ETSI TR 103 229 V1.1.1 (2014-07)

Technical Report
Environmental Engineering (EE);
Safety Extra Low Voltage (SELV) DC power supply network for
ICT devices with energy storage and grid or renewable energy
sources options
2 ETSI TR 103 229 V1.1.1 (2014-07)

Reference
DTR/EE-02042
Keywords
energy management, power supply, renewable
ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis Cedex - FRANCE

Tel.: +33 4 92 94 42 00  Fax: +33 4 93 65 47 16

Siret N° 348 623 562 00017 - NAF 742 C
Association à but non lucratif enregistrée à la
Sous-Préfecture de Grasse (06) N° 7803/88

Important notice
The present document can be downloaded from:
http://www.etsi.org
The present document may be made available in electronic versions and/or in print. The content of any electronic and/or
print versions of the present document shall not be modified without the prior written authorization of ETSI. In case of any
existing or perceived difference in contents between such versions and/or in print, the only prevailing document is the
print of the Portable Document Format (PDF) version kept on a specific network drive within ETSI Secretariat.
Users of the present document should be aware that the document may be subject to revision or change of status.
Information on the current status of this and other ETSI documents is available at
http://portal.etsi.org/tb/status/status.asp
If you find errors in the present document, please send your comment to one of the following services:
http://portal.etsi.org/chaircor/ETSI_support.asp
Copyright Notification
No part may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying
and microfilm except as authorized by written permission of ETSI.
The content of the PDF version shall not be modified without the written authorization of ETSI.
The copyright and the foregoing restriction extend to reproduction in all media.

© European Telecommunications Standards Institute 2014.
All rights reserved.
TM TM TM
DECT , PLUGTESTS , UMTS and the ETSI logo are Trade Marks of ETSI registered for the benefit of its Members.
TM
3GPP and LTE™ are Trade Marks of ETSI registered for the benefit of its Members and
of the 3GPP Organizational Partners.
GSM® and the GSM logo are Trade Marks registered and owned by the GSM Association.
ETSI
3 ETSI TR 103 229 V1.1.1 (2014-07)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 5
Introduction . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 7
3 Abbreviations and symbols . 9
3.1 Symbols . 9
3.2 Abbreviations . 9
4 General architecture of a CPE SELV DC network . 10
4.1 Power distribution efficiency and voltage choice considerations . 12
4.2 Efficiency targets for element of the DC power supply network solution. 13
4.3 Power expendability, modularity and power regulation . 14
4.3.1 Modularity and Power expandability . 14
4.3.2 Transient power regulation . 15
4.3.3 Voltage regulation, ripple, noise, inrush current . 15
4.4 Reliability and maintenance . 16
4.4.1 MTBF . 16
4.4.2 Failure detection and replacement . 16
4.5 SELV plugs discussion . 16
4.6 EMC requirements . 17
4.6.1 EMC emission and immunity . 17
4.6.2 Voltage regulation, ripple, noise, inrush current . 17
4.7 Eco-Environmental specification . 18
4.7.1 Ecodesign . 18
4.7.2 Lifetime . 19
4.7.3 Copper used in distribution and energy efficiency . 19
4.8 Safety aspects . 20
4.9 Control/monitoring aspects . 21
Annex A: Loss and section design for SELV DC network distribution and example . 22
Annex B: Inputs for defining SELV DC network architecture and energy gain assessment
compared to individual adapters . 26
B.1 GGPAH home DC distribution architecture solution . 26
B.2 Emerge Alliance 24 V ceiling distribution specification . 26
B.3 IEEE UPAMD™ P1823™ project . 26
Annex C: Setting solution for DC/DC converter . 27
C.1 UI setting solution . 27
C.2 Cable setting solution . 27
C.2.1 Passive solution example . 27
C.2.2 Digital solution example . 27
ETSI
4 ETSI TR 103 229 V1.1.1 (2014-07)
Annex D: Assessment of the benefit of the SELV DC network . 29
Annex E: Bibliography . 30
History . 31

ETSI
5 ETSI TR 103 229 V1.1.1 (2014-07)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://ipr.etsi.org).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Technical Report (TR) has been produced by ETSI Technical Committee Environmental Engineering (EE).
