On Apr 15, 1:03*pm, g wrote:
On 15/04/2011 07:41, wrote:



So, do you agree that under the condition of two identical
fully charged batteries at exactly 12V, connected in
parallel to a load, the current will flow from both
batteries through the load? *I hope you do.

Your example, while it is correct, have little bearing on real life
problems. The grid can in no circumstances be looked at as identical to
a PV array voltage converted to AC voltage.

Two identical batteries have identical inner resistance, that is why
your example works.

Wrong. Go back to the example in the link, as I suggested to
Homeguy. You have two ideal voltage sources with different voltages
connected through two resistors of different values, one 20 ohms,
the other 10 ohms. That is a basic model of a battery, where the
10 and 20 ohm resistors represent the different internal resistances
of the batteries. So they are batteries with identica voltage, but
different internal resistances.
Very basic stuff. The Kirchoff equations are right
there. All you have to do is change the voltages so that they
are equal.

Solve the equations for the case where the voltage sources
are at identical voltages and you will find that current flows from
BOTH sources. One is NOT at a higher potential than the
other, which is what Homeguy claims must exist for both
to provide current to the load.




As for Homeguy
he apparently believes one has to be at a higher voltage
to "push" current.

He is correct. Why? Because he wants to "push" current into the grid.
With your 2 batteries at the exact same voltage, how do you get current
flowing from the "home battery" to the "grid battery"?

I never said current flows from one battery to the other. It's
apparently
Homeguy and now you who are hung up on that for reasons unknown.
If the voltage sources are equal, no current flows between the two,
which
is the situation that is most desirable when powering
a load with two batteries in parallel. They just BOTH supply part of
the
current to the load resistor.


As I said, go back and solve the equations for the case where the
voltages are equal and you will find that they BOTH supply current
to the load. Because of the differing resistors which would represent
the internal resistance of the batteries, one supplies twice the
current of the other. Capiche?



I have yet to hear him explain how the
* batteries then decide which one it will be and how they
will change their voltage to obtain the allegedly necessary
"push" to get the current flowing.

He does not have to explain that, it is self explanatory when one
understand that there are no perfect conductors with zero resistance in
a power distribution system.

To get power into the grid from a local generated power the voltage has
to be higher. HOW much higher depends on the impedance in the systems.



Imperfections do not render a model useless or change the facts. If
you
want to model the transmission line, then insert some additional
resistors
after the 10 ohm and 20 ohm resistors to model the line. Make a
model
that includes capacitance and inductance too, and make it an AC
circuit . It changes
nothing with regard to the ridiculous requirement that in order to
supply
current, a source can't just be equal in voltageto another source
connected to the same load and that it has to be
higher. If you have a model that shows Homeguy's planet, we'd like
to see it. Until then, Jim's model is perfectly fine.