REFLECTOR: Bus, Battery & Electrical Instrumentation

Sun Jun 19 16:14:54 CDT 2005

In an average alternator (like the one in my Cherokee 235), the buss voltage will drop to 12.7-13.2 if you lose a diode pack. It can go lower once you start drawing extra current (like landing lights, pitot etc.)
One good thing about having an Ammeter is that it will show you right away what is going on with the alternator. 

While I do agree that a Voltmeter will show you what is going on (eventually, after things balance out), an Ammeter gives you some extra info. In an velocity like mine (all electric, electric fuel pumps and ignition/No manual backups) the little extra information could come in handy. 

I have my Rocky Mountain Monitor Volts input hooked to one battery system. The ammeter is before the charging splitter. I have a backup Volts guage that tells me what is going on in the other battery. This way I can monitor all of the systems at a glance (regardless of which battery is online). I also did this kind of backup with Coolant temp, Oil Pressure and Oil Temp guages. 

In a velocity with a "normal" engine, an Ammeter is probably not needed. In an application like mine, I think the extra info can be very handy. 

Kurt Winker
173 FGE Aluminum 4.3L V-6

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

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 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 

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

_______________________________________________
To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector

Visit the gallery!  www.tvbf.org/gallery
user:pw = tvbf:jamaicangoose
Check new archives: www.tvbf.org/pipermail
Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
_______________________________________________
To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector

Visit the gallery!  www.tvbf.org/gallery
user:pw = tvbf:jamaicangoose
Check new archives: www.tvbf.org/pipermail
Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.tvbf.org/mailman/private/reflector/attachments/20050619/e1df592e/attachment.html