# newcomer battery question

Discussion in 'Electronic Basics' started by Anders Lindén, Jan 20, 2004.

1. ### Anders LindénGuest

Hello!

I wonder why there is no currency in this "circuit" between
the two batteries.

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I have heard the explanation that the batteries wants
"balance", and therefore
the electrons from one of the batteries doesnt want to
travel to the other battery,
even if there is a shortcoming of electrons there. But, as I
have understood it,
there are two chambers in a battery that ideally are
isolated from each other and
doesnt "communicate".

/Anders

2. ### Greg NeillGuest

There is no circuit. A circuit is so named because it
implies a closed loop, a complete path around the
components.

3. ### Anders LindénGuest

True, there is no curcuit. I was writing "curcuit" to denote
that I was aware of it.
/Anders

4. ### Greg NeillGuest

no continuing flow. What you've got instead is an exercise
in static electric charge distribution. Assuming both
batteries are overall neutral in charge, connecting them
any which way you please without completing a circuit so
that their chemical energy can drive a current, you'll have
no current flow.

5. ### Anders LindénGuest

But isnt a battery consisting of two chambers that are
isolated from each other?

/Anders

6. ### Ross MacGuest

That's easy....no load no current !!

7. ### John PopelishGuest

The fluid analogy for a battery is a pump that produces a constant
pressure difference between inlet and outlet. Your diagram is thus
equivalent a pump with a tall pipe connected to its outlet and the
weight of the fluid standing in the pipe is balancing the pump's
pressure, so the fluid is standing still. No work is being done so no
energy is being consumed. But there is a pressure difference
(voltage) between the top and bottom connection.

8. ### Greg NeillGuest

Well, it's a little more complicated than that.
Batteries separate charge via chemical means.

But even so, no charge is created out of nothing in
the battery; the total number of electrons and
protons remains the same, hence the battery, taken
as a whole, is neutral.

The potential difference between the two poles of the
battery consists of equal and opposite charges. The
total potential difference depends upon the chemical
potential driving the charge separation, typically
on the order of 1.5V for a unit cell. Once that
potential difference equals that of the chemical
potential, no further charge separation can occur.

If you drop an electron onto the positive terminal,
it will cancel one electron's worth of the charge,
and the chemical cell will be able to separate
another electron and send it to the negative pole
to balance the charge. The entire battery will
then have a net negative charge equal to that of
the single electron that you put on it. This net
charge would make it a bit harder to add another
electron in a similar fashion. After a while,
you'd find it impossible to add more electrons to
the positive pole without first taking some away
from the battery, because the battery will have
a high overall negative charge.

The solution is to take an electron off the
negative pole each time you add one to the
positive one. This keeps the battery overall
neutral in charge. This is also why you need
to have a complete circuit. Otherwise you quickly
accumulate charge which prevents further movement.

When you connect two batteries as you've shown, the
effect is similar to connecting a chunk of inert
metal to one pole of a single battery. There may
be a brief, miniscule pulse of current while the
charge spreads over the metal surface, but it will
amount to a very tiny and short lived shifting of
charges. The whole metal chunk will have a net
1.5V charge with respect to the other pole of the
battery. Once this situation obtains, no further
current can flow.

Let's imagine a simple mechanical analogy. Let's
say our "battery" is a length of pipe filled with
water. In the center of the pipe is a little
pump which tries to pump water from the top of
the pipe to the bottom. It has a fixed pressure
rating, so it tries to maintain this fixed
pressure between the ends of the pipe. When there
are no connection to the "battery", no current
can flow.

Now you stack two of these pipes, one on top of the
other and connect the touching chambers. You still
have no connections to the remote ends. How much
water can flow?

If you connect a tube from the bottom of the stack
to the top, what happens?

9. ### Anders LindénGuest

Ok, put a resistor between the batteries then.

/Anders

net...