Friday, May 25, 2018
Home/Current Issue >  Industry Articles >  Test and Measurement > 

New Approaches to Electrical Power in "Smart" Homes
11mm-thin power disc easily fits into any wall outlet leaving plenty of space for switches and dimmers.

Smart homes might eventually solve our problems with energy efficiency, but we still have a long way to go. All of our home electronic appliances run on DC, including today's LED lighting, so efficient power supply units (PSUs) will play an essential role in significantly reducing power consumption.

Even the ecologically-minded among us have realized that the burgeoning energy revolution has its darker side. Demands for solar energy with prices inflated by the feed-in tariff scheme in conjunction with the premature shutdown of atomic power plants will keep electricity prices on the rise. It comes as little surprise that cost reduction has taken center stage with the energy-saving smart home as the ideal solution to all problems; but will it really save money in the future? After all, there's a heavy investment required in having heating, lighting, blinds, and house services controlled by apps on tablet-PCs, and whether or not your house plants should be watered and pets fed automatically in your absence.

Despite misgivings, the revolution has begun. Many power supply companies have started to provide smart meter modules that deliver information on usage trends. Consumers will start saving once they know how much energy they're using and for what — at least that's the theory. Whether or not this will still be true once the novelty has worn off remains to be seen.

A Waste of Energy
Take a close look, and you'll see that the smart home of tomorrow has one serious weakness left over from the time before the computerized age: while incandescent light bulbs, ovens, cooktops, and electric motors are perfectly happy with an AC power supply, every electronic gadget runs on DC. All of these appliances — TV sets, sound systems, computers, or printers — depend on DC drawn from their own PSUs, and each is geared toward maximum-load conditions. You could entertain your entire neighborhood with a 100W sound system, but you normally wouldn't do this more than a few times a year which means that your PSU is running idle with horrendously poor efficiency for 360 days a year. Furthermore, the linearly regulated PSUs on electrical devices run with efficiencies that hardly pass the 50 percent mark even at full power. Since a well-equipped household will have a good 50 PSUs or more, energy losses will quickly add up to 100W to 200W.

Central DC Mains
A far more efficient solution would be a central DC mains supply that would power all home electronics appliances, including LED lighting — the same easy way you hook up your smart phone up to a USB port to charge. It will be a while before that happens. Even so, it's safe to assume that the rapid switch to LED lighting will speed up the change in attitude. In the meantime, we'll keep on improving with solutions such as efficient mini-PSUs that fit into standard wall outlets, at least doing away with the cable clutter from countless external PSUs.

There wasn't much of a market for mini-PSUs just a few years ago, but now a niche market has grown for products running on a few watts — a development initially spurred on by the one-watt-initiative by the International Energy Agency (IEA) to reduce standby power-use to not more than one watt in 2010, and 0.5 watts in 2013, which has given rise to regulations in many countries and regions.

Saving Energy on Standby
This has forced manufacturers to start early on installing mini-PSUs to handle standby electronics in new products and switching the main PSU on and off by relay. PSUs in sound systems used to draw more than ten watts on standby, but supplying the standby circuit and controlling the relay requires a nominal power rating of a only few watts.
Low-power PSUs offer high efficiency.

Many small devices in home and office settings are also far more efficient today — devices such as micro-controllers which operate in the milliwatt range, or sensors or control units rated at one, two or three watts. These are often used in houses and offices in applications such as remote-controlled window blinds or automatic garage door openers. The savings principle is always the same: standby circuits have their own mini-PSUs that control relays to cut mains power to the main PSU, which is completely inefficient in standby operation.

As a manufacturer of voltage converters, Recom got an early start specializing in developing efficient mini-PSUs, achieving substantial reductions in idle power consumption in this type of PSU.

