Probably between 1600 - 2000 rpm - typically, alternators are running twice
(+/-) crankshaft rpm, so that would be 3200-4000 alternator rpm. Engineers
have to step up the speed so that you get enough output so as not to run off
the battery at idle, with minimal electrical loads, and yet keep top speed
low enough so as not to self destruct when the engine is wound out. I seem
to recall during my early days in Detroit that they were getting generators
up to over 10k rpm, which led to shortened life. And 10k rpm isn't nearly
as much of a problem to an alternator, so running that SD up to the limit of
the IP governor won't kill the alternator (at least not before you do
something bad to the engine itself!)
Werner
----- Original Message -----
From: "Christopher McCann" <[EMAIL PROTECTED]>
To: "Mercedes Discussion List" <mercedes@okiebenz.com>
Sent: Monday, February 05, 2007 4:29 PM
Subject: Re: [MBZ] RPM, alternator, battery charging
So in an 85 300SD and 82 300D...where abouts do you think/guess that RPM
point is past where you don't get any more charging power?
Thanks,
Chris
Werner Fehlauer <[EMAIL PROTECTED]> wrote: Chris - yes, the curve isn't
linear. And the limitation is field magnetic
strength, current capacity of the windings, connections, and controls, and
mechanical rpm limits where things begin to fly apart. But generators and
alternators both generate power from a coil of wire rotating through a
magnetic field, or vice versa. DC generators have another point of
limitation, the commutator and brushes, which can only handle a finite
amount of current for their size before heat burns them up. Alternators
get
around that by rotating the magnetic field, energized through slip rings,
which don't have to carry nearly as much current. Usually, the regulator
limits the current to protect the rectifying diodes from self destruction
from heat, and that should happen before the main coils and insulation
begin
to fry.
So in practice, you are correct - at some point, the protective circuitry
should limit the output current so that it doesn't "cook" itself to death.
Remove the regulator, and it is theoretically possible to get more current
with more rpms, at the risk of ruining the alternator or what's connected
to
it.
Werner
