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:
•
Linear
regulators use a simple feedback circuit to vary how much energy is passed through
and how much is discarded. The regulator produces a lower output voltage by dumping
unneeded energy. This wasteful, inefficient approach makes linear regulators poor choices
for applications that have a large difference between the input and output voltages, or for
Pololu 3pi Robot User’s Guide
© 2001–2019 Pololu Corporation
5. How Your 3pi Works
Page 13 of 85