Low-Power Modules
Switched-mode power supplies are designed in such a way that their optimum efficiency is close to the rated power. The efficiency drops in line with the load, until it is near zero when the device is in no-load mode. This drop, however, is not linear, and many data sheets contain only the peak values. This is often misleading, as has been shown in recent comparison tests carried out at Recom of a number of products from different manufacturers. In these tests, the efficiency, especially in the lower and medium load range, was compared. This efficiency is relevant as power supplies are normally not exactly matched to the rated power and must be able to provide a certain safety reserve. The results were quite surprising.

Despite comparable peak values around 80 percent, the Recom mini power supplies were considerably more efficient in the medium and lower load ranges. At 50 percent load, the efficiency was still near the peak value. At a load of 15 percent, the measured efficiency of the mini power supplies was still between 60 and 70 percent, an excellent result. Because of these vast differences, manufacturers are urged to choose their power supplies with great care and to perform their own tests for efficiency.

Full Load Levels
The need to operate the power supply at near-full load level is far less important today than it had been. The RAC03 (3W) could therefore be used without any problems for applications that require only 1W or 2W. RECOM nevertheless decided to develop separate mini power supplies for 1W and 2W (RAC01 and RAC02, respectively). This was done for a good reason — lower no-load energy consumption. Today, no-load consumption contributes heavily to standby consumption. These new 1W and 2W modules typically reduce the consumption to 30mW rather than just to the limit value of 0.5W set by the one-watt-initiative. This means that the standby power consumption is reduced by up to 94 percent. With these new modules, the issue of standby consumption has thus been put to rest for the foreseeable future.

PSU in the Wall Outlet
State-of-the-art smart home solutions are increasingly used in building installations, and this involves lots of electronic components that require an efficient DC power supply instead of the 230VAC mains supply. Devices such as intelligent contact-free switches that react to gestures to set lighting or heating levels, door openers with built-in fingerprint readers for recognizing people to control entry doors, wall outlets with intelligent power monitoring to cut the power once the connected appliance has spent a certain period on standby, or mini-pumps to water house plants when the owner is away. These applications run on direct current, ideally not from batteries, but from a PSU integrated into the wall outlet.

Recom has launched a series of regulated mini-PSUs — the RAC03-SCR/277 series — designed for easy, quick installation into ordinary wall outlets made possible because of their extremely flat, round shape; there is no need to redecorate after installation. These discs are just 11mm thick and are easy to install behind switches and dimmers to give you direct current right from the wall outlet.

High Efficiency
The flat power discs provide an efficiency of 78 percent at 3W power rating. They can be used anywhere in the world since they accept an input voltage range between 85 and 305VAC. They will even work on three-phase systems in the US, which reach voltages up to 277VAC. These modules are available in output voltages of 3.3, 5, 12 or 24V with output currents of 900, 600, 250 or 125mA, which correspond to their 3W power rating. At just 40mW idle consumption, they run at a tenth of the official requirement for standby operation. The RAC03-SCR model is isolated on the output side at 3kVAC and works at ambient temperatures up to +85°C.

Avoiding EMI at the Source
In addition to maximum efficiency, electromagnetic compatibility also plays a key role in the home environment. Electromagnetic interference (EMI) can be a serious problem given the sensitive nature of so many of today's electronic devices. There are two forms of EMI — conducted and radiated. PSUs designed for use in the home are subject to the much more stringent Class B standard in EN 55022/55024 for this reason; Class B parameters call for interference limits at 10dBµV lower than the Class A standard that applies to industrial settings.

The RAC-series mini-PSUs all have a Class B filter integrated into a molded casing as standard. Filter components such as ferrite cores and chokes can be designed in a more compact form compared to retrofitting external circuitry, since any interference is eliminated directly at source, reducing idle consumption and saving costs for filter components and EMC testing.

This new series has a host of applications in addition to smart home applications, such as building automation or security and communications systems. The new modules have been designed for uncompromised long service lives, are CE and UL-certified, short-circuit-proofed, and come equipped with spike and surge protection.

Contact: Recom Power, Inc., 18 Bridge St., Unit 2F, Brooklyn,, NY 11201 718-855-9710 fax: 718-855-9714 E-mail: Web:

search login