Generalized Test Protocol for Calculating the Energy
Efficiency of Internal Ac-Dc and Dc-Dc Power Supplies
Revision 6.5

EPRI
Dr. Arshad Mansoor
Brian Fortenbery
Baskar Vairamohan
Tom Geist

July 07, 2010

Ecos
Peter May-Ostendorp
Chris Calwell
Ryan Rasmussen
Doug McIlvoy
Jason Boehlke

Revision History
Version Release Date

Notes

1.0

Feb 15, 2004

First draft released.

2.0

June 1, 2004

Section on “Product-specific loading guidelines” added.

3.0

Aug 1, 2004

Definitions of measurement parameters modified tomatch IEEE standard.

4.0

Dec 1, 2004

Comments from Australia on proportional allocation
method received. Enhanced proportional allocation
method to calculate the power supply loading was
included in this revision.

5.0

Aug 1, 2005

Addition of measurement provisions to capture theeffects of cyclically operating cooling fans.
Changes in the power measurement accuracy.

6.0

Mar 15, 2006

Scope was modified to focus on internal power supplies
that are detachable, have nameplate ratings, and use
standard connectors.
Specifications for power measurement equipment
refined.
Addition of provisions to guide measurement of power
supply ac power consumption during standby mode.

6.1

May 8, 2006

Wiring diagram was modified to reduce possibility for
introduction of errors at very low load measurements.

6.2

Nov 30, 2007

Included provision to test power supplies that have
options for fan control through external voltage signal

6.3

Apr 24, 2008

The Server Test Protocol Rev 1.2 cited in the
http://www.80PLUS.org website is merged with the
Generalized Internal Power Supply Efficiency Test
Protocol Rev 6.2 to form this latest revision of test
procedure
Provision to measure dc-dc power supplies is includedin this test procedure

6.4

May 28, 2008

Revised paragraphs 4.2, 4.3, 4.4.1, 4.4.2, 4.4.3 toreflect no mention of testing at 100 VAC input,
collection of data at 10% of rated load on single output
power supplies, and to include collection of fan power
data on single output power supplies at all load settings.

6.4.1

Jul 28, 2008

Inclusion of dc-dc power supply testing.

2

6.4.2

Oct. 13, 2008

Modified paragraphs 1, 2, 3.6, 3.27, 3.28, 4.2.2, 4.4.1,
4.4.2, 5.2, 5.4 Fig.1 & Fig. 2, 5.5, 5.7, 6.1.2, 7.0, 7.1, to
include Climate Savers (CSCI,
http://www.climatesaverscomputing.org/ ) working
group comments.

6.4.3

Oct 22, 2009

Modified paragraph 5.5 to include a method to improve
the accuracy of power factor measurement of power
supplies at low loading conditions.

6.4.5

July 7, 2010

Included a new paragraph 4.4.4 (Method for Fan Load
Power Determination in Storage Power Supplies)
specific to the storage power supplies under section 4.4(Power Supply Fan Control).

3

Sponsors
The generalized internal power supply efficiency test protocol effort was sponsored by California
Energy Commission Public Interest Energy Research (PIER) Program in 2004.
In 2007, the server test protocol was developed which was derived from the generalized power
supply efficiency test protocol. This effort was funded by Bonneville Power Administration,
Pacific Gas & Electric (PG&E), Natural Resources Canada, The Energy Trust of Oregon,
Northwest Energy Efficiency Alliance (NEEA), Snohomish PUD and PacifiCorp.

4

TABLE OF CONTENTSSCOPE ..............................................................................................................................8

1.

Intent .............................................................................................................................8

1.1
2.

REFERENCES...................................................................................................................93.

DEFINITIONS.................................................................................................................10
3.1

Ac-Dc Power Supply .....................................................................................................10

3.2

Ac Signal......................................................................................................................10

3.3

Ambient Temperature ....................................................................................................10

3.4

Apparent Power (S) .......................................................................................................10

3.5

Dc Signal......................................................................................................................10

3.6

Efficiency.....................................................................................................................10

3.7

Enclosed-Frame Modular Internal Power Supply...............................................................10

3.8

Multiple-Output Power Supply........................................................................................10

3.9

Open-Frame Modular Internal Power Supply ....................................................................10

3.10

Output Voltage Bus...................................................................................................11

3.11

True Power Factor.....................................................................................................11

3.12

Crest Factor..............................................................................................................11

3.13

Rated Ac Input Voltage .............................................................................................11

3.14

Rated Ac Input Voltage Range....................................................................................11

3.15

Rated Dc Input Voltage .............................................................................................11

3.16

Rated Dc Input Voltage Range....................................................................................12

3.17

Rated Dc Output Current ...........................................................................................12

3.18

Rated Dc Output Current Range..................................................................................12

3.19

Rated Dc Output Power .............................................................................................12

3.20

Rated Dc Output Voltage ...........................................................................................12

3.21

Rated Input Frequency...............................................................................................12

3.22

Rated Input Frequency Range.....................................................................................12

3.23

Rated Input Current...................................................................................................12

3.24

Rated Input Current Range.........................................................................................12

3.25

Rms (Root Mean Square)...........................................................................................12

3.26

Single-Output Power Supply ......................................................................................13

3.27

Standby Mode ..........................................................................................................13

3.28

Standby Voltage Rail (Vsb)........................................................................................13

5

3.29

Steady State .............................................................................................................13

3.30

Test Voltage Source ..................................................................................................13

3.31

Total Harmonic Distortion (THD) ...............................................................................13

3.32

UUT........................................................................................................................13

3.33

Voltage Unbalance....................................................................................................14

STANDARD CONDITIONS FOR EFFICIENCY TESTING .............................................15

4.
4.1

General Provisions.........................................................................................................15

4.2

Input Voltage and Frequency ..........................................................................................15
4.2.1

Ac Input Voltage and Frequency.............................................................................15

4.2.2

Dc Input Voltage...................................................................................................15

4.3

Power Supply Loading ...................................................................................................15

4.4

Power Supply Fan Control ..............................................................................................16
4.4.1
Multiple-output Power Supply Fan Control through Temperature Sense (Internal
Control) ...........................................................................................................................16
4.4.2
Multiple-output Power Supply Fan Control through External Voltage Signal(External Control) ..............................................................................................................16
4.4.3

5.

