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REGULATING VOLTAGE 201

+3 volts +1.5 volts

+1.5 volts

+1.5 volts 0 volts
Figure 19- 8 Separate cells may
be tapped to derive several different
voltages. Note that the ground
0 volts connection is relative: when ground
is the connection between batteries,
you get both positive and negative
0 volts -1.5 volts voltages.

• With one cell you get the normal 1.5 volts.
• With two cells, you get 1.5 volts when tapping off the first cell, and 3 volts when tapping
off the second cell.
• The polarity of the voltage taps is relative. If you have a two- cell power supply, like that
shown, the center tap can be made ground, or 0 volts. That means connecting to the
negative terminal of the bottom cell actually provides a negative voltage cell, or 1.5 volts.
The positive terminal of the top cell provides +1.5 volts.

Of course, you are not limited to tapping between single cells. If you have eight cells, for
instance, you could tap at every other cell, and get voltages of 3, 6, 9, and 12 volts. Or you
can combine two 6- volt battery packs to produce 6- and 12- volt supplies, or 6- and +6- volt
supplies. These types of split supplies are useful in some kinds of motor connection schemes.
See Chapter 22, “Using DC Motors,” for ideas.

Regulating Voltage

The parts of your robot may need specific voltages to operate properly. This is most often the
case with electronics, which typically require 5 or 3.3 volts. The exact voltage can vary a bit,
but not much. For example, on a 5- volt system, the acceptable voltage levels may be from
4.5 to 5.5 volts. No higher, no lower.

DC motors typically don’t require voltage regulation. Most run fine over a wide range of
G voltages. Increasing the voltage has the effect of making the motor run faster, and vice versa.
R/C servo motors are an exception. Unless otherwise specified, they need to be operated at
between around 4.5 and 7.2 volts.
Voltage regulation is accomplished in a number of ways. Here are the five most common;
the first four are explained in more detail in this chapter.
• Silicon diodes can be used to drop the voltage in increments. This is not true regulation,
but it can be used when all you need is a simple means to achieve a lower voltage. When
put into a circuit, the typical silicon diode will reduce the voltage by about 0.7 volts.

19-chapter-19.indd 201 4/21/11 11:49 AM