[Mariachi]

On Feb 27, 1:28 pm, "D.Kreft" wrote:
On Feb 27, 9:56 am, "Mariachi" wrote:

if the voltage of the alternator goes below the voltage of the
battery, then the battery does supply current for whatever the
alternator cannot handle...

Careful, sir. You've made a misstep three words into your post.
Because the battery and the alternator are wired in parallel, it is
physically impossible for the voltage at the alternator to differ from
that of the voltage at the battery (assuming negligible internal
losses in the connecting wires).

Remember, that at all points in a parallel circuit, the voltage will
be identical everywhere, but current draw may differ at various points
in the circuit. In *series* circuits, the current is the same
everywhere, but the voltage drop across each device is what may
differ. Put into formulas:

Parallel:
Vs = V1 = V2 = V3 = V4
Is = I1 + I2 + I3 + I4

Series:
Vs = V1 + V2 + V3 + V4
Is = I1 = I2 = I3 = I4

Where 'Vs' and 'Is' are the voltage and current at the source,
respectively; and where 'V#' and 'I#' are the voltage and current
measured at each device in the circuit.

-dan

Okay, I know all that... but if you put two car batteries in parallel,
you would get the same voltage but wouldn't the total internal
resistance of the batteries be less than the internal resistance of
one battery. Since you have one internal resistance in parallel with
another internal resistance, the total internal resistance has to be
less than the least internal resistance of one battery. So you would
actually have less voltage drop over the interal resistance of both
parallel batteries, therefore leaving more voltage left for whatever
series loads there are. Therefore you would actually measure a minute
increase in voltage across the two parallel batteries because the
total internal resistance of both batteries in parallel would be less
than one internal resistance of one battery.

And I'm not arguing that the alternator (within its limit) supplies
all the current when the car is turned on, but why is that so? Just
curious...