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "may not", "need", "need not", "will",
"will not", "can" and "cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms
for the expression of provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Introduction
With the massive development and convergence of Telecom and IT, there are more and more customer Premises
Equipment such as ICT devices terminals and home network. Each of them requires an electric adapter and an AC plug
to be powered. That creates a forest of cables and energy losses, so the need of mutualising power at the level of a room
with a SELV DC network has appeared with the benefit of reducing the amount of adapters and plugs, reducing by the
way quantity of material used (plastic, copper, electronic) and thus reducing electronic wastes.
In addition this will allow simpler reuse of the output of this common power supply for new ICT devices by using the
universal power adapters for fixed devices as standardized by ETSI and recommended by ITU-T. There would also be a
significant saving on power consumption from a better efficiency on a wide range of power and reduced no load power
losses.
For each of USB-A charger avoided by connecting a USB-A detachable charging cable to the DC network, it has been
roughly assessed for 1 Billion units, a potential saving of 100 000 tons of power supply material, and 2 TWh
consumption, 1 million tons of CO2 emission each year.
Other benefits are offered to users in the zone or room where the SELV DC networks operate such as autonomy by the
battery and grid energy cost reduction by using renewable energy sources, PV being the easiest to install having a very
long lifetime.
Moreover, it is an enabler and extender of telecom service use in emerging countries where there is no electricity grid
and it brings at the same time some additional electricity for other use such as lighting with LEDs.
Finally, the SELV distribution is the natural extension in rooms of the Building 400 VDC distribution when it will be
widely spread as it seems to be a useful complement to distribution AC to offer more resilience to disaster and improve
efficiency and use of renewable energy at building level in smart cities and micro grids.
ETSI
6 ETSI TR 103 229 V1.1.1 (2014-07)
1 Scope
The present document specifies a Safety Extra Low Voltage DC power supply unit for powering at home or in public
area (stores, hotels, railway stations, etc.) any ICT devices equipped with DC input or any ICT adapter with DC input
compliant with EN 300 132-3-1 [i.17].
It gives information on:
• architecture with multi-outputs or DC network and powering area (room, zone);
• input and output voltage interface;
• configuration of interface voltage;
• optimization of efficiency and cost by mutualising several devices on the same DC power system;
• compatibility with future building using the up to 400 VDC power interface defined in EN 300 132-3-1 [i.17];
• integrated power shutdown management, to save energy as much as possible;
• reliability;
• EMC and resistibility;
• power autonomy to enable standalone power of ICT in case of crisis (electric grid failure, climatic crisis,
earthquake, etc.);
• possibility to use renewable energy especially in emerging countries with no grid or of poor quality grid:
which input interface, and how to make the sizing?
• possibility to power devices other than ICT such as low power light which highly increases life quality and
sustainable development;
• some information on product safety;
• ecodesign principles with assessment of gains in mass of material use, energy and CO2 emission.
The present document also gives an overview of other existing standards in the field.
The detailed description of power generators and power converters or controllers are out of the scope.
2 References
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee
their long term validity.
2.1 Normative references
The following referenced documents are necessary for the application of the present document.
Not applicable.
ETSI
7 ETSI TR 103 229 V1.1.1 (2014-07)
2.2 Informative references
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] Recommendation ITU-T L.1000: "Universal power adapter and charger solution for mobile
terminals and other hand-held ICT devices".
[i.2] Recommendation ITU-T L.1001: "External universal power adapter solutions for stationary
information and communication technology devices".
[i.3] Recommendation ITU-T L.1002 "External universal power adapter solutions for portable
information and communication technology devices".
[i.4] "Code of Conduct on Energy Efficiency of External Power Supplies": European Commission
Directorate-General JRC Joint Research Centre Institute for Energy and Transport Renewable
Energy Unit.
[i.5] ETSI EN 302 099: "Environmental Engineering (EE); Powering of equipment in access network".
[i.6] Recommendation ITU-T K.74: "EMC, resistibility and safety requirements for home network
devices".
[i.7] IEC 61000-3-2: "Electromagnetic compatibility (EMC) -Part 3-2: Limits -Limits for harmonic
current emissions (equipment input current less than or equal to 16 A per phase)".
[i.8] IEC 60038: "IEC standard voltages".
