Thursday, January 21, 2016

Department of Energy Level VI energy efficiency standards for external power supplies

I recently received a question from one of our sales people about to what extent the new Department of Energy’s Level VI will affect our customers, and asked me to comment on it.  As usual with my blogs, let us look at the background.

The power supply industry, in particular those who manufacture external or adapter power supplies, has been aware of the US Department of Energy’s legislation on the efficiency standards for External Power Supplies (EPS).   This legislation was made final on April 11, 2014 and comes into effect February 10, 2016.  The intent is to reduce waste energy both from off-load operation and normal operation.

Details of this lengthy, but detailed, final ruling can be found on this link:!documentDetail;D=EERE-2008-BT-STD-0005-0219

I remember many years back when energy efficiency standards for power supplies were first discussed.  Initially the reaction was “it is only a few Watts, why bother”, but with the staggering number of external power supplies now being used (and it is expected to grow in future years) those few Watts soon adds up to billions of dollars in electricity and the associated environmental pollution.

Most people leave their laptop/tablet/phone chargers plugged in 24 hours a day, and that applies to numerous gaming consoles and other electronic equipment.  Power supplies continue to draw power when not supplying load and legislation has been introduced to set (decreasing) limits year on year by multiple bodies.  In addition that legislation has gradually increased the minimum operating efficiency – this is measured at four loading levels; 25, 50, 75, and 100 percent of maximum rated output current.

There has been though, some debate and confusion about what types of EPSs are actually covered by the legislation.  This is significant as the DoE ruling forbids the imports of these types of power supplies after the February deadline if they do not meet the new efficiency standards.  It is made clear that EPSs for some medical applications (those requiring FDA approval and listing) are exempt.  Spares are also excluded from the import ban.

Looking at the final ruling web-link provided above, it states in section III General Discussion, B. Product Classes and Scope of Coverage, 1. General:

An “external power supply” is an external power supply circuit that is used to convert household electric current into DC current or lower-voltage AC current to operate a consumer product.

1. Is designed to convert line voltage AC input into lower voltage AC or DC output;
2. is able to convert to only one AC or DC output voltage at a time;
3. is sold with, or intended to be used with, a separate end-use product that constitutes the primary load;
4. is contained in a separate physical enclosure from the end-use product;
5. is connected to the end-use product via a removable or hard-wired male/female electrical connection, cable, cord, or other wiring; and
6. has nameplate output power that is less than or equal to 250 watts.

Section 2: Definition of Consumer Product” is where the DoE noted that some companies have made comments questioning the vagueness of the term.  Schneider Electric commented that the definition of consumer product is “virtually unbounded” and “provides no definitive methods to distinguish commercial or industrial products from consumer products.”

The DoE ruling refers to an EPCA (Energy Policy and Conservation) document that defines a consumer product as:

 “any article of a type that consumes or is designed to consume energy and which, to any significant extent, is distributed in commerce for personal use or consumption by individuals.”  For clarification, manufacturers are advised to consult this document:

To answer our salesperson’s question - one thing is for sure, embedded (installed internally to the end equipment) and DIN rail power supplies are not affected by this legislation.  It only applies to EPSs that are contained in a separate physical enclosure from the end-use product.

Does this affect an EPS designed for and sold for use with commercial or industrial products?  I think there will still be some debate on that, but there is strong evidence in the final ruling that they are not covered and hence exempt.  The document refers to “household electric current”, “personal use” and “consumption by individuals”.  It is very clear that if an EPS manufacturer is producing a product that could likely end up in your home, it has to abide with the legislation.

As a note, TDK-Lambda has launched a number of external power supplies that comply with Level VI efficiency standards.  TDK-Lambda’s new industrial products also have low off-load power draws and efficiencies in excess of 90%.

Power Guy

Monday, November 30, 2015

Portable Generators and Electronic Power Supplies

Portable diesel generator sets are often used to provide AC power to temporary outdoor public events, like festivals, promotions and concerts.  It is now common to have large HD screen displays and a host of other electronics being used to provide additional multimedia.
When asked about running electronic power supplies on portable generators, we tend to consider the waveform quality, distortion and high voltage noise spikes.  Upon further research, this may not be our greatest concern.

I mention portable generators, rather than the fixed location, back-up generators that many facilities have in place against power outages.  The fixed generator would typically provide power to a number of different load types, such as heating, cooling, lighting, machinery and office equipment.  These loads would change, but not significantly during operation, and it would be reasonably safe to assume that there would be a “base-load” that remains present at all times.

With a portable location, that might not be the case, particularly during a break in the event schedule or at the end of a set when the power draw drops dramatically.  When this occurs, there could be significant rise in the generator output voltage before it compensates for the light load.

Generator Voltage with Sudden Load Change

Until ISO 8528 was published, generator specifications were governed by local country standards, with many of the tests only ensuring that the generator could handle and recover from large load steps. Now, under the governor section of the standard, in section ISO 8528-1-7, the response regulation states four performance standards.

Class G1 – Used for applications where the connected loads only require the basic parameters to be specified.  This includes general purpose applications like lighting and electrical loads which can easily withstand the input voltage surges.

