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Master/Battery/Alt Field vs. Master/Battery and Alt Field.

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nuckolls.bob(at)aeroelect
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Posted: Fri Jul 05, 2013 5:09 am Post subject: Master/Battery/Alt Field vs. Master/Battery and Alt Field.

At 02:16 PM 7/4/2013, you wrote:

 	  Quote: 	
		  



I'm sure I read a discussion of this question somewhere but can't find it.



I'm building an RV-9A, basic day/night VFR. I'm using the Basic 

Day/Night VFR system diagram available from B&C website. It is 

almost identical to the Z-11 diagram in Bob's book. One difference 

is that the Z-11 uses a 2 poll 3-throw switch (2-10) for the master, 

so that the alternator can be switched on after start. The Basic VFR 

diagram from B&C uses a 2 poll 2 throw switch (2-3) so that the 

alternator field is on during start.



What are the advantages of isolating the alternator field during 

startup? My airplane has a B&C 40 amp alternator. Which approach 

would you recommend?


	


   None. The choice of switches depends on

   how you plan to disable the alternator during

   battery only operations. If you have a field

   supply breaker that can be pulled, then the

   simple 2 pole, 2 throw switch is fine. If

   you've gone the crowbar ov protection route

   then the breaker should be present.



   Alternatively, the 3-position switch duplicates

   the legacy control philosophy that allows a

   battery to be turned on without the alternator . . .

   like the split rocker switch.



   Bob . . .

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mburbidg(at)gmail.com
Guest

Posted: Fri Jul 05, 2013 8:34 am Post subject: Master/Battery/Alt Field vs. Master/Battery and Alt Field.

I'm using the LR3C-14 external regulator and fuse blocks from B&C. My field supply includes a fuse in my fuse block but I cannot pull the fuse during flight.

It sounds like I should either move the field supply to a breaker on the panel that I can pull, or use the 3-position switch.

Another question. All of my 250 hours of flight are in a 1959 C172, which has a generator. There is a master switch with two positions. My question is under what conditions would one operate "battery only"?

Thanks for the help,

Michael-

On Jul 5, 2013, at 6:08 AM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:

 	  Quote: 	

 At 02:16 PM 7/4/2013, you wrote:

> 

> 

> I'm sure I read a discussion of this question somewhere but can't find it.

> 

> I'm building an RV-9A, basic day/night VFR. I'm using the Basic Day/Night VFR system diagram available from B&C website. It is almost identical to the Z-11 diagram in Bob's book. One difference is that the Z-11 uses a 2 poll 3-throw switch (2-10) for the master, so that the alternator can be switched on after start. The Basic VFR diagram from B&C uses a 2 poll 2 throw switch (2-3) so that the alternator field is on during start.

> 

> What are the advantages of isolating the alternator field during startup? My airplane has a B&C 40 amp alternator. Which approach would you recommend?

  None. The choice of switches depends on

  how you plan to disable the alternator during

  battery only operations. If you have a field

  supply breaker that can be pulled, then the

  simple 2 pole, 2 throw switch is fine. If

  you've gone the crowbar ov protection route

  then the breaker should be present.

  Alternatively, the 3-position switch duplicates

  the legacy control philosophy that allows a

  battery to be turned on without the alternator . . .

  like the split rocker switch.

  Bob . . .

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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