Exchanging information at BATTCON 2007 in Florida are Jeff Alber, George Haber and Kurt Uhlir.

This year’s BATTCON International Battery Conference celebrated its 11th year with more than 500 in attendance at this annual event that supports the stationary battery industry. The BATTCON Technical Committee did a fantastic job by selecting a great venue and an even better convention program which consisted of 22 papers by industry specialists and four panels of experts who debated some of the hottest topics in the industry. I have highlighted some of the technical papers below, and the panel discussions had titles such as, 1) Power architecture of large facilities, 2) Should you be considering new technologies?, 3) State of the traditional industry: Are things getting better? and 4) A general open panel discussion.

The BATTCON Trade Show was as big as ever with more than 50 industry suppliers from all over the globe. The conference was preceded by the annual golf outing and by two pre-conference battery-related seminars, titled “Battery Basics” and “Beyond the Fundamentals: Advanced Topic in Lead-Acid Batteries.” The next BATTCON conference is scheduled to be held May 5-8, 2008, in Marco Island, Florida.

Distributed DC Concept for High Density Data Center Applications
Kfir Godrich of EYP Mission Critical Facilities Inc.

described how data center topology is one of the greatest challenges in the industry simply because of the amount of computing power and energy required these days. Godrich stated that if microprocessor technology follows the current trend, then by 2010 the operating temperature of the microprocessor will be equivalent to the temperature of the sun! All joking aside, he noted that most equipment associated with data centers tends to be very inefficient which leads to the fact that 50% of the cost of operating a data center is related to the energy bill. AC/DC converters are inefficient and he is proposing that high voltage DC systems (500-600 volts) could be used in data centers and then DC/DC converters used from there to step the voltage down. He showed data that suggested that the current AC systems are ~60% efficient while his proposed DC2 TM concept would increase the overall efficiency to ~75%.

Design Considerations for Distributed DC Power Applications in Traditional Telecommunication Facilities

Robert Burditt of PECO II Inc. began by asking, “Why adopt a distributed architecture?” The answer is tied to the growing size of a central office power system which demands higher amperages that are impacted by the price of copper and the need for larger battery systems. Distributed power systems on the other hand are smaller, use lower power, less copper, are more amenable to smaller VRLA battery systems and ultimately reduce the chance of total system failure. Despite the benefits, the traditional Telco engineering people tend to resist the change to distributed architectures. The idea of relocating power systems, specifically the batteries, is believed to increase risk and the need for more retraining of technicians. The speaker listed the advantages of a distributed DC architecture and then offered up a list of 12 design criteria for a distributed system architecture. In his conclusion, the speaker suggested that the high current demand of the central office combined with a limited capital budget may initiate the move toward a distributed architecture.

A Stationary Battery in Every Home?
Predicting the Future for Residential Energy

Jim McDowall of Saft America began his presentation by postulating that a second phase of the conversion to distributed power will be the conversion to home-generated power and home energy storage. He stated that the need for transmission reliability combined with distributed resources and storage will contribute to the development of a dynamic power grid in the future. McDowall postulates that the use of “micro-grids” will increase, thus creating a “sub-grid” structure that can be disconnected from the main grid and function autonomously. Homes will make use of “Combined Heat & Power” (CHP) systems in which electricity is produced and excess heat from the generation process is captured and used. The country of Denmark is currently the leader in the use of CHP technology. He also believes that although the use of renewable energy is growing, its use will be limited to about 20% because the grid will be destabilized by large amounts of wind and solar which are, by their very nature, not constant. Today, the energy storage technology of choice for off-grid homes is unquestionably lead-acid batteries. These batteries are typically cost-effective deep-cycle batteries such as golf-cart or marine batteries. The speaker stated that despite low initial costs, he believes these batteries do not provide low life-cycle cost and will ultimately be replaced by Ni-MH or Li-ion batteries.

New IEEE Standard on Electrolyte Spill Control

Stephen W. McCluer of Critical Power & Cooling Services specifically addressed IEEE 1578 – IEEE Recommended Practice for Stationary Battery Electrolyte Spill Containment and Management. This standard has been in development for eight years and is now available as an “approved draft” at http://shop.ieee.org/ieeestore/. It was developed in response to a need for guidance from the technical community that writes and implements safety codes. Some general guidance that was offered was that a battery installation must include containment for 1% of the total battery electrolyte or the electrolyte from one full cell, whichever is larger. It was interesting to note that a spill is defined as an unintended release of more than 1 liter of acid and anything less is just a “leak”. He concluded by stating that this standard does not apply to VRLA batteries and is recommended for all VLA (vented lead-acid) batteries.

Analysis of Battery Cable Faults Using a Dynamic Battery Model

This paper immediately caught my attention when Nosh K. Medora of Exponent Failure Analysis Associates Inc. warned the audience of a potentially dangerous situation that is created by a battery at a very low state of charge. Though I will not go into the details of his dynamic battery model, I will relate the dangerous issue created by a battery at a low state of charge. The basic issue stems from the fact that battery cable circuit breakers and fuses are typically sized based on the short circuit currents taken from manufacturers’s data sheets (for fully charged batteries). Therefore when a fully charged battery is short circuited, the breaker or fuse quickly interrupts the current flow and protects the battery and the cables. This is all copasetic but the situation changes in the case of a battery sitting at a very low state of charge. The author warns that a battery at a low state of charge not only has a lower terminal voltage but also has increased internal resistance (up to 3X). The consequence can be a low fault current and possibly a failure of the fuses or circuit breakers to trip. This long-term low-current fault can cause the battery cables to overheat and possibly ignite! He warns that this condition could also occur in an electric or hybrid electric vehicle and offers measures to protect against this hazard.

