Why are Backup Batteries Needed?
Batteries are used to ensure that critical electrical equipment is always on. There are so many places where batteries are used – it is nearly impossible to list them all.
Some of the applications for batteries include:
- Electric generating stations and substations for protection and control of switches and relays
- Telephone systems to support phone service, especially emergency services
- Industrial applications for protection and control
- Back up of computers, especially financial data and information
- “Less critical” business information systems
Without battery back-up hospitals would have to close their doors until power is restored. But even so, there are patients on life support systems that require absolute 100% electric power. For those patients, as it was once said, “failure is not an option.” Just look around to see how much electricity we use and then to see how important batteries have become in our everyday lives. The many blackouts of 2003 around the world show how critical electrical systems have become to sustain our basic needs. Batteries are used extensively and without them many of the services that we take for granted would fail and cause innumerable problems.
Why Test Battery Systems?
There are three main reasons to test battery systems:
- To insure the supported equipment is adequately backed-up
- To prevent unexpected failures by tracking the battery’s health
- To forewarn/predict death
And, there are three basic questions that battery users ask:
- What is the capacity and the condition of the battery now?
- When will it need to be replaced?
- What can be done to improve / not reduce its life?
Batteries are complex chemical mechanisms. They have numerous components from grids, active material, posts, jar and cover, etc. – any one of which can fail. As with all manufacturing processes, no matter how well they are made, there is still some amount of black art to batteries (and all chemical processes).
A battery is two dissimilar metallic materials in an electrolyte. In fact, you can put a penny and a nickel in half of a grapefruit and you now have a battery. Obviously, an industrial battery is more sophisticated than a grapefruit battery. Nonetheless, a battery, to work the way it is supposed to work must be maintained properly. A good battery maintenance program may prevent, or at least, reduce the costs and damage to critical equipment due to an AC mains outage.
Even thought there are many applications for batteries, standby batteries are installed for only two reasons:
- To protect and support critical equipment during an AC outage
- To protect revenue streams due to the loss of service
The following discussion about failure modes focuses on the mechanisms and types of failure and how it is possible to find weak cells. Below is a section containing a more detailed discussion about testing methods and their pros and cons.
Why do Batteries Fail?
In order for us to understand why batteries fail, unfortunately a little bit of chemistry is needed. There are two main battery chemistries used today – lead-acid and nickel-cadmium. Other chemistries are coming, like lithium, which is prevalent in portable battery systems, but not stationary, yet. Volta invented the primary (non-rechargeable) battery in 1800. Planté invented the lead-acid battery in 1859 and in 1881 Faure first pasted lead-acid plates. With refinements over the decades, it has become a critically important back-up power source. The refinements include improved alloys, grid designs, jar and cover materials and improved jar-to-cover and post seals. Arguably, the most revolutionary development was the valve-regulated development. Many similar improvements in nickel-cadmium chemistry have been developed over the years. (source Megger.com)
Megger Battery Impedance Test Equipment
Determines condition of lead-acid and NiCd cells up to 7000 Ah
On-board Pass/Warning/Fail indications
Robust, repeatable instruments
On-line testing
The BITE 2 and BITE 2P Battery Impedance Test Equipment determine the condition of lead-acid and nickel-cadmium cells up to 7000 Ah. An advanced feature set has been developed that includes Pass/Warning/Fail calculations based on a user-entered baseline value, advanced printing functions and more. The case of the BITE 2P consists of both the transmitter and a carrying case for all of the standard accessories and some of the optional accessories, in an all-in-one unit. The BITE 2 and its accessories fit into a sturdy canvas case with a shoulder strap.
The instruments work by applying a test current across the battery string while on-line, then measuring the total current (ac ripple + test current) and the voltage drop of each cell/jar. It then calculates the impedance. They also measure dc voltage and interconnection (strap) resistance to help determine the overall condition of the entire battery string’s electrical path from terminal plate to terminal plate.
The BITE 2 and BITE 2P receiver stores the readings in its internal memory. These measurements, along with other maintenance data such as ambient and pilot cell temperatures and ac ripple current, assist in determining the overall condition of battery systems. Megger recommends that impedance measurements with the BITE 2 or BITE 2P be made part of a battery maintenance program with readings taken and recorded semiannually for flooded batteries and quarterly for VRLA.
Unlike load cycle testing that involves substantial downtime and repeated discharges, using the instruments require no battery discharge, nor do they stress the battery in any way compared to other techniques. With a test time of less than 20 seconds for each cell and intercell connector, one person can easily, quickly, and precisely measure internal cell impedance, dc terminal voltage and intercell connection resistance without taking the battery system off line.
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