Designing and Testing Battery Charger Systems for

California’s New Efficiency Regulations

Chris Botting, Roger Stockton, Deepak Gautam,

Murray Edington

Department of Research, Engineering

Delta-Q Technologies Corp., Burnaby, BC, Canada

cbotting@delta-q.com, rstockton@delta-q.com,

dgautam@delta-q.com, medington@delta-q.com

Fariborz Musavi

Department of Engineering

Novum Advanced Power at CUI Inc

Portland, Oregon, USA

fmusavi@cui.com

Abstract— The State of California has adopted tough new energy efficiency standards for battery charger systems. These

regulations promise to save cost, energy, and greenhouse gas

emissions, but they also present new challenges to engineers and

managers involved in the planning, design, and system

integration of battery charger systems. This paper aims to

provide guidance by explaining the requirements of the

standard, demonstrating proper test methods, analyzing real-

world test results, and discussing significant factors affecting

compliance. Experimental results and lessons-learned are

presented for modern industrial lead acid battery charge

systems. Although charger hardware conversion efficiency is

important, the software algorithm is at least as important, as is

the efficiency of the battery itself, and the system

interconnections and cabling. Some charger topologies and

battery types will struggle to comply with the standard, and may

be displaced by more efficient technologies.

I. INTRODUCTION

In January of 2012 the California Energy Commission (CEC) adopted a new energy efficiency standard [1] for battery charger systems sold in California. The standard derived from a study [2] which identified battery chargers as a category of products with significant potential for greenhouse gas reductions and energy savings. Fig. 1 illustrates the energy consumed by each charger product group [2]; Lift trucks and golf cars, with the highest per-device energy consumption, are of particular interest. The requirements for golf cars (and other consumer products) went into effect February 1, 2013; the requirements for lift trucks (and other large battery charger systems) go into effect January 1, 2014. The US Department of Energy is proposing similar regulations, which would apply in all 50 states.

The CEC regulations view the battery and charger as an integrated system, used to draw energy from the grid, store it in a battery and release it to power a device, as shown in Fig 2. The efficiency of this system is defined as the total energy released by the battery to the powered appliance divided by the total energy from the grid required to charge and maintain the battery over 24 hours. This approach is technology

neutral, with the resulting energy efficiency being affected by the performance of the charger hardware and software algorithm, the battery, and the system interconnections.

1 10 100 1,000 10,000 100,000

Auto/Marine/RV

Cell phone

Cordless Phones

Personal Audio

Emergency

Laptops

Personal Care

Personal EV

Portable Electronics

Portable lighting

Power Tools

Univ. chargers

Golf cars

Emergency backup lighting

Scanners

Two way radios

Lift Trucks (Class 3)

Lift Trucks (Class 1&2 - 3 phase)

Unit electricity consumption (kWh/yr) – Log Axis

Ba

tte

ry

ch

ar

ge

r

pr

od

uc

t G

ro

up

s (

CE

C)

Figure 1. Battery charger product groups’ electricity consumption

Charge

Control Circuit

Power

Supply

Battery Charger

Battery Charger System

End

User

Battery

Input

Energy Output

Energy

Figure 2. Battery charger system

II. TEST METHOD AND CRITERIA

The CEC test follows a US federal test procedure [3]; a test setup is shown in Fig. 3. Testing is conducted in a temperature-controlled lab, with equipment for automated cycling. Power meters measure AC power into the charger (at the power outlet), and DC power into and out of the battery pack (at its terminals). The test is conducted as follows:

This work has been sponsored and supported by Delta-Q Technologies

Corporation.

978-1-4799-2325-0/14/$31.00 ©2014 IEEE 2690

discharge the battery at a constant current 5 hour rate (C/5) to a cutoff voltage (1.7 V/cell for flooded lead acid), rest for 1 hour, connect AC to the charger for 24 hours (full charge and then maintenance mode), rest 1 hour with AC disconnected, and then repeat the discharge. Two criteria are measured during the procedure. The 24 hour AC energy consumption is measured during the charge, and compared to the DC energy delivered in the second discharge. The maintenance mode AC power is averaged over the last 4 hours of the charge test, after active charging is complete. A complete test profile is shown in Figure 4.

