Smart Phone charging using Ni-Cd and Solar Panel

I have a Ni-Cd battery rated 4.8V 500mA. It has its own charger so I can charge it. Now I want to use this battery (not battery charger) to charge my smart phone. My smart phone's charger has ratings 5V 700mA. When I measure the Ni-Cd open circuit voltage (at full charge) it shows 5.1-5.5 V. So can I use this to charge my phone? Or it won't have enough power to charge my phone.

One more question about charging my phone. I have solar panel rated 8.5V 0.5A (loaded) and 10V 0.65A (open circuit). To charge my phone using this directly, I needed 5V which I tried to obtain by using 7805 voltage regulator. When the phone is not connected the output of the regulator shows 5V. That's perfect, but when I connect my phone the voltage drops to 4.5-4.8 V. So my phone doesn't charge (though it says charging). I could use a DC-DC converter for this but what else could I use. And why is this happening?

b.heuju said:

I have a Ni-Cd battery rated 4.8V 500mA. It has its own charger so I can charge it. Now I want to use this battery (not battery charger) to charge my smart phone. My smart phone's charger has ratings 5V 700mA. When I measure the Ni-Cd open circuit voltage (at full charge) it shows 5.1-5.5 V. So can I use this to charge my phone? Or it won't have enough power to charge my phone.

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The 5V/700mA power supply for the charger circuit in your phone probably does not provide 700mA all the time, maybe only when the phone battery is dead then the current drops slowly as the phone battery is charged. The Ni-Cad voltage will drop as it is discharging until it will not charge your phone anymore. Try it to see.

I have solar panel rated 8.5V 0.5A (loaded) and 10V 0.65A (open circuit).

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The solar panel current is too low which causes its voltage to drop too low when it tries to charge the phone through the 7805 regulator.

Audioguru said:

The Ni-Cad voltage will drop as it is discharging until it will not charge your phone anymore. Try it to see.

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Does that mean I can charge right (until my Ni-Cd voltage drops below some point)? I just needed it to charge my phone when I don't have any charging devices around.

Audioguru said:

The solar panel current is too low which causes its voltage to drop too low when it tries to charge the phone through the 7805 regulator.

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Then what can be done for this to provide 5V even when connecting the phone.

b.heuju said:

Does that mean I can charge right (until my Ni-Cd voltage drops below some point)? I just needed it to charge my phone when I don't have any charging devices around.

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yes

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b.heuju said:

One more question about charging my phone. I have solar panel rated 8.5V 0.5A (loaded) and 10V 0.65A (open circuit).

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are you sure about the 8.5V at 0.5A?

put in a current limiter to limit the current and thus keep the voltage up, and you might be off with a LDO regulator rather than 7805

kam1787 said:

put in a current limiter to limit the current and thus keep the voltage up, and you might be off with a LDO regulator rather than 7805

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How can putting a current limiter help? Also if I lower (limit) the current to a small value then it will take more time to charge my phone, won't it?

About the LDO regulator, what is it? Can I make one?

Maybe one of these will do the job:

**broken link removed**

pebe said:

Maybe one of these will do the job:

**broken link removed**

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Its not something I am looking for. I want to make something on my own that will do the trick.

It will cost you a lot more to make it than buy it.

pebe said:

It will cost you a lot more to make it than buy it.

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Its not available at our place, I have searched it. And also I would have liked to learn quite a few tricks by making one of my own. Thanks anyway.