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Alternators on aircraft

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bbradburry(at)bellsouth.n
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Posted: Fri Jul 26, 2013 12:12 pm Post subject: Alternators on aircraft

How often is there a scenario where an aircraft or automobile alternator needs to be balanced?  Is this something that needs to be considered?  

   

Bill B  

       [quote][b]

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billp(at)wwpc.com
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Posted: Fri Jul 26, 2013 4:15 pm Post subject: Alternators on aircraft

Generally or specifically, never. 

The only time they give trouble in general is if the bearings are worn out or if there's a bad diode. Rarely there's problems with bushes since not much current goes through them. They do wear out like everything. Bad bearings are sometimes the result of an over tightened belt. 

There's nothing to wear asymmetrically so if they're balanced from the factory they're good for life. 

Bill



On Jul 26, 2013, at 13:10, "Bill Bradburry" <bbradburry(at)bellsouth.net (bbradburry(at)bellsouth.net)> wrote:

[quote]               

How often is there a scenario where an aircraft or automobile alternator needs to be balanced?  Is this something that needs to be considered?  

   

Bill B  

        	  Quote: 	
		  

	


[b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jul 27, 2013 7:43 pm Post subject: Alternators on aircraft

At 03:10 PM 7/26/2013, you wrote:

  	  Quote: 	
		   How often is there a scenario where an aircraft or automobile alternator needs to be balanced?  Is this something that needs to be considered?

  

 Bill B 	


   Depends on how you define 'need'. B&C started

   balancing their rotors many years ago based

   on the fact that belt driven alternators on

   a Lycoming cruise at about 2x the rpm in cars.

   2x speed is 4x the vibrational forces due to

   unbalance.



   Van's used to sell a larger pulley to 'slow

   down' the alternators he sold/recommended.

   Takes care of the cruise vibration but degreades

   output at ground ops rpms.  B&C elected to

   maintain the performance and do a simple

   operation to mitigate vibration.



   B&C's track record has been exemplary. Would

   it have been noticeably degraded if not balanced?

   Don't know. It's a bearing life issue and doesn't

   represent a large cost-of-ownership or flight

   risk.



   If your experience shows that you're shucking

   bearings too often, then balancing or slowing

   down are options. If you buy a B&C, those

   concnerns are addressed with the package.



 

 

   Bob . . .    [quote][b]

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racerjerry

Joined: 15 Dec 2009
Posts: 202
Location: Deer Park, NY

Posted: Sun Jul 28, 2013 4:08 am Post subject: Re: Alternators on aircraft

If you swapped to a different alternator pulley and are experiencing a vibration, that MIGHT be the source of your problem.  If you wish, you can do a rough balance check by disassembling the alternator, mounting the pulley on the armature and check for a ‘heavy’ spot’ by supporting the armature on its own bearings.  Alternatively, you can support the armature on level ‘knife edges’ on the bare armature shaft.  Or just retract/remove the brushes and if the armature spins freely in its case, you should be able to detect a ‘heavy spot.’  



This procedure will only check for a static imbalance; which will probably suffice.  Most balancing correction marks that I have seen have been directly on the pulley (heavy) end.  Besides, anything rigid and dynamically balanced will also always be in perfect static balance and exhibit no signs of a ‘heavy spot.’

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