Class G2 – Required for applications where regulation is not that critical and temporary deviations are acceptable.  Lighting systems, pumps, fans and hoists have some tolerance to frequency and voltage.

Class G3 – Applications where the equipment demands are moderately severe and includes telecommunications equipment and thyristor-controlled loads.

Class G4 – Required for applications where the demands are extremely severe.  This typically includes data-processing and computer equipment.

The limits for these deviations are shown below.

*Class G4 systems are usually customer specified

For different regions around the world this means the following overshoot profiles are possible:

The input voltage rating for many off the shelf AC-DC power supplies is 85/90Vac to 264Vac.  Recently though, a number of manufacturers have added a peak voltage rating of 300Vac for five seconds.  This is usually found on enclosed type of product, like TDK-Lambda’s RWS-B series of 50 to 600W industrial power supplies.

TDK-Lambda’s RWS-B

Looking at the tables above, the newer generation of power supplies with a peak rating of 300Vac for 5 seconds may be used on Class G3 generators.  Depending on the extent of the anticipated load changes where there is a base-line of fixed load, can probably be used with Class G2.

As open frame (embedded) power supplies tend to be used in ITE equipment, that surge rating is not usually specified, and a Class G4 generator should be utilized.

The concern is that the choice of generator will probably lie with the event organiser, and they may opt for a lower cost Class G1 or G2 if they are not familiar with the standards.  If an equipment manufacturer believes that their product may get used with portable generators, they should consider using an AC-DC power supply with a 300Vac surge rating.  Any product literature should state the minimum class of generator to be used for reliable operation.

Thursday, October 29, 2015

Power Supply Safety Reports and Certifications

One can find a great deal of information on a power supply by studying the manufacturer’s datasheet and other technical articles, but sometimes more information is required for the actual installation.  Where is this information?  It is in the power supply’s safety reports and certifications.  Failure to review and follow these can cause delays when system certification is sought.

To keep this article simple, we will just review a product that is certified to IEC 60950-1.

Usually there are three main documents; the CB certificate, an IEC 60950-1 CB report and / or EN 60950-1 test certificate and of course for North America, the UL or CSA 60950-1 test report.  Due to confidential information like schematics, full test reports are often restricted and may only be released with a non-disclosure agreement (NDA).  Fortunately reproduction is allowed by the test houses for the relevant pages of the report.

Usually the CB test certificate, which should always accompany the CB test report, is just two or three pages.  This is often public information and details the part numbers that have been certified, their input and output ratings along with the safety standard (including revisions and amendments).  Its function is to give a quick snapshot of the product and to show if all the certifications are current.  A product that has out of date certifications may only be suitable where the safety bodies have allowed the use of “grandfathering” for older systems, and will not suitable for new designs or major system upgrades.

To reduce cost, many power supply manufacturers are using the CE Mark to indicate compliance with EN 60950-1 rather than pay for and maintain a separate EN 60950-1 test report and certificate.  In this case the CB test certificate (and CB test report) will indicate that the product was “additionally evaluated to EN 60950-1”.  This is perfectly acceptable.

Even an abridged CB or UL 60950-1 test report (the full report may extend to over 300 pages) has useful information.  The section “Engineering Conditions of Acceptability” has the all-important details for how the product should be used.

For example:

Are the outputs SELV?  Those outputs that are not should be insulated or have their access restricted to ensure that an operator or service technician cannot receive an electric shock.

Do any outputs have hazardous energy levels?  240VA is considered potentially dangerous if a screwdriver or metallic item accidentally shorts them, and a cover should be installed to protect them.  Metal watch straps have caused serious burns to car mechanics when they have shorted the positive battery terminal to the automobile body.

Is “field wiring” allowed?  If not, any cabling has to be attached by trained personnel.  Products like DIN rail power supplies do allow field wiring and do not have crimped wire terminations.

The maximum investigated branch circuit rating is given.  This reflects the size of the circuit breaker that was used during the safety testing, particularly when abnormal tests were performed.

The investigated Pollution Degree rating is stated.  A rating of 2 is normal for office or laboratory equipment.  That product should not be used where a pollution degree of 4 is required for an outside application where it may be subject to rainfall.

Proper bonding to the end-product main protective earthing termination is listed as required or not required.  Failure to correctly earth the product can result in electric shock.

The temperature class of any magnetic component components is given.  Usually this is Class A (105oC) and system testing should check to make sure that is not exceeded under worse case conditions.

“The following end-product enclosures are required:” Here the types of enclosures are indicated for mounting the power supply in.  If an open frame power supply is being used, the report will state that it has to be housed in an enclosure.

Other notes may be listed, like product orientation.
Many power supply companies are now posting this information on their website, along with the CE D of C (Declaration of Conformity); even some distributors are doing this too.  The recent surge of amendments to the standards though is keeping many webmasters busy!

Monday, August 31, 2015

IEC/UL/EN 60950-1 Amendment 2

CENELEC (Comité Européen de Normalisation Électrotechnique) published what is believed to be the last change to the EN 60950-1 standard in August 2013.  60950-1 covers general safety requirements for Information Technology Equipment (ITE).  Commonly known as “Amendment 2”, the safety files will now refer to either EN 60950-1:2006 + A11:2009 + A1:2010 + A12:2011 + A2:2013 or EN 60950-1:2006/A2:2013.  The date of withdrawal is July 2nd, 2016 and power supply manufacturers are updating their files to the new version of the standard.

