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@polybikeuser
Just looked at the youtube site for this and saw the Heath Robinson contraption Specialized put together to power a laptop, bearing in mind the overall design I was rather surprised it wasn't painted white and didn't have any London decals.
They're using a wheel to drive a DC generator that they then run through an invertor to produce AC current that they then plug a battery charger into (duh, a transformer that converts AC back to DC) to charge the laptop's battery.
Unless I'm missing some very clever/technical detail wouldn't it be rather more efficient to take the DC current produced, run it through some kind of smoothing circuit, if neccessary run the resultant DC current through a transformer to get it to the right voltage and use this to charge the laptops battery?