Fan Load Considerations for Single-output Power Supplies........................................17

INSTRUMENTATION AND EQUIPMENT......................................................................17
5.1

General Provisions.........................................................................................................17

5.2

Test Voltage Source.......................................................................................................17

5.3

Test Dc Loads ...............................................................................................................19

5.4

Test Leads and Wiring ...................................................................................................19

5.5

Measurement Instrumentation Accuracy...........................................................................20

5.6

Test Room ....................................................................................................................22

5.7

Warm-up Time..............................................................................................................22
LOADING CRITERIA FOR EFFICIENCY TESTING .....................................................23

6.
6.1

General Provisions.........................................................................................................23
6.1.1
Proportional allocation method for loading multiple and single-output ac-dc anddc-dc power supplies ..........................................................................................................23
6.1.2
Method of Current Allocation for Measuring the Ac or Input Dc Power
Consumption of a Computer Internal Power Supply in the Standby Condition ...........................27

7.

MEASUREMENT PROCEDURES...................................................................................28
7.1. Test Report ......................................................................................................................29

6

8.
APPENDIX A: EXAMPLE EFFICIENCY REPORT FOR A MULTI-OUTPUT
POWER SUPPLY......................................................................................................................30
9.

APPENDIX B: INTERNAL POWER SUPPLY DISCUSSION...........................................31

10.

APPENDIX C: SERVER POWER SUPPLY DISCUSSION ...............................................34

7

1. ScopeThis document specifies a test protocol for calculating the energy efficiency of internal ac-dc anddc-dc power supplies. Internal power supplies are located in the same housing as the product thatthey power. An example of this type of power supply is a desktop computer power supply thathas multiple output voltages: +12 V, +5 V, +3.3 V, and -12 V (See Appendix B). External
power supplies – often referred to as ac adapters – are contained in a housing separate fromthe devices they power and are not included in the scope of this document. The test protocol inthis document applies specifically to power supplies that meet the following criteria:i.

Power supplies that have detailed input and output ratings on their name plate or inavailable literature from their manufacturer, specifying the maximum loads that cansafely be placed on each individual dc output voltage bus and, where necessary,groupings of those voltage busses

ii.

Power supplies that have connectors that allow the dc output voltage busses to beconnected and disconnected from the powered product non-destructively

iii.

Power supplies that can be easily detached from the housing of the product they power
without causing harm to other circuits and components of the productPower supplies physically integrated within the main circuit board of the device they are
powering are specifically not covered by this test procedure, as are power supplies that have a
combination of ac and dc output voltage busses. Building upon the efficiency test protocol
outlined in Section 4.3 of IEEE Std. 1515-2000, IEEE Recommended Practice for Electronic
Power Subsystems: Parameter Definitions, Test Conditions, and Test Methods, this test protocol
establishes consistent loading guidelines for ac-dc and dc-dc internal power supplies.

1.1
Intent
The intent of this document is to use existing industry standards that have been created forelectronic test and measurement to develop a consistent and repeatable method for measuring theenergy efficiency of single and multiple output ac-dc as well as dc-dc internal power supplies.
Existing standards occasionally give conflicting approaches and requirements for efficiency
testing, all of which this test protocol seeks to clarify.

8

2. References
The following list includes documents used in the development of this proposed test protocol. If
the following publications are superseded by an approved revision, the revision shall apply:
1. IEEE Std 1515-2000, IEEE Recommended Practice for Electronic Power Subsystems:
Parameter Definitions, Test Conditions, and Test Methods.
2. IEEE Std 519-1992, IEEE Recommended Practices and Requirements for Harmonic
Control in Electrical Power Systems.
3. IEC 62301 Ed 1.0, Household Electrical Appliances – Measurement of Standby Power
4. Draft IEC 62018 Ed. 1, Energy Management Requirements.
5. UL 60950, 3rd Edition, Information Technology Equipment – Safety – Part 1: General
Requirements, April 1, 2003.
6. IEC 61000-4-7 Ed.2, Electromagnetic Compatibility (EMC) - Part 4-7: Testing and
Measurement Techniques - General Guide on Harmonics and Interharmonics.
Measurements and Instrumentation, for Power Supply Systems and Equipment
Connected Thereto.
7. IEC 61000-3-2, Electromagnetic Compatibility (EMC) – Part 3-2: Limits – Limits for
Harmonic Current Emissions (Equipment Input Current ≤ 16 A per Phase).
8. IEC 60050, International Electrotechnical Vocabulary - Electrical and Electronic
Measurements and Measuring Instruments.
9. IEEE 100, The Authoritative Dictionary of IEEE Standards Terms.
10. Power Supply Design Guidelines (website: http://www.formfactors.org), Intel
Corporation.
11. Server System Infrastructure (SSI) Power Supply Design Guidelines (available at
http://www.ssiforum.org/ ), Intel Corporation.
12. IEC 60950-1 Ed 2.0, Information technology equipment - Safety - Part 1: General
requirements, Dec 8, 2005

9

3. Definitions
For the purpose of this document, the following definitions apply. For terms not defined here,
definitions from IEC 60050, IEC 62301, and IEEE 100 are applicable.
3.1
Ac-Dc Power Supply
Devices designed to convert ac voltage into dc voltage for the purpose of powering electricalequipment.
3.2
Ac Signal
A time-varying signal whose polarity varies with a period of time T and whose average value iszero. (ref. IEEE Std 1515-2000)
3.3
Ambient Temperature
Temperature of the ambient air immediately surrounding the unit under test (UUT). (ref. IEEE
Std 1515-2000)
3.4
Apparent Power (S)The product of RMS voltage and current (VA). Also called the total power.
3.5
Dc Signal
A signal of which the polarity and amplitude do not vary with time. (ref. IEEE Std 1515-2000)
3.6
Efficiency
The ratio, expressed as a percentage, of the total real output power (produced by a conversion
process) to the real power input required to produce it, using the following equation:

