Matronics Email Lists :: View topic

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

What alternator size

Matronics Email Lists Forum Index -> AeroElectric-List

View previous topic :: View next topic

Author Message

fvalarm(at)rapidnet.net
Guest

Posted: Mon Oct 15, 2012 1:44 pm Post subject: What alternator size

How to choose the correct alt size?



If my theoretical max sustained current draw on the airplane is 35-40 amps,

will a 40 amp B and C alternator be sufficient?  In other words, is there

room to spare or is 40 amps the maximum?  And is this at max engine RPM or

cruise or does it matter?



The majoring of the electrical requirements are for things rarely used such

as pitot heat, strobes, lights etc.  Is it acceptable to use the SD-8 backup

alternator to provide the remaining amps when all those loads are required?



I assume that there needs to be head room so that the battery can re-charge

after a high load event, but I don't know how much this will add to the

total load.



I really don't want a 60 amp alternator if a 40 will suffice without any

significant downsides as the weight savings is significant.



Bevan

- 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:

http://www.matronics.com/Navigator?AeroElectric-List

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Oct 15, 2012 3:02 pm Post subject: What alternator size

At 04:43 PM 10/15/2012, you wrote:

 	  Quote: 	
		  

How to choose the correct alt size?



If my theoretical max sustained current draw on the airplane is 35-40 amps,

will a 40 amp B and C alternator be sufficient?  In other words, is there

room to spare or is 40 amps the maximum?  And is this at max engine RPM or

cruise or does it matter?



The majoring of the electrical requirements are for things rarely used such

as pitot heat, strobes, lights etc.  Is it acceptable to use the SD-8 backup

alternator to provide the remaining amps when all those loads are required?



I assume that there needs to be head room so that the battery can re-charge

after a high load event, but I don't know how much this will add to the

total load.



I really don't want a 60 amp alternator if a 40 will suffice without any

significant downsides as the weight savings is significant.


	


   Have you done a load analysis? 15 years ago I did one for

   an RV that came up 27 amps worst case (pitot heater on).

   For most of us, the current draw for the various electro-whizzies

   is going down . . . not up.



   Check out the files at



http://tinyurl.com/9rt6ymn



   where you'll find some spread-sheet examples of load analysis

   conducted by members of the list. You can go the pure

   manual route using a pencil and this form



http://tinyurl.com/7jqypwj



   Fill this out for EACH bus (main, e-bus, battery bus)

   and fill in CONTINUOUS draw currents for each

   electro-whizzy used during a particular phase of

   flight. You don't every run everything all the time.



   The rule of thumb is to have 25% of an alternator

   capacity in reserve for battery charging. So see

   if you can fly your airplane on 30A or less . . . I'm

   betting you can . . . much less.

   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:

http://www.matronics.com/Navigator?AeroElectric-List

fvalarm(at)rapidnet.net
Guest

Posted: Mon Oct 15, 2012 11:25 pm Post subject: What alternator size

Thanks Bob,



Yes I have done a load analysis (on paper) for cruise flight.  I suppose I

was including a few things that I shouldn't have such as fuel boost pump and

P-mag current since those would be zero under normal cruise conditions.



Also, I am finding a discrepancy between published numbers from various

sources.  



Maybe I will just measure each of the (larger draw) items directly and

record the actual values.  Shouldn't be too difficult.



Thanks for the spreadsheet link.



Bevan



--

- 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:

http://www.matronics.com/Navigator?AeroElectric-List

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Oct 16, 2012 5:54 am Post subject: What alternator size

 	  Quote: 	
		  

Maybe I will just measure each of the (larger draw) items directly and

record the actual values.  Shouldn't be too difficult.



Thanks for the spreadsheet link.


	




   Do your thinking 'out loud' here on the List.

   Inquiring minds want to know!



   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:

http://www.matronics.com/Navigator?AeroElectric-List

james(at)etravel.org
Guest

Posted: Tue Oct 16, 2012 10:41 am Post subject: What alternator size

Yes, and the thing is, the battery reserve is there for the once-in-a-while time when you really do need everything on. Â Even a small battery will give youÂ for many hoursÂ those couple of amps extra that you might need. 



James

On 16 October 2012 08:24, B Tomm <fvalarm(at)rapidnet.net (fvalarm(at)rapidnet.net)> wrote:

[quote] --> AeroElectric-List message posted by: "B Tomm" <fvalarm(at)rapidnet.net (fvalarm(at)rapidnet.net)>

 

 

Thanks Bob,

 

 Yes I have done a load analysis (on paper) for cruise flight. Â I suppose I

 was including a few things that I shouldn't have such as fuel boost pump and

 P-mag current since those would be zero under normal cruise conditions.

 

 Also, I am finding a discrepancy between published numbers from various

 sources.

 

 Maybe I will just measure each of the (larger draw) items directly and

 record the actual values. Â Shouldn't be too difficult.

 

 Thanks for the spreadsheet link.

