Digital radio working hard on drawing power even when it sleeps

Thanks to one Mike Meakin and Made By Monkeys’ American cousin on Design News for highlighting how sometimes it can take a lot of energy to get a little rest. Take digital radios…

digital-radio-draws-power-asleep.jpgThanks to one Mike Meakin and Made By Monkeys’ American cousin on Design News for highlighting how sometimes it can take a lot of energy to get a little rest. Take digital radios…

It was carrying out an energy audit on his home appliances that alerted Mike to the power consumption of a one-year-old digital radio. Even when it was supposedly ‘off’, or ‘sleeping’, it was apparently consuming five and a bit Watts, for just being plugged into the mains.

“I had previously noticed that the radio’s mains adaptor got a little warm when it was plugged in,” writes Mike. “But a quick check on the manufacturer’s website confirmed that this was ‘normal’. In my mind anything that gets warm must be consuming energy,  so I thought to myself “time for some more detailed investigation.”

My bench power supply (carefully set to 9V output) and connected directly to the radio reported a current consumption of about 200mA during normal reception at low volume (1.8W), which only reduced to 140mA when it was ‘sleeping’ (1.3W).

I have heard that digital radios are power hungry and was reminded that my boyhood six transistor radio only consumed about 15mA from its puny 9V, PP3 battery at full volume and did the same thing (well, sort of) as my flashy digital box!

My measured power consumption figures roughly agreed with the manufacturer’s published figures, but I was measuring the DC input power to the radio-not the AC mains input power. The manufacturer appears to have done the same and perhaps conveniently “forgotten” about the power supply losses in its quoted figures?

The radio is supplied with a (cheap) conventional, copper wire, iron core transformer power supply. Wikipedia informs me that such small transformers may be ‘no more than 85% efficient, with considerable loss even when not supplying any load.’ This seemed to be the case as I measured a power consumption of 2.9W when the PSU was not even connected to the radio, and a further loss of about 1W during standby or normal operation. So, in standby, the radio consumed 1.3W and the power supply three times that amount = 3.9W. In comparison, my 32? LCD television consumes a total of just 2W in standby.

The manufacturer’s web site boasts of its ‘Green Credentials’ and a May 2009 press release trumpets that its radios “use much less energy than a low-energy light bulb”. While this is true it seems a pity that they don’t use a more efficient power supply with their product.

As an experiment I substituted the supplied transformer power supply with a low-cost, 9V switcher power supply. This reduced the total standby power to 2.1W – easily halving the ‘wasted’ power-albeit at an increased capital cost.

Although these small amounts of power may seem insignificant, multiplied by hundreds of thousand of users it all adds up. Surely minimizing the losses would be a good thing?

I am still curious to know just what the radio is actually doing in this sleep mode. All I can see is an LCD display showing the current time,  which I assume requires activity of the radio circuitry to receive time data.”



  1. After my previous comments on the power consumption of my digital radio, Pure kindly sent me an Evoke-1S to evaluate. This model incorporates their ‘EcoPlus’ energy saving technology.
    I immediately noticed that the ‘linear’iron/copper transformer power supply that my older radio used had been replaced with a custom made ‘switcher’ supply rated at 6.0 Volts, 2.0 Amps that was more conveniently smaller and lighter than the old one. Repeating my previous DC input power measurements I noted that the radio consumed just 70mA (420mW) in standy and about 300mA (1.8 Watts) at low sound volume.
    Measuring the AC power consumption with my (same) ‘cheapo’ Maplin power meter I noted a standby power consumption of 1.5 Watts and a low volume consumption of 2.3 Watts. These figures were better than with their published specifications. As a further saving it is possible to configure the radio for ‘energy saving’ and when set, I measured just 0.8 Watts
    standby power consumption. I then checked the AC supply current a using a conventional AC meter and measured just 3.5mA which confirmed my ‘power’ measurements.
    These figures demonstrate the reduced operating power consumption of the circuitry and the greatly improved efficiency of the switcher power supply which were impressive and more than lived up to the manufacturers claims.
    As with my old radio the reception and audio sound quality were excellent.
    This episode shows that some manufacturers are taking energy saving seriously and that with a bit of development effort products can be greatly improved. Whether this will ‘save the planet’ is perhaps, debatable ?

  2. Fair Doos ! Thank you Jason for your detailed explanation of the figures which I accept.
    My radio is indeed a pre-‘EcoPlus’ version and it was unfair of me to mistakenly compare the power consumption figures with the latest version of the Elan DX40.
    I should add that the radio itself is excellent and receives Radio 4 perfectly where analogue radios fail entirely.
    I am still curious to know what it is actually ‘doing’ when it is standby/sleep mode ?

