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Capacitor

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george.mueller(at)aurora.
Guest

Posted: Wed Feb 14, 2007 7:39 am Post subject: Capacitor

I am installing a Rotax 912 in a Zenith 701.  I see some installations with a capacitor and some without.  Recent posts have indicated a downside to the capacitor in that it can cause some problems if the alt switch is shut off with the engine running.  What are the pros and cons of the capacitor?   

 

 

 

 

George in Milwaukee 

Zenith 701 912

  [quote][b]

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daberti(at)sbcglobal.net
Guest

Posted: Wed Feb 14, 2007 1:41 pm Post subject: Capacitor

I've  had no problems with my installation; although, my capacitor is slightly smaller  than the one specified by Rotax.  I also added an over-voltage protection  circuit to my system as recommended by Bob at Aeroelectric.  I purchased  both from him.  

 [quote]   --

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jkuehn(at)mountaintime.my
Guest

Posted: Wed Feb 14, 2007 5:00 pm Post subject: Capacitor

I also installed components from Bob at AeroElectric, including the over 

voltage protector and the capacitor.  As I understood it, without the 

capacitor, if for some reason the battery was disconnected from the 

system while the engine was running, with no capacitor, the engine will 

quit, while with it, it will keep running.  I was basically so impressed 

by Bob's design approach, which is essentially:  "if it can break, 

eventually it will, so either design a backup or make the system 

inessential for continued flight."  I have no problems with any of this 

stuff, and running the engine on BATT only is no problem as far as I 

know.  Bob would be the guy to ask about this!



Jack



Dave wrote:



[quote] I've had no problems with my installation; although, my capacitor is 

 slightly smaller than the one specified by Rotax.  I also added an 

 over-voltage protection circuit to my system as recommended by Bob at 

 Aeroelectric.  I purchased both from him. 



     --

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thilo.kind(at)gmx.net
Guest

Posted: Wed Feb 14, 2007 6:43 pm Post subject: Capacitor

Hi there,

I have the standard capacitor installed as per Rotax recommendation. 5 years with no problem so far. 

I don't understand why the engine should quit, when the battery is disconnected. The ignition system of the Rotax is totally independend of the electrical system. The engine will keep running with the master switch off (which essentially disconnects the battery).

The capacitor is required to smoothen out any waviness in the current coming from the alternator, which might cause problems with the avionics and introduce funny sounds in the headsets.

Thilo Kind

-------- Original-Nachricht --------

Datum: Wed, 14 Feb 2007 17:59:49 -0700

Von: Jack Kuehn <jkuehn(at)mountaintime.myrf.net>

An: rotaxengines-list(at)matronics.com

CC: 

Betreff: Re: Capacitor

[quote] 

 <jkuehn(at)mountaintime.myrf.net>

 I also installed components from Bob at AeroElectric, including the over 

 voltage protector and the capacitor.  As I understood it, without the 

 capacitor, if for some reason the battery was disconnected from the 

 system while the engine was running, with no capacitor, the engine will 

 quit, while with it, it will keep running.  I was basically so impressed 

 by Bob's design approach, which is essentially:  "if it can break, 

 eventually it will, so either design a backup or make the system 

 inessential for continued flight."  I have no problems with any of this 

 stuff, and running the engine on BATT only is no problem as far as I 

 know.  Bob would be the guy to ask about this!

 Jack

 Dave wrote:

 > I've had no problems with my installation; although, my capacitor is 

 > slightly smaller than the one specified by Rotax.  I also added an 

 > over-voltage protection circuit to my system as recommended by Bob at 

 > Aeroelectric.  I purchased both from him. 