[i.9] IEC 60950-1: "Information technology equipment - Safety - Part 1: General requirements".
[i.10] ETSI EN 300 132-2: "Environmental Engineering (EE); Power supply interface at the input to
telecommunications and datacom (ICT) equipment; Part 2: Operated by -48 V direct current (dc)".
[i.11] IEC 60896 series: "Stationary lead-acid batteries".
[i.12] ETSI ES 202 336 (all parts): "Environmental Engineering (EE); Monitoring and control interface
for infrastructure equipment (Power, Cooling and environment systems used in telecommunication
networks)".
[i.13] IEC 60364-4-41: "Low-voltage electrical installations - Part 4-41: Protection for safety -Protection
against electric shock".
[i.14] IEC 62430: "Environmentally conscious design for electrical and electronic products".
[i.15] ETSI TS 103 199: "Environmental Engineering [EE]; Life Cycle Assessment (LCA) of ICT
equipment, networks and services; General methodology and common requirements".
[i.16] Recommendation ITU-T L.1410: "Environmental impact Assessment method for goods network
and service".
[i.17] ETSI EN 300 132-3-1 (V2.1.1): "Environmental Engineering (EE); Power supply interface at the
input to telecommunications and datacom (ICT) equipment; Part 3: Operated by rectified current
source, alternating current source or direct current source up to 400 V; Sub-part 1: Direct current
source up to 400 V".
[i.18] IEEE UPAMD™ P1823™: "Universal Power Adapter for Mobile Device".
[i.19] IEC TC 100: "Project P1683 of Technical Specification of "Universal charger for PC".
[i.20] Recommendation ITU-T K.66: "Protection of customer premises from overvoltages and
overcurrents".
[i.21] ISO 11898-3: "Road vehicles -- Controller area network (CAN) -- Part 3: Low-speed, fault-
tolerant, medium-dependent interface".
ETSI
8 ETSI TR 103 229 V1.1.1 (2014-07)
[i.22] Recommendation ITU-T K.21: "Resistibility of telecommunication equipment installed in
customer premises to overvoltages and overcurrents".
[i.23] EU directive on charger efficiency and no load power Energy Star V2.
[i.24] Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and Their
Disposal.
[i.25] IEC 60320-1: "Appliance couplers for household and similar general purposes - Part 1: General
requirements".
[i.26] ISO 14040: "Environmental management -- Life cycle assessment -- Principles and framework".
[i.27] ISO 14044: "Environmental management -- Life cycle assessment -- Requirements and
guidelines".
[i.28] "The first thousand optimized solar BTS stations of Orange group, A very positive experience full
of learning", Didier Marquet Orange et alii., IEEE Intelec 2011 Amsterdam.
[i.29] "Spread of DC power in telecom/data centres and homes/offices with renewable energy and
energy autonomy" Didier Marquet (Orange), Toshimitsu Tanaka (NTT-f), Kensuke Murai, Tanaka
Toru, Tadatoshi Babasaki (NTT), IEEE/Intelec 2013 Hamburg.
[i.30] Darnel study, "External AC-DC Power Supplies: Economic Factors, Application Drivers,
Architecture/Packaging Trends, Technology and Regulatory Developments", Tenth Edition, Feb
2011.
[i.31] GSMA 2010: "Green Power for Mobile", Bi-annual Report November 2010.
[i.32] ITU-D: "ICT 2011 development outlook".
[i.33] "New power supply optimiSed for new telecom networks and services Didier Marquet et alii,
France Telecom CNET, Jean-Paul Gabillet et alii ALCATEL-CIT", IEEE Intelec 1999
Copenhagen.
[i.34] Recommendation ITU-T K.85: "Requirements for the mitigation of lightning effects on home
networks installed in customer premises".
[i.35] IEC 62619: "Secondary cells and batteries containing alkaline or other non-acid electrolytes -
Safety requirements for large format secondary lithium cells and batteries for use in industrial
applications". ®
[i.36] Emerge Alliance .
NOTE: Available at: http://www.emergealliance.org/.
[i.37] Green Grid Platform At Home voluntary organization in Japan.
NOTE: Available at http://ggpah.org/.
[i.38] GeSI-ITU-T Study 2012, An Energy-aware Survey on ICT Device Power Supplies.
