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Re: Wiring Question

To: MG T Digest <mg-t@autox.team.net>
Subject: Re: Wiring Question
From: yd3@nvc.net
Date: Tue, 07 Jun 2005 00:19:29 -0500
Scott:

Bud does a good job of describing which wire of the dynamo goes to which 
terminal of the regulator.

You also mention the ignition or charge lamp.  A few points to remember.

1)  The charge lamp has no "ground" and is insulated (isolated) from the 
chassis.
2)  When the engine is running above 1000 RPM and the dynamo charging both 
wires to the charge lamp have a potential of about 12 volts. One wire has
the 12.6 volts of the battery and the other has 13+ volts of the dynamo.  As 
there's practically no potential difference between the two feed wires
(13.5-12.6=1 volt for a 12 volt lamp), the lamp goes out.
3)  When the engine is off there is no 13+ volt potential coming from the 
dynamo.  So one wire has a 12.6 volt potential (from the battery) and the
other is zero.  The difference between the two potentials is 12.6 volts.  Thus 
the light lamps fully.
4)  When the engine is idling quite slowly, the lamp may glow dimly.  At that 
time the dynamo is perhaps putting out 6 volts.  The wire from the
dynamo to the charge lamp has 6 volts on it while the one coming from the 
ignition switch has battery voltage of 12.6 volts.  Thus there is a
difference of about 6 volts (12.6-6=6.6), and the lamp glows as if a 12 volt 
lamp is hooked up to a 6 volt battery.

Regards,
Blake

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