Table I presents the CEC’s energy efficiency criteria for battery charger systems with a battery greater than 1000 Wh. The battery charger system has to pass (1) the 24 h energy consumption test and (2) the maintenance mode power and no-battery power draw (stand-by mode) test in order to meet the CEC regulation. For a typical electric golf car charge system, with a 5 kWh lead acid battery pack, the resulting criteria are about 67% total energy efficiency (from wall AC “in”, to battery DC “out”), and an average maintenance power draw around 12 W.

AC SourceAC Power

Meter

DC Power

Meter

UUT

(Charger)

Data Logger

UUT

(Test

Battery)

Dynamic

Load

115V

60Hz

115V

60Hz

I

DC

DC

I

DC

External Current

Sensor

Shunt

Airspeed

Meter

V

Thermocouple

(ambient)

Thermocouple

(electrolyte)

Figure 3. CEC Test Setup

Figure 4. Complete CEC test profile (discharge, wait, charge, wait, discharge)

Table I CEC Standard for Battery Charger Systems [1]

Performance Parameter Standard

Maximum 24 hour charge and maintenance energy (Wh)

(Eb = capacity of all batteries in ports and

N = number of charger ports)

For Eb greater than 1000 Wh:

Watt-hours

Maintenance Mode Power and No Battery Mode Power (W)

(Eb = capacity of all batteries in ports and

N = number of charger ports)

The sum of maintenance mode power and no

battery mode power must be less than or equal to:

Watts

-30

-20

-10

0

10

20

30

40

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36

Cu

rren

t (A

) a

nd

Tem

pera

ture (

°C)

Avera

ge C

ell

Vo

lta

ge (

V/c

ell

)

Elapsed Time (hours)

Vpc(pack)

I

T(ambient)

T(electrolyte)

5 Hour Discharge C/5 Rate

5 Hour Discharge C/5 Rate

24 Hour Minimum Charge Time 1 Hour Minimum

Rest

1 Hour Minimum

Rest

2691

III. FACTORS AFFECTING SYSTEM EFFICIENCY

There are a number of factors affecting CEC compliance. The most obvious is the efficiency of the charger hardware. However, real-world testing reveals other significant factors, including the charger software algorithm, the battery type, and the system interconnections.

The efficiency of the charger depends mainly on the hardware topology used for converting AC to DC power. Common topologies include ferroresonant, SCR-based phase-angle control, and high frequency switching. Of these, the high frequency switching topology has the highest efficiency, as well as superior power factor, THD, and output ripple (particularly in a two-stage converter), relative to the less efficient traditional incumbent technologies.

The charger’s software algorithm dictates the rate at which charge is applied, and when charge is terminated. Of these, the latter has the larger effect on energy consumption. The charge rate determines where the charger operates relative to its peak efficiency, but the charge termination determines how much extra energy is applied in the form of potentially-wasteful overcharge. Lead acid batteries require some degree of overcharge to compensate for their coulombic inefficiency, fully convert active material, and generate gas bubbles to stir their electrolyte and prevent acid stratification. The industry consensus for deep-cycle flooded lead acid batteries is that they require at least 10% more amp-hours of charge than was removed, that is 110% charge return; beyond this there are diminishing returns, as more energy is wasted in heat and gas generation [4].

Figure 5 and Table II show the effects of both charger hardware and software. Three golf car chargers have been tested on similar battery packs. The high frequency charger clearly has better efficiency relative to the other two; it has only half the loss, and passes CEC easily. But of the other two chargers, the SCR charger outperforms the ferroresonant by a wide margin, not due to charger hardware (the SCR charger is slightly less efficient), but due to software (the ferroresonant applied about 20% more overcharge than was required).

Not all batteries are equally efficient. Some lead acid batteries require more than 110% charge return to optimize battery life for long warranty periods; 113% to 115% is common for some makes and models. On the other hand, sealed lead acid batteries generally require less than 110% charge return, sometimes less than 105%. Some modern battery chemistries, like lithium ion and nickel metal hydride, have effectively 100% coulombic efficiency; combined with lower internal resistance, this can result in energy efficiencies at least 10% higher than lead acid.

Figure 6 and Table III show the effect of battery charge return. Three industrial lead acid traction batteries have been tested with similar high frequency chargers. The consumption for a flooded battery requiring high charge return can be double that of an efficient sealed AGM (absorbed glass mat) battery.

