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Date: Thu, 26 May 2005 21:32:13 -0500
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Amps consumed data
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Most (all?) unmodified, internally regulated alternators would need an 
overvoltage-controlled relay to disconnect the B lead in order to 
protect the electronics from overvoltage in the case of a regulator 
failure. Some failure modes of the regulator could cause continued 
(unregulated) power to the field winding & therefore unregulated output 
from the alternator.

Was that as hard to read as it was to write?

Charlie
(flying without protection)

Finn Lassen wrote:

> Yes, you'll need a relay in series with the "fat" wire, IF you have an 
> internally regulated alternator that does NOT stop putting out voltage 
> when the "thin" wire is disconnected. Looks like Bernie's alternator 
> will not need that relay. No need to introduce an unneeded additional 
> component - another point of possible failure.
>
> Finn
>
> Jim Sower wrote:
>
>> Finn Lassen wrote:
>>
>>> The small wire goes to its separate circuit breaker. The crowbar is 
>>> connected to this wire (and ground).
>>> When the crowbar circuit senses an over-voltage, it clamps that wire 
>>> to ground (and pops the circuit breaker).
>>> Only works on your kind of alternator that stops putting out voltage 
>>> on the fat wire when it doesn't get voltage in on the "thin" wire.  
>>> I have an internal regulator, so all I have is a "fat" (B+) wire.  I 
>>> jump the B+ terminal of the Alt to the "F" terminal with a couple 
>>> inches of 17 ga wire.  I connect and disconnect the B+ to the rest 
>>> of the airplane with a "master" relay powered by the Alt switch on 
>>> the panel and protected by Nuckolls' crowbar.  In an over voltage 
>>> situation, the relay opens.  The Alt is disconnected from the 
>>> airplane and I could care less what the voltage is. As someone else 
>>> asked, does it really stop putting out voltage on the fat wire - 
>>> easily measured on the fat wire with a voltmeter - voltage should 
>>> drop to maybe 13.2 V as opposed to the 15 - 16 Volts when alternator 
>>> is delivering power.
>>>
>>> Finn
>>