Power Electronics

Let's Rethink Efficiency Standards For Battery Chargers

In 1992, the Environmental Protection Agency (EPA) established the voluntary Energy Star program to recognize efficient electronic products. The Energy Star program established a maximum standby power consumption requirement for certification. The program benefits consumers by providing an easy way to recognize products that will save them money on energy costs. Moreover, the program benefits all of us by reducing the demand for natural resources and pollution from fossil fuels.

Energy Star also has increased sales of higher-value power supplies, which is a benefit to the power sources industry and encourages equipment manufacturers to buy higher-value power supplies. In general, the energy savings exceed the added cost of a more efficient power supply.

More recently, the Natural Resources Defense Council found that significant energy savings could be achieved by using power supplies with higher active-mode efficiency. The EPA and other governmental and regulatory agencies, both foreign and domestic, have developed standards for active-mode efficiency for power-conversion products. Included among these are legal mandates that go into effect in 2006 in Australia and California.

In January 2005, the EPA established an active-mode efficiency requirement for Energy Star certification applicable to external power supplies. However, battery chargers for power tools and other cordless appliances were excluded from the external power supply requirements. Then in August, the EPA introduced a new draft requirement specifically for battery chargers.

The EPA draft requirement for battery chargers is remarkably different from previous certification requirements for Energy Star for other classes of equipment. Prior Energy Star requirements included a standby-mode maximum power dissipation requirement of 0.5 W. This requirement was not included in the draft for battery chargers. The Energy Star draft requirements for battery chargers also differs markedly from existing and proposed requirements for battery chargers in foreign countries, which, in some cases, have more stringent requirements for standby power for battery chargers than for external power supplies.

Other recent requirements, both foreign and domestic, have recognized the importance of active-mode energy efficiency. The EPA draft battery charger requirement does not contain an active-mode efficiency requirement. One might argue that this is justified because battery chargers are seldom operated in a mode in which they are charging a battery, but operate mostly in maintenance and standby modes. However, one also should consider how much of the battery charger's energy is drawn in the active mode. The draft includes no explicit power-efficiency requirement and no explicit maximum power level for any operating mode.

The requirements for certification only apply to the maintenance and standby modes of operation and require a measure of energy and the determination of an energy ratio that is inversely proportional to the manufacturer's battery rating. There are internationally recognized standards for battery rating that could be used, but Energy Star certification can be achieved without application of the accepted standards for battery rating. Under the draft requirements for battery chargers it would be theoretically possible for a manufacturer that conservatively rates its battery charger to fail to meet the certification requirement while another manufacturer with a lower-efficiency battery charger meets the requirement.

Clearly, the new Energy Star certification requirements for battery chargers could better serve the public. Certification requirements should be as uniform as possible to create a sense of fairness and legitimacy for the process. As a first draft for the battery charger requirement, the EPA should adopt the requirement for external power supplies. Changes to the requirements for battery chargers should only be made where the facts and the data justify a change. The EPA should independently confirm the facts and data that would justify any changes to the requirements already established for external power supplies. After all, a battery charger is a power supply and it is external.

Ernie Wittenbreder earned an MS degree in electrical engineering from John Hopkins University and a MS degree in physics from Lehigh University. He holds 20 patents, has published 14 papers and technical articles, and regularly conducts professional advancement courses and seminars for power supply design engineers.

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