Earlier this month, the U.S. Department of Energy (DOE) issued a pre-publication Federal Register notification, describing the first U.S. energy efficiency requirements for battery chargers (BC). The DOE has been working on BC efficiency requirements since its original proposed standard in early 2012.
The regulation is based on a single metric, Unit Energy Consumption (UEC), that limits the annual energy consumption for 7 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).
Similar to the previous proposal, 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(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. Constants per BC product class
| Product Class # | Active + Maintenance (ta&m) | Standby (tsb) | Off (toff) | Charges (n) | Threshold Charge Time |
|
| # | Description | Hours per Day* | Number per Day | Hours | ||
| 1 | Low-Energy | 20.66 | 0.10 | 0.00 | 0.15 | 137.73 |
| 2 | Low-Energy, Low-Voltage |
7.82 | 5.29 | 0.00 | 0.54 | 14.48 |
| 3 | Low-Energy, Medium-Voltage |
6.42 | 0.30 | 0.00 | 0.10 | 64.20 |
| 4 | Low-Energy, High-Voltage |
16.84 | 0.91 | 0.00 | 0.50 | 33.68 |
| 5 | Medium-Energy, Low-Voltage |
6.52 | 1.16 | 0.00 | 0.11 | 59.27 |
| 6 | Medium-Energy, High-Voltage |
17.15 | 6.85 | 0.00 | 0.34 | 50.44 |
| 7 | High-Energy | 8.14 | 7.30 | 0.00 | 0.32 | 25.44 |
*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
| Product Class # | Product Class Description |
Rated Battery Energy (Ebatt)2(Wh) |
Special Characteristic or Battery Voltage |
Maximum UEC (kWh/yr) (as a function of Ebatt)2 |
| 1 | Low-Energy | ≤ 5 | Inductive Connection1 | 3.04 |
| 2 | Low-Energy, Low-Voltage | < 100 | < 4 V | 0.1440 × Ebatt + 2.95 |
| 3 | Low-Energy, Medium-Voltage |
4 – 10 V | For Ebatt < 10Wh, 1.42 kWh/yr; Ebatt ≥ 10 Wh, 0.0255 × Ebatt + 1.16 |
|
| 4 | Low-Energy, High-Voltage |
> 10 V | 0.11 × Ebatt + 3.18 | |
| 5 | Medium-Energy, Low-Voltage |
100 - 3000 | < 20 V | 0.0257 × Ebatt + .815 |
| 6 | Medium-Energy, High-Voltage |
≥ 20 V | 0.0778 × Ebatt + 2.4 | |
| 7 | High-Energy | > 3000 | - | 0.0502 × Ebatt + 4.53 |
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)
Because of testing issues encountered with "back-up" battery chargers and uninterruptible power supplies (UPSs), the DOE decided to exclude these products from this ruling. The DOE is currently working on a separate rulemaking for UPSs.
The BC standard applies to all covered products that are manufactured in, or imported into, the United States. Compliance to the efficiency levels will become mandatory in 2018, two years after publication in the U.S. Federal Register. It will preempt California's current Title 20 Battery Charger efficiency standard at that time. For more information on the DOE rulemaking, visit the DOE battery charger rulemaking page. For a copy of the test procedure, click here. For a copy of the pre-publication NOPR, click here.