NOTE: Available at http://www.itu.int/ITU-T/climatechange/report-ict-device.html.
[i.39] CENELEC EN 55022: "Information technology equipment - Radio disturbance characteristics -
Limits and methods of measurement".
[i.40] CENELEC EN 55024: "Information technology equipment - Immunity characteristics - Limits and
methods of measurement".
ETSI
9 ETSI TR 103 229 V1.1.1 (2014-07)
3 Abbreviations and symbols
3.1 Symbols
For the purposes of the present document, the following symbols apply:
I current
Pu Useful Power of the load
R resistance
U voltage
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
AC Alternating Current
ASCII American Standard Code for Information Interchange
CAN Controller Area Network
CMOS Complementary Metal Oxyde Semiconductor
CPE Customer Premises Equipment
CPS Common Power Supply
DC Direct Current
DIN Deutsches Institut für Normung
GGPAH Green Grid Platform At Home
GHG Green House Gas
HF High Frequency
ICT Information and communications technology
LCA Life Cycle Assessment
MPPT Maximum Power Point Tracker
MTBF Mean Time Between Failure
NTT Nippon Telegraph and Telecom
PC Personal computer
PoE Power over Ethernet
PSU Power Supply Unit
PV PhotoVoltaïc
PWM Pulse-width modulation
RH Relative Humidity
SCCP Short Chain Chlorinated Paraffins
SELV Safety Extra Low Voltage
UCPS Universal Common Power Supply
UPA Universal Power Adapter.
UPAMD™ Universal Power Adapter for Mobile Devices
VAC Volt in Alternating Current
VDC Volt in Direct Current
XML eXtended Mark-up Language
ETSI
10 ETSI TR 103 229 V1.1.1 (2014-07)
4 General architecture of a CPE SELV DC network
Many studies are showing the extension of the use of ICT terminals in Customer Premises all over the world. For
example the ITU-D outlook [i.32] is showing that Telecom network and terminals are developing in Emerging countries
faster than the electric grid.
For the mobile network a GSMA study [i.31] and for example an IEEE/intelec 2011 paper [i.28] have shown that the
massive deployment would be more based on renewable energy and single legacy Diesel generator could be replaced by
hybrid power system. As a consequence of this fast Telecom network development, there is an increased need of
electricity in customer premises, that can bring at the same time more comfort and social benefit, such as low power
consumption lighting for emerging countries. The universal adapter solution already promoted for powering ICT
devices Recommendation ITU-T L.1000 [i.1], Recommendation ITU-T L.1001 [i.2] or Recommendation ITU-T L.1002
[i.3] ensures the compatibility with renewable energy systems such as those based on PV modules, either small system
in SELV voltage and these Recommendations introduce compliance of the chargers with EN 300 132-3-1 [i.17] at
building level. IEEE/intelec paper 2013 [i.29] is showing a possible start of wide spread of these solutions.
As in many homes there is not only one terminal but several, and because there is a need of shared charging points for
users (public or private), it appears that a DC network solution could be an optimized solution. It was already stated as
already presumed in IEEE/Intelec 1999 paper [i.33].
Other solutions based on AC inverter using for example DC from solar PV module or battery allow the use of AC
adapter but the efficiency and reliability is poor. Even if the up to 400 VDC interface is possible for complete swap of
the distribution inside buildings but it seems there is also a space for a more optimized and progressive zone or room
lower voltage DC network. The best solution for safety is a SELV voltage lower than 60 VDC in compliance to
IEC 60364-4-41 [i.13]. The DC voltage level, would depend on the environment where it is used (e.g. dry or wet). For
maximal safety, it seems better to keep this limit for wet area not at the maximum value of 120 VDC. 30 VDC limit is
even better for human safety if there is a serious risk of water ingress.
Considering the increasing need of security and availability of ICT, this solution can also in developed countries. Japan
has an initiative on that in greengrid@home [i.37]. There will be compatibility with up to 400 VDC network.
In addition, a SELV DC network mainly for telecom, health and safety ICT can bring at the same time a back-up
possibility for more autonomy and less failure of sensible ICT devices while reducing the use of fossil energy resources
and the CO2 emission and other environmental or human risks.
Figure 1 is presenting the general architecture of a home SELV DC grid able to power home CPE equipment. It can also
be applied in other customer premises: small office, commercial or business building. Not all possible voltage
converters are represented, refer to DC distribution network description list in this clause.
