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Newbie with PM alternator feed question

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jun 12, 2015 8:23 pm Post subject: Newbie with PM alternator feed question

 	  Quote: 	
		  

  	  Quote: 	
		  Trying to sort things out as I proceed and appreciate this forum and your literature! 	


   Pleased that you find it useful. I need to take

   care of some other pressing business. I'll see if I

   can sketch a diagram of what I've described above

   and post it later today.

 	


   I've posted a drawing that describes on/off control

   of a 3-phase PM alternator with Over Voltage Protection



  http://tinyurl.com/n9tottf



 



 

   Bob . . .    [quote][b]

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blues750

Joined: 06 Jun 2015
Posts: 56

Posted: Sat Jun 13, 2015 8:40 am Post subject: Re: Newbie with PM alternator feed question

Bob,



I thank you very much!  Will review/study and see what I can do.  Meanwhile, I continue to dig into my favorite book this year... 12th Ed AeroElectric Connection



Dave

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blues750

Joined: 06 Jun 2015
Posts: 56

Posted: Mon Aug 10, 2015 2:59 pm Post subject: Re: Newbie with PM alternator feed question

Follow on questions...



Having trouble reconciling the tinyurl link wiring that you posted versus the wiring diagram for the B&C OVPM package (505-500) I planned on using.  Appear to be only one relay to control on/off of the alternator via the capacitor and R/R versus your sketch with two relays for two of three phases.  Also, why the need to fuse each phase of the alternator prior to the R/R as depicted in the B&C diagram?  I feel like I'm missing parts of the big picture   



Thanks for indulging my queries!



Dave

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user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Aug 10, 2015 4:59 pm Post subject: Re: Newbie with PM alternator feed question

Bob's drawing uses two relays because they switch the AC from the dynamo.  B&C uses only one relay because it switches the rectified DC.  Either way will work.

  It is not a good idea to put fuses or circuit breakers in series.  The B&C drawing has 3 in series: the 40 amp battery fuse, the 30 amp breaker, and the 20 amp fuses.  A short circuit that trips the 30 amp breaker is likely to also blow the 40 amp fuse.  Not only would dynamo power be lost, but also the battery.

  The 20 amp fuses are not necessary because dynamo current is self limiting.  What really needs protection are the dynamo wires and aircraft battery.  The 30 amp breaker satisfies that requirement in the B&C drawing, as does the 40 amp fuse in Bob's drawing.

Joe

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Joe Gores

blues750

Joined: 06 Jun 2015
Posts: 56

Posted: Mon Aug 10, 2015 5:37 pm Post subject: Re: Newbie with PM alternator feed question

 	  user9253 wrote: 	
		  Bob's drawing uses two relays because they switch the AC from the dynamo.  B&C uses only one relay because it switches the rectified DC.  Either way will work.

  It is not a good idea to put fuses or circuit breakers in series.  The B&C drawing has 3 in series: the 40 amp battery fuse, the 30 amp breaker, and the 20 amp fuses.  A short circuit that trips the 30 amp breaker is likely to also blow the 40 amp fuse.  Not only would dynamo power be lost, but also the battery.

  The 20 amp fuses are not necessary because dynamo current is self limiting.  What really needs protection are the dynamo wires and aircraft battery.  The 30 amp breaker satisfies that requirement in the B&C drawing, as does the 40 amp fuse in Bob's drawing.

Joe 	




Thanks Joe...



(1) Is dynamo current "self limiting" a characteristic of all 3 phase PM type alternators? (dynamos?)  Would gladly eliminate those three 20 amp c/b's if not required!



(2) Was planning on a 40A ANL type fuse for the 10 ga wire from the relay to the primary bus.



(3)  Was not planning on fuse/circuit protection from the battery to the primary bus.



Appreciate all thoughts and input.  I hope to post my schematic as an attachment as soon as I have an idea of what I'm doing  



Dave

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user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Aug 10, 2015 6:43 pm Post subject: Re: Newbie with PM alternator feed question

All alternators and dynamos are self current limiting.  They can only do so much work.  If loaded to much more than their rated capacity, the voltage will start to drop.  Another concern is heat.  If fully loaded, an alternator could get too hot if not adequately ventilated.

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Joe Gores

blues750

Joined: 06 Jun 2015
Posts: 56

Posted: Tue Oct 13, 2015 10:40 am Post subject: Re: Newbie with PM alternator feed question

[quote="nuckolls.bob(at)aeroelect"] 	  Quote: 	
		  

  	  Quote: 	
		  Trying to sort things out as I proceed and appreciate this forum and your literature! 	


   Pleased that you find it useful. I need to take

   care of some other pressing business. I'll see if I

   can sketch a diagram of what I've described above

   and post it later today.

 	


   I've posted a drawing that describes on/off control

   of a 3-phase PM alternator with Over Voltage Protection



  http://tinyurl.com/n9tottf



 

Bob,



After doing a more detailed electrical load budget / requirements study, it looks like it will really be near the limits of the 30A rated PMA I currently have in my build.  I am considering increasing the 30A PMA to a 50A PMA by changing to a 50A alternator stator the company has available.  With that in mind, what do I need to do with the components on the drawing you provided earlier.  Do I need to spec different relays or capacitor?  Any other considerations? Your thoughts and insight will be much appreciated



Thanks!



Dave

 

   Bob . . .     	  Quote: 	
		  [b]

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