Battery voltage vs. current.
The
power
put out by a battery is measured by multiplying the volts by the amps, giving a
measurement in watts (W). For example, at the point marked in the graph, we have a voltage of
0.9 V and a current of 0.6 A, this means that the power output is 0.54 W. If you want more power,
you need to add more batteries, and there are two ways to do it:
parallel
and
series
configurations.
When batteries are connected in parallel, with all of their positive terminals tied together and all of
their negative terminals tied together, the voltage stays the same, but the maximum current output is
multiplied by the number of batteries. When they are connected in series, with the positive terminal
of one connected to the negative terminal of the next, the maximum current stays the same while the
voltage multiplies. Either way, the maximum power output will be multiplied by the number of batteries.
Think about two people using two buckets to lift water from a lake to higher ground. If they stand next
to each other (working in parallel), they will be able to lift the water to the same height as before, while
delivering twice the amount of water. If one of them stands uphill from the other, they can work together
(in series) to lift the water twice as high, but at the same rate as a single person.
In practice, we only connect batteries in series. This is because different batteries will always have
slightly different voltages, and if they are connected in parallel, the stronger battery will deliver current
to the weaker battery, wasting power even when there is nothing else in the circuit. If we want more
current, we can use bigger batteries: AAA, AA, C, and D batteries of the same type all have the same
voltage, but they can put out very different amounts of current.
The total amount of
energy
in any battery is limited by the chemical reaction: once the chemicals are
exhausted, the battery will stop producing power. This happens gradually: the voltage and current
produced by a battery will steadily drop until the energy runs out, as shown in the graph below:
Pololu 3pi Robot User’s Guide
© 2001–2019 Pololu Corporation
5. How Your 3pi Works
Page 12 of 85
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