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Build Your Own Combat Robot
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Battery Rated Capacity Multiply By 6-Minute Capacity 6-Minute Current 6-Minute Voltage
Type
NiCad 4.4Ahr 0.90 4.0Ahr 40 amps 10.3 volts
NiMH 6.5Ahr 0.92 6.0Ahr 60 amps 10.3 volts
SLA 12.0Ahr 0.33 4.1Ahr 41 amps 11.5 volts
SLA 17.5Ahr 0.33 5.8Ahr 58 amps 11.5 volts

TABLE 5-1 Battery Performance Characteristics

If you have the battery manufacturers’ data sheets, you can determine the actual
battery-specific values yourself. If you don’t have the data sheets, you can use the
“Multiply By” column values as a rule of thumb to estimate the 6-minute capacity
from the original battery amp hour specifications. In Figure 5-2, the 6-minute
run-time capacity of the 12Ahr battery was 4Ahr. This is a third of the Ahr rating
of the original battery. Also, from Figure 5-2, you can see where the 0.9 and 0.92,
6-minute conversion factors for the NiCad and NiMH batteries come from.
The following two equations show how to estimate the 6-minute and the peak
current capacity of a battery:

5.2

5.3
The first equation addresses the 6-minute capacity, where C 6min is the average cur-
rent the battery can deliver for 6 minutes, in amps; K is the 6-minute conversion
f
factor, as seen in Table 5.1; and C is the original battery Ahr specification. In the
batt
second equation, the peak current capacity is C peak .

Battery Rated Max. Current Voltage @ Max. Rated Weight Rated Power 6-Minute
Type Current Volts Density Power Density
NiCad 100 amps 7.90 volts 1.4Kg 3.1Ahr/Kg 2.9Ahr/Kg
NiMH 100 amps 10.30 volts 1.8Kg 3.6Ahr/Kg 3.3Ahr/Kg
SLA 120 amps 10.22 volts 4.1Kg 2.9Ahr/Kg 1.0Ahr/Kg
SLA 175 amps 9.78 volts 5.9Kg 3.0Ahr/Kg 1.0Ahr/Kg

TABLE 5-2 Battery Performance Characteristics