DC vs AC for charging a phone

[Ed Borden]

Can anyone in-the-know spell out the "inefficiency" case against DC
for charging a cellphone? I've heard it with my ears but it would be
great to have the details down on paper so it can be incorporated into
the pitch with a little more authority and hard facts.

[pare [dse]]

Hi,
Got a note from Rene Pare about the efficiency difference of charging a cell phone DC or AC wise.
There's little or no difference, the battery is DC so whether the DC/AC converter is outside the
device (net adapter) or inside (AC/DC converter IC) is of little importance. Both options convert
at about 90% efficiency these days (with switching technology).

Inside the phone there is probably another converter (DC/DC) that can't be omitted even when
the phone is DC powered. Hope to have helped you a bit,

Eric Sprik
Electrical engineer
M.A.D. center
 

René Paré

pa...@dse.nl

[Ed Borden]

I'm talking about the entire "energy lifecycle" from what it takes to
generate power at the plant to distribution to the home, to
conversion. All of this versus a microgenerator using wind or solar
directly to the phone in DC.

[Ken Boak]

Ed,

I would strongly dispute the efficiency figures stated in a previous post.

The typical ac switched mode phone charger (costing $2 in China) is a poster child for cost reduced consumer electronics, and not one for energy efficiency.

It has an efficiency of between 60 and 75% - and not the "high 90's" which is only achievable in high-end platinum or titanium rated PC power supplies.

This is why the home-sized dc grid to power all of your electronic toys makes more sense than a dozen individual, low quality ac power supplies.

PC supply manufacturers are being encouraged to exceed 80% efficiency - but as this adds more cost  - they are understandably slow to respond

Here's a wikipedia entry that details the drive for 80 plus

http://en.wikipedia.org/wiki/80_PLUS 

Super Flower from Taiwan specialise in very high efficiency PSUs - with platinum rated units that exceed 90% efficiency across a wide range of power outputs

http://www.super-flower.com.tw/products_detail.php?class=2&sn=1&ID=85&lang= 

We live in a society of disposable consumer electronics - and we are carrying more are more powerful devices in our pockets - all of which need to be recharged regularly.  My smart phone has a battery which barely lasts a day , whilst my old Nokia would last almost a week between recharges.  

Is this a step forward in energy saving  - no.  We all still have to carry two devices - a phone and a laptop to function efficiently in the modern tech community.

If you want to recharge a mobile phone from solar, it's perfectly possible with a $10 solar panel, which you can place on a window sill.  Having a spare battery charging by day, which you swap over in the evening is one way of maintaining continuity.

Here's some nice cheap PVs from our friends at Seeed in Shenzhen - well suited to directly recharging a smart phone.

http://www.inmojo.com/store/seeed-studio/item/1w-solar-panel-75x100/ 

Combine it with a single axis solar tracker and you have a simple gadget which comes close to the $10 budget.

Here's a prototype I cooked up earlier   http://www.youtube.com/watch?v=PoBZ_TWSSNU

Ken

[Ed Borden]

Ken, that video is seriously badass!! How much more efficiency/output
does something like that produce versus just sticking it on the side
of a building and never touching it (assuming that it was a
high-exposure wall)?

Regarding the efficiency of the converters, it's obvious we need some
practical experiments to illustrate this... Maybe we can produce those
as part of this so at least we know for sure what we're talking about
here.