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Z-16 OV simplification ?

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rv8ch

Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

Posted: Sun Jun 18, 2006 10:06 pm Post subject: Z-16 OV simplification ?

 	  Quote: 	
		   A buddy homebuilder, who does research in electricity, finds the OV 

 protection in figure Z-16 somewhat complex, and advocates using a simple 

 component similar to a Zener to prevent overvoltage.

 

 Any comment or opinion on the pros and cons, or hidden issues ?


	


Eric sells a device for this purpose:



  http://www.periheliondesign.com/suppressors.htm



I've got one, but I also have OV protection to

try to cut off the alternator so it doesn't just

keep putting out energy.



-- 

Mickey Coggins

http://www.rv8.ch/

#82007 finishing

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_________________
Mickey Coggins
http://www.rv8.ch/

Gilles.Thesee(at)ac-greno
Guest

Posted: Mon Jun 19, 2006 1:26 am Post subject: Z-16 OV simplification ?

Hi Mickey,

 	  Quote: 	
		  



 I've got one, but I also have OV protection to

 try to cut off the alternator so it doesn't just

 keep putting out energy.



What are the advantages of one over the other ?
	


And what is the point of having both ?



Thanks,



Regards,

Gilles

http://contrails.free.fr

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khorton01(at)rogers.com
Guest

Posted: Mon Jun 19, 2006 2:10 am Post subject: Z-16 OV simplification ?

On 18 Jun 2006, at 21:07, Gilles Thesee wrote:



 	  Quote: 	
		   

 <Gilles.Thesee(at)ac-grenoble.fr>



 Hi Bob and all,



 A buddy homebuilder, who does research in electricity, finds the OV  

 protection in figure Z-16 somewhat complex, and advocates using a  

 simple component similar to a Zener to prevent overvoltage.



 Any comment or opinion on the pros and cons, or hidden issues ?


	


The zener would need to be sized to handle a lot of watts, as it  

would have to dissapate the amperage of the alternator at whatever  

set point the zener had.  How many amps could a 60 amp alternator  

produce, if the voltage regulator failed?  80a?  80a times 16v = 1280  

watts.  How big and expensive is a 16v zener rated for 1280w,  

continuously?  The ones I've found only seem to be rated to handle  

that power level for a very short period.  They don't look beefy  

enough to handle it continuously.



Kevin Horton         RV-8 (finishing kit)

Ottawa, Canada

http://www.kilohotel.com/rv8

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Gilles.Thesee(at)ac-greno
Guest

Posted: Mon Jun 19, 2006 3:03 am Post subject: Z-16 OV simplification ?

Kevin,



Thank you for your message.



 	  Quote: 	
		  

 The zener would need to be sized to handle a lot of watts, as it would 

 have to dissapate the amperage of the alternator at whatever set point 

 the zener had.  How many amps could a 60 amp alternator produce, if 

 the voltage regulator failed?  80a?  80a times 16v = 1280 watts.  How 

 big and expensive is a 16v zener rated for 1280w, continuously?  The 

 ones I've found only seem to be rated to handle that power level for a 

 very short period.  They don't look beefy enough to handle it 

 continuously.

I should have mentionned that the figure Z16 concerns the Rotax PM 
	


alternator. The rated output is in the vicinity of 20 amps.

That's about 300 W for the Zener or whatever takes its place.

Does it look like a more manageable power ?



By the way, it just occurs to me that if you rely on this component only 

to tackle with an OV event, you need some means of alerting the crew of 

the OV condition.



Thanks

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nuckollsr(at)cox.net
Guest

Posted: Mon Jun 19, 2006 7:36 am Post subject: Z-16 OV simplification ?

At 03:07 AM 6/19/2006 +0200, you wrote:



 	  Quote: 	
		  

<Gilles.Thesee(at)ac-grenoble.fr>



Hi Bob and all,



A buddy homebuilder, who does research in electricity, finds the OV 

protection in figure Z-16 somewhat complex, and advocates using a simple 

component similar to a Zener to prevent overvoltage.



Any comment or opinion on the pros and cons, or hidden issues ?


	




   A company called Pelican Aviation proposed this many years ago.

   There's a member of this list who called me one evening to report

   that he'd experienced a problem with the first running of his

   electrical system . . . seems the system suffered an ov event.

   After we discussed the means for deducing and correcting root cause,

   he noted in passing that the "little plastic thing on the back

   of the alternator disappeared". Seems the Pelican supplied zener

   diode from b-lead to ground simply exploded leaving a couple

   of bare wires.



   Yes, if you have a zener diode rated to soak up ALL the excess

   energy available from a runaway alternator, it would be required

   to dissipate say 16v at 60 amps or 960 watts in some aircraft;

   and 16v at 20A (320 watts) in a Rotax system described in Z-16.

   That's a real boss-hog zener. Further, adding such a zener would

   only keep the voltage from rising, it would not SHUT OFF or DISCONNECT

   the offending system.



   Bob . . .

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Gilles.Thesee(at)ac-greno
Guest

Posted: Tue Jun 20, 2006 2:22 pm Post subject: Z-16 OV simplification ?

 	  Quote: 	
		   16v at 20A (320 watts) in a Rotax system described in Z-16.

   That's a real boss-hog zener.

  


	


Bob,



Thank you.

Is the problem the same with a transil ?



Regards,

Gilles

http://contrails.free.fr

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nuckollsr(at)cox.net
Guest

Posted: Tue Jun 20, 2006 7:47 pm Post subject: Z-16 OV simplification ?

At 12:11 AM 6/21/2006 +0200, you wrote:



 	  Quote: 	
		  

<Gilles.Thesee(at)ac-grenoble.fr>

>16v at 20A (320 watts) in a Rotax system described in Z-16.

>   That's a real boss-hog zener.

>



Bob,



Thank you.

Is the problem the same with a transil ?


	


   Yes. TVS, Transorbs, Transil, etc are all cousins of the

   zener diode. They're designed to avalanche (break down)

   when reverse biased and at reasonably calibrated voltages.



   Instead of designing for accuracy and stability as voltage

   regulators, transient catchers are optimized for power and

   speed . . . but they're still linear mode gizmos. So while

   a 1500 watt Transorb is barely larger physically than a

   1N5400 series diode that's rated to dissipate 3A at 0.7 volts

   indefinitely, that's just over two watts.



   Guess what? A 1.5KE series transient suppressor is rated

   for 1500 watts . . . for milliseconds.  See:



http://www.aeroelectric.com/Mfgr_Data/Semiconductors/15ke.pdf



   The operative word for using these devices is "transient" meaning

   relatively short (tens of milliseconds) events. A runaway alternator

   is an all-day event until you get it turned off . . . linear

   voltage clamping devices tied to the output of alternators are

   not OV protection devices.



   They might mitigate load dumps but folks on the list have reported

   problematic results in tests where load dump events trashed

   a Transorb.



   OV protection needs to be discriminating (not to nuisance

   trip on true transient conditions) but they also need

   to have absolute control over the alternator in terms of

   shutting it off.



   Bob . . .



      ---------------------------------------------------------

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

      ---------------------------------------------------------

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Gilles.Thesee(at)ac-greno
Guest

Posted: Wed Jun 21, 2006 2:26 pm Post subject: Z-16 OV simplification ?

 	  Quote: 	
		  

   OV protection needs to be discriminating (not to nuisance

   trip on true transient conditions) but they also need

   to have absolute control over the alternator in terms of

   shutting it off.



  

Bob,
	




Thanks again.



Regards,

Gilles

http://contrails.free.fr

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