A way to design VRLA battery for high availability

Most sealed VRLA batteries currently being manufactured and bid for UPS applications in the USA have a five year design or target life. This can vary upwards with reduced ambient, cycling, and manufacturer, or downwards with factors already discussed. Unlike their more expensive flooded counterparts, VRLA cells tend to fail about as often open circuit as short circuit. This is due primarily to dry-out of electrolyte due to venting of generated hydrogen & oxygen from electrolytic charge & discharge through the one-way valves. As alluded to earlier, dry-out has an extremely high impact on reliability since a single open circuit cell can make an entire string inoperative.

VRLA batteries are generally supplied one string per cabinet in medium to large systems. There can be as little as one string, or as many as 5 or 6 strings deployed to provide the required reserve time. Since a great many UPS systems are purchased “low bid” and many end users do not know the difference, the battery systems provided with such systems could be the cheapest that meet reserve time specification. This will invariably mean single string, or sometimes worse, two string designs for as little as 5 – 10 minutes of reserve time in UPS systems 150-200 KVA or smaller in size. Single string batteries are the most common supplied today. They are very cost-effective and, as empirical data confirms, quite satisfactory for many if not most UPS applications, but not for true high availability applications. Tow strings can actually be worse than one for some low reserve time applications because if either of the two is lost, the entire load is lost – even for a split second outage. This fact is rather ironic, since VRLA battery strings are relatively inexpensive and easy to parallel.

The better way to design with VRLA for high availability applications is to understand the costs, as well as the reliability over time of the various elements of your UPS systems and use that in the decision matrix. Looking at the UPS, battery (single string), and genset components of an overall system, batteries are least expensive, most prone to fail, and have highest impact on critical load crash potential.

If you want to know more about VRLA battery, you can just visit Leoch International, which is an excellent manufacturer of lead acid battery. The company is a public company which has over 10 year’s history and it is very reliable and dependable. If you are interested in the company, you can search for more information in the internet. The office website is http://www.leoch.com.