[DML] Re: Car's use of electricty / alternator & battery question

["twinenginedmc12" <twinenginedmc12@xxxxxxxxxxxxxxxxx>]

"
An alternator should be able to deliver it's rated output current-at-
voltage indefinitely, although the max output may vary a bit with
temperature. If an alternator delivers a very high output but
overheats or burns out when run that way for long, the rating is not
accurate.
"

That above statement is key.  The alternator should be able to deliver
its rated output indefinitely.  And it can, above a certain rpm. 
Below that rpm, it can't.

The size of the alternator is chosen as the smallest, cheapest
provider of enough power to meet the average requirements, plus a
little margin.  The more margin, the more expensive the part is.
The less margin, the more the electrical system will tax the battery.
It's a compromise.

I base this on common sense, and on the fact that I have at least one
vehicle, in which I have documentation that states the alternator
can't meet the electrical requirements of the vehicle below a certain
speed.  I don't know categorically whether the Delorean fits in this
category or not, but why wouldn't it?

You guys are all correct, as far as I can tell.

The alternator and/or the battery power the car, depending on the load
and rpm.

The alternator does "rest", that is, there are periods in which it is
running rather lightly.  These conditions are high rpm, low electrical
load, low temerature.  

It's a good bet that if you drive the alternator under heavy load, at
low rpms, with a soft battery, in high temperatures, that it will fry
eventually.

Rick






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