∑P

o ,i

η=

i

Pin

Eq. 3-1

×100

where Po, i is the output power of the ith output. The input power (Pin), unless otherwise specified,includes all housekeeping and auxiliary circuits required for the converter to operate, including
any integrated cooling fans for Multiple-output power supplies, and excluding them for Singleoutput power supplies.
3.7
Enclosed-Frame Modular Internal Power Supply
A power supply encased in a modular enclosure, as shown in Figure B-1 (a). The enclosure is
installed inside the appliance and has easily accessible inputs and outputs.
3.8
Multiple-Output Power Supply
Power supplies designed to provide most of its rated power on more than one main dc output
voltage. There may be other low power dc output voltage(s) for standby power.
3.9Open-Frame Modular Internal Power Supply
A power supply whose components are grouped on a single printed circuit board but are notenclosed in a case, as shown in Figure B-1 (b). Such power supplies are installed inside the10appliance that they power, have easily accessible inputs and outputs, and can be separated fromthe appliance without causing damage to other components and circuits.
3.10 Output Voltage Bus
Any of the dc outputs of the power supply, to which loads can be connected and current andpower supplied. These busses may supply power at different voltage levels depending on thedesign of power supply and the product being powered.
3.11 True Power Factor
True power factor is the ratio of the active, or real, power (P) consumed in watts to the apparent
power (S) drawn in volt-amperes, withPS

Eq. 3-2

S = P2 + Q2

Eq. 3-3

PF =

and

Where
PF is power factor,
P is active power in watts,
Q is reactive power in volt-amperes,
S is total power in Volt-amperes.
This definition of power factor includes the effect of both displacement and distortion in the
input current (and/or voltage) waveform. (ref. IEEE Std 1515-2000)
3.12 Crest Factor
The crest factor is defined as the ratio of peak current to rms current (or peak voltage to rms
voltage). For a pure sinusoidal waveshape the crest factor is 1.414, while for a pure constant dc
load the crest factor is 1.0.
3.13 Rated Ac Input Voltage
The supply voltage declared by the manufacturer in the specification of the power supply. For asingle-phase power supply, this refers to line-to-neutral voltage, and for a three-phase power
supply, this refers to the line-to-line voltage.
3.14 Rated Ac Input Voltage Range
The supply voltage range (minimum/maximum) as declared by the manufacturer in thespecification of the power supply.
3.15 Rated Dc Input Voltage
The nominal dc supply voltage declared by the manufacturer in the specification of the power
supply which is typically provided on the power supply nameplate.

11

3.16 Rated Dc Input Voltage Range
The range of dc input voltage declared by the manufacturer in the specification of the power
supply.
3.17 Rated Dc Output Current
The dc output current for each output dc bus of the power supply as declared by the
manufacturer in the specification or nameplate of the power supply. If there is a discrepancy
between the specification and the nameplate, the nameplate rating shall be used.
3.18 Rated Dc Output Current Range
The dc output current range (minimum/maximum) for each output voltage bus of the power
supply as declared by the manufacturer in the specification of the power supply.
3.19 Rated Dc Output PowerThe maximum dc output power as specified by the manufacturer. This may apply to the total
power for all voltage busses, some subset thereof, or a single voltage bus.
3.20 Rated Dc Output Voltage
The dc output voltage for each output voltage bus of the power supply as declared by the
manufacturer in the specification of the power supply.
3.21 Rated Input Frequency
The supply ac input frequency of the power supply as declared by the manufacturer in thespecification of the power supply. This is applicable only for ac-dc power supplies.
3.22 Rated Input Frequency Range
The supply ac input frequency range (minimum/maximum) of the power supply as declared by
the manufacturer in the specification of the power supply. This is applicable only for ac-dc
power supplies.
3.23 Rated Input Current
The input current of the power supply as declared by the manufacturer in the specification of thepower supply. For a three-phase supply, rated input current refers to the input current in eachphase.
3.24 Rated Input Current Range
The input current range (minimum/maximum) for a power supply as declared by the
manufacturer in the specification of the power supply. For a three-phase supply, rated input
current refers to the input current in each phase.
3.25 Rms (Root Mean Square)
The square root of the average of the square of the value of the function taken throughout theperiod. For instance, the rms voltage value for a sine wave may be computed as:

12

T

1
VRMS =V 2 (t )dt
T ∫0

Eq. 3-4

where
T is the period of the waveform,
V(t) is the instantaneous voltage at time t,
VRMS is the rms voltage value.
(ref. IEEE Std 1515-2000)
3.26 Single-Output Power Supply
Power supplies designed to provide most of its rated power on one main dc output voltage. Theremay be other low power dc output voltage(s) for standby power.
3.27 Standby Mode
Standby represents the mode during which all dc power is delivered through the standby voltage
rail of the power supply (see Section 3.28).
3.28 Standby Voltage Rail (Vsb)
The standby voltage rail is the output voltage bus that is present whenever ac /or dc power isapplied to the input/inputs of the supply. (ref. Intel Power Supply Design Guidelines Rev. 0.5)
3.29 Steady StateThe operating condition of a system wherein the observed variable has reached an equilibrium
condition in response to an input or other stimulus in accordance with the definition of thesystem transfer function. In the case of a power supply, this may involve the system output being
at some constant voltage or current value. (ref. IEEE Std 1515-2000)
3.30 Test Voltage Source
The test voltage source refers to the device supplying power (voltage and current) to the unit
under test (UUT).
3.31 Total Harmonic Distortion (THD)
The ratio, expressed as a percent, of the rms value of an ac signal after the fundamental
component is removed to the rms value of the fundamental. For example, THD of current can be
defined as:

THD I =

I 22 + I 32 + I 42 + I 52 + ....... I n

2

Eq. 3-5

I1

where In is the rms value of nth harmonic of the current signal.
3.32 UUT
Unit under test. (ref. IEEE Std 1515-2000)
13

3.33 Voltage Unbalance
The maximum difference between rms phase to neutral or phase-to-phase voltage amplitudes at
the UUT input terminals. For example, for a wye-connected, three-phase system
VUNB = (max[V AN ,VBN , VCN ] − min[VAN , VBN , VCN ])Eq. 3-6

where
VAN , VBN ,VCN are the phase voltage magnitudes, and
VUNB is the maximum phase voltage unbalance.
Percent voltage unbalance is calculated by multiplying the maximum voltage unbalance by 100
and dividing the result by the average of the three phase voltages.

