Current Cottonpickers experiments
Its the weekend and I've been meaning to sort out the iPad charging for ages... so I'm currently playing with solar iPads...
I've been wanting to make a solar ipad cover for months, but Apple have some trickery to make it hard.
Apple uses sensing resistors on the usb data lines, and require tight voltage control. For solar this is an issue.
I started with 5v and 6v panels and of course the Apple devices wouldn't charge. So I moved on to putting in tracks on the panels and resistors. This helped, and my iPad started to charge. Nice but I found that with 6v panels it was too high for the iPad, so I put in a 4xnimh battery pack to lower the voltage. This worked great, but is no good for a solar cover.
So I'm playing with voltages, resistors and diodes to get the combination right so I can charge the iPad with a simple cover.
Today I finally managed to get my solar cover moving. This is a 1200ma (or 1.2amp) panel bonded to a magnetic ipad cover. I think its the highest current solar cover by some margin. Its got the sensing resistors set to 1.2 amp to match the panel, but I think the voltage dipping is why it hit 850ma today, when I think it could go higher. I'll test tomorrow if the UK can manage some sun....
When tested today in early sun I saw 850ma into the ipad. I suspect it wont hit the full panel spec, but should see 900ma or maybe 1amp in better conditions than UK in late Oct.
I've now tested on the iPad1, and it charges nicely but of course, the ipad doesn't accept the magnetic cover.
I've now also tested the iPad2 and charges brilliantly !!
Finally I've tested the iPad3 and this has 'sticky' charging. If cloud covers the sun and lowers the charging rate it remembers this lower rate even if the sun comes out again and will charge at the lower rate. To remedy you need to unplug and replug back in to get the full rate again, or put up with lower rate. Shoud it ever go below 100ma it will go back up to 100ma as that seems to be a threshold. Below 820ma it will say 'not charging' but actually charges fine.
So for now , this is an iPad2 Cover
Size is the size of the ipad cover.
weight is 340g.
The 3 pics show the Cottonpickers Magnetic Solar iPad Cover : (yes!) attached to iPad (3).
When I finalise it, I'll be selling for $49 delivered anywhere but in the meantime I'll keep trying the various combinations to get the best from this.