iPhone and PV charging

A few weeks ago I was looking around the lab at the remnants of old projects and realised that we probably had enough bits to put together a solar powered charging station for phones. I.e. a 30 Watt PV panel (don’t buy from Farnell), a 12Volt Battery, and a PV charge controller.

I got an old 3 way cigarette lighter socket in Halfords, chopped the cable, added powerpoles, a fused connection to the battery and I now can charge my iPhone at my desk in work.

So, at break yesterday I was asked how much I was saving by charging my iPhone via solar energy.  I had no clue, so I let my iPhone die completely last night and re-charged it while checking the charge current on a Watt’s up meter.  I got tired of looking at it after 3 hours, but you can see the results on the graph below.

For the first 2 minutes, it stayed steady at 360mA, then the phone switched on and it started charging normally.  About 45 minutes at 340mA, before the current started to drop away.  At 20ma charging current I stopped the experiment.  If we allow a fudge factor for the accuracy of the Watt’s up meter, and the efficiency of the Apple charger  (I was running the test off a DC supply) and say about 10watt/hours, that translates to 0.00129 cent per charge or thereabouts.

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