PV Gap

Oscar Said:

How long will this 1.5v AA battery power 1 LED on a solar walkway light?

We Answered:

At a low discharge rate (the LED probably draws about 20ma) the AA alkaline battery should have about 2 AH available or approximately 100 hours. So if it is on only at night, or for about 12 hours it should last for 8.3 days.

Walter Said:

Do LED lights hurt some plants?

We Answered:

i doubt that lighting would harm your plants...sounds more like damage from ice or snow

Miguel Said:

Will a voltage or current regulator be useful in a solar powered LED circuit?

We Answered:

A VR is useful if you expect greater-than-design voltage at the source - and your circuit is sensitive to over-voltage. Otherwise it is not necessary. For instance if your solar panel will deliver 12V at 1A, and all you need is 6V at 0.5A, you will need a VR (with the proper heat-sink) to control voltage. You could do it with power-resistors, the values for which can also be calculated, but that is a calculation vs. a straight-forward solution.

You can also approximate with resistors and then clamp with a zener to prevent over-voltage.

If you don't have to drop the input voltage, then a VR (or other form of regulation) will not be required.

Henry Said:

Setting up a solar powered LED night light?

We Answered:

I agree that a relay is useless. Everything needs to be very low power (i.e. use MOSFETs). Capacitors might work if you use the new "ultracapacitors", or DLC's, which have huge capacitance and tiny leakage.
Since it's solar powered, you'll have a photocell. You can use this also as the light detector. When the photocell is producing current, charge your battery or ultracapacitor. When photocell voltage drops below some threshold, turn on the LED.
A simple way to go would be to use two or three photocells in series, and run through a diode to your battery/ultracapacitor. THen, run the battery/capacitor positive terminal to the source of a p-channel MOSFET, and run the drain to your LED (with a series resistor to control brightness). Control the gate of the MOSFET with the positive terminal of the photocells.
When the photocell voltage drops a few volts below the battery, the MOSFET will turn on, energizing the LED. When the photocell is .7V more than the battery voltage, the battery will charge.