ETSI
11 ETSI TR 103 229 V1.1.1 (2014-07)
Other local
Generator
AC or DC Power Grid Wind
PV module
Fuel cell
Energy
Water turbine
storage:
Stirling type
Battery,
Muscular type
Solar Flywheel,
(sport, animals)
Power supply
Controler
…
…
SELV primary DC bus
SELV
Power output management
distribution
network
Star distribution
DC/AC inverter
Option
Sub DC bus
DC/DC
or DC node
device
device
device device device device
NOTE 1: This architecture can include also an optional reverse power feeding module connected to the DC
distribution network compliant with EN 302 099 [i.5].
NOTE 2: DC/DC Converter on sub DC bus or DC nodes are called POL.

Figure 1: Architecture of a SELV DC power system and distribution grid solution in CPE
This architecture takes into account other studies and ongoing standardization:
• Darnel study on charger and power supply, [i.30] ®
• Emerge Alliance 24 V distribution for lighting and ICT device in office or commercial building rooms [i-36]
• ITU-T SG5 L.1000 [i.1], L1001 [i.2], L.1002 [i.3]
• IEEE UPAMD™ P1823™ [i.18]
• IEC TC 100 P1683 [i.19] on universal interface for computers [i.19]
• SELV home power distribution in Japan Green Grid Platform At Home [i.37]
Refer to annex B for more details.
The power generating system includes:
• A primary SELV DC bus where are connected: energy storage, primary power supply using DC or AC grid,
generators and output power distribution management system.
• A SELV DC distribution network feeding power to loads directly or through DC/DC and sub distribution.
NOTE 1: The input liaison of the controller to the external sources (grid, PV, wind generator, etc.) is out of the
scope of this CPE primary distribution.
NOTE 2: The DC grid is compliant with EN 300 132-3-1 [i.17], and should be compliant with future standards for
DC safety and DC plugs under definition by IEC.
ETSI
12 ETSI TR 103 229 V1.1.1 (2014-07)
The SELV DC distribution network includes:
• SELV DC power output management including protected outputs against short-circuit and optional limitation
of power or energy consumption.
• Possible DC subdistribution of different types: bus, star.
• Connection nodes.
• Optional Voltage DC/DC adapter or converter that can be dedicated or common to several devices: it can be
floor level converter (e.g. 24/12 V) or final POL converter (e.g. 12/5 V).
• Optional DC/AC inverter for using existing AC adapters of devices.
• Optional DC/DC step-up converter (e.g. 24/300 V) for using existing DC adapters of devices.
• Plugs for detachable power cable towards devices.
NOTE 3: The power output management and the battery management have to share information. They can be
designed as a common unit.
NOTE 4: Due to possibility of DC/DC conversion in this network there can be more than 1 SELV voltage used to
optimize the copper section and voltage drops and losses on the cables.
4.1 Power distribution efficiency and voltage choice
considerations
A detailed study in annex A is showing the relation between the voltage, the power and the cable section and length.
It appears that 5 V is clearly too low a voltage for power higher than 10 W, 12 V or 10 - 15 V range could be
convenient till 100 W for lower distance than 10 meters as it is in small vehicle for DC sub-network allowing reuse of
common accessories manufactured for car.
It should be noticed that 24 V has been chosen for bigger vehicles such as vans, and that manufacturers have considered
higher voltage for high class vehicles equipped with high power comfort equipment. After a long trend to 36 V or 42 V,
the new trend in car industry is 48 V with dual battery 12 V lead-acid for starter, 48 V for other accessories.
In fixed or mobile homes 12 V is already very common for lighting with incandescent bulbs or LED lights and for small
accessories with motors (fans, etc.). For large working zones or office rooms Emerge Alliance [i.36] is promoting 24 V.
A good compromise could be also a voltage range of 18 V - 28 V that match the common voltage range of battery by
using two "12 V" blocs in serie and a 24 V solar panel voltage.
Power over Ethernet is based on voltage up to 60 V, but such a high voltage can create some complications for battery
and single PV panel solution for only hundreds of watts. PoE is already standardized and is based on specific cable for
Ethernet and worldwide standardized connector. However, thin copper pairs may not be the best solution for long life
time in salted environment and there can be over cost to use communication cables for power purposes.
