Page 224 - Robot Builder's Bonanza

USING BATTERY CELLS IN A BATTERY HOLDER 193

Parallel connection Series connection
(double the current) (double the voltage)
+ +

Wires end-to-end Wires side-to-side
Figure 19- 3 Batteries with solder tabs may be
wired side to side or end to end, whatever makes the
best shape for the intended use.

- -
Figure 19- 2 Batteries can be connected in series
or in parallel. Parallel connection is seldom used, as
current from the strongest battery is drained even
when the pack is not connected to a circuit.

Voltage Number of Cells Voltage Number of Cells
2.4 2 9.6 8
4.8 4 12 10
7.2 6 14.4 12

In- between voltages are also possible, using an odd number of cells. Seven cells of either
NiCd or NiMH batteries is 8.4 volts, for example. You just need to make sure your battery
charger is adjustable for that voltage. Some chargers will work with packs within a range— say,
9.6 to 18 volts. The recharger automatically adjusts to the proper voltage.
Use a polarized connector so you can easily hook up your battery to the rest of your robot.
Never leave the wires bare, as this increases the chance of a short circuit. Shorting freshly
charged batteries can cause fire or burns and can permanently damage the battery.

Using Battery Cells in a Battery Holder

Perhaps the most convenient method of using batteries with your robot is with a battery
holder. Electrical contacts in the holder form the proper connections from the cell- to- cell; the
voltage at the holder terminals is the sum of all the cells.
Holders are available for all the common battery sizes and even for some of the
not- so- common ones. (However, if you plan on using the fractional AA size, or one of the
subsizes, you are better off building a battery pack, as detailed previously.) Holders for two and
four cells are among the most common. Battery holders come in either plastic or metal. The
plastic holders are a tad more bulky, but they are lighter, cheaper, and easier to mount.
Battery holders often must conform to the shape of the object they are used in, so there
are plenty of variations in how the cells are laid out— for example, a four- cell holder may ori-
ent the cells all in a single row, or it might pack them side by side. See Figure 19- 4 for some
examples of single- side battery holder layouts. There are even more variations for battery
holders with cells on both sides.

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