 >

 >     --

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NYTerminat(at)aol.com
Guest

Posted: Wed Feb 14, 2007 6:55 pm Post subject: Capacitor

In a message dated 2/14/2007 9:44:02 P.M. Eastern Standard Time,  thilo.kind(at)gmx.net writes:

  	  Quote: 	
		  Betreff:    Re: Capacitor



 	  Quote: 	
		   --> RotaxEngines-List message    posted by: Jack Kuehn

    <jkuehn(at)mountaintime.myrf.net>

 

    As I    understood it, without the 
	


 	  Quote: 	
		   capacitor, if for some reason the battery    was disconnected from the 

 system while the engine was running, with    no capacitor, the engine will 

 quit, while with it, it will keep    running. 	
 The charging circuit is independent of the  ignition.  It has nothing to do with keeping the engine running. The  capacitor is there to alleviate any spikes from the charging dynamo.  

  	  Quote: 	
		  I was    basically so impressed 
	


 	  Quote: 	
		   by Bob's design approach, which is    essentially:  "if it can break, 

 eventually it will, so either    design a backup or make the system 

 inessential for continued    flight."  I have no problems with any of this 

 stuff, and running    the engine on BATT only is no problem as far as I 

 know.  Bob    would be the guy to ask about this! 	
 The battery is not needed to keep the engine  running.

  	  Quote: 	
		  
	


 	  Quote: 	
		      

 Jack

	
 
	


  

  [quote][b]

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Gilles.Thesee(at)ac-greno
Guest

Posted: Thu Feb 15, 2007 1:40 am Post subject: Capacitor

NYTerminat(at)aol.com a écrit :

 	  Quote: 	
		   *e ignition.  It has nothing to do with keeping the engine running. 

 The capacitor is there to alleviate any spikes from the charging dynamo. *



     ...



 *The battery is not needed to keep the engine running.*

Hi all,
	




True for the 912 and 912S, but the Rotax 914 is electrically dependant, 

and does need an electrical source to keep the engine running.

One needs two independant electrical sources to have a reasonable engine 

redundancy.



At the time, I made some lengthy experiments with the Rotax alternator 

and regulator. The capacitor is definitely needed to ensure proper 

working of the regulator.

Some info here :

http://contrails.free.fr/elec_ducati_en.php



The main failure mode for the regulator, is from to high current draw. 

It does seem reasonable to expect more than about 12 amps continuous.

The regulator doesn't come to life if a sufficient voltage is not 

applied to the sense wire, or if the alternator stalls, and the battery 

or regulator is depleted.



As already stated, Bob Nuckolls has designed remarkable circuits for the 

Rotax installation, including OV protection, which I think is a must 

because of the miserable service record of the Rotax regulator.

Due to its shortcomings, I ended up bench testing and installing a 

Schicke GR 4 regulator.



Regards,

Gilles Thesee

http://contrails.free.fr

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Gilles.Thesee(at)ac-greno
Guest

Posted: Fri Feb 16, 2007 2:41 pm Post subject: Capacitor

Max,

 	  Quote: 	
		    



 The Ducati regulator is fairly simple


	


As you know, our perception of the working of the regulator is not 

similar to yours.

It took us several bench test sessions to get a clear notion.

Is your opinion based on data we are not aware of, or did you make 

deductions from existing data ?

 	  Quote: 	
		  

 On the other hand, moving the capacitor behind the battery

 switch might slowly burn the switch or relay with its 

 inrush current.

   


	




Not sure I clearly understand the circuit you are referring to.

Bob Nuckolls' figure Z provides anything that is needed to design a safe 

and efficient Rotax circuit with OV protection, and no damage to the 

ship's circuits, whatever the action on the master switch in flight.

 	  Quote: 	
		   Well, this is a controversial subject, but in my opinion 

 the capacitor is not needed 

   


	




The electricity experts I submitted the regulator to do not agree with 

this statement.

I would be really willing to publish any additional study or data you 

have collected to support this.

 	  Quote: 	
		   Does anybody know if Harley-Davidson uses any capacitor

 in their similar style PM-generator regulator ? 

   


	




You really trying to design your aircraft circuits the Harley-Davidson way ?



Regards,

Gilles

http://contrails.free.fr

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