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Primary and B/U Alt Fields on Master Bus

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Bud K

Joined: 11 May 2021
Posts: 2
Location: Table Rock Lake MO

Posted: Wed May 12, 2021 6:18 pm Post subject: Primary and B/U Alt Fields on Master Bus

I am planning an avionics upgrade on an RV-4.  The airplane currently has and SD-8 back up dynamo as well as an internally regulated alternator. I plan on installing a Garmin GPS175 and heated pitot and a Dynon Skyview to allow me to fly IFR.  I am planning to rearchitect the electrical system as part of the upgrade.  I plan on implementing an Essential Bus architecture similar to figure Z-12, dual alternator, single battery. 



Question #1. Why are both the primary and B/U alternator fields powered by the master bus? Wouldn't it be prudent to power at least the B/U alternator field from the E-bus in case you have to shut down the Master bus, thereby disabling both alternators? I know that the SD-8 can be 'self exciting', however, if it is not, the B/U alternator would be shut down. 



Question #2. Shouldn't the B/U alternator B lead go the battery side of the Battery Contactor as opposed to master bus side? Wouldn't that charge the battery partially offsetting the power draw from E-bus devices.

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_________________
Bud
RV-4

art(at)zemon.name
Guest

Posted: Wed May 12, 2021 7:42 pm Post subject: Primary and B/U Alt Fields on Master Bus

Bud,

It sounds like you are building an airplane with a panel much like I put into my BD-4C. I have MGL instead of Dynon but also used the GPS175 and have a heated pitot tube. I started out planning to implement an essential bus, as you described, until I did my electrical load analysis. I have a B&C standby alternator which provides about 30 amps when the engine is at cruise RPM. It turns out that that is sufficient to run everything in the airplane except the pitot heat and the autopilot servos.

Were I to lose the primary alternator in IMC, the battery could easily carry the load which the standby alternator could not cover until I reached VMC and could turn off the pitot heat. Autopilot is optional anyway. That means that, even without the essential bus, a primary alternator failure is almost a non-event.

That realization made my electrical system much simpler.

Can you upgrade your SD-8 to a bigger standby alternator?

    -- Art Z.

On Wed, May 12, 2021 at 9:31 PM Bud K <budkeil(at)gmail.com (budkeil(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "Bud K" <budkeil(at)gmail.com (budkeil(at)gmail.com)>

 

 I am planning an avionics upgrade on an RV-4.  The airplane currently has and SD-8 back up dynamo as well as an internally regulated alternator. I plan on installing a Garmin GPS175 and heated pitot and a Dynon Skyview to allow me to fly IFR.  I am planning to rearchitect the electrical system as part of the upgrade.  I plan on implementing an Essential Bus architecture similar to figure Z-12, dual alternator, single battery. 	


-- 

https://CheerfulCurmudgeon.com/Friendship is like a stone. A stone has no value, but when you rub two stones together properly, sparks of fire emerge. 

Rabbi Mordechai of Lechovitz

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Bud K

Joined: 11 May 2021
Posts: 2
Location: Table Rock Lake MO

Posted: Thu May 13, 2021 4:28 am Post subject: Re: Primary and B/U Alt Fields on Master Bus

Art, 

Yes I could upgrade to a larger, pad mounted alternator but would rather use what I have.  I recognize the added expense and complexity of going the e-bus route.  And yes, that pitot heat power is over half of my e-bus load.  I don't see myself continuing to fly in IMC with a primary system failure and would head to VMC ASAP.



Since your B/U alternator has the capacity, did you implement the e-bus architecture or put everything on a main bus?

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_________________
Bud
RV-4

art(at)zemon.name
Guest

Posted: Thu May 13, 2021 1:45 pm Post subject: Primary and B/U Alt Fields on Master Bus

Bud,

I put everything on one bus except a couple of tiny loads which are attached to a small always-on bus. Here are all of my wiring diagrams. The file 



[img]https://drive-thirdparty.googleusercontent.com/16/type/application/pdf[/img] engine.pdf

 is the one that has the bus architecture and the alternators.

