Re: 12V source for lighting

[raf40@oes.amdahl.com (Richard Funnell)]

>The "system" *DEPENDS* on the battery to filter the voltage surges, which
>can easily be in the multiple *HUNDREDS* of volts without the battery
>there to suck up all those excited electrons. Without the battery in place
>to smooth out those voltage transients, you start frying electronics in
>very short order . . .
>
>                                        -RDH

The battery is really performing 2 major functions.  The first is that the
alternator puts out AC, which is then rectified (by the main diodes).
Without the battery in place, you would see a complex wave form consisting
of three phases of rectified AC.  The voltages wouldn't be that high (I'd
guess @20 VDC).  The other function of the battery is to absorb voltage
transients caused mainly by electrical motors being shut off.  These
voltages are very brief spikes, but these could get into fairly high
voltages (I won't bother guessing).

Either way, I still believe that the large gauge cable at the alternator is
a fine connection to the battery.  If bulbs do get fried, I would guess it
is because there will be virtually no voltage drop between the battery and
the alternator at headlight current levels.  Higher voltage produces
brighter light but shorter bulb lifetimes.  If this turned out to be a
serious problem, a series diode could be used to add a predictable
half-volt drop, but I wouldn't think that would be necessary.

Richard Funnell,
San Jose, California
'83 urQ
'87 560 SL