HelpA Solar Cell Charger Problem

Thread Starter

Ray Hwang

Joined Mar 30, 2014
3
Recently I've got a solar cell.Given the proper sunlight ,the open-circuit voltage is 6.3V and the short-circuit current is 70mA.
Now I wanna get a output voltage 5.1V.
Use only basic circuit elements,diodes\transistors\capacitors\inductors\ICs,etc.No MCU and FPGA.
No MPPT(Maximum Power Point Tracking) required.
Could everybody give me some ideas?
A freshman from East China Normal University.
Lots of thanks!
 

Thread Starter

Ray Hwang

Joined Mar 30, 2014
3
Stick 17 Ohm 5-10 Watt resistor in series, this will drop 1.2 volts, 6.3-1.2=5.1 volts.
The cell output is not constant,fluctuating between 0~6.3V .The target is that once the cell voltage is over a startup voltage,then the circuit works and stablizes the circuit output on 5.1V . The startup voltage should be as low as possible. I think the output end could be like this.



But I don't know how to raise the low voltage to a higher one?
Maybe I need a boost converter?
And how to improve the efficiency?
 

shteii01

Joined Feb 19, 2010
4,644
The cell output is not constant,fluctuating between 0~6.3V .The target is that once the cell voltage is over a startup voltage,then the circuit works and stablizes the circuit output on 5.1V . The startup voltage should be as low as possible. I think the output end could be like this.



But I don't know how to raise the low voltage to a higher one?
Maybe I need a boost converter?
And how to improve the efficiency?
That does not make sense. Solar cell is not a motor, it does not have startup. Sun is out, you get some voltage. No sun, no voltage.
 

alfacliff

Joined Dec 13, 2013
2,458
d1 is not needed, the solar cell is a diode already. you dont need the capacitor, and get a zenner to limit the voltage to what is safe for the battery.
 

wayneh

Joined Sep 9, 2010
17,495
d1 is not needed, the solar cell is a diode already....
It is true that a blocking diode might be included in a larger panel, but it is rarely a part of a solar "cell".

If there's no current source to cause reverse current into the solar cell, then D1 has no function except to smooth out a transient shadow on the solar cell, to power the load for a few seconds after the cell is no longer illuminated.
 

Thread Starter

Ray Hwang

Joined Mar 30, 2014
3
d1 is not needed, the solar cell is a diode already. you dont need the capacitor, and get a zenner to limit the voltage to what is safe for the battery.
yeah sorry I forgot to mention that the load could be a Li ion or Li poly battery.I know it is not proper to connect the battery directly to the output,and an battery manage ic is required,but I think as the first step,to get a 5.1V could be more realistic
 

Bernard

Joined Aug 7, 2008
5,784
Depending on the battery, probably could connect panel thru a shottky diode to battery. Internal resistance of panel will drop V. At max power out V will be about 5 V. Disconnect at batt. V of 4.2V. After short test get a proper control chip. Home built Li [ except for LiFePO3 ] chargers make me nervous.
 
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