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I'm building an iPhone solar charger and I'm not very good with electronics but I want to know how long it would take to charge an iPhone 6 fully. The panel I'm using has:

Watt 0.36W
Voltage 3.60V
Current 100mA (0.10A)
Voltage (oc)   4.80V
Current (sc)  120mA (0.12A) 

An iPhone 6 battery is 1810mAh

I'm using a 5v step up so it works with iPhone. So does anyone know how long it would take to fully charge an iPhone?

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    \$\begingroup\$ Several days... \$\endgroup\$ – Ignacio Vazquez-Abrams Oct 14 '15 at 9:48
  • \$\begingroup\$ What current does an iPhone take when charging from 5V? How much of that current is used for charging the battery? \$\endgroup\$ – Andy aka Oct 14 '15 at 9:48
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    \$\begingroup\$ Your iPhone battery holds around 7 Watt Hours of energy. Since your solar panel produces 0.36 Watts, you are looking at a minimum of 19Hours (7 WH/0.36W) to charge your battery. That ignores losses in the converters and charging circuitry. \$\endgroup\$ – JRE Oct 14 '15 at 9:52
  • \$\begingroup\$ And assumes full insolation. \$\endgroup\$ – Ignacio Vazquez-Abrams Oct 14 '15 at 9:53
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Most likely it will not start charging the iPhone at all, taking its battery charging control into account

I used a 5V/500mA solar panel, which put out a max of 5V/250 mA. This was not enough to charge my iPhone 4, I had to use a powerbank as a buffer. Now I have a 5V/8W solar panel which works, but I still prefer the powerbank method to not ruin my phone's battery.

A day of european summer sun can charge my iPhone now to 100%.

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The battery in an iPhone 6 is 6.91Wh.

It's important to calculate in Wh because Ah can only be considered if voltages are matched. In this case 3.6V vs 3.82V means we're not far off, but it's an easy 'mistake' to make.

Your panel can deliver 0.36W when properly loaded. Theoretically that gives a charge time of 19.2 hours. If all DC/DCs are 85% efficient you're looking at 26.6 hours.

Additionally Li-ion charging is a 2-stage process, which means it may take even longer to fully reach 100%. Also the sun may not be as bright, there are nights, etc. So I would give it 3-4 days on this panel.

Chances are the iPhone won't even accept a charge from a source with this little power.

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The nominal voltage of the battery and the panel are about the same, so we can ignore the two rounds of DC-DC conversion and divide the 1810mAh by 100ma to get 18 hours in the best case. The conversion will not be 100% efficient, so add 10-20%. And the panel is only capable of 100ma in full direct sunlight, so I'd say at least three 8-hour days of sun.

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  • \$\begingroup\$ Ive found a 500ma panel so that would cut the time right? so going on your comment above, 1810mAh by 500ma plus 20% would be around 5 hours right? \$\endgroup\$ – del09 Oct 14 '15 at 9:59
  • \$\begingroup\$ If it actually outputs 500ma, yes (see kamuro's answer) \$\endgroup\$ – pjc50 Oct 14 '15 at 10:00
  • \$\begingroup\$ This only works if the battery voltage and panel voltage are equal, which is likely not the case. \$\endgroup\$ – Hans Oct 14 '15 at 10:38
  • \$\begingroup\$ The post explictly says the panel nominal voltage is 3.6V, which is the same as the nominal voltage of lithium mobile phone batteries. Both are inexact values: the battery voltage goes up as you charge it and the panel open circuit voltage is 4.8V. \$\endgroup\$ – pjc50 Oct 14 '15 at 11:08

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