VUNB % =

VUNB
× 100
 V AN + VBN + VCN 


3



Eq. 3-7(ref. IEEE Std 1515-2000)

14

4. Standard Conditions for Efficiency Testing
4.1
General Provisions
Input voltage, frequency, output bus loading, and in some cases, the duty cycle of the fan inside
the power supply are among the variables that can impact the efficiency of an internal power
supply. Sections 4.2, 4.3, and 4.4 below recommend a minimum set of requirements in order tocontrol these variables while measuring internal power supply efficiency. Beyond theseminimum conditions, the manufacturer and user of the power supply may determine additional
requirements, such as harmonic distortion or unbalance specification as needed.
4.2
4.2.1

Input Voltage and Frequency
Ac Input Voltage and Frequency

An ac reference source shall be used to provide input voltage to the UUT. As is specified in IEC
62301, the input to the UUT shall be the specified voltage ± 1% and the specified frequency ±1%. The UUT shall be tested at one of two voltage and frequency combinations: 115 V at 60 Hz
or 230 V at 60 Hz.
The UUT shall be tested at one of the above voltage and frequency combinations that is closest
to its nameplate input voltage and frequency. If voltage and/or frequency ranges are not specified
by the manufacturer (or the nameplate value is unclear), the UUT shall not be tested.
4.2.2

Dc Input Voltage

A dc reference source shall be used to provide input voltage to the UUT. As is specified in IEC
62301, the input to the UUT shall be the specified voltage ± 1%. The commercially available dc
servers have a typical input voltage of ±48V dc. The dc-dc power supplies will be tested at +48V
or -48V dc depending upon the nameplate rating.
Note:
Efficiency measurement for dc-dc power supplies is carried out in a similar fashion as ac-dc
power supplies. In the case of dc-dc power supplies, there will be no specifications for power
factor, total harmonic distortion and frequency. There are no changes in the loading
calculations for dc-dc power supplies. The efficiency of the dc-dc power supplies is still
calculated as the ratio of output (dc) power to the input (dc) power.
4.3
Power Supply Loading
The efficiency of the UUT shall be measured at 20%, 50% and 100% of rated nameplate output
power. Efficiency measurements at lower loading conditions (less than 20% of nameplate output
current) may be recorded to support data collection on industry performance of operational
efficiency for power supplies that are typically operated in redundant configurations. Other
loading conditions may be identified that are relevant to the manufacturer and user of the power
supply. For power supply loading purposes, the standby voltage rail is treated as other dc output
voltage rails. Procedures for precisely determining load points for server power supplies aredescribed in detail in Section 6.1.1.
In some cases, the manufacturer may specify a minimum current requirement for each bus of thepower supply. In these cases, it is important to ensure that calculated current load for a specific15load point is not lower than the minimum current requirement (this is of particular concern inlower load conditions such as 5% and 10%). In cases where the minimum current requirement
exceeds the test method’s calculated load point for a given voltage bus, the value of theminimum current requirement should be used to load the bus rather than the calculated load
current. The percent load of the load point shall be properly recorded in any test report based on
the new load values used for the busses with minimum loading requirements.
Prior to power measurements, the UUT shall be allowed to operate at each load point for at least
15 minutes in order to allow the power supply to reach a steady state of operation. A steady stateof operation has been reached if the total input power reading over two consecutive five-minuteintervals does not change by more than ± 1%

4.4
4.4.1

Power Supply Fan Control
Multiple-output Power Supply Fan Control through Temperature Sense(Internal Control)

In some power supply designs, the duty cycle (expression of percent on time) of a cooling fan iscontrolled by the temperature of the internal heat sink. If the heat sink inside the power supply
reaches a certain set temperature value, the fan switches on. If the heat sink cools down below
the set temperature value, the fan switches off. The duty cycle of the fan can then influence theefficiency of the power supply especially during the time of measurement. In order to capture theeffect of the duty cycle of the fan on the efficiency of the power supply, the input and output
power measurements shall be integrated over a period of 30 minutes1 (after thermal equilibriumof the power supply is reached) or five fan cycles, whichever is reached first (one fan cycle
consists of one on pulse followed by one off pulse). For power measurement procedure refer tosection 4 of IEC 62301 (Measurement of Standby Power).
4.4.2

Multiple-output Power Supply Fan Control through External Voltage
Signal (External Control)

In some power supply designs, there may be provisions for external speed control of power supply
fans through an available connector pin. In such cases, the power supply fan is set to run at a default
minimum speed preset by the manufacturer. The computing system that houses such power supplies
monitors the thermal picture of the system, and when a set of threshold levels are exceeded, a voltage
signal is sent to the power supply to increase the speed of the power supply fan. For units with thistype of fan speed control, the unit under test will be tested with the fan speed control pin set to the
DISABLED position, which will set the fan to run at default minimum speed. The fan speed shall not
be altered or changed during the course of testing the unit under all loading conditions.
If the manufacturer submitting the unit for test requires any control signal to be applied to the fan
speed control pin, the information must be provided at the time of submittal. In this case the power
required for the higher speed fan will be included in the efficiency calculation.

1

Accumulated energy approach to get average power consumption (Please refer to section 4.3, IEC 62301 Ed 1.0):
Where the instrument can accumulate energy over a user selected period, the period selected shall not be less than 5
minutes. The integrating period shall be such that the total recorded value for energy and time is more than 200
times the resolution of the meter for energy and time. Determine the average power by dividing the accumulated
energy by the time for the monitoring period.

