Johnny B Good Wrote in message:
On Thu, 26 Apr 2018 23:58:17 +0100, Dave Plowman (News) wrote:

In article ,
Johnny B Good wrote:
The point is when calculating near anything car electrics wise is you
have to make allowances for the voltage when running being rather
higher than the nominal 12v. As very little is only ever used with
the engine stopped. And when starting the engine, you also need to
allow for the voltage dropping considerably due to the starter load.

This where the positive coefficient of the 2.2W ignition warning
lamp's
filament resistance might prove useful[1] since even a good condition
12v car battery's terminal voltage will fall to around the 8 to 10 volt
mark from the starter cranking load (once the motor has accelerated to
cranking speed - the voltage can easily dip to less than 6 volts on the
initial starting surge of 300 odd amps or more before it settles down
to the 100 or so amps once up to cranking speed).

Doesn't really matter, since it would be silly for the alternator to be
attempting to charge the battery while the starter is operating.

Hence note[1]. :-)

Appendix shurely?
--
Jim K