REFLECTOR: Bus, Battery & Electrical Instrumentation

[Keith Hallsten]

Larry,

 

What was the voltage on the bus when you had the bad alternator diode?  I
would expect that it would be lower than usual, and a voltmeter would show
that an issue was present.  If the voltage was, say, 14 volts the battery
would have charged.  

 

My point is that a voltmeter will tell you everything you need to know as a
pilot.  An ammeter might be handy when troubleshooting, which should be done
on the ground.

 

Keith

 

 

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From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Laurence Coen
Sent: Sunday, June 19, 2005 7:44 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Bus, Battery & Electrical Instrumentation

 

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 <mailto:KeithHallsten at quiknet.com>  Hallsten 

To: 'Velocity Aircraft <mailto:reflector at tvbf.org>  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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