I want to build a simple solar charging picnic table camp light...just enough to let me know where the table is... I was thinking along similar lines as those walkway solar powered lamps.

Criteria:

Source Power: 3.6VDC NiMH
Light Source: White diode(s)
On/Off switch
Variable brightness
Photo-resistor controlled
Adjustable sensitivity
Charger Power: Solar cells

All the knobs are simple. Essentially I need a charging unit by day and a battery operated light by night. The controls just allows me to conserve energy.

If any of you could draw me up a quick circuit I would really appreciate it!

Thanks

Brian

 

Here's a circuit I've been using and does a pretty good job. Not sure about the 3.6 volts, but should work with minmal adjustments. For 3.6 volt batteries, you'll need around 4.5 volt solar panel.

Adjustable brightness to save battery power... Think the additional circuitry would probably use as much or more, but the PIC guys will disagree...

The parts aren't critical, breadboard it with what you got, and see if it'll do the job, pretty simple.

Attached Images

NightSwitch.jpg (41.1 KB, 31 views)

 

Any ideas as to how well this might work? Or if it will at all?

Questions:

1) Should the max voltage of the solar cell (in fun sun) be no more than the battery voltage (3.6V)?
2) If so, could replacing D1 (1N914) with a 3.6V Zener diode regulate it?

Attached Images

circuit1.gif (4.9 KB, 22 views)

 

Ni-MH cells are charged with current, not with voltage. The voltage from the solar cells after the 0.7V drop by the diode must be high enough to supply the charging current, about 1.4V per cell x 3= 4.2V + 0.7V= 4.9V minimum.

Energizer recommends reducing the trickle-charging current when the battery is fully charged. The fading sun and clouds will do it for you.

Attached Images

Ni-MH charging voltage.PNG (35.7 KB, 6 views)

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Uncle $crooge

 

Here is a circuit from a commerical solar moonlight. It uses the solar cell to sence if it is dark/light and controls the on\off switching of a Yellow LED. Notice there is no current limit resistor for the LED. In the interest of utimate cheapness, the manufacturer relies on Q2s beta and R3 to limit LED current. I've posted this schematic to point out how to eliminate the CDS cell from your circuit. For the transistors you can use 2N3904s.
On another note, NIMH batteries are a poor choice because they don't like to be over charged whereas NICADs will tolerate over charge much better. The NIMHs will overcharge in a bright area (Or Summer) if the circuit is optimized for dimmer (Winter) conditions.

Attached Images

SolarMoonLights.gif (5.7 KB, 20 views)

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