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PM Alternator filter Capacitor - best practices

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Aug 01, 2012 2:23 pm Post subject: PM Alternator filter Capacitor - best practices

At 04:57 PM 8/1/2012, you wrote:

  	  Quote: 	
		   What would be considered best practice for installation of the large electrolytic capacitor used to filter the output of a PM alternator:

  

 Mount it on the hot side of the firewall and protect the occupants

  

 Mount it on the cool side of the firewall and protect the capacitor

  

 Would appreciate any speculations, -john-

 	


   It's utility is limited. See in particular,

   the second page of 



  http://tinyurl.com/cz7ekrf



   even with no capacitor, the noises are

   well under Mil-STD-704 limits for DC

   power systems. So mounting it 'cool'

   probably bodes best for service life

   and has little effect on system

   performance.



 

 

   Bob . . .    [quote][b]

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jloram

Joined: 07 Nov 2009
Posts: 54
Location: United States

Posted: Wed Aug 01, 2012 3:47 pm Post subject: PM Alternator filter Capacitor - best practices

Hmmmm... so why do we use this cap?

  

 -john-

  



 [quote]         From:    owner-aeroelectric-list-server(at)matronics.com    [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of    Robert L. Nuckolls, III

Sent: Wednesday, August 01, 2012 3:23    PM

To: aeroelectric-list(at)matronics.com

Subject: Re:    PM Alternator filter Capacitor - best    practices

   

At 04:57 PM 8/1/2012, you wrote:

    	  Quote: 	
		  What would be considered best practice for      installation of the large electrolytic capacitor used to filter the output      of a PM alternator:

 

Mount it on the hot side of the firewall and protect      the occupants

 

Mount it on the cool side of the firewall and      protect the capacitor

 

Would appreciate any speculations,    -john-

	


  It's utility is limited. See in    particular,

  the second page of 



http://tinyurl.com/cz7ekrf



  even with no    capacitor, the noises are

  well under Mil-STD-704 limits for    DC

  power systems. So mounting it 'cool'

  probably bodes    best for service life

  and has little effect on system

     performance.

   

  Bob . . .  	  Quote: 	
		  



href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-List

href="http://forums.matronics.com">http://forums.matronics.com

href="http://www.matronics.com/contribution">http://www.matronics.com/c

	
[b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Aug 02, 2012 4:28 am Post subject: PM Alternator filter Capacitor - best practices

At 10:18 PM 8/1/2012, you wrote:



So we're not trying to control the bandwidth of the regulator loop 

with the cap? Does the battery do that? Guess I don't really know 

what the frequency response of a lead-acid battery is. Probably 

dependent on the state of charge and the condition of the battery. 

And the load varies all over the place, both real and imaginary 

components.... What would it look like with and without the cap if 

the battery were out of the loop? ... Scary!



http://tinyurl.com/bqa6q9p



   Finely tuned loop dynamics with these regulators is wishful

   thinking. Here's an exemplar schematic for a PM regulator:



http://tinyurl.com/bwomjjz



   I split out the two functions (regulation and

   warning light)



http://tinyurl.com/c8usyw2



http://tinyurl.com/c6doa97



   As you can see in the v-reg schematic,

   there are no reactive components that

   would shape closed-loop response. A battery

   is a very poor 'filter' . . . it delivers

   energy at 12.5 and below . . . accepts

   energy at 13.8 and above. That's about

   1.3 volts of span where the battery is

   dynamically 'unhooked'.



   It stands to reason that the capacitor

   would have the greatest effect when the

   alternator set point was too low (under

   14.5) and the system was lightly loaded.



I'm running 3 phase (old Jab 3300).



   Interesting. I think your regulator is

   still quite similar . . . it just adds

   another diode/scr pair.



Once I get this thing fired up I'll run some tests and let you know 

what happens...



   I have a fast switching, dynamic load bank

   I built for tests at HBC some years back.

   It would be interesting to use it along

   with a data acquisition system on the

   test bench to explore the closed loop

   response of these systems.



