Battery Systems for Mission Critical Infrastructure - Design, Maintenance and Testing (3)

Refer to the Previous Article: Battery Systems for Mission Critical Infrastructure - Design, Maintenance and Testing (2)

Valve-regulated Lead-acid (VRLA) Batteries

VRLA batteries currently are very popular. They are known as "nonmaintenance" batteries, mostly because of the fact that they are sealed and employ a "recombinant technology." The fact that the battery is sealed ensures the preserving of the electrolyte, no matter the position of the battery cell (you can even turn it upside down). Recombinant technology means that the oxygen released from the positive plate ends up in the negative plate, where it recombines with hydrogen and turns into water. This process preserves the battery water.

Just as it has for vented batteries, IEEE has developed a standard, 1188-2005, IEEE Recommended Practice for Maintenance, Testing, and Replacement of VRLA Batteries for Stationary Applications (https://standards.ieee.org/findstds/standard/1188-2005.html).

Even though VRLA batteries are sealed, there are always dangers associated with installing and maintaining batteries. Only trained and knowledgeable personnel should work around batteries. In addition, unauthorized personnel should not have access to the batteries. The battery area should not be used as storage for tools or anything else. All personnel should use personal protective equipment, such as goggles, gloves, and safety shoes, while working on batteries.

The table shows typical steps to be taken when adverse situations are witnessed.

Just as with vented batteries, inspection is an important part of maintenance. IEEE recommends monthly, quarterly, and yearly inspections. But this recommendation is for general use. For mission critical facilities or processes, there needs to be a weekly inspection as well.

The monthly inspection for VRLA batteries is more or less the same as the one for vented lead-acid batteries. This inspection includes the following areas -

A visual inspection of:

1. The general condition of the area. The area (room) should be maintained as clean as possible so that dirt or excessive dust does not cover the battery cells. Unclean equipment is harder to assess during a visual-only inspection.
2. The battery cells, looking for cracks. This inspection is important because a crack in the cell’s outer shell could allow the electrolyte to leak.
3. The battery terminals for corrosion. Corrosion of the battery terminals will increase the resistance of the connection, thereby decreasing the amount of current supplied by the battery system.

A measurement of:

1. The float voltage at the battery terminals. If the battery system performs at a float voltage outside the manufacturer’s recommended range, the battery’s life expectancy would be adversely affected.
2. Room or area temperature and ventilation. The temperature is important because it affects the battery’s life expectancy. Ventilation is important because proper movement of the air mitigates high concentrations of hydrogen, which is a byproduct of chemical processes in the battery cells. High concentrations of hydrogen in the air significantly increase the risk for explosions.
3. The float current of the string. A high float current would adversely affect the battery life, as it increases the temperature in the cell.

The quarterly inspection includes measurements of the following:

1. The cell’s internal Ohmic values. Care should be taken to use the same method each time so that a credible baseline is set. If the Ohmic values change drastically (30% to 50%), a battery replacement might be warranted.
2. The temperature of the negative terminal of each cell. A higher temperature than other cells could indicate a higher charging current. Higher temperatures adversely affect the battery life.
3. Cell voltages. Both high and low voltages could be problematic. Prolonged low voltage-lower than the manufacturer’s limit-without an increase in temperature could indicate an internal problem. Prolonged high voltage-higher than the manufacturer’s recommended limit-could impact the battery life by accelerating the dryout.

The yearly inspection is then limited to measuring the following:

1. Cell-to-cell and battery terminals resistance. If the value is 20% or more than the baseline, corrective actions should be taken, such as cleaning the connections and retorquing.
2. Battery-charger ripple current. It could impact the battery temperature.

Next Article:
Battery Systems for Mission Critical Infrastructure - Design, Maintenance and Testing (4)

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