Solar LED lawn lights

[hsjrev]

My parents have a small lake at the back of their property and it's far too expensive to have electricity run back there. My father likes to fish way after dark and uses a flashlight to get around on the pier and dam. I got them some solar lawn lights (cat. 162174)
from Home Despot that have one white LED inside powered by two AA rechargeable batteries that are charged by a solar cell on top of the light. They work as advertised but only put out a tiny amount of light. They're OK to mark hazards but they don't put out enough light to see the ground around them very well. I was wondering if it would make them brighter or hurt anything or to add another LED or two in series. With the one LED, they're still burning at the same (dim) intensity when the morning light causes them to shut off. I wouldn't care if they ran out of juice around midnight because nobody goes down there that late anyway. Will it hurt the nicad AA's to discharge them completely every day instead of partially like it does now? Thanks for any info.

[Josey]

As an alternative to these solar lawn lights, which are usually too dim and not reliable, you could set up a very small solar system.

All you'd need is a solar panel (less than $300), a deep-cycle battery, and a small controller ($20 or less) to prevent the panel from overcharging the battery.

Then you could hook up much brigher lights. A timer switch could turn it off after midnight.

It may be more money, but it would be a long-lived and reliable system with much more utility.

[Pellidon]

I got one at Harbor Freight for $7. It does have three AA rechargeables in it and one led. Brightness is good for what it does.

During the winter months the poor thing couldn't keep up unless it was a cloudless day. I kind of felt sad for it. Now that it is brighter longer it should fare better. There were several times when it just pooped out. Close inspection showed that it was still on but barely. I think it has 1200 mah batteries. Probably couldn't charge fully 2100's in dead of winter.

Josey's idea is better. Over spec the charger so if there is a couple of days of minimal sunlight you can still handle it. One cell and a 12 volt battery should drive many dozens of 5mm led clusters for days and never know there is a drain.

[gwbaltzell]

Josey's solution (especially with a good quality fluorescent, still much more efficient than LED) will provide a lot of light. These mass-market solars are usually not worth trying to mod. except for one thing. Remove the diffuser and replace the LED with a wide angle blue-green (cyan) one and carefully aim it. The eye will see these about 2 1/2 times brighter. Aim it to light any nearby pathway. It would be possible to add a second LED (not in series, but another resistor and LED) but because these use more than 1 cell (battery) you run the risk of reverse charging a cell, as with any multicell pack. This damages the cell.

BTW - how far is it? You can bury a lot of low voltage wire for the cost of a good solar power system!

[TrueBlue]

I have been trying to get a Malibu fluorescent flood light that has a large solar panel and four AA 900 mA cells to work with one or more high intensity LEDs. For the LED I wanted to convert a 2-AA battery LED flashlight to work in the system.

The reason I picked that flashlight is because it was only $5 at Ebay, it has a battery voltage booster circuit for a longer run time and I broke the flashlight so it doesn’t work as a flashlight anymore. I broke it because it seemed the head was loose and I tightened it not knowing the head was directly wired to the switch…SNAP! Repairing the wires just junked the guts of the light so nothing would fit right anymore.

But my problem is that I know fluorescent lights have high voltage going into the tube and I don’t have a schematic to see where the high voltage is or where the power gets turned on. I couldn’t plug the LED directly into the high voltage or it would be instant voltage death for the LED. I could tap into the low voltage power if I knew where the power switches. If I could figure out where the low voltage is and where the power is switched the whole system would work. There is enough voltage in the system to make the LEDs work; I get a reading of 5.93-volts. I know fluorescent lights are far more demanding of power and less rugged than the more efficient and durable LEDs.

Heck, I’m not even sure the light has a photocell because I can’t find one. I suspect the floodlight senses a voltage drop on the solar panel and when the voltage coming out of the solar panel is too low the circuit automatically switches to the batteries.

I’m sure in a couple of years Malibu will have a system like this with high intensity LEDs to replace the fluorescent tubes. The Malibu fluorescent floods are not great for what they are advertised for. They are too dim; useless as a floodlight. I use the lights as accent lights for my house and they barely do that. With an LED conversion we could have great accent lights or decent area lighting.

I’m sure there is money to be made in a system like this.

[gwbaltzell]

Fluorescents can be much more effecient than current LEDs. On a unit of this size its likely about the same, but you'd need a bunch of cheaper LEDs or several Luxeons to equal the output. If there is only one circuit board (likely) you'd have to reverse engineer it to figure out were to wire the LEDs. Why use solar to light a house that has 110V? A few LEDs running off a wall wart will likely cost less than a dollar a year!

[TrueBlue]

[img]/ubbthreads/images/graemlins/smile.gif[/img] Higher than 12-volts scare me and I don't want to play with that. I would have to wire under the house, under the bricks and concrete, through the brick planters, under the Juniper trees and the roots to get to a location I want for the accent lights. And I won't mention what happens if I want to move the lights a couple feet to a different location. So a moveable light is a far easier option.

I used an LED flashlight around to locations I wanted for accent light and the little 4 LED light gave me a better spot/accent light then the Malibu light did.

[gwbaltzell]

I was suggesting a wall wart (pre-made 110V to low voltage transformer) and using cheap wire like that already designed for low voltage outdoor lighting. Wire can be hidden in a shallow slit in the soil or under mulch. Tap off at each point you want a light and connect a resistor and LED. If you really must have solar, a few design pointers. If more than one battery is used the design should not allow discharge below 0.8 V per cell. Because the solar panel must be large enough to charge on overcast and mid-winter days, the design must prevent over charge. The battery pack should have enough capacity to last several heavy overcast days in a row. Lets take this last factor. 4 LEDs running at spec. would draw 80 mA times the longest night, say 14 hours. Now lets say 4 heavy overcast days. Now if we're just using resistors to limit the current, our voltage needs to exceed the Vf of the LED (typically 3.2V - 3.6V. Midpoint voltage of NiCd and NiMh is 1.2V so 4 cells and twice the prior mAh calculation gives us 8960 mAh each cell. These are not AA cells. Most mass market solar lights do not follow any of these design requirements because of one reason: cost.

BTW your fluorescent can put out several hundred volts.