Just thinking out loud, -john-



p.s. ran into a message the other day that you wrote back in 2007. 

Said you worked for H.L Yoh as a civilian instructor in the early 

60's... Same here! At the Naval ETA school on Treasure Island. Wasn't 

that fun. I learned more electronics in six months instructing those 

kids than four years of collage!



   You got that right! I was teaching in the

   top 4 weeks of a 26 week school at Great

   Lakes. I went to work on a Friday and they

   handed me a syllabus for my first section

   of students along with a copy of "the bible",

   Termnan's Electrical Engineering Handbook



http://tinyurl.com/cbvvjx9



   and said, "you get your first class of 20

   next Monday." As long as I stayed a day ahead

   of the class . . . things went well . . .

   and yes, a lot of fun. After four or

   so passes through the class materials and

   figuring out a half dozen ways to explain each

   concept, it sorta creeps into your DNA. There's

   no better way to learn something than to

   be chartered to teach it.



   Do you have access to a fast data acquisition

   system that you could hook to your bus for

   some hard data gathering?



   I've used cousins to this critter . . .



http://tinyurl.com/3jtrxx4



   on several tasks at HBC with great results.

   Being able to jump on an airplane and get

   hard data in flight without having to involve

   a dozen folks from the instrumentation lab

   was a powerful tool.



   You might consider getting one of these

   and use it to graph some of the performance

   qualities of your system. It would be a great

   augmentation of my ripple studies.

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Aug 02, 2012 4:28 am Post subject: PM Alternator filter Capacitor - best practices

At 10:18 PM 8/1/2012, you wrote:



So we're not trying to control the bandwidth of the regulator loop 

with the cap? Does the battery do that? Guess I don't really know 

what the frequency response of a lead-acid battery is. Probably 

dependent on the state of charge and the condition of the battery. 

And the load varies all over the place, both real and imaginary 

components.... What would it look like with and without the cap if 

the battery were out of the loop? ... Scary!



http://tinyurl.com/bqa6q9p



   Finely tuned loop dynamics with these regulators is wishful

   thinking. Here's an exemplar schematic for a PM regulator:



http://tinyurl.com/bwomjjz



   I split out the two functions (regulation and

   warning light)



http://tinyurl.com/c8usyw2



http://tinyurl.com/c6doa97



   As you can see in the v-reg schematic,

   there are no reactive components that

   would shape closed-loop response. A battery

   is a very poor 'filter' . . . it delivers

   energy at 12.5 and below . . . accepts

   energy at 13.8 and above. That's about

   1.3 volts of span where the battery is

   dynamically 'unhooked'.



   It stands to reason that the capacitor

   would have the greatest effect when the

   alternator set point was too low (under

   14.5) and the system was lightly loaded.



I'm running 3 phase (old Jab 3300).



   Interesting. I think your regulator is

   still quite similar . . . it just adds

   another diode/scr pair.



Once I get this thing fired up I'll run some tests and let you know 

what happens...



   I have a fast switching, dynamic load bank

   I built for tests at HBC some years back.

   It would be interesting to use it along

   with a data acquisition system on the

   test bench to explore the closed loop

   response of these systems.



Just thinking out loud, -john-



p.s. ran into a message the other day that you wrote back in 2007. 

Said you worked for H.L Yoh as a civilian instructor in the early 

60's... Same here! At the Naval ETA school on Treasure Island. Wasn't 

that fun. I learned more electronics in six months instructing those 

kids than four years of collage!



   You got that right! I was teaching in the

   top 4 weeks of a 26 week school at Great

   Lakes. I went to work on a Friday and they

   handed me a syllabus for my first section

   of students along with a copy of "the bible",

   Termnan's Electrical Engineering Handbook



http://tinyurl.com/cbvvjx9



   and said, "you get your first class of 20

   next Monday." As long as I stayed a day ahead

   of the class . . . things went well . . .

   and yes, a lot of fun. After four or

   so passes through the class materials and

   figuring out a half dozen ways to explain each

   concept, it sorta creeps into your DNA. There's

   no better way to learn something than to

   be chartered to teach it.



