# To using solar cell powered garden light that uses a single 1.2 volt rechargeable battery.

#### garybuska

Joined Aug 12, 2014
23
Hello every one I have a question that I hope has not been asked recently.
Because solar cells are limited by the amount of sunlight they see there output fluctuates.
Is it possible to design a circuit that will keep the output at a constant voltage with out adding a lot of other parts?
What I would like to do is to make a circuit to add to a typical solar cell powered garden light that uses a single 1.2 volt rechargeable battery.
On a Clear day I have observed that most of the solar cells I have will put out 2 to 3 volts without a battery to charge.
But as expected when it clouds up the voltage will drop down to under 1 volt which will not fully charge the battery and the led will not stay on all night.
Is there a way to make the voltage a constant 2 to 3 volts as long as there is some sun light?
Gary Buska

#### Kermit2

Joined Feb 5, 2010
4,162
You CAN boost voltage, but you must reduce current output to do so.
On a cloudy day, the amount of power a solar cell can make is greatly reduced.
Even with a voltage boost to reach charging voltage, the current available to the battery will likely not be enough to charge it.
Power in can never be increased by a circuit. Only voltage or current can be changed, but always with the other changing in the opposite direction
If you double voltage out, you cut current by half.

#### crutschow

Joined Mar 14, 2008
34,079
The power available under cloudy conditions is so small that it likely is not worth the effort to try to boost it.

#### wayneh

Joined Sep 9, 2010
17,493
You could reconfigure a solar garden light, I think, to play with the concept. You'll need two of them, with one hacked to charge the battery and the other one working normally.

Every one of these lights I have seen boosts (and pulses) the voltage to the LED. This is how a 3V LED can run from a 1V battery. But I think you could use the same boost circuit to charge a battery instead of light the LED. You would need to control the pin that turns off the LED when the panel is in the sun. You want the boost circuit to run when it's light, not dark.

With this hack you might find some conditions (light level) where you get charging from the boost when you get none from the usual setup. But overall, I predict this will give less charging than the typical configuration because to will likely reduce efficiency in full sun.

#### garybuska

Joined Aug 12, 2014
23
Thanks for the replies everyone I had not thought about the current output.

#### garybuska

Joined Aug 12, 2014
23
You could reconfigure a solar garden light, I think, to play with the concept. You'll need two of them, with one hacked to charge the battery and the other one working normally.

Every one of these lights I have seen boosts (and pulses) the voltage to the LED. This is how a 3V LED can run from a 1V battery. But I think you could use the same boost circuit to charge a battery instead of light the LED. You would need to control the pin that turns off the LED when the panel is in the sun. You want the boost circuit to run when it's light, not dark.

With this hack you might find some conditions (light level) where you get charging from the boost when you get none from the usual setup. But overall, I predict this will give less charging than the typical configuration because to will likely reduce efficiency in full sun.
I actually tried this and the results were not that good and like you said when you had full sun it reduced efficiency.
I think the problem came from the other output confusing the circuit and acted as a resistor.
I thought of using a SCR but decided against it.

#### hp1729

Joined Nov 23, 2015
2,304
Hello every one I have a question that I hope has not been asked recently.
Because solar cells are limited by the amount of sunlight they see there output fluctuates.
Is it possible to design a circuit that will keep the output at a constant voltage with out adding a lot of other parts?
What I would like to do is to make a circuit to add to a typical solar cell powered garden light that uses a single 1.2 volt rechargeable battery.
On a Clear day I have observed that most of the solar cells I have will put out 2 to 3 volts without a battery to charge.
But as expected when it clouds up the voltage will drop down to under 1 volt which will not fully charge the battery and the led will not stay on all night.
Is there a way to make the voltage a constant 2 to 3 volts as long as there is some sun light?