Bob---I have the same Delco 55 amp alternator. With the engine idling around
800,. turning on the headlights will cause a drop of about 50 rpm. (At one time
it was closer to 150 rpm, till I fitted a better block-to-ground connection)
Could be (my) the mild cam not up to the task at low idle rpms, like Vance
suggested? No longer a big deal, but it is still a noticeable drop. Also the
voltmeter will eventually show a drop of maybe .5V when idling with a load on
the battery.
Dick
-----Original Message-----
From: Bob Danielson
Sent: Monday, September 15, 2008 11:57 AM
To: 'Triumph List', 6pack@autox.team.net
Subject: [6pack] Alternator Output vs RPMs
I'm having a discussion with a TR6 friend who has a Delco 55 amp alternator
on his car like I do. He says that every time his Perma-Cool electric fan
comes on (he doesn't have a mechanical fan) he sees a 400 RPM drop (stock
mechanical tach) in engine speed. His reasoning is that when an accessory
calls for power the alternator has to work harder and, in turn, the engine
works harder.
I thought that an alternator's output was fairly constant and had no impact
on engine RPMs and vice versa. I just went out and let my car settle into a
steady idle with the volt gauge reading a steady 14.x with just the electric
fuel pump running. Raising the RPMs the had no impact on the gauge reading.
I turned on the headlights, electric fan, heater fan, radio and electric
fuel pump and saw the volt gauge only drop to 13.x but there was no impact
on RPMs. Raising the RPMs with that full load had no impact on the volt
gauge. This is what I'd expect to see happen, but I'm no expert. Does it
make sense that his RPMs would drop when his fan comes on?
Just curious.
Bob
Bob Danielson
1975 TR6 CF38503U
Running w/ Throttle Body Injection
Toyota 5 Speed & Nissan LSD
http://tr6.danielsonfamily.org
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