Page 110 - Build Your Own Combat Robot

Chapter 5:
It’s All About Power
note These equations are rule-of-thumb–type equations for estimating current capacity 91
in a battery. To obtain the exact values, consult the battery manufacturer’s data sheets. Some
high-performance batteries have a much higher peak current capacity, while other batteries’
peak current capacity is measured in millisecond time frames. These questions provide a good
starting point for estimating the life of a battery.

E lectrical Wiring Requirements

Another part of the battery selection process is selecting the proper wire sizes be-
tween the batteries and the motors. The electrical wires must withstand the cur-
rent requirements without overheating. The wire’s current rating is determined by
the gauge of the wire and the type and thickness of the insulation around the wires.
If the wire size is too small for the amount of current passing through it, the wire
will heat up to the point where the insulation will melt—and in the worse case, the
wire may melt. Table 5-3 shows the conservative American Wire Gauge (AWG)
values for various maximum currents through copper wire. This table is a good
starting point for selecting the appropriate wire sizes for your robot.
The figures in Table 5-3 are conservative and considered safe for normal home
use. But some robot builders use #12 wires for 200-plus amps, #10 for 350-plus
amps, #8 for 500-plus amps, and #4 for 1,000-plus amps. (These are peak amp
draws; average amp draws are much lower.) The key is to use the high-tempera-
ture insulation.

Current Minimum AWG
13 amps #20
18 amps #18
20 amps #16
28 amps #14
38 amps #12
53 amps #10
78 amps #8
105 amps #6
142 amps #4
196 amps #2
266 amps #0

TABLE 5-3 American Wire Gauge Copper Wire Minimum Current Ratings