Build Your Own Combat Robot

90 Build Your Own Combat Robot
Battery
Type
Rated Capacity Multiply By 6-Minute Capacity 6-Minute Current 6-Minute Voltage
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 �
Battery
Type
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:
The first equation addresses the 6-minute capacity, where C 6min is the average current
the battery can deliver for 6 minutes, in amps; K f is the 6-minute conversion
factor, as seen in Table 5.1; and C batt is the original battery Ahr specification. In the
second equation, the peak current capacity is C peak .
Rated Max. Current Voltage @ Max. Rated
Current Volts
Weight Rated Power
Density
6-Minute
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 �
5.2
5.3