REFLECTOR: Bus, Battery & Electrical Instrumentation

Sun Jun 19 23:13:18 CDT 2005

Terry,
The rectifier is an array of diodes.  
Yes, an ammeter will show you what current is actually passing through that
particular wire.  However, it's my contention that you probably don't know
exactly what the capacity of your battery is at any particular moment, so
knowing the current doesn't actually tell you what you really want to know
("How long do I have before the panel goes dark?").  Also, the ammeter only
tells you what the current is in one wire, which may not be the wire you
would most want to know about in that set of circumstances.  Therefore, the
ammeter is often not particularly useful to you as the pilot.  
The best approach is simply to drop ALL non-critical loads as soon as you
know your alternator is inop, and leave them off until the landing field is
in sight.  At that point you can use whatever juice is left in the battery
to lower gear, show lights, communicate, etc.  If you find there is no juice
left, just drop gear and land.
However, if you have done a reasonable job sizing the battery, and replacing
it before it's at death's door, the battery should have plenty of power to
support minimal enroute loads for the duration of fuel on board, plus what
you will need for the approach and landing.
This is the theory behind the AeroElectric Connection recommendation for an
"endurance" bus, which powers only a few key enroute items, and does not
require a contactor to power it.  Then flipping off the main bus and
flipping on the endurance bus alternate feed assures that you have all of
the big current users off. 
Keith 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Terrence Miles
Sent: Sunday, June 19, 2005 6:30 PM
To: reflector at tvbf.org
Subject: RE: REFLECTOR: Bus, Battery & Electrical Instrumentation

Lar, Keith,
I'm not the smartest bunny in the woods on this...but Larry could be mean 
retifier and not diode w/ regards the field windings?  Also Ammeter could 
help in flight as you download to show actual load being pulled off the 
source into the users and back to ground.  In the event of an alternator out

this might help you look around some more to make sure that all is off.  
Knowing the draw of your min in-flight load can only be done w/ an ammeter.
Terry

>From: "Keith Hallsten" <KeithHallsten at quiknet.com>
>Reply-To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
>To: "'Velocity Aircraft Owners and Builders list'" <reflector at tvbf.org>
>Subject: RE: REFLECTOR: Bus, Battery & Electrical Instrumentation
>Date: Sun, 19 Jun 2005 13:02:04 -0700
>
>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
>
>
>
>
>
>   _____
>
>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
>
>
>
>
>   _____
>
>
>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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