On Mon, 27 Dec 2004 06:15:14 -0800, Jay in the Mojave
wrote in :

Hello Programo5:

At 15 dollars each, and used sounds like there are not in premium shape.

It may be possible to have them rewound for a higher current, for
running a 4 or 8 pill amps. My 4 pill 2SC2789 amp will draw 75 to 80
amps with no problem.

A 105 amp alternator may have a higher peak current capability than
just 105 amps. I have never measured it but I would think it would have
say a 10 to 20 percent higher peak intermittent rating. Anybody know
about this or measured it?


The current rating is for a specific RPM which is typically high. The
current drops off to a bare minimum at idle which is why you sometimes
see the idiot light come on while waiting at a stop light.


Most Installations I have seen with a 8 pill amp have had only a 100 amp
or so Alternator. So when the 8 pill amp wants to draw say double of
what a 4 pill amp will draw something like 150 to 160 amps or more, the
Alternator will put out its maximum output current, but the voltage will
drop, and the battery will start to put out current. And when the amp is
unkeyed the Alternator will try to recharge the battery, at a rapid
rate. Its possible to get behind the curve of the Alternator charging
the Battery, and the battery can over heat and possible be damaged with
high current charging over a long period of time.


Starting-type (auto) batteries are designed for fast charging.
However, a deep-cycle battery would be ruined by such cycling.


A lot of guys use large batteries. I think the large batteries is a bad
call as the Alternator should be able to source all the current, to keep
the voltage as close 14 volts under load to keep the out put power up
there.


Lead-acid batteries under charge (engine running) have a thing called
"surface charge" that's higher than the nominal 12.6 battery voltage.
Larger batteries have a larger surface charge, and when under load
they tend to keep up the system voltage better than smaller batteries.


And if a second Alternator is installed it can be wired to also
charge the vehicles battery or run the electrical system should the
stock Alternator fail.


You might have a problem with the regulators. If more than one
alternator is used it's best to run the second from a 'slave'
regulator that's controlled by a 'master' on the first alternator. If
you don't then one alternator will pull the full load until the
voltage drops down to the regulated voltage of the second. The result
is "stepped" regulation and can be quite noisy.


When the guys volt the amps, running more than 14 volts to increase the
out put power even more, then you must have one or more Alternators that
will have the current capability to maintain the higher voltage.


Max current is dictated only by the wire size. Without the regulator,
voltage is limited by the PIV of the rectifiers and the insulation
breakdown voltage. The latter is usually very high (~600 volts) so if
the rectifiers have a reasonably high voltage rating then you can
trash the internal regulator and use an external regulator to get
voltages up to 100 volts or more, depending on how fast you can spin
the rotor. But if all you want is max current at 16 to 18 volts then a
smaller pulley would probably do the trick.


The
Alternators outputs can be connected together as they are diode isolated
internally, so feedback from one alternator into another alternator will
NOT happen.

One of the really neat installations I saw at one of the shoot-outs, was
a Bird Watt meter modified to also be able to indicate the amplifier
input voltage and current. And many guys have a separate volt and amp
meter on the dash to indicate the voltages and currents, pretty neat-o.


......uh, voltmeters and ammeters in the dash aren't exactly new ideas.
Neither are voltmeters and ammeters at the input to the amp -- that's
how input power is measured. The old "5-watt" CB radios were rated by
their input power, and years ago the ham radio limits were also by
input power. Nothing new here except the modification of a Bird to do
the job of a cheap multimeter.