# Solar cell charger

Discussion in 'General Electronics Discussion' started by Karthik rajagopal, Jul 10, 2016.

1. ### Karthik rajagopal

241
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May 9, 2016
Hi all,
I wanted to make a cell phone charger for my project for which I was searching the circuit on Google. What I noticed that the wires from the solar panel are connected to the voltage regulator and to the cell phone. My doubt is that while a cloud is passing the sunlight will be blocked by it there by reducing the voltage from the solar panel and there will be a drop in the input voltage of the regulator which will affect the phone charging. If the passing of the clouds are frequent won't the phone get damaged as there is no stable output voltage?

2. ### BobK

7,682
1,688
Jan 5, 2010
I doubt that it would get damaged any more than it would get damaged if plugged into a mains powered charger and the power went off. But you might want to use a circuit that cuts it off completely when it cannot produce something close to 5V output. A continuous 2 or 3V might be handled badly by the phone.

Bob

3. ### Karthik rajagopal

241
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May 9, 2016
Will the voltage regulator operate when the input voltage is less than 5 v if I am going to use a 7805?

4. ### duke37

5,364
772
Jan 9, 2011
A 7805 needs about 2V to operate so needs 7V input.
There are low drop out regulators which need less than 2V.

5. ### BobK

7,682
1,688
Jan 5, 2010
When the input is insufficient, the regulator will put out a lower, unregulated voltage.

Bob

6. ### Karthik rajagopal

241
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May 9, 2016
So what kind of a regulator to use. can u please tell me a voltage regulator with lower voltage drop?

7. ### Chemelec

291
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Jul 12, 2016
What is your Solar Panel's Voltage and Current Rating?

8. ### Sunnysky

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Jul 15, 2016
Vbat charge =75% Voc from PV ( open cct) is near ideal +5% for bright and -5% for dim

If the array is small on a cloudy day then you need large mirrors to reflect more sky diffused energy to PV for slight improvement, otherwise SOL.

The phone will regulate the voltage if impedance of PV s low enough.. V/I=Z. i.e. current source is high enough, otherwise phone will load PV and drop voltage too much and thus also PV efficiency which is near ideal at 75% then efficiency drops with PV voltage

Last edited: Jul 17, 2016
9. ### Sunnysky

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Jul 15, 2016
dont use 7805, choose proper size PV array and voltage

10. ### Karthik rajagopal

241
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May 9, 2016
My solar panel voltage rating is 7v and current rating is 100 mA.

11. ### Karthik rajagopal

241
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May 9, 2016
Then can you suggest me voltage regulator for this please.

12. ### Chemelec

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Jul 12, 2016
I would just put a 1N4001 Diode in series with the panel and than connect it directly to your phone.
This diode will reduce the voltage by 0.6 volts and it will also prevent the battery from discharging back into the solar panel, when there is no sun.

13. ### Karthik rajagopal

241
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May 9, 2016
The battery will get damaged as the voltage given by the solar panel is 8.5 v and the required voltage is 5 v.

14. ### Sunnysky

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Jul 15, 2016
is that the PMT load voltage or open cct Voc? PV is a current souce and phone has a V regulator

15. ### Chemelec

291
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Jul 12, 2016
NOT LIKELY to damage anything.
The Output Current is NOT HIGH Enough.

16. ### Sunnysky

488
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Jul 15, 2016
unless you define your phone and intended solar panel, the rest is pointless. the reverse blocking diode protects the PV and battery from drain, which may already exist in the phone.

yes clouds will lower input power by solar power diffusion.. forget about implementation details until you define what you are working with, or simply phone model and desired charge time in hours and location availability of solar power.

Last edited: Jul 23, 2016