any *efficient* psus?


14 posts
by Holy One » Sun Jul 29, 2012 1:41 pm
whats the point of getting all excited about the pis low power usage if your crappy psu wastes 50x more as heat?

are there any actual plug in psu's that are made from stuff other than chocolate? :D
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by redhawk » Sun Jul 29, 2012 1:44 pm
None of my switch mode power supplies overheat it sounds like you've having some bad luck.

Richard S.
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by Montala » Sun Jul 29, 2012 1:46 pm
redhawk wrote:None of my switch mode power supplies overheat it sounds like you've having some bad luck.

Richard S.

I suppose that reply begs the question "how are we supposed to know which ones are 'switch mode' power supplies anyway?", as it isn't always apparent from a brief description.
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by johnbeetem » Sun Jul 29, 2012 2:24 pm
Montala wrote:I suppose that reply begs the question "how are we supposed to know which ones are 'switch mode' power supplies anyway?", as it isn't always apparent from a brief description.

Take a look at the input voltage range. I don't know of a way to build a reasonable linear power supply with 100VAC to 240VAC input range, and I'd be surprised to find a linear wall wart with such an input range unless it had a manual voltage range switch. OTOH, automatically using a wide input voltage range is easy with a switching power supply.
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by Holy One » Sun Jul 29, 2012 2:47 pm
I have studied the list of recommended psus on the elinux wiki and they are all unavailable or highly inefficient in protracted use. The one I wanted to get, the RS wall wart psu, is out of stock with months lead time on availability. So just wondering, srsly, are there any that don't waste 50w of heat through the socket?As in: can people please link to a specific item that they know for certain is efficient in operation.

I want my pi always-on and using a mobile phone charger is, frankly, a titanic oxymoron in this regard: its really wasting as much power as an atom netbook would use. So very much self defeating if using a rubbish psu.

How about this: https://www.amazon.co.uk/Output-Univers ... 011&sr=1-5

That seems more like it?
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by duke2k7 » Sun Jul 29, 2012 7:55 pm
Not sure if it helps or hinders, but so far, my iPhone wall charger is working brilliantly on my Pi...

5 volts at 1 amp, so well within the Pi's limitations for amperage.

Seems that HTC chargers also have 5 volts at 1 amp as well, so they should be cool.

And for those who have a Kindle, just use that USB cable rather than buying one... :mrgreen:
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by Holy One » Sun Jul 29, 2012 10:06 pm
yeah the point of the thread is not what works, its what works efficiently.
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by Holy One » Mon Jul 30, 2012 2:33 pm
ok so I found this: http://www.kenable.co.uk/product_info.p ... ts_id=5642
data sheet: https://www.distrelec.de/ishop/Datashee ... ng_tds.pdf

I'm not clear of the use of 'switching' in this context. It seems to be a bit of marketing spin to pass off a psu with an actual switch on it as 'switching' without being very specific if that applies to the internal functioning smps or not. Sheesh.

Also it compies with eup in the datasheet but is being sold as CEC Level V. Again not sure if srs.

It was £11.50 inc VAT and delivery so I'll give it a shot. :D
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by jbeale » Mon Jul 30, 2012 3:10 pm
I tested a few 1A 5V USB power supplies as you see here. They range from 67 to 72% efficient while delivering 1 A. In other words, while delivering 5 W of useful electrical power they are wasting about 1.5 W, which is not too bad.

https://picasaweb.google.com/1099282360 ... 4502902834
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by alexeames » Mon Jul 30, 2012 4:06 pm
Holy One wrote:I'm not clear of the use of 'switching' in this context.


That's a joke right? :lol:

You're posting a thread being very critical and fussy about the efficiency of psus and you don't know the difference between linear and switching voltage regulators? :o

http://en.wikipedia.org/wiki/Voltage_regulator#Active_regulators

Unless I read you wrong, that is. ;)

Let's just say that switching regulators are, in the main, vastly more efficient than linear ones. (And no, it's not because they have a switch on them for marketing purposes.) :roll:
My Pi uses 2 watts - what what? ---- HiRes early production Pi photos RS Front Back | Farnell Front Back
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by Montala » Mon Jul 30, 2012 5:47 pm
jbeale wrote:I tested a few 1A 5V USB power supplies as you see here. They range from 67 to 72% efficient while delivering 1 A. In other words, while delivering 5 W of useful electrical power they are wasting about 1.5 W, which is not too bad.

https://picasaweb.google.com/1099282360 ... 4502902834

A very nice selection of power supplies which won't unfortunately help those of us here in the UK, as they will not be available in the same configuration.

Perhaps someone who has access to the necessary equipment to do a similar test on a few UK models... although I do accept that they probably all come from China anyway!
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by jbeale » Mon Jul 30, 2012 6:07 pm
The four 5V 1A USB power supplies I tested were all close in efficiency, leading me to suspect most of the product you'll find in that category will be similar. If one was very inefficient, you would know, because it would get hot under load. A 5 watt linear supply will be somewhat larger than those are, due to the volume of iron in the transformer needed.

For what it's worth, the UNIFIVE UBX305 model on the left in the photo does have interchangeable wall plugs, including the UK style, and it can run on any input voltage from 90 to 264 Vac according to http://www.unifive.com.tw/images/pdf/catalog_2012.pdf
but I do not know if it is actually available for sale to consumers in the UK, it might be an OEM only product. Like nearly all electronic products today, it is manufactured in the far east, the company itself is in Taiwan.
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by permaband » Wed Aug 01, 2012 2:17 pm
Holy One wrote:ok so I found this: http://www.kenable.co.uk/product_info.p ... ts_id=5642
data sheet: https://www.distrelec.de/ishop/Datashee ... ng_tds.pdf

I'm not clear of the use of 'switching' in this context. It seems to be a bit of marketing spin to pass off a psu with an actual switch on it as 'switching' without being very specific if that applies to the internal functioning smps or not. Sheesh.

Also it compies with eup in the datasheet but is being sold as CEC Level V. Again not sure if srs.

It was £11.50 inc VAT and delivery so I'll give it a shot. :D


This is a great psu. I have one, ordered from those guys and it never gets warm to the touch under load. Highly recommended if you are planning to run your pi as a webserver or other always-on role. Just make sure you flip it over to 5v before first turning it on. :D
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by permaband » Wed Aug 01, 2012 8:53 pm
edit just to clarify this is a 'switching' power supply and is highly efficient compared to a phone charger you got for £3 off fleabay. its 1000ma output and has a micro USB jack bundled.
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