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Alternator Field Switch

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FLYaDIVE(at)aol.com
Guest

Posted: Fri Jun 30, 2006 12:41 am Post subject: Alternator Field Switch

In a message dated 6/29/06 7:23:43 PM Eastern Daylight Time, 

endspeed(at)yahoo.com writes:



 	  Quote: 	
		   Is there a reason to have a field switch? 

  

  

  Bob Sultzbach

=============================
	


Bob:



There are two reasons for a Field Switch:

1 - To isolate the alternator from the electrical system.

This is helpful in diagnosing a problem and when the ACU goes off line and 

you want it to cool and reset.

2 - In case of an electrical fire.



There are also some not as relevant reasons:

Voltage spikes when starting

Reducing load on the starting of the engine

Control of the alternator or alternators

Barry

"Chop'd Liver"

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brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Fri Jun 30, 2006 2:12 am Post subject: Alternator Field Switch

On Jun 30, 2006, at 4:38 AM, FLYaDIVE(at)aol.com (FLYaDIVE(at)aol.com) wrote:

 	  Quote: 	
		  There are also some not as relevant reasons:

Voltage spikes when starting

Reducing load on the starting of the engine

Control of the alternator or alternators

	


I don't really want to pick a fight but these wives' tales seem to persist: voltage "spikes" and engine load when starting. I have certainly seen low voltage caused by starter load but I just don't know where voltage "spikes" would come from. Likewise, the load from the alternator on an engine turning at 150-200 RPM during cranking is inconsequential as the alternator is not turning fast enough to produce an output above battery voltage so it is delivering no current and hence placing no load on the engine. The only load the alternator places are frictional loads, and those exist whether the field is active or not, and the slightly extra battery drain of 2 or 3 amps to excite the field.

 Brian Lloyd                         361 Catterline Waybrian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

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_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

willslau(at)alumni.rice.e
Guest

Posted: Fri Jun 30, 2006 3:07 pm Post subject: Alternator Field Switch

On  that note, just got my new Sport Aviation magazine, and the technical counselor  article is all about needing an avionics master switch to protect your  electronics from spikes caused by "inductive kicks". That'll probably be enough  to keep these OWTs going stronger than ever. Argh.

  

 William Slaughter

 [quote]   

   --

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