to 14 Volt are that after startup the vast 22,000 microfarad capacitor is  soaking up voltage until it has reached full capacitance; only after full  capacity is reached, the system achieves the full 14 Volts, and the sudden  jump occurs.  If the engine has been run in the last couple of days, the  system reaches 14 Volts immediately, since the capacitor has not in the  short time 'bled' its charge.  The delay and jump only occur after the  system has sat without running for a long while.

  

 The same applies to the mysterious noise, ie doesnt  occur after recent running... but I will apply my stethoscope to the regulator  to see if thats the source.

  

 Yes weather here is fine, lovely sunshine all  day!  But the politics and post election violence has been disastrous for  the country (as you may have seen on TV).

  

 Regards to all

 Richard



   [quote][b]

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jan.de.jong(at)xs4all.nl
Guest

Posted: Wed Jan 16, 2008 1:20 pm Post subject: Rotax 912 electronic noise

Hallo Richard,

Forget about the capacitor. At 14 volts it can only hold 14 x 0,022 =0,3 

Coulombs. A 10A source charges it in  0,3 / 10= 0,03 seconds.

Your only large "capacitor" is the battery. If might support a 10A 

charging current for a little while, drawing down the bus voltage, but 

12V seems low.

Regards,

Jan de Jong



Richard Lamprey wrote:

 	  Quote: 	
		   Thanks Craig and Mike for your inputs.  I have limited knowledge of 

 electrics, but my thoughts about the sudden jump from 12 V to 14 Volt 

 are that after startup the vast 22,000 microfarad capacitor is soaking 

 up voltage until it has reached full capacitance; only after full 

 capacity is reached, the system achieves the full 14 Volts, and the 

 sudden jump occurs.  If the engine has been run in the last couple of 

 days, the system reaches 14 Volts immediately, since the capacitor has 

 not in the short time 'bled' its charge.  The delay and jump only 

 occur after the system has sat without running for a long while.

  

 The same applies to the mysterious noise, ie doesnt occur after recent 

 running... but I will apply my stethoscope to the regulator to see if 

 thats the source.

  

 Yes weather here is fine, lovely sunshine all day!  But the politics 

 and post election violence has been disastrous for the country (as you 

 may have seen on TV).

  

 Regards to all

 Richard

 *

 *

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rampil

Joined: 04 May 2007
Posts: 870

Posted: Wed Jan 16, 2008 2:43 pm Post subject: Re: Rotax 912 electronic noise

Hi Richard,



I am not sure that probabilities favor the electrics hypothesis.

Most electronics without moving parts remain quite silent unless they

are in the terminal stage of releasing their electronics, steam and smoke.



Have you ruled out air, coolant, or oil flowing through some constriction?



Carbon pile voltage regulators could make noise as the carbon heated,

but I think that species went extinct in the 1960s. 



Best of Luck!

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_________________
Ira N224XS

ward.t(at)xtra.co.nz
Guest

Posted: Wed Jan 16, 2008 3:30 pm Post subject: Rotax 912 electronic noise

Richard,

Maybe Vacuum pump, or air driven Artificial Horizon or Directional Indicator 

or electrical Turn and Slip?

Best of Luck.

Tim

Tim Ward

12 Waiwetu Street,

Fendalton,

CHRISTCHURCH 8052

NEW ZEALAND



Ph :64 03 3515166

Mob:  021 0640221



email:

ward.t(at)xtra.co.nz

---

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