16

4.4.3

Fan Load Considerations for Single-output Power Supplies

In typical single-output power supplies (typically used in the rack mount servers and blade server
applications) the fans are sized not only to remove heat from the power supply but also the heatfrom the system. In order to facilitate the system designer’s use of different cooling strategies forthe system, the power consumed by the fan will not be included for efficiency calculations. If thepower supply has an internal fan, then the manufacturer will give provision to supply external
power to the fan during the power supply efficiency testing. If the power supply does not have aninternal fan and if it fails to operate during the efficiency testing due to thermal cutoff, then an
external fan shall be used to cool the power supply. The power consumed by the external fan
shall not be included in the efficiency calculations. In both cases the fan power used during
testing at each load setting will be recorded for data collection in determining industry
performance of efficiency with and without fan power.
4.4.4

Method for Fan Load Power Determination in Storage Power Supplies

Storage system power supplies are different than the single- or multi- output power supplies.
They typically are two voltage rail systems (meeting neither single-output nor multi-output
definitions) and include a fan(s) that provide cooling air for the storage system as well as thepower system. Some of the storage power supplies may have additional outputs as an exception.
Measurement of power supply efficiency as an indicator of good energy efficient designs is
inaccurate if the power to internal system fans is included.
This protocol will address Storage system power supplies in the same manner as single-output
server power supplies. Testing will be done at 230Vac, 60Hz Input. Inclusion or exclusion of
fan power in the efficiency calculation will be addressed consistently with existing provisions for
single-output and multiple-output power supplies; for storage system power supplies, fan power
will be excluded from the efficiency calculation.
Storage system power supplies tested per this protocol must be modified to provide for external
power to drive the internal fans. If measuring fan power, or if the required efficiency
measurement includes the impact of the fan, the modification must allow internal power supply
control of the fan speed and fan power will be measured and recorded at each loading condition.

5. Instrumentation and Equipment
5.1

General Provisions

These procedures are meant to ensure the accurate and consistent measurement of power
supplies across testing laboratories. Please refer to Annex B of IEEE 1515-2000, IEEE
Recommended Practice for Electronic Power Subsystems: Parameter Definitions, Test
Conditions, and Test Methods, for guidelines for general test practices and to section 4, Annex B
and D of IEC 62301, Ed. 1.0, Measurement of Standby Power, for a discussion on evaluating
measurement uncertainty.
5.2
Test Voltage Source
The input voltage source shall be deemed inadequate and different voltage source shall be used
if the input voltage varies at any point during the test by more than ± 0.1% of the specified
source voltage for the test (115 Vac or 230 Vac or ± 48 Vdc).

17

Regardless of the ac source type, the THD of the supply voltage when supplying the UUT in thespecified mode shall not exceed 2%, up to and including the 13th harmonic (as specified in IEC
62301). The peak value of the test voltage shall be within 1.34 and 1.49 times its rms value (asspecified in IEC 62301).
There are no THD, frequency or voltage unbalance specifications for the dc source.

18

5.3

Test Dc Loads

Active dc loads such as electronic loads or passive dc loads such as rheostats used for efficiency
testing of the UUT shall be able to maintain the required current loading set point for each output
voltage within an accuracy of ± 0.5%. If electronic load banks are used, their settings should be
adjusted such that they provide a constant current load to the UUT.
5.4
Test Leads and Wiring
Appropriate American Wire Gauge (AWG) wires have to be selected for different part of wiring
connections depending on the maximum current carried by the conductor in order to avoid
overheating of wires from excessive loading and to reduce excessive voltage drop across thewires which may lead to incorrect efficiency measurements. For detailed information andguidance on measurement and wiring, please refer to Annex B in IEEE 1515-2000. The Table
B.2, “Commonly used values for wire gages and related voltage drops” in IEEE 1515-2000 gives
the relation between the voltage drop across the conductor as a function of three variables:
current carried by the conductor, conductor AWG, and conductor length. The voltage drop acrossthe conductor carrying the current must be added or subtracted to the appropriate voltage
measurements if the input and output measurements of the UUT are not taken directly at theconnector pins.

Figure 1 Input and Output Voltage Measurements

19

The generic test setup can be made as shown in Figure 2 below. The ac power meter used in theefficiency test should be capable of measuring the ac voltage, ac current, ac power, power factor,
and total harmonic distortion of current. If a dc source is used instead of an ac source, thenappropriate dc meter shall be used to measure dc input voltage, current and power. The dc power
meter should be capable of measuring dc voltage, dc current, and dc power on all dc voltage
inputs or outputs of the device. All power metering equipment should meet the accuracy
requirements described in section 5.5 of this document. The dc load(s) shall be capable ofdrawing constant current during the course of the test and shall meet the tolerances specified in
section 5.3 of this document.

Figure 2 Generic Efficiency Test Setup

5.5
Measurement Instrumentation Accuracy
Power measurements shall be made with a suitably calibrated voltmeter and ammeter or power
analyzer as specified under IEC 62301. Measurements of power of 0.5 W or greater shall bemade with an uncertainty of less than or equal to 0.5% at the 95% confidence level.
Measurements of power of less than 0.5 W shall be made with an uncertainty of less than orequal to 0.01 W at the 95% confidence level. Input power shall be made using an averaging
technique over a minimum of 32 input cycles utilizing the measurement instrument averaging
function.
For appliances connected to more than one phase, the power measurement instrument shall beequipped to measure total power of all phases connected.
Dc measurements for voltage shall have an uncertainty of less than 0.1%. Current and Powermeasurements shall have an uncertainty of less than 0.5%.
20For further details please see Annex D of IEC 62301 and ISO Guide to the Expression ofUncertainty in Measurement.
5.5.1

Power Factor (PF) Measurement Accuracy

Accuracy of power factor (PF) measurements at light loading is dependent upon test setup andnoise content of the ac source. Interaction between the ac source and the power factor correction(PFC) circuit can cause an error in PF measurement when using power analyzer instrumentation.
This error is significant and can cause as much as 30% error in PF measurements at light loading
conditions below 50% of power supply rating. Testing laboratories must ensure that the ac
source does not interfere with power factor measurements at light loads. The method to be usedin this protocol is described below.
Place a Line Impedance Stabilization Network (LISN) in series with the output of the ac source.
The LISN should have 50 µHenries inductance in both the Line and Neutral wires. In addition aparallel capacitor should be installed after the LISN and placed as close as possible to the power
analyzer input terminals. The capacitor should be 1.0 µFarad and rated for a minimum of 250Vac
working voltage. The capacitor forms a high frequency circuit with the unit under test, care must
be taken to ensure the cable length from capacitor body to the power analyzer and the cable
length from power analyzer to unit under tests is less than 1 meter. The intent is to minimize thelead inductance between the capacitor and the unit under test. The diagram below (Figure 3)
shows the recommended test set up with LISN and the parallel capacitor.

