Section 7: Batteries

Sealed Gel Cell

Another type of deep-cycle battery construction is the sealed gel-cell. They don’t use removable battery caps. The electrolyte is in the form of a gel rather than a liquid. The sealed construction allows the batteries to be mounted in any position without spilling. The advantages are no maintenance (to the battery itself—the system will still require routine maintenance), long life (800 cycles claimed) and low self-discharge. The disadvantages are high initial cost and the possibility of damage from overcharging.

While there are many manufacturers of quality flooded batteries, there are only a few manufacturers of suitable gel-cells. Don’t confuse gel batteries with maintenance free batteries. The latter is typically a standard liquid electrolyte type battery without caps for adding water, and if the electrolyte gets low, you replace the battery.

AGM (absorbed glass mat) batteries are similar to gel-cells and deep-cycle types may be used in inverter applications.

Environment

For long life and good performance, batteries need to be located in protected, ventilated enclosure insulated from extremes in temperature.

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. Do not locate the inverter in the same space as the batteries, unless the batteries are of the sealed gel- cell type.

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.

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 charger. This should be considered when designing the system. If extremely cold temperatures are expected at the location of a system, a heated equipment room 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 the battery. If the batteries are insulated, the heat can be kept in the batteries to keep them warmer. This will substantially increase the performance of the system.

Prosine 2.5/3.0 Installation & Operation Guide

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