   Do you have access to a fast data acquisition

   system that you could hook to your bus for

   some hard data gathering?



   I've used cousins to this critter . . .



http://tinyurl.com/3jtrxx4



   on several tasks at HBC with great results.

   Being able to jump on an airplane and get

   hard data in flight without having to involve

   a dozen folks from the instrumentation lab

   was a powerful tool.



   You might consider getting one of these

   and use it to graph some of the performance

   qualities of your system. It would be a great

   augmentation of my ripple studies.

   Bob . . .

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Tundra10

Joined: 14 Jun 2010
Posts: 102
Location: Scarborough, Ontario

Posted: Thu Aug 02, 2012 7:55 am Post subject: Re: PM Alternator filter Capacitor - best practices

So should the capacitor and 1K resistor be deleted from Z13/8 ?



Note 20 indicates the purpose of the capacitor is to smooth the voltage if the battery is offline.  However, there is no intentional way of disconnecting the battery, and there are very few failures that could result in the battery being disconnected while the SD-8 still remains connected to the battery bus.



In Z13/8 the SD-8 is only turned on in the event of a main alternator failure.  Maybe in this circumstance, a little noise in the audio is not significant to the completion of the flight (assuming the capacitor actually helps in a given installation).



Jeff Page

Dream Aircraft Tundra #10

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jloram

Joined: 07 Nov 2009
Posts: 54
Location: United States

Posted: Thu Aug 02, 2012 3:08 pm Post subject: PM Alternator filter Capacitor - best practices

Thank you for the schematics. Most instructive!



 	  Quote: 	
		  

 p.s. ran  into a message the other day that you wrote back in 2007.

 Said you  worked for H.L Yoh as a civilian instructor in the

 early 60's... Same  here! At the Naval ETA school on Treasure

 Island. Wasn't that fun. I  learned more electronics in six

 months instructing those kids than four  years of collage!



    You got that right! I was  teaching in the

    top 4 weeks of a 26 week school at  Great

    Lakes. I went to work on a Friday and  they

    handed me a syllabus for my first  section

    of students along with a copy of "the  bible",

    Termnan's Electrical Engineering  Handbook



 http://tinyurl.com/cbvvjx9


	


And   thank you for Villard's Memoir. I loved reading every bit of it! 

Like every self-respecting EE I have kept my copy of Terman.



[img]cid:229104122(at)02082012-1950[/img] 



 	  Quote: 	
		  

    and said, "you get your first class of  20

    next Monday." As long as I stayed a day  ahead

    of the class . . . things went well . .  .

    and yes, a lot of fun. After four  or

    so passes through the class materials  and

    figuring out a half dozen ways to explain  each

    concept, it sorta creeps into your DNA.  There's

    no better way to learn something than  to

    be chartered to teach it.

 

And in every other class you'd get one  'ringer'. A kid fresh out of engineering school who would nail you to the chalk  board at the slightest slip-up!!! You either got those guys on your side right  away or you were in for some tough sledding! 
	




 	  Quote: 	
		      Do you have  access to a fast data acquisition

    system that you  could hook to your bus for

    some hard data  gathering?



    I've used cousins to this critter .  . .



 http://tinyurl.com/3jtrxx4


	


[img]cid:229104122(at)02082012-1957[/img] I have a couple of these first generation  DI-148Us.

 It will run at 11 KHz sampling rate on one  channel.

  

 Tell me more about your dynamic load bank.  Sounds like just the ticket.

 



 	  Quote: 	
		  ...

    You might consider getting one of  these

    and use it to graph some of the  performance

    qualities of your system. It would be a  great

    augmentation of my ripple  studies.

    Bob . . .



 

I'd be happy to contribute!  
	


I'm probably a month away from first start and  another month coming down off the high!!,  -john-

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