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current drain in alternator with engine off

To: "Triumphs List" <triumphs@autox.team.net>
Subject: current drain in alternator with engine off
From: "Anthony Rhodes" <spamiam@comcast.net>
Date: Wed, 23 Feb 2005 20:01:12 -0500
I am helping to do some wiring modifications to a friends TR4A.  It has been
off the road for a couple of years, and just prior to that it had an
alternator upgrade.  We upgraded the wiring to handle the output of the
alternator and added more fused circuits, added headlight relays, etc.

Anyway, I wanted to minimize the possibility of burning something out and
simply had my ohmmeter across the leads which would go to the battery
terminals.  With everything off it showed a resistance of about 5100 ohms.  I
expected it to be a lot larger resistance than that.  I started disconnecting
circuits, but the resistance never changed.  When I pulled the main brown wire
off the solenoid, then the resistance did go to infinity.  Nothing else would
change the resistance until I pulled the plug on the alternator.  Then the
resistance again went to infinity.

I have the voltage sense wire connected directly to the output stud of the
alternator.  The alternator SEEMS to work fine with the engine running (the
ignition light extinguishes itself), but I have not actually tested the output
under significant load.

When I pull the plug on the alternator (engine off, of course), then the
resistance goes to infinity.  It appears that the sense circuit has a small
current drain (about 3 milliamps).  IS this normal?  If not, then what is
wrong?  If it is normal, then I guess I need to put the voltage sense circuit
on a switched circuit....

-Tony




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