Long-Term Evaluation of Battery Maintenance Testing Activities at the New York Power Authority

After many years of maintaining their own DC power systems with various levels of success, the New York Power Authority decided to use an outside contractor for system maintenance and testing. William Cantor of TPI described the battery maintenance and test program that was developed for this purpose. The NYPA has many different locations with each having as many as 10 to 20 DC systems. The size of these systems ranges from 12 to 250 volts at 100 to 4,000 amp-hours. A comprehensive program was developed whereby each DC system was inspected annually per IEEE 450 and fully tested every five years. Newly installed batteries are given a performance/acceptance test soon after installation. The testing procedure encompassed the entire DC system with full load testing with infrared thermography. The author’s conclusions indicate that the thermography proved to be extremely useful in diagnosing connectivity issues such as those of the DC breaker connections. Battery test data was used to predict battery life and the need for battery replacement. End of battery life varies from system to system but the author is convinced that AC ripple current does have a long-term negative effect on battery life (despite what has been found by others in the past). He also stated that the IEEE 450 maintenance and testing protocol is effective and cost effective.

High Reliability Flooded, VRLA, and Front Terminal UPS Battery Design: Past, Present and Future

Stephen L. Vechy of EnerSys began by describing the development of the mainframe computer, the subsequent need for reliable power and the beginning of a whole new power application – uninterruptible power systems. He went on to describe the development of flooded lead-acid batteries specifically for UPS applications. These batteries had thinner plates (more plates with more surface area for more power), thinner separators (lower electrical resistance), higher specific gravity acid (more conductive 1.250 S.G. vs. 1.215) and copper inserts in the battery posts (for lower electrical resistance and better torque retention). Further improvements were introduced in the form of VRLA battery technology which eliminated maintenance, spills and the need for watering. These batteries were introduced and well accepted because of their low cost and small footprint, but problems surfaced as batteries succumbed to dry-out and thermal runaway. As Vechy says in his paper, at this point in time everyone got angry at the battery industry and conferences like BATTCON were born. The VRLA industry did come together and addressed the problems, redesigned batteries, developed alloys, improved cabinets and used temperature- compensated charging systems. In the meantime, the interest in flooded UPS batteries did not wane. The industry has responded with improved battery designs, better alloys, multi-cell jars, radial grids, double lugs and wrapped plates. So after 30+ years the UPS industry is still going strong and is still somewhat divided in the use of flooded lead-acid and VRLA batteries.

VRLA / AGM Batteries and Cyclic Applications

Pascal Haring of Oerlikon Stationary Batteries Ltd. presented data pertaining to specific VRLA design variables that lead to improved cycle life performance in batteries that are discharged to moderate DoD’s of ~40% and at relatively high discharge rates (>2*C10). He begins by reminding us that cycle life is typically limited by the positive and negative active mass, which wears out and the battery loses capacity. He therefore proposed a test matrix to evaluate the effects of 1) positive active mass, 2) electrolyte (acid) density, 3) electrolyte quantity and 4) float charge voltage. The testing involved cycling two 6-volt mono-blocks of each battery design in series. The end of life was determined when the battery reached an average cell voltage of 1.80 volts per cell during a specified time or the capacity was lower than 80% of the rated capacity. The results showed that indeed premature failure can be induced cycling to 40% DoD at I > 2*C10. He called these types of cycling parameters “the danger zone” for certain battery designs. He then presented data that showed that the best cycle life performance under these conditions was obtained by reducing the positive active mass in terms of g/AH, using increased positive paste densities, employing lower specific gravity acid and designing cells with thicker positive plates. All the details of the exact paste and battery designs were presented.

A Battery for My Fuel Cell?

This talk focused on how fuel cells are operated and the need for additional “bridge power” in many applications. John P. Gagge Jr. of EnerSys began by discussing the challenges related to fuel cell design and operation. The key issues are many and include cost, runtime, durability, reliability, manufacturability, fuel supply (hydrogen, methane, methanol, etc.), maintenance, emissions, energy density and start-up delay or lag time. Fuel cells offer exceptional performance in terms of most issues like runtime and emissions but are hampered by things like energy density and start-up delay. This is where the battery comes in. If a fuel cell system were to be designed to back up a DC bus in a telecom application, a battery would definitely be required to: 1) bridge short power outages and prevent “short cycling”, 2) provide power to the fuel cell during startup, 3) provide bridge power to the load during fuel cell warm-up, 4) provide load leveling during short power transients and 5) provide power during fuel cell shutdown. Gagge proposed that the best battery for this application is a thin plate pure lead (TPPL) lead-acid battery. These batteries have excellent high-rate performance and are known to experience very low self-discharge. Data was presented for a 70Ah TPPL battery that was discharged at the 2KW rate for 10 seconds, rested for 30 sec and then recharged for 15 seconds at the same 2kW rate. This cycle was continuously repeated and the battery was given a 3-hour capacity test every 500 cycles. It exceeded 6,000 cycles in this micro-cycle mode, thus demonstrating its ability to perform in this application. This particular battery design has been shown to have a 2-year shelf life (low self-discharge) and has been demonstrated to deliver a 10-year no-maintenance product life. The speaker noted that regardless of the manufacturer or fuel cell design, it is apparent that a battery will be required for interim back-up power for short cycle and bridge power applications.