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Newbie with PM alternator feed question

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Oct 13, 2015 1:13 pm Post subject: Newbie with PM alternator feed question

 	  Quote: 	
		   

 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! 	


   A FIFTY amp PM alternator?  Drops into the existing

   stator space? What rectifier/regulator do they recommend?



   Forgive my raside eyebrows . . . that's a BIG jump in

   performance . . . which is physically possible

   with bigger magnets, more iron, etc. But to make

   it a drop-in replacement raises some questions.



   Are there links to the company and to any data

   they offer for this 'upgrade'?



   Also, could you share your load analysis with

   us? It would be interesting to see how you've

   walled off the various requirements for the

   alternator-out failure mode.



 

 

   Bob . . .    [quote][b]

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blues750

Joined: 06 Jun 2015
Posts: 56

Posted: Wed Oct 21, 2015 6:14 pm Post subject: Re: Newbie with PM alternator feed question

Bob,



Working on the details with ULPower (the engine manufacturer).  Not so much a concern for my endurance scenarios, but if I want to use everything I'm going to have on the aircraft, (continuous loads), I am in excess of 30 amps.  I have my notes which I will edit a bit and post.  I would very much like some outside review of my "plans" to see if I am on the right track with things...just need a few days to get back into my notes.  Thanks for the interest and patience!



Dave

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Oct 22, 2015 8:00 am Post subject: Newbie with PM alternator feed question

At 09:14 PM 10/21/2015, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "blues750" <den_beaulieu(at)yahoo.com>



 Bob,



 Working on the details with ULPower (the engine manufacturer).  Not so much a concern for my endurance scenarios, but if I want to use everything I'm going to have on the aircraft, (continuous loads), I am in excess of 30 amps.  I have my notes which I will edit a bit and post.  I would very much like some outside review of my "plans" to see if I am on the right track with things...just need a few days to get back into my notes.  Thanks for the interest and patience!



 Dave 	


   Take a look at the documents on the website at:



  http://tinyurl.com/9rt6ymn



   You'll find the load-analsysi work product of

   several List members in Excel spread sheets.

   There is also a blank planning form that I use

   as the FIRST step of planning a new electrical

   system.



   Fill out one page for each bus . . . battery,

   main, e-bus, engine, etc. List the load and

   it's demands under each of the flight conditions.



   I've run load analysis studies on a lot of airplanes,

   one that even included pitot heat STILL came to

   less than 27A for a max continuous running load.



   It's really easy to get bogged down in the notion

   that an alternator be sized to run everything all

   the time . . . 



 

 

   Bob . . .    [quote][b]

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blues750

Joined: 06 Jun 2015
Posts: 56

Posted: Sat Oct 24, 2015 12:26 pm Post subject: Re: Newbie with PM alternator feed question

[quote="nuckolls.bob(at)aeroelect"]At 09:14 PM 10/21/2015, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "blues750" <den_beaulieu>



 Bob,



 Working on the details with ULPower (the engine manufacturer).  Not so much a concern for my endurance scenarios, but if I want to use everything I'm going to have on the aircraft, (continuous loads), I am in excess of 30 amps.  I have my notes which I will edit a bit and post.  I would very much like some outside review of my "plans" to see if I am on the right track with things...just need a few days to get back into my notes.  Thanks for the interest and patience!



 Dave 	


   Take a look at the documents on the website at:



  http://tinyurl.com/9rt6ymn



   You'll find the load-analsysi work product of

   several List members in Excel spread sheets.

   There is also a blank planning form that I use

   as the FIRST step of planning a new electrical

   system.



   Fill out one page for each bus . . . battery,

   main, e-bus, engine, etc. List the load and

   it's demands under each of the flight conditions.



   I've run load analysis studies on a lot of airplanes,

   one that even included pitot heat STILL came to

   less than 27A for a max continuous running load.



Thanks Bob...



    	  Quote: 	
		  It's really easy to get bogged down in the notion

   that an alternator be sized to run everything all

   the time . . . 	
 



I have read that for planning purposes, one should reduce the alternator rating by 20% - with that thought my 30A alternator would nominally be used as a 24A power source for continuous duty.  Yes/no?

 

 

   

...I will do more homework and hopefully present some better, more complete info.  Looking forward to feedback from you and the group!



Dave

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Oct 26, 2015 6:17 am Post subject: Newbie with PM alternator feed question

 	  Quote: 	
		  



 I have read that for planning purposes, one should reduce the alternator rating by 20% - with that thought my 30A alternator would nominally be used as a 24A power source for continuous duty.  Yes/no?

  

  	


   Sortof . . . There's a fundamental notion in 

   aircraft electrical system design that you

   should have enough alternator capacity to

   recharge a largely depleted battery in

   60 minutes of flight. So if you've managed

   to get an engine started after dragging the

   battery down to 20% of capacity -AND- it's

   a 17 a.h. battery, then there should be approx

   9A of 'excess' alternator capacity available

   to recharge a battery. If you've only got 30A

   total, then your full up running load needs

   to be 21A or less.



   For decades, Cessna and contemporaries were

   content to bolt the same 60A alternator to

   all their single engine models . . . which

   generally provided LOTS of excess snort.

   Further, if the battery is maintained/managed

   well -AND- you never launch into IFR -AND-

   your engine always starts in a few blades

   then the rule of thumb for 20% reserve becomes 

   somewhat useless.



   THIS is why airplanes with smaller alternators

   benefit from an accurate load analysis along

   with some judiciously crafted standard operating

   procedures. If you're going to launch IFR then

   KNOWING that your battery capacity is sufficient

   to your battery only endurance goals is pretty

   important you your wife and kids.



  	  Quote: 	
		     

 ..I will do more homework and hopefully present some better, more complete info.  Looking forward to feedback from you and the group! 	


   If you don't have a copy of the 'Connection, you

   can download a .pdf from the website . . . or

   purchase a paper copy there too . . . but given

   the limited capability of your alternator combined

   with the electrically dependent engine, I recommend

   you educate yourself in the finer details of

   energy management for CONFIDANT/COMFORTABLE flight.

   Then sift the pebbles and twigs out with folks here

   on the List . . .



   I looked at the engine website briefly but didn't

   see any mention of a 50A option alternator. Can

   you point me to the information you were offered?



 

   Bob . . .    [quote][b]

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