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Why3 different alt disconnect relay wiring in Z schematics

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Aug 13, 2009 3:32 pm Post subject: Why3 different alt disconnect relay wiring in Z schematics

At 12:02 PM 8/13/2009, you wrote:

 	  Quote: 	
		  



Here are the links to the schematics:



http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z16M.pdf


	


   The preferred methodology for PM alernator control assuming

   you're NOT depending on the AC output waveform to drive

   an engine tachometer as shown in . . .



http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z20L.pdf



   where we see the AC windings permanently connected

   to the rectifier/regulator. Here, alternator control reverts

   to the older philosophy of opening the DC power output

   lead from the R/R.  Z20L.pdf had been plotted but not uploaded

   to the server. Z20K.dwg was still up and needed deletion.

   Must have been one of those late night deals . . .



   Note that Z-21 was a special adaptation to accommodate

   electronic controlled fuel injection . . .



   further, it suggests a means by which alternator control

   relay power to energize can come from either the battery

   or the alternator.



 	  Quote: 	
		  http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z21A.pdf


	


   Any of these drawings will perform as advertised and should

   be applied pending a match of your design goals and installed

   equipment with the matching Z-figure.

        Bob . . .



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

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

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messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Fri Aug 14, 2009 12:58 pm Post subject: Re: Why3 different alt disconnect relay wiring in Z schema

Thanks, Bob 



 	  Quote: 	
		  The preferred methodology for PM alernator control... 	




I understand that you prefer this method, but I don't know why. 



Are you saying it's better to place the alt disconnect AFTER the regulator (as in Z-20 and Z-21) than BETWEEN the alternator and regulator (as in Z-16)? I had heard disconnecting a PM regulator wired with the relay after the the regulator could damage the regulator. You would want a failed regulator disconnected, but what would happen if a good regulator were taken offline?



Also, if the regulator fails and is taken offline by a relay placed after the regulator, could the failed regulator present a fire hazard by continuing to heat up from the uninterrupted supply of power to it from the alternator? If so, could a relay placed between the alternator and regulator, instead of after the regulator, cut the power to the failed regulator and prevent this?



 



 	  Quote: 	
		  ...assuming you're NOT depending on the AC output waveform to drive 

an engine tachometer 	




I don't know if I need the AC waveform for the tach or not. The Jabiru manual shows a magnetic sensor plugged into a tach sensor tab on the engine. 2 leads go from there to the tach gauge on the panel. I don't know if I have this sensor or sendor.



If I don't have it or can't get it, then I suppose I would need to use one of the alternator AC leads. Is one method preffered over the other?



And Z-20L shows a wire spliced into one of the alternator output leads going to the tach. So if I do need an AC lead, why wouldn't this work in Z-20L?



 	  Quote: 	
		  ... Z-21 . . .  suggests a means by which alternator control 

relay power to energize can come from either the battery 

or the alternator. 	




I don't understand how this works and why this is an advantage.

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_________________
Dan

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Aug 14, 2009 5:10 pm Post subject: Why3 different alt disconnect relay wiring in Z schematics

At 03:58 PM 8/14/2009, you wrote:

 	  Quote: 	
		  



Thanks, Bob 

 > The preferred methodology for PM alernator control...

I understand that you prefer this method, but I don't know why.


	


   Because it totally removes the alternator's ability

   to deliver power by breaking the AC output power

   leads. Breaking the DC power output lead will not

   allow you to disconnect the alternator from a shorted

   rectifier regulator thus putting the alternator at-risk

   for second-failure follwing a regulator failure.



 	  Quote: 	
		  Are you saying it's better to place the alt disconnect AFTER the 

regulator (as in Z-20 and Z-21) than BETWEEN the alternator and 

regulator (as in Z-16)?


	


   No, directly in the AC output lead . . . but if

   your tachometer depends on the AC frequency

   signature of the alternator for measuring

   engine speed, then you can't put the disconnect

   at the preferred point.



 	  Quote: 	
		    I had heard disconnecting a PM regulator wired with the relay 

 after the the regulator could damage the regulator.


	


   Some regulators may indeed be at risk if the system

   is operating unloaded  . . . but I doubt it. It's

   a voltage rating issue for the semiconductors inside

   the regulator. It's not a big deal to craft a rectifier

   regulator tolerant of unloaded, full speed operations.



   The two designs for PM regulators that I participated

   in were NOT at risk for no-load, hi-speed ops.

 	  Quote: 	
		    You would want a failed regulator disconnected, but what would 

 happen if a good regulator were taken offline?


	


   If the regulator is designed to live in the world

   to which it's sold, then it shouldn't be a problem.

   It's easy to do, it's what we did, but I can't speak

   for others. Disconnecting the AC input lead is, therefore,

   the preferred, low-risk philosophy for ALL regulators.



 	  Quote: 	
		  Also, if the regulator fails and is taken offline by a relay placed 

after the regulator, could the failed regulator present a fire 

hazard by continuing to heat up from the uninterrupted supply of 

power to it from the alternator? If so, could a relay placed between 

the alternator and regulator, instead of after the regulator, cut 

the power to the failed regulator and prevent this?


	


   No fire risk. You might burn some alternator wires

   but this isn't inherently hazardous beyond damage

   to the alternator itself. If your tachometer doesn't

   require a signal from the alternator, go with  Z-16.



   Bob . . .

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messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Fri Aug 14, 2009 6:22 pm Post subject: Re: Why3 different alt disconnect relay wiring in Z schema

 	  Quote: 	
		  The preferred methodology for PM alernator control assuming 

you're NOT depending on the AC output waveform to drive 

an engine tachometer as shown in http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z20L.pdf where we see the AC windings permanently connected 

to the rectifier/regulator. Here, alternator control reverts 

to the older philosophy of opening the DC power output 

lead from the R/R. 



....Thanks, Bob  

> The preferred methodology for PM alernator control... 

I understand that you prefer this method, but I don't know why....... 

 



......Because it totally removes the alternator's ability 

to deliver power by breaking the AC output power leads.

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_________________
Dan

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Fri Aug 14, 2009 6:35 pm Post subject: Re: Why3 different alt disconnect relay wiring in Z schema

 	  Quote: 	
		  The preferred methodology for PM alernator control assuming 

you're NOT depending on the AC output waveform to drive 

an engine tachometer as shown in http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z20L.pdf where we see the AC windings permanently connected 

to the rectifier/regulator. Here, alternator control reverts 

to the older philosophy of opening the DC power output 

lead from the R/R. 



....Thanks, Bob 

> The preferred methodology for PM alernator control... 

I understand that you prefer this method, but I don't know why....... 

......Because it totally removes the alternator's ability 

to deliver power by breaking the AC output power leads. 	




Sorry about double posting. Meant to hit the preview button 



It seemed to me you were saying the Z-20 method of breaking the DC leads was best, but now I see you mean breaking AC is best, like in Z-16.



So even if I ran the tachometer off the AC leads, I'd only have no tach when the alternator is offline. I haven't seen the tachometer show up on anybody's Ebus list, so going with the preferred AC disconnect might be better even in this situation.

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