 

 Bevan

 

 --

- 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:

http://www.matronics.com/Navigator?AeroElectric-List

dave.saylor.aircrafters(a
Guest

Posted: Tue Oct 16, 2012 11:14 am Post subject: What alternator size

We had a customer who "kind of" knew his alternator wouldn't support his entire load.Â  He flew a few hours at night with "everything on", then in the pattern at his destination, put the flaps down, which drew enough to open the master relay.Â  His battery-backed-up EFIS and GPS went into 30-second countdown-to-shutoff mode, which he overlooked while trying to figure out why everything else had gone dark, and he found himself with everything dark on short final.

  

He has bigger alternator now.

Dave Saylor

831-750-0284 CL

 



On Tue, Oct 16, 2012 at 11:40 AM, James Kilford <james(at)etravel.org (james(at)etravel.org)> wrote:

[quote]  Yes, and the thing is, the battery reserve is there for the once-in-a-while time when you really do need everything on. Â Even a small battery will give youÂ for many hoursÂ those couple of amps extra that you might need.   



James

On 16 October 2012 08:24, B Tomm <fvalarm(at)rapidnet.net (fvalarm(at)rapidnet.net)> wrote:

[quote]   --> AeroElectric-List message posted by: "B Tomm" <fvalarm(at)rapidnet.net (fvalarm(at)rapidnet.net)>

 

 

Thanks Bob,

 

 Yes I have done a load analysis (on paper) for cruise flight. Â I suppose I

 was including a few things that I shouldn't have such as fuel boost pump and

 P-mag current since those would be zero under normal cruise conditions.

 

 Also, I am finding a discrepancy between published numbers from various

 sources.

 

 Maybe I will just measure each of the (larger draw) items directly and

 record the actual values. Â Shouldn't be too difficult.

 

 Thanks for the spreadsheet link.

 

 Bevan

 

 --

- 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:

http://www.matronics.com/Navigator?AeroElectric-List

james(at)etravel.org
Guest

Posted: Tue Oct 16, 2012 11:48 am Post subject: What alternator size

The load analysis spreadsheet is our friend!

On 16 October 2012 20:11, Dave Saylor <dave.saylor.aircrafters(at)gmail.com (dave.saylor.aircrafters(at)gmail.com)> wrote:

 [quote]We had a customer who "kind of" knew his alternator wouldn't support his entire load.Â  He flew a few hours at night with "everything on", then in the pattern at his destination, put the flaps down, which drew enough to open the master relay.Â  His battery-backed-up EFIS and GPS went into 30-second countdown-to-shutoff mode, which he overlooked while trying to figure out why everything else had gone dark, and he found himself with everything dark on short final.

   

He has bigger alternator now.

Dave Saylor

[url=tel:831-750-0284]831-750-0284[/url] CL

 



On Tue, Oct 16, 2012 at 11:40 AM, James Kilford <james(at)etravel.org (james(at)etravel.org)> wrote:



 

[quote]  Yes, and the thing is, the battery reserve is there for the once-in-a-while time when you really do need everything on. Â Even a small battery will give youÂ for many hoursÂ those couple of amps extra that you might need.    



James





On 16 October 2012 08:24, B Tomm <fvalarm(at)rapidnet.net (fvalarm(at)rapidnet.net)> wrote:

 



[quote]   --> AeroElectric-List message posted by: "B Tomm" <fvalarm(at)rapidnet.net (fvalarm(at)rapidnet.net)>

 

 

Thanks Bob,

 

 Yes I have done a load analysis (on paper) for cruise flight. Â I suppose I

 was including a few things that I shouldn't have such as fuel boost pump and

 P-mag current since those would be zero under normal cruise conditions.

 

 Also, I am finding a discrepancy between published numbers from various

 sources.

 

 Maybe I will just measure each of the (larger draw) items directly and

 record the actual values. Â Shouldn't be too difficult.

 

 Thanks for the spreadsheet link.

 

 Bevan

 

 --

- 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:

http://www.matronics.com/Navigator?AeroElectric-List

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Oct 16, 2012 11:52 am Post subject: What alternator size

At 02:11 PM 10/16/2012, you wrote:

 	  Quote: 	
		  We had a customer who "kind of" knew his 

alternator wouldn't support his entire 

load.Â  He flew a few hours at night with 

"everything on", then in the pattern at his 

destination, put the flaps down, which drew 

enough to open the master relay.Â  His 

battery-backed-up EFIS and GPS went into 

30-second countdown-to-shutoff mode, which he 

overlooked while trying to figure out why 

everything else had gone dark, and he found 

himself with everything dark on short final.



He has bigger alternator now.


	




    Yeah . . . BUT . . . why didn't he have a low volts

    warning light? If the light is OUT, the battery is

   NOT being discharged.

   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:

http://www.matronics.com/Navigator?AeroElectric-List

Display posts from previous:

	Matronics Email Lists Forum Index -> AeroElectric-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum