No, the alternator is not self governing without the regulator. Rated
output is the power level it can safely operate at continuously. In this
case it is rated at 34 amps. If you bypass the regulator and allow the
alternator free reign, the output current will increase with rotational
speed, the same as the generator. When the engine speed gets to 3300 rpm
the alternator output current is up to its rated value, which is the test
to verify that the alternator can put out that much current. If you were
to increase engine speed beyond 3300 rpm the output from the alternator
would climb higher, beyond its rated output, and in continuous use it would
then eventually self destruct. The regulator is there to limit the
alternator to 34 amps or less, depending on the charge condition of the
battery and the curent draw of the accessories. If the regulator fails in
the full on condition, the alternator will self destruct at higher speed,
same as the generator.
The significant difference with the generator is that it is only designed
to put out about 22 amps (rated output). If the battery charge level is
low, and all of the electrical devices in the car are turned on, it is easy
for the current demand to exceed the rated capacity of the generator. And
the generator will try to satisfy the demand if the regulator allows
it. When the regulator fails full on, and the current demand of the
vehicle electrical system is say 30 amps, the generator can do that at
sufficient speed, which is when is suffers internal meltdown.
That same thing is just a little harder to do with the alternator, because
the alternator is capable of putting out a higher sustained current without
damage. With an alternator rated for 34 amps, the system electrical demand
would have to be higher than 34 amps to damage the alternator. All of the
(standard) electrical devices in the car combined do not draw that much
current when they are working properly, except for the battery. So with an
alternator the battery has to be quite low on charge to demand enough
current to fry the alternator, even if the regulator is stuck full on.
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com
-----------------------------------------------------
At 04:50 PM 11/13/01 +0000, Paul Hunt <paul.hunt1@virgin.net> wrote:
>The factory output test for the 16ACR says to "bridge the regulator green
>connector 'F' to earth" i.e. bypass the regulator so that the alt produces
>its maximum possible output. It then says to run the engine with an
>ammeter in series with the output wire and at 3300rpm you should see 34
>amps i.e. the rated output of the alt. So the rated output seems to be
>independant of the regulator, i.e. it is probably governed by the
>specifications of the field and output windings.
>
>----- Original Message -----
>From: Barney Gaylord <barneymg@ntsource.com>
>Sent: Monday, November 12, 2001 5:01 PM
>
> > .... the problem you run into is when you force the device (either
> one) to put out more current that it is rated for. This is usually a
> result of a failure of the voltage regulator to the full on condition,
> and in my experience the dynamo seems to be much more susceptible to this
> problem. If you were to connect a 12 volt supply wire directly to the
> field terminal on the dynamo and run the engine at highway cruising
> speed, you can expect imminent failure of the dynamo in a matter of five
> minutes or less. BTDT (more than once).
///
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