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For a school project, I want to make a solar iPhone charger (specifically for the iPhone 4) and I've spent about a week looking up stuff all over the Internet, and I'm stuck for the hundredth time. First, I had my mind set on an iPhone charger (if you're interested, it can be found here: http://www.instructables.com/id/Solar-7-up-Solar-phone-charger-in-a-bottle/%29) that basically uses a homemade 5V solar panel, which is plugged into a 3.7V 2000mAh LiPo battery, and then plugged into LiPo Rider Pro (which is apparently a lithium charge board that has a battery charge regulator and also steps up the voltage to 5V which is the required voltage for USBs). Anyways, a male to female USB cable is plugged into the LiPo Rider Pro and then you can use your iPhone USB charger to plug into the male to female USB cable to charge your phone via the LiPo battery (which is charged from the sun). I think this is how it goes... The instructable is unclear when it gets to plugging into the LiPo Rider Pro, and I've spent a long time trying to figure it out. (If anyone actually reads the instructable, feels that it's easy to explain the part about the LiPo Rider Pro, and feels inclined to do so, I would really appreciate it.)

Because of my uncertainty, I kept looking and came across another solar lithium battery iPhone charger (again, if interested: http://www.instructables.com/id/Lithium-Battery-Solar-USB-iPhone-Arduino-Charger/). I think it's very similar to the first one except this one uses a lithium battery charge controller and a DC-DC USB boosting circuit. My guess is that the LiPo Rider Pro is basically a board that includes both of these things? A 1N4001 diode is also used; use of the LiPo Rider Pro seems to make a diode unnecessary? What kind of confuses me is that the author of the first instructable calls the LiPo Rider Pro a "lithium charge board" and I kind of assumed that that's the same thing as a "lithium battery charge controller" which is used in this second instructable. The second one seems to have additional materials, and I'm unsure if that's better or worse.

So in sum, I guess my question is: what is "better", the LiPo Rider Pro (from the first instructable) or a lithium battery charge controller + a DC-DC USB boosting circuit + a 1N4001 diode (second instructable)? From my ignorant point of view, the LiPo Rider Pro seems better as it seems like an all-in-one. Yes, I've read both product descriptions, but I still don't really understand.

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Both do the same, the LiPo Rider Pro just has everything on board. The 1n4001 diode used in the second instructable is used to prevent battery discharging though the solar panel at night, prevents reverse current through the solar panel when the usb charging (powering the lipo charger through usb) is used, and prevents the solar panel from affecting the charger when both light and usb charging is used. The LiPo rider has the same type of protection.

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  • \$\begingroup\$ Is the LiPo Rider V1.1 basically the same as the LiPo Rider Pro? The only difference seems to be that the LiPo Rider Pro has maximum 1A load output and more LED indicators. I'm asking because I just discovered the Lipo Rider V1.1 wiki and it is much more helpful. Specifically, I was wondering if this setup: seeedstudio.com/wiki/images/7/7a/Lipo-Rider-v1.2-usb.JPG could be applied to the LiPo Rider Pro in the exact same way. \$\endgroup\$ – Seven Mar 17 '13 at 15:16
  • \$\begingroup\$ It also says The destination USB port is where the destination device is to be connected. Power to the destination device will be supplied by the Lipo Rider board. The supply will be either from solar panel, lithium battery or source USB port. Hoping this applies to the LiPo Rider Pro.. So if I connect a solar panel, lithium battery, and an iPhone charger to the LiPo Rider pro, then do both the solar panel and the battery charge the phone? At the same time? (And of course the LiPo Rider Pro will always keep the solar panel and battery's voltage at 5V?) This is what I'm most confused about. \$\endgroup\$ – Seven Mar 17 '13 at 15:21
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    \$\begingroup\$ From seeedstudio.com/wiki/… it shows three scenarios. Note, there is a battery on/off switch. It also says USB Mode: Solar Power charges lithium battery. Lithium battery supplies destination USB device And if you look at the schematic in Eagle, you will see that the solar panel output connects only to the charger ic. The battery connects to the regulator ic, through the on/off switch. \$\endgroup\$ – Passerby Mar 18 '13 at 0:16
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Indeed, the LiPo Rider Pro board is the better option out of these two.

Nevertheless, what you want to do will be a good way to learn that charging a smartphone phone with solar energy is very inefficient. In the very optimistic scenario that you get 5V and 130mA it would still require 11 hours, assuming there are no losses in your circuit or in your phones charger. Realistically speaking, in a very hot summer with ideal conditions you can hope to get 130mAh for ~4 hours a day. A minimum of 25% would be lost with conversions. Thus it would take at least 4 days to charge the phone if you leave it off.

If the phone is in standby, it will never charge with a solar cell that small.

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