Hi Frank
I sugest you do a little reading about Alternators. They indeed
are current limited devices. Mostly by the internal magnetics.
With out boosting the field voltage way above 12V the maximum
current available will be very close to the device rateing.
(35 A for the stock Alpine V alternator) With a short across the
output you will have very low voltage available for the field and
it likly will not put out more than an amp or two.
This is one of the reasons the control for an alternator is so much
simpler than for a generator, no current limiting relay is needed.
Now shorting the battery is a whole nother story.. It will be able
to source several hundred amps.. probably leading to a bent ammeter
pointer and a fire in short order...
Yes modern automotive alternators will put out more current.. up to 100A ..
its needed for all the accessories common to todays cars..
The next generation of cars will need even more with things
like electric suspension being proposed..
An alternator would make a good mobile welder.. you want a current
limited source to do welding. Getting 100A from a "heavy duty"
one should be no problem.. Controling the field voltage makes a
convient maximum welding current control.
Steve F
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Steve Finberg W1GSL w1gsl(at)mit.edu
PO Box 397082 MIT Br Cambridge MA 02139-7082 617 258 3754
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Frank Marrone wrote..
Well, you might get hundreds of amps if you short out an alternator. I
Sure.. Pick your alternator.. There is one about a mile from here
now putting out about 7000 A allowing me to type this... The last
time someone shorted it the whole street exploded... He died :-(
don't know all that much about Alpine and Tiger alternators but a typical
Thanks for admitting it
'mercan alternator will not limit to a safe current level if shorted. I
Well what is a safe current? What do you think limits the
current when charging a almost dead battery?
would find it hard to believe that any alternator would simply limit to 35
amps when shorted.
Thats the way it was designed
The limiting factor would be any fuseable elements in
the circuit and/or the resistance of the alternator windings and the short
circuit path.
It would be much to inefficent and generate much too
much heat to use for normal current limiting ..
The typical fuse wire in the output is to prevent a
fire if the internal rectifiers short out and draw
large currents from the Battery.
I would find it easy to believe that a hundred of amps could
be drawn from a respectable alternator under short circuit conditions. The
I have a preacher friend you might want to meet..
He ...believes... :-)
.
preceeding comments are true for typical voltage regulating systems. If
The Alpine regulates output voltage just like the
american alternators... infact you can use the same
modern regulator ciruit module.
the Lucas 10AC senses current then it might limit to a safe current but a
current limiting charging system would indeed be a novelty for a '60s
vintage automobile with a lead acid battery.
Indeed an alternator was a bit novel in the 60's especially
for a British car.
There used to be a company that sold an arc welder which consisted of a
briggs or equivelent gas motor driving what looked to be a heavy duty car
alternator. the rectifiers were mounted external. the things got damn hot
but they worked and I'm sure they delivered in excess of a hundred amps
under short circuit conditions.
Did they use a Lucas 10AC alternator? :-) How do you think
they controlled the welding current.. Why do you think
a small welder will put out "in excess of a hundred amps"
So what.. I am sure I can get someone to build you any size
custom alternator especially if we get some extra room
by making the rectifers external.
Frank Marrone MK I Tiger B9471116
marrone(at)wco.com '97 Crown Vic LX
Yamaha Seca 900 (aka XJ900RK)
'79 Spitfire
'66 Ford LTD
'88 Nissan 4WD p'up
Steve F
*******************************************************************************
Steve Finberg W1GSL w1gsl(at)mit.edu
PO Box 397082 MIT Br Cambridge MA 02139-7082 617 258 3754
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