Cheers,

    -- Art Z.

On Thu, May 13, 2021 at 7:40 AM Bud K <budkeil(at)gmail.com (budkeil(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "Bud K" <budkeil(at)gmail.com (budkeil(at)gmail.com)>

 

 Art, 

 Yes I could upgrade to a larger, pad mounted alternator but would rather use what I have.  I recognize the added expense and complexity of going the e-bus route.  And yes, that pitot heat power is over half of my e-bus load.  I don't see myself continuing to fly in IMC with a primary system failure and would head to VMC ASAP.

 

 Since your B/U alternator has the capacity, did you implement the e-bus architecture or put everything on a main bus?

	


-- 

https://CheerfulCurmudgeon.com/Friendship is like a stone. A stone has no value, but when you rub two stones together properly, sparks of fire emerge. 

Rabbi Mordechai of Lechovitz

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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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nuckolls.bob(at)aeroelect
Guest

Posted: Thu May 13, 2021 7:36 pm Post subject: Primary and B/U Alt Fields on Master Bus

At 09:19 PM 5/12/2021, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Bud K" <budkeil(at)gmail.com>



 I am planning an avionics upgrade on an RV-4.  The airplane currently has and SD-8 back up dynamo as well as an internally regulated alternator. I plan on installing a Garmin GPS175 and heated pitot and a Dynon Skyview to allow me to fly IFR.  I am planning to rearchitect the electrical system as part of the upgrade.  I plan on implementing an Essential Bus architecture similar to figure Z-12, dual alternator, single battery. 



 Question #1. Why are both the primary and B/U alternator fields powered by the master bus? Wouldn't it be prudent to power at least the B/U alternator field from the E-bus in case you have to shut down the Master bus, thereby disabling both alternators? I know that the SD-8 can be 'self exciting', however, if it is not, the B/U alternator would be shut down. 



 Question #2. Shouldn't the B/U alternator B lead go the battery side of the Battery Contactor as opposed to master bus side? Wouldn't that charge the battery partially offsetting the power draw from E-bus devices.

 	


   My apologies, I got some replies mistaken

   for queries. Scratch my recent post to the

   thread.



   If you're running an SD-8 aux alternator,

   you need to be looking at Z-13.



 

 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

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ashleysc(at)broadstripe.n
Guest

Posted: Fri May 14, 2021 8:07 am Post subject: Primary and B/U Alt Fields on Master Bus

Hi Art;

Great electrical drawing and parts list. I haven't analyzed it, but very professionally done.

Cheers!   Stu.

From: "Art Zemon" <art(at)zemon.name>

To: aeroelectric-list(at)matronics.com

Sent: Thursday, May 13, 2021 2:43:52 PM

Subject: Re: Re: Primary and B/U Alt Fields on Master Bus

Bud,

I put everything on one bus except a couple of tiny loads which are attached to a small always-on bus. Here are all of my wiring diagrams. The file 

[img]https://drive-thirdparty.googleusercontent.com/16/type/application/pdf[/img] engine.pdf

 is the one that has the bus architecture and the alternators.

Cheers,

    -- Art Z.

On Thu, May 13, 2021 at 7:40 AM Bud K <budkeil(at)gmail.com (budkeil(at)gmail.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: "Bud K" <budkeil(at)gmail.com (budkeil(at)gmail.com)>

 Art, 

 Yes I could upgrade to a larger, pad mounted alternator but would rather use what I have.  I recognize the added expense and complexity of going the e-bus route.  And yes, that pitot heat power is over half of my e-bus load.  I don't see myself continuing to fly in IMC with a primary system failure and would head to VMC ASAP.

 Since your B/U alternator has the capacity, did you implement the e-bus architecture or put everything on a main bus?

-- 

https://CheerfulCurmudgeon.com/Friendship is like a stone. A stone has no value, but when you rub two stones together properly, sparks of fire emerge. 

Rabbi Mordechai of Lechovitz

- 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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