Figure 3 Revised Test Setup to Improve Accuracy of Power Factor Measurement at Light Load
Conditions

21

5.6
Test Room
As is specified in IEC 62301, the tests shall be carried out in a room that has an air speed close to
the UUT of ≤ 0.5 m/s, and the ambient temperature shall be maintained at 23°C ± 5°C
throughout the test. There shall be no intentional cooling of the UUT by use of separately
powered fans, air conditioners, or heat sinks. The UUT shall be tested on a thermally nonconductive surface.
5.7
Warm-up TimeInternal temperature of the components in a power supply could impact the efficiency of the unit.
As a general recommendation before testing, each UUT shall be loaded up to the test load for aperiod of at least 15 minutes or for a period sufficient that the total input power reading over two
consecutive five-minute intervals does not change by more than ± 0.2%.

22

6. Loading Criteria For Efficiency Testing
6.1
General Provisions
Loading criteria for ac-dc or dc-dc power supplies shall be based on rated dc output current andnot on rated dc output power. For example, consider the 50% loading condition for a 50 W, +5 V
single-output power supply with a rated dc output current of 10 A. The load condition isachieved by adjusting the dc load (using a rheostat or electronic load bank) connected to the 5 V
bus output so that 5 A of current is flowing on the bus. This is not equivalent to adjusting theload bank until the load on that bus dissipates 25 W of power, because voltage regulation may
not remain constant under a range of loading conditions.
For power supplies with multiple output voltage busses, defining consistent loading criteria ismuch more difficult, because each bus has a rated dc output current. The sum of the power
dissipated from each bus loaded to these rated currents may exceed the overall rated dc output
power of the power supply. A proportional allocation method is recommended for providing
consistent loading guidelines for multiple output internal ac-dc power supplies. This method is
described in detail in the next section.
6.1.1

Proportional allocation method for loading multiple and single-output acdc and dc-dc power supplies

This section shows a procedure for developing loading guidelines based on a proportional
allocation method. Required measurements shall be taken at loading points 20%, 50% and 100%of rated output power. A measurement at 10% may be recorded for both single and multi-output
power supplies. The UUT’s nameplate specifies the maximum rated dc output current on each
output voltage bus, and care should be taken not to exceed those values. However, loading thebusses to their individual current maximums often will exceed the overall rated dc output powerof the power supply. In some cases, ratings are established for a subgroup of the output voltage
busses. These subgroup ratings can also be exceeded if the busses are loaded to their individual
current maximums. The following sections provide procedures for loading multiple-output ac-dc
power supplies by using a calculated derating factor (D).
6.1.1.1

Method of Proportional Allocation Based on Overall Power Supply Rated Dc
Output Current With No Sub-group Ratings
The manufacturer has provided rated dc output current limits for each bus and an overall rated dc
output power for the power supply. The approach for loading criteria is as follows:
Assume a power supply with four output voltage busses. A sample output specification of thispower supply is shown in Table 6-1.

23

Table 6-1: Labels for Output Variables

Rated Dc Output
Voltage of EachBus

Rated Dc Output
Current of Each
Bus

V1

I1

V2

I2

V3

I3

V4

I4

Rated Overall Dc
Output PowerP

Step 1: Calculate the derating factor D using the procedure outlined in Eq. 6-1.
D=P
(V1 ∗ I1 ) + (V2 ∗ I 2 ) + (V3 ∗ I 3 ) + (V4 ∗ I 4 )Eq. 6-1

Step 2: If D ≥ 1, then it is clear that loading the power supply to the rated dc output current forevery bus does not exceed the overall rated dc output power for the power supply. For this case,the required output dc current on each bus for X% loading can be determined by
I bus = I n *X
100

Eq. 6-2

where Ibus is the required output dc current for that bus at X percent load and In is the rated dc
output current for that bus. For example, Table 6-2 shows the guideline for 50% loading of thepower supply based on D ≥ 1.

Table 6-2: 50% Loading Guideline for D ≥ 1

Output Voltage
of Each Bus

50% Loading
Guideline

V1

0.5*I1

V2

0.5*I2

V3

0.5*I3

V4

0.5*I4

Step 3: If, however, D < 1, it is an indication that loading each bus to its rated dc output current
will exceed the overall rated dc output power for the power supply. In this case, the following
loading criteria using the derating factor can be adopted:

24

I bus =D ∗ X ∗ In
100

Eq. 6-3This effectively derates the output dc current of each output voltage bus such that at 100% load,
the overall load will equal the rated dc output power of the power supply. It also derates otherload levels. For example, Table 6-3 shows the guideline for 50% loading of the power supply
based on D < 1.
Table 6-3: 50% Loading Guideline for D < 1

