On 08/08/2012 07:27, Vic wrote:
>> The 12v laptop power is also more efficient. Fewer power conversion steps.
> No, that's not true.
>
> All these PSUs are switch-mode; their efficiency is dictated by the design
> and the selection of components.
>
It is true.
If you use a 240V intermediate stage, you have to convert 12V to 240V,
then down-convert back to your final voltage and each stage it unlikely
to be better than 90% efficient, so if you manage 80% overall
efficiency, you're doing well. Add to that that the best efficiency will
be at a high load and in the real world you may well be nearer 60%.
One single conversion from 12V to wanted voltage will almost certainly
be more efficient.
I have a couple of adaptors, both from Maplin.
I can't verify the models as they're both on my boat in Essex, but...
this looks like the laptop one:
http://www.maplin.co.uk/120w-laptop-car-adaptor-44736
and this looks like the USB one:
http://www.maplin.co.uk/micro-dc-to-usb-adaptor-274029
They have a range of others.
Gordon.
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