BATTERIES
Trace Engineering Co. Inc. Tel (360) 435-8826 Part Number 3179
5916 195
th
Street, NE Fax (360) 435-2229 Effective August 6, 1998
Arlington, WA 98223 USA www.traceengineering.com Page
43
require routine maintenance), long life (800 cycles claimed) and low self-discharge. The
disadvantage is high initial cost and the possibility of damage from overcharging.
While there are many manufacturers of quality non-sealed batteries, there are only a few
manufacturers of suitable gel-cells. Don’t confuse sealed batteries with maintenance free batteries.
The latter is typically a standard liquid electrolyte type battery without caps for adding water, and
when the electrolyte gets low, you replace the battery.
AGM (absorbed glass mat) batteries are similar to gel-cells and may be used in inverter applications.
Environment
For long life and good performance, batteries need to be located in protected enclosures insulated
from extremes in temperature. These environmental factors are discussed in the following sections.
Location
Batteries should be located in an accessible location with access to the battery caps and terminals.
At least six inches of clearance above is recommended. They must be located as close as possible
to the inverter, but can not limit the access to the inverter and the inverter’s over-current protection
device.
The over-current protection device must be located per code within 18 inches of the battery
installation, and must be covered to prevent possibility of discharging material in the event of a short
circuit.
Enclosures
Batteries must be protected inside a ventilated enclosure. The enclosure should be ventilated to the
outdoors from the highest point to prevent accumulation of hydrogen gasses released in the charging
process. An air intake should also be provided at a low point in the enclosure to allow air to enter the
enclosure to promote good ventilation. For most systems, a one-inch diameter vent pipe from the top
of the enclosure is adequate to prevent accumulation of hydrogen.
Temperature
The effective capacity of a battery is reduced when cold. This phenomenon is more significant with
lead-acid type batteries compared to alkaline types. When the internal temperature of a lead-acid
battery is 32°F (0°C) the capacity can be reduced by as much as 50%. This effectively reduces the
size of the system’s “gas tank”, requiring more frequent “refueling” by the back-up source (usually a
generator). This should be considered when designing the system. If extremely cold temperatures
are expected at the location of a system, either a heated equipment room or alkaline batteries should
be considered.
If the system is located in an unheated space, an insulated enclosure is highly recommended for the
batteries. During the charging process, the batteries release heat due to the internal resistance of
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