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Alternator Contactor

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doramsey(at)gmail.com
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Posted: Tue Aug 02, 2011 5:46 am Post subject: Alternator Contactor

At Oshkosh, I sat in on an "electrical system design" forum.   The presenter at the end presented there little box that they sell with all the contactors, fuses, and overvoltage protection in it.  One of the contactors was an "alternator contactor".   So I decided to stop by their booth and ask questions. Here is our conversation:

   

  Why do you need an alternator contactor?  The field is going to be 5 amps or less, you can use a switch for that.  "Our contactor is on the alternator output".   Why do you need that, once you kill the field its going to shut down the alternator?   "You can still have a run away alternator with the field shut off"   Hmmm.

   

 So my question is, can you really have a runaway alternator with the field shut off?  My B&C controller is focused on the field juice, and just wondering how much risk I have of an issue.

  [quote][b]

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nuckolls.bob(at)aeroelect
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Posted: Tue Aug 02, 2011 6:55 am Post subject: Alternator Contactor

At 08:43 AM 8/2/2011, you wrote:

At Oshkosh, I sat in on an "electrical system design" forum.   The 

presenter at the end presented there little box that they sell with 

all the contactors, fuses, and overvoltage protection in it.  One of 

the contactors was an "alternator contactor".   So I decided to stop 

by their booth and ask questions. Here is our conversation:



Why do you need an alternator contactor?  The field is going to be 5 

amps or less, you can use a switch for that.  "Our contactor is on 

the alternator output".   Why do you need that, once you kill the 

field its going to shut down the alternator?   "You can still have a 

run away alternator with the field shut off"   Hmmm.



   There is a exceedingly tiny chance that the alternator

   designer didn't do his homework and the alternator develops

   and internal short from field lead to some hot conductor

   within. Saw this happen one time at Mooney . . . they

   experienced an un-controllable runaway on a prototype

   alternator they were testing.



So my question is, can you really have a runaway alternator with the 

field shut off?  My B&C controller is focused on the field juice, and 

just wondering how much risk I have of an issue.



    Chances of this happening in real life are

    zero. Who is this organization? I'll send them

    a couple of books.



   Bob . . .

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