The 48 V voltage has the advantage of compatibility with telecom equipment EN 300 132-2 [i.10], but such voltage
could be a little bit too high for small PV systems as explained for Ethernet PoE. It is not well adapted for small battery
capacity as it requires more cells in series to manage than 12 V or 24 V.
New single PV panel of some hundreds Watts have voltage of about 50 V but the battery regulator can in general adapt
the output voltage to 12 V or 24 V battery.
If AC is required, a wide range of inverters using either 12 V, 24 V or 48 V exists.
Energy efficiency and cost are maximized by reducing the number of conversion stages and a battery for small power
system (< 1 kW) using a reduced number of cells whatever is the technology, so using 12 V or 24 V is very common in
small PV systems. Maybe a 12 V system with possible extension to 24 V could be a solution. It can be also a good
choice for compatibility with car voltage and many existing fixed or portable equipment. It is also well suited to small
energy systems. There can be a possible 3 wire distribution in 12 V and 24 V with or not common return.
ETSI
13 ETSI TR 103 229 V1.1.1 (2014-07)
Figure 2 gives an example of possible implementation with two SELV DC voltage levels for multi-floor home:
• A 24 V battery bus voltage (e.g. 18 V - 28 V) for home distribution
• A constant voltage (chosen between 12 V and 14 V) for room distribution
If 48 V is required for PoE or telecom reverse power feeding with power interface as defined in EN 302 099 [i.5], as it
is not a general case, it could be considered as a specific load and does not impact the primary bus and the DC network
voltage choice.
PV 1 kW (50 – 90 V)
DC/DC
converter
DC/DC
converter
Public
AC grid
DC/DC
converter
DC/DC
converter
47-51 V
DC bus
DC/DC AC/DC
DC/DC
converter battery charger
converter
Figure 2: Example of possible SELV network implementation
with two SELV voltage levels: home 48 V and room 12 V
For higher power, 48 V or 60 V and even higher voltage would be preferred to reduce cable section inside home
distribution (see clause 4.7.3) and are convenient as large PV modules are working at 50 V or more voltage. It would
allow lighter battery blocks as capacity can reach some hundreds of Ah and tens of kg even in Lithium technology.
4.2 Efficiency targets for element of the DC power supply
network solution
The loss in cable should not be higher than 5 % of load use. Detailed calculation is in annex A.
AC or DC grid power supply module
The efficiency and no load of primary AC/DC power supply or DC/DC adapter modules used on this SELV DC
network should comply with values defined for AC/DC adapters in table 1. The efficiency of power supply from AC or
DC grid should follow latest Code of Conduct on Energy Efficiency of External Power Supplies [i.4] Version 5.
ETSI
14 ETSI TR 103 229 V1.1.1 (2014-07)
No load power should be lower than 30 mW and lower than 150 mVA.
NOTE 1: Comparison made on 4 loads 25 %, 50 %, 75 % and 100 % on a set of individual power adapters of
5 W - 20 W and a common power supply in the SELV grid have shown a gain of about 10 % inefficiency
by using a power supply of more than 60 W. There is also an additional gain due to less no load power
consumption.
NOTE 2: For higher AC/DC power system of some hundred of W used in server, there can be even more gain,
because power supply efficiency can reach more than 90 %.
Battery efficiency
Self discharge of battery or any other energy storage should be lower than 1 % per day from 0 °C to 45 °C when the
battery state of charge is below 90 % of its capacity.
Energy efficiency of cycle charge/discharge should be higher to 80 %.
Battery charge control
The battery charger controller for local sources (PV, wind, etc.) has an efficiency higher than 95 % for power ranging
from 10 % to 100 % of the generator. The controller power consumption should be lower than 1 W in standby mode.
It is recommended to use a MPPT controller for solar module or wind generator.
On latitude lower than 30 degree, the MPPT is not necessary.
NOTE 3: An on-off regulation is to be avoided, as it will create additional small cycles charge-discharge ageing the
battery. A floating solution is much better in that respect. This is the case for PWM and MPPT charge
controller.
