Batteries and battery systems are the most important component of any UPS system. UPS batteries are the engine, or the power source, if the utility power fails or some type of power anomaly is experienced. Batteries are the most common failure/problem within any UPS system. Batteries can also be found in emergency generators and substation control power.
VRLA (Valve Regulated Lead Acid)
Valve Regulated Lead Acid UPS batteries, are also sometimes called “maintenance free” batteries. The term “maintenance free” comes from the fact that you are not able to add fluid to the battery. The term “valve regulated “means these batteries limit the inflow and outflow of gas to the cell. VRLA batteries are the most popular UPS battery type currently, mainly due to cost, availability, safety, and low maintenance. If VRLA battery environments are neglected and become overheated, this can lead to catastrophic issues such as thermal runway.
Wet Cell
Also called a “flooded cell battery,” wet cells contain spillable liquid, and must be properly orientated and protected from damage. These cells require a higher level of maintenance than its sealed counterpart but offer long, extended run-time, and 20-year design life.
Battery Safety
Performing regular inspections on battery systems presents a unique challenge from other electrical power systems in that you cannot simply turn them off for maintenance or corrective action. Batteries are safe when operated and handled properly. However, they do contain volatile, and therefore potentially, hazardous materials which can cause burns and other serious injuries.
Battery Hazards
- Electrolyte (Sulfuric Acid)
- Flammable Gasses (Hydrogen)
- Electric Shock (large banks)
- Physical hazards (weight)
Battery PPE
- Googles
- Face shield
- Rubber gloves
- Rubber apron
- Eye wash station
Battery Maintenance
Proper routine maintenance is the most critical element to ensure UPS performance. A single defective battery in a string can bring down the entire system during an interruption. Performing regular inspections on battery systems presents a unique challenge from other electrical power systems in that you cannot simply turn them off for maintenance or corrective action.
Specific Gravity
The specific gravity of the battery electrolyte can determine the state of charge. The higher the specific gravity of the electrolyte, the higher the state of charge.
Float Voltage
Measuring float voltage is one of the more traditional methods of testing a battery, but it’s important to understand that a correct cell voltage doesn’t indicate anything except that the cell is fully charged.
Intercell Connections
Validate intercell connection resistance using a low-resistance ohmmeter. Batteries cannot be more than 20% above the installation value or ceiling value set by the system designer per IEEE standards.
Internal Resistance
Battery Impedance tests are performed to determine the internal ohmic value and indicate the overall health of a battery. A lower internal resistance generally indicates a higher capacity; therefore an increase in internal resistance over time can indicate declining battery capacity, or degradation.
