Charging at High and Low Temperatures (2)?
The charge
acceptance of a NiCd at higher temperatures is drastically reduced. A battery that provides
a capacity of 100 percent if charged at moderate room temperature can only accept 70
percent if charged at 45°C (113°F), and 45 percent if charged at 60°C (140°F) (see
Figure 4-7). Similar conditions apply to the NiMH battery. This demonstrates the typically poor
summer performance of vehicular mounted chargers using nickel-based batteries. Another reason for poor battery performance, especially if charged at high ambient
temperatures, is premature charge cutoff. This is common with chargers that use absolute temperature to terminate
the fast charge. These chargers read the SoC on battery temperature alone and are fooled
when the room temperature is high. The battery may not be fully charged, but a timely href="http://www.good-battery.co.uk/battery-charger.html">charge cut-off protects the
battery from damage due to excess heat. The NiMH is less forgiving than the NiCd if charged under high and low temperatures. The NiMH cannot be fast charged
below 10°C (45°F), neither can it be slow charged below 0°C (32°F). Some industrial
chargers adjust the charge rate to prevailing temperatures. Price sensitivity on consumer
chargers does not permit
elaborate temperature control features.
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