Figure 5. Breakdown of energy use for three chargers, % of CEC limits

Table II: Breakdown of efficiency for three charger types

Charger Type High Frequency Ferroresonant SCR

Charge Return (%) 108.9% 131.2% 109.0%

Charger Efficiency (%) 90.1% 82.2% 80.4%

Battery Efficiency (%) 79.3% 64.7% 78.5%

System Efficiency (%) 71.5% 53.2% 63.1%

Figure 6. Breakdown of energy use for three batteries, % of CEC limits

Table III: Breakdown of efficiency for three battery types

Battery Type AGM Sealed Flooded-A Flooded-B

Charge Return (%) 102.6% 109.2% 115.1%

Charger Efficiency (%) 86.4% 87.8% 89.6%

Battery Efficiency (%) 86.7% 79.4% 75.8%

System Efficiency (%) 74.9% 69.6% 67.9%

67.0% 67.0% 67.1%

17.5%

36.5%

18.4%

9.3%

22.4%

20.9%

60%

70%

80%

90%

100%

110%

120%

130%

High Frequency Ferroresonant SCR

En

erg

y, %

of

CE

C L

imit

(>1

00

% i

s fa

il)

Charger Loss

Battery Consumption

Discharge Energy

66.5% 67.0% 67.0%

10.2%

17.4% 21.4%

12.1%

11.8%

10.2%

60%

65%

70%

75%

80%

85%

90%

95%

100%

AGM Sealed,

102% Return

Flooded,

110% Return

Flooded,

115% Return

En

erg

y, %

of

CE

C L

imit

(>1

00

% i

s fa

il)

Charger Loss

Battery Consumption

Discharge Energy

2692

Finally, the impedance of system interconnections is a measurable factor. Losses in the AC and DC cables can be affected by the gauge and length of cables, the quality and stranding of the copper, and the contact resistance of any inline connectors. Interconnection losses can be aggravated by power quality. For example, a single stage charger which doesn’t effectively reject the AC line frequency ripple could have DC output current with an RMS value significantly above its average value, increasing DC cable losses (and losses in the battery itself). As shown in Table IV, a 650W single stage high frequency has 30W loss in the output DC cable as compared to only 17W with a two stage charger. Similarly, a charger with low power factor and high total harmonic distortion can increase AC cable losses.

Table IV: Impact of power quality on losses in DC cables

Charger Type 650W Single Stage 650W Two Stage

Average Current (A) 13.3 13.5

RMS Current (A) 17.5 13.5

Losses in a 100mΩ DC

Cable (W) 30 17

Charger full-load

efficiency excluding losses

in AC and DC Cables (%)

91 % 91 %

IV. CONCLUSIONS AND FUTURE WORK

California’s new battery charger system efficiency requirements were explained, proper test procedures were demonstrated, and real-world results were presented. Complying with the standard requires a holistic view of the battery charger system, including charger hardware and software, battery type and efficiency, and interconnections. The approach is technology neutral, however certain charger and battery types will struggle to comply, and may ultimately be displaced by more efficiency technologies, such as high frequency chargers and more modern battery chemistries and constructions.

REFERENCES

[1] APPLIANCE EFFICIENCY REGULATIONS, CALIFORNIA CODE OF REGULATIONS TITLE 20, SECTIONS 1601 THROUGH 1608. BATTERY CHARGER SYSTEMS AND SELF-CONTAINED LIGHTING CONTROLS. CEC-400-2012-011-CMF

[2] S.F. Porter; P. Bendt; J. Swofford; J.C. Hebert, “Codes and Standards Enhancement (CASE) Initiative for PY2010: Title 20 Standards Development – Analysis of Standard Options for Battery Charger Systems”, 2010.

[3] UNIFORM TEST METHOD FOR MEASURING THE ENERGY CONSUMPTION OF BATTERY CHARGERS. 10 CFR Section 430.23(aa) (Appendix Y to Subpart B of Part 430) (2011)

[4] Edward C. Kellogg, Jorge Araiza Jr., Richard Cromie, Jordan W. Smith, P.E., “Energy Efficiency in Electric Golf Carts: Evaluation and Comparison of Charging and Drive technologies.” IEEE Vehicle Power and Propulsion Conference, 2009. VPPC '09. Pages:1279, 1285.

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