Standby comfortable but energy inefficient

The former ‘green’ theme of energy efficiency has become a household issue in an energy-conscious society. The old filament bulb disappears step by step, and washing machines and dishwashers have become unsaleable without energy-saving programs. But most industrialised societies waste energy on a massive scale by indulging in comfortable ‘standby mode’ in domestic electronics.

Although we see the incandescent lamp replaced step by step by energy-saving lamps, the standby mode in many electronic devices has escaped attention.

Many households have 40 to 50 electric units permanently on the supply, although they are only in use sporadically.

Take the fax for example, we may use it only once or twice a month, however we hold it for 720 hours on standby mode.

Until quite recently, electrical devices had an OFF switch - OFF meant off - energy consumption was at zero. Then small plug-in power supplies became fashionable for each unit, making these more easily adaptable on the worldwide market.

Plug-in power supplies do not feature on/off switches for cost reasons, however they consume substantial no-load current.

The manufacturer saves money, passing costs to the consumer.

Using remote controls made television viewing that much more comfortable. Who operates the ON/OFF switch on the TV set? Surely only a small minority.

Electrical devices with their power supplied linked to the mains are in continuous ‘standby mode’. The supply voltage for this standby function is, for costs reasons, tapped from the power supply.

In standby mode only some of the operating circuit is off the mains - the power supply continues to operate in a no-load mode. This power supply has been designed to operate at substantially higher power levels and therefore reaches, under no-load condition, very poor efficiency levels. Such units consume continuously 10 to 20 W, although they appear to be in the off mode.

The standby power rating for fashionable halogen lighting easily reaches 10 W, as does the printer of fax units. Units that operate with transformers and conventional converters can propel the standby power consumption to 200-300 W in a household.

The European Union has introduced the EU-Directive ‘EuP’ (Energy using Products) to save energy. The main aim is an increase of the energy efficiency over the lifetime of a product. This directive is aimed at all household and office products - from the electric toothbrush, the coffee machine and radio to PCs, printers, telephones and modems and home entertainment.

All these products are normally on standby - sometimes even during holidays.

The power required for this standby function exceeds that required for urban and long-distance travel by roughly 30% in most industrialised countries. Unchecked, this development would require in Europe a total energy level as used by Denmark, only for our comfort.

The private will to save energy is in conflict with traditional behaviour, therefore the EuP-Directive is aimed at the introduction of new and more energy-efficient power supplies. Thus power consumption for standby modes must be reduced to 25% of current levels by 2020 (and not by 25%). These levels must be achieved despite an expected increase in the number of electrical products.

This would save in Germany alone the equivalent of four nuclear power stations.

Electrical appliances that are switched off under remote control are allowed to consume a maximum of 1 W for units launched after 7 January 2010. In cases where an additional display is operated this rating is increased to 2 W. In three years’ time these values will be halved. Larger power supplies exceed these limits already under no-load - quite apart for classic transformer-based power supplies.

Electrical units with a power rating of more than 50 W cannot feasibly keep within the above limits. Units with power ratings beyond 100 W have to rely on separate circuits for the mains supply and the standby function.

The main power supply is isolated via a relay from the mains during standby operation, as was the case when the unit was taken from the mains by an ON/OFF switch. A highly efficient AC/DC converter with 4 W rating, such as the Recom RAC04, provides the power for the infrared unit and the LED display. This converter has been designed for low power and therefore operates with high efficiency and minimal no-load power.

No-load power varies slightly with the rated voltage, for a RAC04-12SA with 12 V output, values as low as 100 mW are not unusual.

The concept of a modern hi-fi system has no individual units connected to the mains. The time when an array of power supply plugs was a standard feature, absorbing significant energy, is definitely over. The main power supply function has been laid out to ensure that the available power is transformed into a perfect sound pattern – for as long as the consumer expects this. As soon as the OFF button on the remote control unit is activated, the AC/DC converter RAC04 takes the unit from the mains supply.

Although the whole system is on standby, only a few 100 mW are drawn from the mains. In contrast, older systems drew 10 or 20 W.

Solutions such as this are manifold at home and in the office. Take, for example, window shutters, which can be operated by a remote control or by sunshine. The principle is always the same. While the main supply is switched off, an array of small and highly efficient standby power supplies take over.

Apart from the energy consumption, ‘electromagnetic compatibility’ is another feature for home systems high on the agenda. Radiated and conducted interference must be kept to a minimum.

Following the electro-smog debate for mobile phones, nobody wishes to introduce additional sources of interference. Therefore, all power supplies for domestic use must meet the stringent Class B -standard to EN55024 - featuring an interference 10 dBuV less than the industrial standard Class A rating.

All Recom converters of the RAC series have fully integrated filters in the potted case. All interference is eliminated at the source, so that the filter components required are smaller than those used in external filtering, therefore having a positive effect on the energy consumption during no-load operation.

Using an integrated module has the added advantage of cost saving for component purchase and EMC testing.

The RAC family is isolated up to 3 kV, short-circuit protected and overvoltage and overload protected. The ambient temperature rating is -40 to +70°C.

Being a European manufacturer with global operations, the company uses only components from known suppliers, which are screened and tested before released for production. An ‘Environmental-Laboratory’ was set up in Gmunden, Austria, where all products are tested under HALT conditions. A high-resolution electronic microscope supports the quality screening process.

Recently it was possible to document that a well-known brand manufacturer of switching transistors had carried out changes in his manufacturing process, which caused long-term problems for reliability. These efforts are time and cost intensive, but are absolutely necessary to ensure the long-term reliability of products. For the RAC04, 40 years is specified as the MTBF to MIL-HDBK-217F.

The new converters are compact. The RAC04 has a volume of 17 cm³ and a power density of about 0.25 W/cm³. The larger RAC20 with a 20 W rating has a power density of 0.60 W/cm³.

Following the partial demise of the incandescent lamp, standby features in home electronics have become the target of energy-saving measures. At this point it has to be conceded that standby operation sometimes actually saves energy, as in the case of PC operation. A PC without a standby mode would have to remain fully on the mains supply to avoid long start-ups.

Still we are only at the beginning of a radical new start and re-orientation.

Green power and eco design are on the political agenda - even home automation is gaining momentum - starting with the documentation of the actual energy consumption of individual units/appliances and extending to user-oriented controls.

Such concepts can be remotely controlled and operated.

Recom Electronic GmbH

www.recom-international.com