UL & CSA announced their update to 60950-1 on October 14th, 2014, but unlike Europe, the Amendment 2 revision is not mandatory to existing files.  New products though are being certified to UL 60950-1, 2nd Edition, 2014-10-14 and CAN/CSA C22.2 No. 60950-1-07, 2nd Edition, 2014-10.

This should be the last change as June 2019 will see the move to IEC 62368-1:2014 for both IEC 60950-1 and IEC 60065.  The changes are considered as mainly clarifications to smooth that transition.  The safety bodies have commented on their websites that there would be minimal impact to power supply manufacturers for Amendment 2.

The changes for most power supplies for Amendment 2 are:

Any graphics used are to comply with ISO standards and must be explained in the installation manual.

Humidity testing has been introduced for equipment “designated for tropical regions”.  CCC & CQC certifications for China are already referring to this.

Similarly, to reflect a common Chinese requirement for 5,000m operation, the addition of a symbol will indicate if the equipment is to be operated at a maximum of 2,000m.  This is not an issue for UL, EN or CB.

Non lead acid batteries (with the exception of button cells) must comply with IEC 62133, and will only affect a very limited number of power supplies.

The use of VDRs - voltage dependant resistors – (a major change for Edition 1), have had a flammability requirement added.

As a note, all the self-certified Declarations of Conformity for CE marking will have to be re-written and posted.

Wednesday, July 29, 2015

Using Droop Mode Current Share Power Supplies

Connecting power supplies in parallel is commonly used to increase the available output power or to provide system redundancy in the event of a power supply failure.  The correct and reliable way to connect two or more power supplies in parallel is to have them equally share the load current.

If “brute force” current share is used (connecting power supplies in parallel without regard to load sharing), it can lead to one or more of the units operating in overload and a reduced field life due to overheating.  Here is an earlier article I wrote:

There are two main (analog) techniques for getting power supplies to share the load - “active” and “droop” mode. 

Active current share uses a signal wire interlinking two or more power supplies.  Simply put, the voltage on the wire is proportional to the total current supplied to the load.  That voltage is used to “inform” a unit that it is not contributing enough current, thus raising its output voltage to produce more current.  In telecom and datacom systems, the power supplies are usually rack mounted and plugged in to a pcb backplane.  The current share connection is therefore identical from installation to installation.

On the other hand, industrial applications tend to use hard wired DIN rail mount power supplies.  The cable routing can change dramatically between installations.  Cable lengths can be quite long causing the current share signal connection to be vulnerable to EMC interference from motors and relay switching.  One solution that does not need any current share connection is droop mode.

Droop mode is a very simple way of paralleling power supplies.  The output voltage drops (droops) in proportion to the current drawn from the power supply.  If one power supply is supplying more current than the others, the output voltage will fall and load balancing will occur.  Certain electronic loads can be sensitive to variations in the supplied voltage (3.3V or 5V for logic ICs for example), but typically 12V, 24V or 48V outputs drive relays, DC-DC converters or motors and are more tolerant to droop mode current share.

Very often this feature is standard on DIN rail power supplies 100W and above and is enabled by either a switch, or like on TDK-Lambda’s DRF series (shown below), the removal of a wire link or jumper on a connector.
TDK-Lambda DRF DIN rail power supply

When the DIN rail power supply is not operating in parallel, the switch is closed (or wire link kept in place).  The internal control circuit will compare the output voltage to a reference (Figure 1).  Any change in the output voltage due to load will be compensated for, and the output regulation will be minimal – in the order of 10mV.
Figure 1

When two or more power supplies are connected in parallel, the switches (or links) are opened (Figure 2).

Figure 2

As the output current increases, the voltage across the shunt will add to the voltage across the output, causing the control circuit to compensate and lower the power supply’s output voltage.

As an example, for the 24V 10A TDK-Lambda DRF240-24-1 power supply, the droop characteristic is at 64mV / A.  Table 1 shows the output change against load when droop mode current share is enabled.

Output Voltage
Output Current

Table 1

When using power supplies in droop mode current share, care must be taken to:

1. Set the output voltages of the power supplies to the same voltage.  The output voltage can be adjusted slightly higher if needed, to offset for the droop voltage*

2. Use the same length and same gauge of wire from the output to the load for each unit

3. Note any additional de-rating stated by the manufacturer.  This avoids tolerances from overloading a unit

4. Do not exceed the manufacturer’s recommendation for the number of power supplies that can be paralleled.

5. Make sure the parallel switch is in the right position, or the wire link is removed!
* If the power supplies are being used in redundant mode with ORing diodes, set the output voltages higher to compensate for the forward voltage drop (Vf) of the diode.  The function of these diodes is to prevent the bus voltage from being pulled down due to an internal short in a faulty power supply.  The diodes should be rated to carry the full output current of the power supply.

Redundant mode connection with ORing diodes

Power Guy
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