diy Solar Iphone charger

[wannabe]

I've been workin on a solar Iphone charger, I've already built the solar panels which produce 8.4vdc or 5.5vdc both at 500ma current, i already have the schematic to make myi phone accept it, i would like to know how to get the 5vdc that the i phone requires, ive tried a 7805 voltage regulator, but only produces 3.3vdc, ive tried a car charger which produces 5.45vdc, or 4.05vdc could anyone help me get the 5v or tell me if those voltages are ok for the iphone without damaging it. thanks in advance for any information

 

[giftiger_wunsch]

There's only a 10% difference between 5V and 5.5V, so I doubt the extra 500mV is going to make a huge amount of difference. Does anything in the iphone documentation suggest a margin for charging voltage?

Don't take my word for it without confirmation, but I see no reason why using 5.5V would damage a device meant to be charged at 5V. And for such a small difference, maybe you could simply use a resistor to prevent the extra current caused by the 500mV increase; you could use that to cause a 500mV voltage drop. Someone else can help you with the details

 

[marcbarker]

How much sunlight did you find that you need for your "500 mA current" you mention ?

How did you measure this "500 mA current"

 

[giftiger_wunsch]

Actually, I had a very similar idea to this very recently, but haven't had chance to start developing it yet since I've had other projects going; I'm intending to use a salvaged calculator solar cell to trickle-charge AA NiMH batteries. I managed to get a surprising amount of power out of it when placed in sunlight. Even overcast, I got a decent current from it. Can't remember exactly how much current now though.

Wannabe, I hope your project is successful. I'd be interested in knowing how well the charger works.

 

[wannabe]

How much sunlight did you find that you need for your "500 mA current" you mention ?

How did you measure this "500 mA current"

the 500 mA are what the solar cells are rated at at the moment i dont have an ammeter or multi meter that can measure more than 200mA

 

[giftiger_wunsch]

the 500 mA are what the solar cells are rated at at the moment i dont have an ammeter or multi meter that can measure more than 200mA

Ah... that's not incredibly helpful then. The 500mA will most likely be the absolute maximum in intense light. You'll need an ammeter to see how much you're really going to get out of it in varying light conditions.

 

[marcbarker]

You'll need an ammeter to see how much you're really going to get out of it in varying light conditions.

If you haven't got something to measure the current with, try a light bulb maybe as an indicator. Be careful though, don't let the bulb get too close to the solar panel, because if it picks up light from the light bulb, all hell breaks loose!

 

[giftiger_wunsch]

all hell breaks loose!

You get an inconclusive reading... not quite all hell breaking loose

 

[wannabe]

thanks for the info, i'll try the light bulb, then i'll have to go aquire an ammeter, which is probably the preferred method, thanks again.

 

[marcbarker]

You get an inconclusive reading... not quite all hell breaking loose

What I had in mind was the panel picking up the light shining on the panel it would start an endless feedback loop and blow the light bulb through over-current from this 500 mA solar panel!

 

[wannabe]

i understand, but i particularily enjoyed the dramatic effect of all hell breaking loose

 

[giftiger_wunsch]

What I had in mind was the panel picking up the light shining on the panel it would start an endless feedback loop and blow the light bulb through over-current from this 500 mA solar panel!

Yes... an endless feedback loop with probably less than 0.1% overall efficiency. I doubt there's much danger of that happening. The bigger concern would be using a bulb which can't withstand the power output of the solar panel in direct sunlight. Sunlight trumps the light created by a bulb being powered by a solar cell utilising a small proportion of the energy from the sunlight...

 

[marcbarker]

Yes... an endless feedback loop with probably less than 0.1% overall efficiency. ..

Aw! you've gone and spoilt it now!

Solar panel rated current is at "StandardTestConditions" which is just over 1 kW / sq metre of 'sunlight' illumination. On earth you'll only get natural STC
in places like Nevada and on the equator!

 

[giftiger_wunsch]

Aw! you've gone and spoilt it now!

Solar panel rated current is at "StandardTestConditions" which is just over 1 kW / sq metre of 'sunlight' illumination. On earth you'll only get natural STC
in places like Nevada and on the equator!

I had a feeling they'd probably do their very best to 'legitimately' exaggerate the current capabilities. It's definitely worth using an ammeter to find out how much current you'll really get.

When I make my NiMH-charger i'll probably simply use a resistor to limit the max current through the battery to 0.1C, and the rate of charge will just depend on the intensity of the light on the panel. Easy way to save money by using renewable energy