Output Voltage
of Each Bus

50% Loading
Guideline

V1

D*0.5*I1

V2

D*0.5*I2

V3

D*0.5*I3

V4

D*0.5*I4

6.1.1.2

Method of Proportional Allocation Based on Overall Power Supply Rated Dc
Output Current with Sub-group Ratings
In some cases, the power supply manufacturer specifies the rated dc output power for a subgroupof busses in addition to the overall rated dc output power of the power supply. An example ofthis type of power supply is a computer power supply with an overall rated dc output power of
330 W and a rated dc output power of 150 W for the +5 V and +3.3 V busses combined. Loadingeach bus to its individual rated dc output current may now exceed both the overall power
supply’s rated dc output power and the subgroup’s rated dc output power. This section outlines a
procedure for ensuring that both the subgroup and overall current ratings are not exceeded.
Assume a power supply with six output voltage busses with an overall rated dc output power PT.
Let the rated dc output power for subgroup busses 1 and 2 be PS1-2 and a rated power for
subgroup busses 3 and 4 be PS3-4 and the ratings for bus 5 and 6 be simply equal to the product of
their individual voltages and currents. A sample output specification of this power supply isshown in Table 6-4.
Table 6-4 Output Variable Labels for Maximum Rating of Subgroup Output Voltage Bus

Output Voltage
of Each Output
Bus

Maximum Rated
Output Currentof Each Bus

Maximum Rated Output
Wattage for Subgroups
V1, V2 and V3, V4

V1

I1

V2

I2

V3

I3

V4

I4

V5

I5

PS5

V6

I6

PS6

Maximum Power
Supply Total
Rating

PS1-2
PS3-4

25

PT

Step 1: Calculate derating factors DS1 to DS6 for each of the subgroups as shown in Eq. 6-4.
DS1−2 =

PS1−2
(V1 * I1 + V2 * I 2 )DS 3−4 =PS 3−4(V3 * I 3 + V4 * I 4 )Eq. 6-4

PS 5
DS 5 =(V5 * I 5 )DS 6 =PS 6(V6 * I 6 )If the derating factor DS ≥ 1, then it is clear that when the subgroup is loaded to the rated dc
output currents, the subgroup rated output powers will not be exceeded and there is no need forderating.
However, if one or more DS factors are less than 1 then the subgroup power will be exceeded if
the outputs are loaded to their full output currents and there is a need for derating.
Step 2:
There is also a need to check whether the sum of the subgroup maximum rated powers is greaterthan the total maximum power rating of the power supply (PT). If the sum of the subgroupmaximum rated powers is greater than the overall power rating of the power supply then asecond derating factor DT must be applied. This factor is calculated as shown below:
DT =

PT

Eq. 6-5

PS1−2 + PS 3−4 + P5 + PS 6

If DT ≥ 1 then no derating is needed.
If DT < 1 then the derating for each of the outputs has to be applied and is shown below.
For example, Table 6-5 shows the guideline for X% loading of the power supply based on DS < 1
and DT < 1.

26

Table 6-5 Output Loading Current Calculation for Each Individual and Sub-group Bus Voltages

OutputVoltage

OutputCurrent
Rating

V1

I1

Subgroup

Output Loading Current

DT * DS 1− 2 * I 1 *

X
100

1-2
V2

I2

DT * DS 1− 2 * I 2 *

X
100

V3

I3

DT * DS 3− 4 * I 3 *X
100

DT * DS 3−4 * I 4 *

X
100

3-4

6.1.2

V4

I4

V5

I5

5

DT * D S 5 * I 5 *

X
100

V6

I6

6

DT * D S 6 * I 6 *X
100

Method of Current Allocation for Measuring the Ac or Input Dc Power
Consumption of a Computer Internal Power Supply in the Standby
Condition

Measurement of the ac or input dc power consumption of computer internal power supplies
operated in standby mode shall be conducted by connecting the power supply to an ac or dc
voltage source, as appropriate, through its power input and applying the following current loads
to its standby voltage rail/rails that represent 20%, 50%, and 100% of its nameplate rated load
currents. (ref. Intel Power Supply Design Guidelines Rev. 0.5)
For power supplies designed to power other electronic products, measurement of the ac or input
dc power consumption in standby mode shall be conducted by connecting the power supply to an
ac or dc voltage source, as appropriate, through its power input and applying current loads to thestandby voltage rail equal to 20%, 50%, and 100% of its nameplate current rating. Testers may
choose to test the ac or dc input power consumption during standby mode at other load points inaddition to the above recommended load points if these loads better characterize the real loads
placed on the standby voltage rail when installed in its intended product.

27

7. Measurement Procedures
1. Record all the input and output specifications of the ac-dc or dc-dc power supply
provided by the manufacturer in the power supply specification sheet. These may
include one or more of the following specifications:•

Rated input voltage (ac or dc)•

Rated input voltage range (ac or dc)•

Rated input current (ac or dc)•

Rated input current range (ac or dc)•

Rated input frequency (not applicable to dc input)•

Rated input frequency range (not applicable to dc input)•

Rated output dc power•

Rated output dc current•

Rated output dc current range•

Rated output dc voltage•

Rated output dc voltage range•

Record the ambient temperature at the site of the test.

2. Calculate the loading criteria for each output voltage bus for each loading level
defined by the loading guidelines used for the UUT.
3. Complete the test setup with the source, UUT, load, and measurement
instrumentation. Refer to IEEE 1515 Annex B, General Test Practices, for general
guidelines and recommended practices for measurement and instrumentation setup
for testing power supplies.
4. Set the power source input voltage and frequency (if programmable) as per the test
requirement.
5. Load the output voltage busses (using either a rheostat or an electronic dc loadbank) based on the loading criteria established for the UUT within the tolerance
levels specified in this protocol.
6. If the fan turns on intermittently, then follow the procedure outlined in section 4.4.
7. Measure and record the following at each load condition with the minimum
resolution as indicated below. Record the instrumentation used and the range setting
for each reading. Record the actual point of measurement for each reading.. For dc
values, record separate values for each dc output voltage bus:•

Average ac input power or dc input power in case of dc-dc power supplies(four significant digits)•

Rms ac input voltage or dc input voltage (four significant digits)•

Rms ac input current or dc input current (four significant digits)28•Power factor ( two significant digits) not applicable to dc-dc power supplies•

Total harmonic distortion of input current (three significant digits) for ac
input only.