DC/DC optional module in final subdistribution
The DC/DC optional module are used:
• from battery voltage (e.g. 24 V, 36 V, 48 V, 60 V) to room DC network (e.g. 12 V, 24 V) with efficiency
higher than 90 %
• in final conversion to useful voltage (e.g. 12/5 V USB-A POL DC/DC converter)
In all cases, no load power should be lower than 30 mW.
The efficiency should be calculated at loads 10 %, 25 %, 50 %, 75 % and 100 %.
The insulation is not required.
4.3 Power expendability, modularity and power regulation
4.3.1 Modularity and Power expandability
The architecture is designed modular which requires some precautions.
Primary bus:
It should be built to accept higher power and current than one module is able to give in order to allow expendability.
Power modules or sources
New modules as depicted in figure 1 can be connected to the primary DC bus in parallel mode providing the global
current and power limits are respected for the bus and connectors.
The AC/DC source are equipped with AC plugs either using IEC 60320-1 [i.25] connector or an intermediate backplane
to have only one AC plug for several AC/DC modules.
NOTE: The home or office 400 VDC sockets and plugs of current lower than 10 A are under standardization in
IEC.
ETSI
15 ETSI TR 103 229 V1.1.1 (2014-07)
Battery
There can be extension from 12 V to 24 V by serial blocs, and of capacity by putting battery in parallel.
The battery management matches the bus current and power limit with the battery capacity and type. There should be a
clear configuration setting procedure and the default mode is a safe configuration. This is very important for safety
operation and to get a long battery lifetime.
Grid power supply unit
There can be extension in the limit of the primary bus and respecting the battery current limit.
PV controller and panels
There can be PV extension in the limit of the controller, the primary bus and respecting the battery current limit.
That means that input PV modules should respect input voltage and current of the controller.
PV panels in parallel work at the same voltage.
Other sources
The limit conditions are the same as PV.
Loads
The loads are limited by the maximum current allowed in connectors and in the distribution and by output protection.
The battery can also imposes its limit.
The autonomy of the system can be also a limit. Normally to ensure long lifetime of the battery, the overall load
expressed in current should not be higher than C/20, where C is the nominal capacity of the battery at the corresponding
discharge rate.
4.3.2 Transient power regulation
Modern ICT are being designed to dynamically optimize their energy performances. Their consumption is more and
more variable and related to the dynamical behaviour (e.g. service, bit rate, etc.). The power distribution will then
experience loads power transients on all the power range. So the voltage and current regulation should be fast and
precise enough. Typically considering electrolytic capacitor at the input of device, a typical regulation time of 20 ms to
recover normal voltage range would be convenient.
The considered AC input of AC/DC PSU is in the range defined in IEC EN 60038 [i.8] nominal voltage range.
4.3.3 Voltage regulation, ripple, noise, inrush current
The SELV DC voltage distribution should provide a clean power. So the ripple are limited, regulation to dynamic load
change is defined. The battery sizing and cable impedance is also defined for limiting inrush current effect providing
these inrush currents are limited. Absolute or relative values are given in table 1.
Table 1: Regulation, ripple, inrush current
Voltage regulation within ±5 % @ rated voltage
Ripple/Ripple noise within ±2 % @ rated voltage
Current limitation of Controlled to match battery limitation and recharge
Power characteristics AC/DC charger curve
Interface Dynamic characteristic Under study
Inrush current Under study
characteristic
Start-up characteristics Under study

The inrush current and big load variations can create a voltage disturbance for other loads, but also for sources
controller and regulation on the DC bus system when there is no battery or when the battery is ageing and its impedance
is becoming higher.
ETSI
16 ETSI TR 103 229 V1.1.1 (2014-07)
Low frequency ripple measurement method is measured with an oscilloscope on an electrolytic capacitor of 47 µF and a
HF capacitor of 100 nF in parallel which simulates power input stage of ICT/telecom equipment.
4.4 Reliability and maintenance
4.4.1 MTBF
The MTBF of battery should be higher than 100 000 h over the life time period (see clause 4.7.1 ecodesign and
clause 4.7.2 lifetime).
NOTE: MTBF is supposed constant excluding youth failures and end of life failures.
The MTBF of power electronic should be higher than 100 000 h.
Further studies are required depending on distribution configurations and power sources reliability.
