REFLECTOR: Bus, Battery & Electrical Instrumentation

[michalk]

Set your voltmeter to AC voltage.  That will pick up ripple.

Jim Sower wrote:
> 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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