REFLECTOR: Bus, Battery & Electrical Instrumentation

[Laurence Coen]

Keith,

I experienced such a failure mode on my old Cherokee once.  Alternators generally have three separate windings, each with there own diodes.  Metal fatigue broke a lead off a single diode.  The alternator made power, but not quite enough.  As a result it would come real close to floating the load but not enough to recharge the battery.  It took about a month to kill the battery.  The second time the battery died I pulled the alternator and found the problem.

Larry Coen
N136LC
  ----- Original Message ----- 
  From: Keith Hallsten 
  To: 'Velocity Aircraft Owners and Builders list' 
  Sent: Saturday, June 18, 2005 1:57 PM
  Subject: RE: REFLECTOR: Bus, Battery & Electrical Instrumentation


  Al,

  If your alternator stops producing, the voltage on the bus powered by the ammeter will instantly drop to whatever the battery(s) tied to that bus will support.  That cannot be more than 12 volts or so.  Therefore, a low-volts alarm set at 12.5 volts will instantly warn of alternator failure.  That's why I don't think an ammeter is necessary.  I am not aware of any failure mode for an alternator that will result in low amperage without corresponding low voltage.

  Keith 

   


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  From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Al Gietzen
  Sent: Friday, June 17, 2005 11:35 PM
  To: 'Velocity Aircraft Owners and Builders list'
  Subject: RE: REFLECTOR: Bus, Battery & Back Order

   

    What voltage do you all trigger the low voltage

  warning?  I am guessing that since alternator produce 14V and the

  battery is at 12, simplistically it should be set to 13V or so, taking

  the middle.  Is there a standard value that is the "industry standard"?

   

  My engine monitor will read bus voltage and the current from the alternator.  I can set the alarm limit for low current output (probably something lower than what it takes to just run the engine) to give early detection of low alternator output.  Possibly one reason for an ammeter. 

   

  Al



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