Early this month, the U.S. Department of Energy (DOE) published a final rulemaking describing the country’s first Energy Conservation Standards for Battery Chargers (BCs). It’s been a long time coming – the Department first proposed BC efficiency requirements in early 2012.

The charger regulation is based on a single metric, Unit Energy Consumption (UEC). It limits the annual energy consumption for 7 different classes of BCs. Expressed as a function of battery energy (E batt ), a charger’s UEC reflects the “non-useful” energy consumed in all modes of operation (i.e. the amount of energy consumed but not transferred to the battery as a result of charging).

A charger’s UEC is calculated using one of the two equations shown below. If a BC is tested and its charge test duration (minus 5 hours) exceeds the threshold charge time listed in Table 1 below, equation (ii) is used to calculate UEC. If not, equation (i) is used.

(i) UEC = 365(n(E 24 – 5P m – E batt )24/t cd + (P m (t a&m – (t cd – 5)n) + (P sb t sb ) + (P off t off ))

(ii) UEC = 365(n(E 24 – 5P m – E batt )24/(t cd – 5) + (P sb t sb ) + (P off t off ))

Where: E 24 = 24-hour energy consumption, E batt = measured battery energy, P m = maintenance mode power, P sb = standby mode power, P off = off mode power, t cd = charge test duration, and t a&m , n, t sb , and t off are constants used based upon a device’s product class, and found in Table 1 .





Table 1 Constants per BC product class

*If the total time does not equal 24 hours per day, the remaining time is considered unplugged time, resulting in zero power consumption.

The maximum allowable UEC levels are shown in Table 2 below.

Table 2 Maximum allowable UEC per BC product class

1 Inductive connection is designed for use in a wet environment (i.e. electric toothbrushes), 2 Ebatt = rated battery energy as determined in 10 CFR Part 429.39 (a)

The DOE decided to exclude “back-up” battery chargers and uninterruptible power supplies (UPSs) from this ruling because of specific product testing issues. The Department is currently working on a separate rulemaking for UPSs.

The BC standard applies to all covered products manufactured in, or imported into, the United States. It becomes effective on August 12th of this year, with a mandatory compliance date of June 13, 2018. It will preempt California’s Title 20 Battery Charger efficiency standard at that time.

For a copy of the new efficiency standard and additional information on this rulemaking, click here (scroll down to Efficiency Standard for Battery Chargers).

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