REFLECTOR: Bus, Battery & Electrical Instrumentation

[Jim Sower]

Bad diodes are pretty tough to trouble shoot unless you have a scope, 
and who's got a scope? Larry did good IMO to find it as quick as he did. 
Open diode does weird things to the "ripple" on the voltage trace and 
might make avionics noisy, but if your ICS and all is really well 
filtered, you have kind of taken away that trouble shooting tool.
Does anyone know of a simple way to detect out of bounds Alt ripple? ... 
Jim S.

Keith Hallsten wrote:

> 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 <mailto:KeithHallsten at quiknet.com>
>
>     *To:* 'Velocity Aircraft Owners and Builders list'
>     <mailto:reflector at tvbf.org>
>
>     *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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