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# Charging batteries using photovoltaic cells

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#### Destiny99

##### Newbie level 1
I want to ask about the charging of battery from photovoltaic cells, As we know the voltage and current produced by the cells depend on the intensity of light but the sun light always varies with time. What IC or circuit can I use to maintain the voltage and current simultaneously so the power produced can be maintained at a constant rate?

Re: Photovoltaic Cell

though the current varies i think the voltage remains relatively constant.... to satisfy the idea you are suggesting you would be needing a constant power source which is not possible with a photovoltaic cell....

Re: Photovoltaic Cell

well, I have tested the solarcells at the noon and I get the voltage and current quite different. Example : when I measure it with the brightest sun light I get about 21 V but when it gets cloudy I only get about 15-18 V. The same results happen to the current. What I have on my mind is Do I have to use voltage regulator to make the voltage remains constant but if I use it I think the efficiency will drop greatly. Does anyone have any idea how to solve this problem?

Re: Photovoltaic Cell

you can make a regulator but it should have a output voltage lower compared to the minimum of the photovoltaic cell output....
maybe you can step up or step down this voltage using dc to dc converters ...

Photovoltaic Cell

The output voltage can be stabilized by using a DC-DC converter. So if the the voltage drop below the threshold, you can step-up the voltage. if its above the threshold, you can step-down the voltage. Let the current be fluctuating, but you must limit the upper threshold of the current using a resistor.

Re: Photovoltaic Cell

rikie_rizza said:
The output voltage can be stabilized by using a DC-DC converter. So if the the voltage drop below the threshold, you can step-up the voltage. if its above the threshold, you can step-down the voltage. Let the current be fluctuating, but you must limit the upper threshold of the current using a resistor.

Thanks for the advise. But I still have few questions about it. You wrote that it is okay to let the current be fluctuating but as I had tested earlier the current really fluctuating in a wide range. Ex: When the voltage is about 21 V I measure the current at about 0.5 A. But when the voltage drop about 15 V, the current also drop but only less than 100m A. If I have to let the current still fluctuating, I think it is still quite important to make it as linear as the voltage or I think I still have to narrow the range of the currents. What do you suggest?

Re: Photovoltaic Cell

there are good DC-DC converters with good output current regulation....it mainly depends on the value of parameters chosen and the load...

Photovoltaic Cell

Current regulator means limiting current so its stable at some threshold. Also, current is a product. High current can be easily limited, but low current is hard to raise. If the current is that low, than you cannot do anything about it except add another 'factory'... which is the solar cell.

Re: Photovoltaic Cell

Is it possible for you to implement a circuit that would implenet constant current constant voltage algorithm for you for charging the battery.
Obviously the battery would have a limit to maximum charging current. You could design for that.
Just thought hope it helps you

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