4.4.2 Failure detection and replacement
The replaceable elements are the following:
• batteries;
• power modules;
• output high power connectors for DC distribution with screw for cable and connector replacement;
• replaceable fuses or circuit breakers.
The following list gives some possible fault detections leading to alarms (LEDs, or messages):
• Low battery threshold
• Very low battery threshold corresponding to imminent disconnexion of load
• Battery voltage too high
• Battery loss of capacity over a defined threshold Battery temperature too high (this indicates a risk of short
lifetime)
• DC bus disconnected
• One output failure
• 24 h without solar input
• 24 h without mains input
NOTE: The alarms depends on options on the system (solar, mains, etc.).
If a remote interface is provided, it should be compliant with ES 202 336-1 interface [i.12].
4.5 SELV plugs discussion
Some ongoing-standards are trying to define the plugs at the device side in USB specification, in IEC project for PC
[i.19], in IEEE UPAMD™ [i.18]. The last one is also considering the possibility of using the same plug for power
supply side. The advantage is also the use of signal pins and a very compact design.
The legacy plugs used nowadays for non electrician users are:
• USB A: on PC side or on Recommendation ITU-T L.1000 [i.1] charger side or on some other devices. This
plug is dedicated to 5 V and 1,5 A limited, maybe some more in future specification from USB association or
in IEC standard. They have advantage of mixing signal pins.
ETSI
17 ETSI TR 103 229 V1.1.1 (2014-07)
• Car cigarette plugs are usually designed for typically 13,8 V (10 V - 15 V) - 10 A. Many ICT chargers are
already compatible with these plugs and voltage. They have no signal pin.
• Caravanning 12 V (10 V - 15 V) plugs for at least 10 A, They are more compact than cigarette plugs and there
is no signal pin. They exist in wall socket configuration, which is convenient for home distribution.
• Coaxial barrel plugs can reach 30 V - 6 A for PC recharge. They are rather used on ICT side.
• Barrels plugs with 1 pole as middle pin : they are safe 12 V - 5 A and maybe some more voltage. They are
used on Universal Power Adapter in Recommendation ITU-T L.1001 [i.2] and L.1002 [i.3].
• HIFI speaker plugs. As they are specific to sound, there is a risk of error that can create damages to equipment.
• DIN standard plugs, they are used in many configurations with different numbers of pins, and especially for
medical power adapters with ratings till 60 V and some A.
NOTE: Banana plug are very common and can reach 25 A. But in general, they are not coupled and so not error
free and not very friendly for a non electrician user. Some of them have the same shape and diameter as
AC plug, so the error can be very dangerous and produce big damage to equipment.
Many other specific SELV plugs exists in industry, e.g. for battery recharge.
It should be better to create a brand new one and use existing one already common in cars (because used for ICT
recharge).
There are also research or development of plug less surface contact interconnection as for portable tools or wireless
energy transfer.
In the past there has been project in IEC to define SELV wall socket.
The preliminary conclusion could be to define a dedicated series of wall sockets for 12 V, 24 V or 48 V.
For 24 V, there may be some intention to do so in some industry Alliance such as Emerge Alliance [i.36].
4.6 EMC requirements
This clause covers the whole system and its elements (DC/DC or AC/DC converter, energy and storage sources power
controller, DC output power management unit, distribution cables, DC plugs).
The EMC of Universal charger, CPS, generators and sources connected to the DC network is out of the scope.
NOTE: The power factor of AC supply should be compliant with IEC 61000-3-2 [i.7].
4.6.1 EMC emission and immunity
Recommendation ITU-T K.74 [i.6] includes all EMC, resistibility useful for the DC network, while ICT equipment
EMC is out of the scope of the present document.
NOTE: Recommendations ITU-T K.21 [i.22] and ITU-T K.85 [i.34], EN 55022 [i.39], and EN 55024 [i.40] are
included in the Recommendation ITU-T K74 [i.6].
4.6.2 Voltage regulation, ripple, noise, inrush current
The SELV DC voltage distribution should provide a clean power. So the ripple are limited, regulation to dynamic load
change is defined. The battery sizing and cable impedance is also defined for limiting inrush current effect providing
these inrush current are limited. Absolute or relative values are given in table 2.
ETSI
18 ETSI TR 103 229 V1.1.1 (2014-07)
Table 2: Regulation, ripple, inrush current
Ri
...