The U.S. Department of Energy (DOE) is getting closer to finalizing its federal battery charger (BC) efficiency standard. It recently published a Notice of Proposed Rulemaking (NOPR) for test procedures along with a Supplemental Notice of Proposed Rulemaking (SNOPR) outlining mandatory minimum charger efficiency requirements for compliance.
The NOPR proposes several changes to the current test procedure for measuring BC energy use, including:
- Limiting the number of batteries selected for testing to a single unit for BCs capable of charging different batteries. The battery with the highest rated voltage and/or highest rated charge capacity should be selected for each charger.
- Excluding back-up battery chargers embedded in continuous use devices. The DOE is currently considering the regulation of battery back-up systems (including uninterruptible power supplies) as part of a separate rulemaking.
- Harmonizing DOE's test procedure with the latest version of IEC 62301 regarding instrument resolution and measurement tolerance
- Changing how lead acid batteries are conditioned and discharged to align with the method currently used for all other battery chemistries (excluding lithium-ion)
On the efficiency requirement side, the DOE’s SNOPR proposes using a single metric, Unit Energy Consumption (UEC), to limit the annual energy consumption for seven different classes of BCs. Expressed as a function of battery energy (Ebatt), 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 device 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(E24 – 5Pm – Ebatt)24/tcd + (Pm(ta&m – (tcd - 5)n)) + (Psbtsb) + (Pofftoff))
(ii) UEC = 365(n(E24 – 5Pm – Ebatt)24/(tcd – 5) + (Psbtsb) + (Pofftoff))
Where: E24 = 24-hour energy consumption, Ebatt = measured battery energy, Pm = maintenance mode power, Psb = standby mode power, Poff = off mode power, tcd = charge test duration, and ta&m, n, tsb, and toff, are constants used based upon a device’s product class, and found in table 1.
Table 1. Proposed 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 proposed maximum allowable UEC levels are shown in table 2 below.
Table 2. Proposed maximum allowable UEC per BC product class
Notes: Inductive connection is designed for use in a wet environment (i.e. electric toothbrushes), Ebatt = measured battery energy
If adopted, the new standard would apply to all covered products that are manufactured in, or imported into, the United States, starting two years after final ruling is publication.
A stakeholder meeting to discuss both documents will be held on September 15th, 2015 in Washington, DC. To participate in the meeting via the web, click here. Those wishing to attend in person should notify Ms. Brenda Edwards at (202) 586-2945 or Brenda.Edwards@ee.doe.gov. Additional information and documentation on the DOE’s BC rulemaking activities can be found here.