C&D Technologies RS-990 Liberty Series 1000 - Manual (Page 24)

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When the voltages of individual cells are lower than normal, it is
possible to conclude that insufficient charging has occurred.
The following are possible causes of cell voltage variations:
• Panel voltmeter reading high - This results in a low float voltage.
Re-calibrate the panel voltmeter.
• Poor intercell/inter-unit or terminal connections - If any
connection is found to be higher than 20% of the initial installation
values, disassemble and clean contact surfaces and reassemble.
• A temperature variation of more than 5°F (2.8°C) between cells -
Warmer cells drop to a lower voltage, because they require more
float current to keep them fully charged. Avoid exposing batteries to
external heat sources, which can cause temperature imbalance.
3.4 Effects of temperature
A lead-acid battery is an electro chemical device. Heat accelerates
chemical activity; cold slows it down. Normal battery operating
temperature is 77°F (25°C). Higher than normal temperatures have
the following effects on a lead-acid battery:
• Increases capacity
• Shortens life
• Increases internal discharge or local action losses
• Lowers cell voltage for a given charge current
• Raises charging current for a given charge voltage
• Increases the rate of dry-out of electrolyte
Lower than normal temperatures have the opposite effect and reduce
capacity. In general, at proper float voltage, a battery in a cool
location will last longer than one in a warm location.
Note: No temperature correction is required when operating at 77°F
+/- 10°F, (25°C +/- 5.5°C). The following correction factors
apply for a range not exceeding +/- 30°F from nominal. For
further
assistance with temperature correction factors, contact C&D
Technologies.
If the operating temperature is other than 77°F (25°C), it is recommend-
ed that the float voltage be changed as follows:
For temperatures other than 77°F (25°C), correct float voltage by 2
mV per degree F (3.6 mV per degree C):
• Add 2 mV (0.002 Volts) per degree F (3.6 mV per degree C) below
77°F (25°C)
• Subtract 2 mV (0.002 Volts) per degree F (3.6 mV per degree C)
above 77°F (25°C)
Note: Temperature compensation will materially improve battery
service life when provided.