Jim Weir wrote in message
And as somebody else has pointed out, running a series string close to the
bottom limit of Vcc and hoping that a single resistor will provide constant
current to these devices will cook them when Vcc rises to the charging voltage.

No designer in his right mind would use a circuit in this manner.

Jim

The more the supply varies the less effective the technique is. I
picked the simple resistor design with certain assumptions. When it
comes down to it, the voltage doesn't vary all that much on a properly
operating electrical system. That big 'ole battery is like an anchor
on the supply bus. Over voltage condition blows the breaker.

What if the alternator quits? Well how far down do you want to go on
the discharge? You could get a range of zero to 14 volts if you
consider a discharged battery, thats a pretty tough range to design
for isn't it? I can think of a lot of systems that will malfunction
when supplied from a discharged battery. Even normal lights will go
out of spec on a discharged battery.