  3. Hi
    I’m writing in response to the July 11th posting referencing Mike Meakin’s Design News article – titled ‘DAB radio power consumption tests’.
    While some of the points raised in Mike’s article are valid, the piece is generally misleading with regards to PURE’s DAB radios and does not provide a fair assessment of the actual situation. It’s important to point out that the DAB equipment being referenced isn’t entirely reflective of where DAB technology is today, and particularly where we (PURE), the designer and manufacturer of the product used in Mike’s article, are at too.
    In 2006 PURE undertook a drive to reduce the environmental footprint of all our radio products in the form of a reduction in power consumption (while playing and while in standby), using materials from recycled and sustainable sources, optimizing packaging size, and using components that minimized environmental impact. It set an entirely new standard of design and development within PURE which was named ‘EcoPlus’ and it was our intention that all future products would (and do) adhere to these new standards. On top of this EcoPlus development was extended to included the redesign and manufacture of some existing PURE products too – like the Élan DX40 used in Mike’s article – and it’s here where we need to draw attention to a couple of points raised.
    The description and readings of the PSU in Mike’s article are being taken from the older – pre EcoPlus product but are being cross-referenced and compared to published figures for the newer EcoPlus radios found on our website. One of the many EcoPlus modifications to the Élan DX40 forced a change to the PSU type and it now ships as standard with a 12v switch mode power supply rather than the older 9V linear, non EcoPlus version used in Mike’s article – and the difference is considerable (and not because we ‘forgot’ about power supply losses in our quoted figures). The off-load power consumption of the EcoPlus switch mode PSU is 0.3W rather than the 2.9W stated in the article, and to make easier reading I’ve broken down the specifications of the two types of PSU under discussion…
    Using the linear PSU (9v, 1.5A), non EcoPlus radio used in Mike’s article:
    Standby: 4.95W
    Operation: 4.95W (zero volume, for consistency across PSU measurements)
    Using the switch mode PSU (12V 0.8A) supply, new EcoPlus radios.
    PSU OFFLOAD: 295mW
    Standby (energy saving OFF): 2.05W
    Standby (energy saving ON): 1.15W
    Operation: 2.2W
    Mike’s findings are mostly correct for the older non-EcoPlus versions of the radio but at the same time highlights exactly why PURE embarked on the new EcoPlus standard of design, and EcoPlus development hasn’t stopped either. PURE now test to EN62087:2003 (the measurement for the power consumption of audio, video and related equipment) and many of our products now meet the strict Energy Saving Trust (EST) requirements of sub 1W standby, sub 3.5W operational (with 50mW of audio). If you consider the power requirements of modern EcoPlus DAB products like the PURE Siesta (0.7W standby 2.5W operational) and the PURE Evoke-1S (0.7W standby 3.3W operational) then you start to see a clear picture of just how far DAB technology has come – and in what is a relatively short period of time.
    You can read more about our EcoPlus standard by visiting our website at:
    Jason Voice
    Jason Voice, Technical Support Manager
    PURE, Home Park Estate,
    Kings Langley, Herts, WD4 8LZ, UK
    Tech Support +44 (0)1923 277477
    PURE is a division of Imagination Technologies Ltd.

  4. An interesting article, and an example of poor design. However, mains adaptors and chargers attract an undue amount of attention. I heartily commend the book “Sustainable Energy without the Hot Air” by David Mackay (available as a free downloadin electronic), where, as he points out, it’s “every big helps”. Lots of wasteful chargers add up to something substantial. Lots of the other stuff we use adds up to something enormous.

  5. If you’re serious about saving energy and even better idea is to switch off the mains at the wall, if you have that kind of socket, or unplug.
    This is what I do with phone chargers and radios. In fact, the radio is permenantly ‘on’, I use the switch on the mains outlet to control the power. Obviously, this is not so easy in countries where mains sockets are not switched and I accept unplugging can be laborious but it sure saves all those wasted Watts for things that don’t need constant power and have no battery back-up for clocks etc!

  6. Yeah, and the shocking thing is that – even consuming that extra power – it still sounds worse than FM radio! Not progress.

  7. I have noticed that some transformers used in power adaptors have the stack of laminations welded together instead of being clamped.
    My understanding is that the laminations are insulated from each other to reduce eddy losses so welding them back together is a bad idea.
    I had one such transformer that got hot and hummed with no load. I replaced it with a similarly rated sensibly constructed one and it no longer gets hot or makes any noise, presumably it is far more efficient.

  8. My pure radio has the option of turning the energy saving option on or off in sleep mode, has yours maybe gone the wrong way?
    Having said that, I’m going to try mine out with a single appliance electricity meter tonight – I’ll let you know if it differs to what Pure say it should be.

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