Solar Walkway Lights

[**DONOTDELETE**]

Hey, I was wondering if any of you knows how to make a solar powered walway light from scratch. I am wanting to do it but, dont know where to start. I also think that the ones they sell in wallyworld are a bit over priced.

 

[Lux Luthor]

I don't know what to tell you, but I did come across this link a few days ago. They're more like table lamps, but they could possibly mounted to the ground. Not too cheap, and I haven't tried them. Just my 2 cents worth.

 

[Silviron]

Unless you really want to do it for a "learning experience" or for "bragging rights"- why bother?

I recently bought a box with TWO amber solar LED walkway lights at WalMart for under $15.00 (plus tax). You couldn't even buy all the parts you need from surplus sources for that price....

That said, it can be a pretty simple project-
Here is how the Walmart lights are constructed:

Solar cell + terminal ---->
Blocking diode (to prevent batteries discharging into solar cell)->| --->
+ terminal rechargable battery ---->
LED---->
- terminal Rechargable battery--->
- terminal of solar cell

Solar cell should be wired parallel to battery, with blocking diode in series, but LED should not be in series with the solar cell.

There is also a small IC on the board that holds the LED and the blocking diode- I don't know what it is for sure, but I'm guessing that it has two purposes: As a voltage regulator, (the solar cell can produce about 7V at peak sunlight exposure, and is charging 2 AA NiCds), so they might be regulating the voltage to prevent overcharging, AND as a "switch" to keep the LED from lighting while the solar cell is charging the battery.

Plus you need something to mount it in, keep the rain off, etc.

 

[Steelwolf]

If what Silviron says is true, then it would be far better to buy the lights from WalMart. Just getting the solar cells may cost you half what the WalMart stuff sell for.

On the other hand, there are some modifications you could do to it, which I am about to undertake with mine. Bear in mind that my lights are old and I don't mind screwing around with them since they were destined for the scrap heap anyway.

I found that placing my lights in the positions for maximum mood effect meant that they were frequently in partial shade. Hence they couldn't charge fully and usually couldn't last the night. Remember that the voltage from the solar cells has to be at least a volt or two above the voltage of the storage device to effect charging and in partial light, the solar cells may not be able to deliver the full voltage, thus not even charging the cells. Of course the sky is frequently cloudy too which compounds the problem.

The mod I have in mind involves a flyback transformer and will boost the available power to the proper voltage, irregardless of the voltage available from the solar cells. Of course, power is proportional, so there will be less current, but that just means less chance of blowing up the batteries during the charging cycle. Also, since we're all LED enthusiasts here, I will also replace the standard bulb (it looks like something from a Mini-Mag) with a bunch of LEDs. With the reduced power consumption, I might be able to go for a few days of storms before my lights die.

BTW, the circuit mentioned by Silviron may indeed be a regulator, but I doubt it because manufacturers seldom give much leeway in the capacity of the solar cells, hence my need for the project above. More likely, the circuit is to switch on the light automatically when the sun goes down.

 

[php_44]

One of the many projects I want to tackle but never have the time for is to just buy standard walkway lights (AC powered), and convert them to LED/Solar. I'd swap out the incandescent bulbs and replace with a LED aray, then use a central (5-10W) solar panel, battery, and controller to power the whole string. That way I can put the lights where I want them, the solar panel where it will get the most daylight, and the battery inside where it will stay warm. I can then resize the battery and or the solar panel as my needs arise - and can AC power the lights if I have to. I can also choose my own LED color and select a variety of fixtures to make it look nicer.

 

[Evan]

There are 2 problems to be solved in a solar walk light (besides the obvious); avoiding deep discharge and avoiding overcharge.

Electronics Goldmine is selling the board out of a Cronar Walklight. It has a Lm357 op amp, a transistor, a photocell, and supporting items like the blocking resistor to prevent dark discharge. Attached is a socket with a 6 volt 75mA bulb. The boards were 50 cents on sale, a buck now. To put them to use you would need a 6 volt 1.2 Ah gell cell and a solar panel that produces about 9 volts open circuit like the small 6" square amorphous cells the circuit was made to work with. The op amp detects when the photocell is in the dark or light to turn the light on or off, and when the battery is getting weak turn the light off. The system seems to depend on the solar cell not putting out so much that the light won't fully discharge the battery by morning, and so they kind of cheap shot the overcharge problem by avoiding it.

I've got a few of these circuits and plan to try a mod on them. First I'll use a pair of 6x6 solar panels to collect more power, then I'll use a 4 Ah or 10 Ah 6 volt battery to hold more power. I plan to put a 6.8 volt zener across the battery to avoid overcharging it. I will then replace the 6 volt bulb with a cluster of LEDs (maybe 4 strings of 2 yellow (or 1 white) with about 100 ohms in series with each string to limit current. I plan to leave this at my weekend campsite to collect power all week and only turn it on to provide a dusk to dawn beacon on weekends.

Anyone else ever use a zener to limit charge voltage and prevent overcharge? It is a simple shunt regulator, but it seems just a little too cheap & easy.

 

[Steelwolf]

Evan, I think using a zener diode shunt to limit the charging voltage would be fine in this context. The solar cells give you free energy, so don't feel guilty about squandering it when your batteries are fully charged. The main thing here is to protect your batteries from overcharging. Just remember to use a suitable sized diode to prevent burnout from excessive current.

In some electronic hobby manuals, there is a solar charger circuit that will regulate the current so that the batteries are not blasted with too much current. It will also trickle charge the batteries when they have reached full charge so that the charge is maintained. I have not looked closely at the design, so I'm not sure how all this is accomplished.