Page 52 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

One disadvantage to NiCd batteries is that they have a lower voltage,
1.2 V per cell. So a C cell battery will deliver about 1.2 V instead of 1.5 V.
The effect becomes more pronounced when using multiple cells. For
instance, a “9V” NiCd battery made from six NiCd batteries will deliver
approximately 7.2 V.
Automotive lead-acid batteries are rechargeable but are not suitable for
robotics. The reason is that automotive batteries are not designed to be
completely discharged (run down) before being recharged. These bat-
teries can supply high currents for short periods of time (car starting)
and need to be recharged almost immediately.
Completely discharging the electric power a rechargeable battery
contains before recharging the battery is called deep cycle. There
are deep-cycle lead-acid batteries available, mostly because of the
solar power industry, but you will find these batteries carry a higher
price tag. When building robotic systems, you should use deep-cycle
rechargeable batteries.
Secondary batteries, while initially more expensive, are cheaper in
the long run. Typically secondary batteries can be recharged 200 to
1000 times. In many cases a simple recharging circuit can be built
into the robot so that it becomes unnecessary to remove batteries
for charging. 31

Rating secondary batteries
NiCd NiCd batteries and sealed lead-acid batteries are the most
common rechargeables, with NiCd batteries being more popular.
Both types of batteries have lower energy densities than primary
batteries.
NiCd batteries only provide 1.2V per cell, in comparison to pri-
mary batteries which provide 1.5V per cell. Manufacturers claim
that NiCd batteries are good for 200 to 1000 charge-recharge
cycles. However, NiCd batteries will die fast if they aren’t
recharged properly. The life expectancy of NiCd batteries is 2 to
4 years. Without use, a fully charged NiCd battery will lose its
charge in 30 to 60 days.

NiCd batteries are designed to be recharged at 10 percent of
their rated capacity. This means that if a particular NiCd battery
is rated at 1 Ah, it is safe to recharge the battery at 100 mA
(1 A/10 100 mA). The terminology used to describe the above
recommended recharge rate is “C/10.”

NiCd batteries are designed to be charged using a constant current
at the C/10 rates. Because of inefficiencies, it is necessary to charge

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