•

Dc output voltage (four significant digits)•

Dc output current (four significant digits)•

Dc output power•

Note: Power Factor and total harmonic distortion are not applicable to dcdc power supplies

8. Calculate the efficiency of the power supply for the loading condition using theequation:

∑P

o ,i

η=

i

Pin

× 100

Eq. 7-1

Where, Pin is the recorded input power and Po,i is the output power of the ith bus.
9. Repeat this procedure for other loading conditions.
10. Measure and record the power consumption of the UUT in standby mode at the load
points specified in section 6.1.2 of this document.
Note: When testing for efficiency of data center power supplies at light loads the accuracy may
be impacted by circuit operating states. It is possible that the synchronous rectification circuitry
may begin operation in a discontinuous mode and cause lower efficiency readings.

7.1. Test Report
In the test report, graphically display the key data (measured and calculated) from the test alongwith a description of the power supply that includes the manufacturer’s model name and model
number, specifications, and loading criteria. Include in the test report footnotes or an appendix
that records instrumentation used, range settings for each measurement, and measurement
location for each recorded measurement. Appendix A provides an example test report for an acdc power supply and a graphical representation of power supply efficiency under different
loading conditions. For additional information on power supply test reports and other relevant
information, refer to the website http://www.efficientpowersupplies.org .

29

8. Appendix A: Example Efficiency Report for a Multi-Output Power
SupplyNote: For more sample test reports please visit http://www.80plus.org

30

9. Appendix B: Internal Power Supply Discussion
The common housing structures for internal power supplies considered in this test procedure areenclosed-frame and open-frame as shown in the Figure B-1. Internal power supplies within an
enclosure could be fan-cooled.

(a) Enclosed Frame Internal Power Supplies(b) Open-frame Internal Power Supplies

Figure B-1. Examples of a) enclosed frame and b) open frame internal power supplies (Courtesy

Astec Power, Artesyn Technologies)
Output ratings of a cross-section of internal power supplies used in various product classes andtheir loading criteria are shown in the tables below.
31

Table B-1: output specification of a 300 W internal power supply for an ATX 12 V form factor
desktop personal computer

Voltage Rail
NumberOutput Voltage

Min. Current(A)

Max. Current(A)

Peak Current
(A)

V1

+12

1.0

18.0

19.5

V2

+5

0.5

26.0

--

V3

+3.3

0.5

27.0

--

V4

-12

0.0

0.8

--

V5

+5 (Standby)

0.0

2.0

2.5

Table B-2: output specification of a 220 W internal power supply for an TFX 12 V form factor
desktop personal computer

Voltage Rail
NumberOutput Voltage

Min. Current(A)

Max. Current(A)

Peak Current
(A)

V1

+12

1.0

15

17

V2

+5

0.3

13

--

V3

+3.3

0.5

17

--

V4

-12

0.0

0.3

--

V5

+5 (Standby)

0.0

2.0

2.5

Table B-3: Output specification of a 200W internal power supply for a cathode Ray Tube (CRT)
Display

Voltage Rail
Number

Dc Bus Voltage(V)

Continuous Current
Rating (A)Required Voltage
Regulation

V1

135

0.75

+/- 1V

V2

30

1.2

5%

V3

15

0.5

5%

V4

7

1.2

5%

Table B-4: Output specification of a 55W internal power supply for a Liquid Crystal Display (LCD)

Voltage Rail
Number

Dc Bus Voltage(V)

Continuous Current
Rating (A)

V1

12

1.2

5%

V2

5

8

3%

32

Required Voltage
Regulation

Table B-5: Output specification of a 360W internal power supply for a Plasma Display Panel (PDP)

Voltage Rail
Number

Dc Bus Voltage(V)

Continuous Current
Rating (A)Required Voltage
Regulation

V1

170

1.3

+/- 2V

V2

65

0.9

5%

V3

15

0.9

5%

V4

13.5

0.6

7%

V5

12

0.6

5%

V6

5

0.7

5%

V7

5 (standby)

0.15

5%

Table B-6: Output specification of a 30W internal power supply for a digital set top box

Voltage Rail Number Dc Bus Voltage (V) Continuous Current Rating (A)
V1

30

0.03

V2

18

0.5

V3

12

0.6

V4

5

3.2

V5

3.3

3.0

33

10. Appendix C: Server Power Supply Discussion
The common housing structures for server power supplies considered in this test procedure are
rack-mountable units as shown in Figure C-1.

(a) Single Output Server Power Supply: -54VDC(b) Dual Output Server Power Supply: 48VDC and 5VDC(c) Multiple Output Server Power Supply: 12VDC, 5VDC, 3.3VDC & -12VDC

34

Figure C-1. Examples of rack-mountable server power supplies that have (a) single output (TDI),(b) dual outputs (C & D Technologies), and (c) multiple outputs (Delta Electronics)

Each of the three server power supplies shown in Figure C-1 has a unique output connector
interface, resulting in an additional step necessary to measure their efficiencies.
Examples of server power supplies operating in a data center are shown in Figure C-2. Notice
how power supplies are configured redundantly such that two individual power supplies power
one single server or server bank. If one of the power supplies fails, the other will assume theentire load. This scheme protects data center operators from unnecessary downtime.

Redundant
power
supplies, size
1U

Redundant
power
supplies, size
2U

Redundant
power
supplies, size
2U
Redundant
power
supplies, size
1U

35

Figure C-2. Examples of redundant server power supplies in a data center (courtesy of ElectricPower Research Institute)Server power supplies vary widely in their nameplate characteristics, such as output power andvoltage. A representative sample of one-unit (1U) rack-mountable server power supplies andtheir nameplate ratings are listed in Table C-1.
Table C-1: Specifications of a sample of server power supplies

Manufacturer

Rated
OutputPower (W)Size

Category

Voltage
Outputs(V dc)

A
B
C
D
E
F

1325
1900
540
500
750
2000

1U
3U
1U
1U
2U
1U

Dual Output
Single Output
Single Output
Multiple Output
Multiple Output
Dual Output

12V, 3.3V
48V-54V
12V, 5V, 3.3V, -12V, 5Vsb
12V, 5V, 3.3V, -12V, 5Vsb
48V, 5V

36