Pololu 3pi Robot - Manual (Page 11)

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:
Battery voltage vs. time.
A rough measure of the amount of energy stored in a battery is given by its milliamp-hour (mAH) rating, which
specifies how long the battery will last at a given discharge rate. The mAH rating is the discharge rate multiplied by
how long the battery lasts: if you draw current at a rate of 200 mA (0.2 A), and the battery lasts for 3 hours, you would
call it a 600 mAH battery. If you discharge the same battery at 600 mA, you would get about an hour of operation
(however, battery capacity tends to decline with faster discharge rates, so you might only get 50 minutes).
Note: If you have purchased rechargeable batteries for the 3pi, you should fully charge them before
you first use them. You should never attempt to program your 3pi if its batteries are drained or
uncharged. Losing power during programming could permanently disable your 3pi.
5.b. Power management
Battery voltage drops as the batteries are used up, but many electrical components require a specific voltage. A special
kind of component called a voltage regulator helps out by converting the battery voltage to a constant, specified
voltage. For a long time, 5 V has been the most common regulated voltage used in digital electronics; this is also
called TTL level. The microcontroller and most of the circuitry in the 3pi operate at 5 V, so voltage regulation is
essential. There are two basic types of voltage regulators:
Pololu 3pi Robot User's Guide © 2001–2014 Pololu Corporation
5. How Your 3pi Works Page 11 of 63