Cheap Solar Garden Light Hack





Introduction: Cheap Solar Garden Light Hack

I purchased several of these little solar garden lights from Walmart for 97 cents each. From past experience I know that if you can get these to function for more than a month, consider yourself very lucky. The light output is very weak, and the rechargeable batteries they put in these are the cheapest they could find. They figure if they only charge 97 cents, it's easier to just buy more replacements than it is to complain about it.

For this Instructable, you will need:

Instead of buying more replacements, or complaining, I decided to go a 3rd route and make them function better by replacing two of the components that make them so cheap. I replaced the sad little white LED with a brighter (and yellow) LED to get some decent light output, and I replaced the cheap battery with a better quality rechargeable Ni-Cad so they would last much longer.

Step 1: What's Inside...

The clear plastic lens separates easily from the main black housing by twisting them apart. The housing will come apart into two pieces when you remove the two screws. Inside you will find the cheap battery, in this case a 2/3 AA. The link above is where I found my rechargeable Ni-Cads for about $11 for a pack of 4. The circuit board is (or should be) held in place by a bit of silicone adhesive. Pry this loose with a flat screwdriver and the circuit board should come out easily. Remove any excess bits of adhesive.

Step 2: Removing the LED

Get your fine tip soldering iron and some braided wick to remove the old LED. You can get by without the wick, but using the wick to remove excess solder makes this much easier. Some of these lamps have little sleeves covering the leads. Don't lose these. Not only do they prevent shorting, they also make a nice gauge to control how far the LED leads go into the circuit board.

Step 3: Adding the New LED

Once the old LED is out, insert the new LED (and sleeve on each lead) making sure to put the longer lead into the positive (+) side. If you reverse the polarity/leads, it won't work. Solder the leads in place and clip off any excess from the solder side of the board, then bend the LED 90 degrees so that it will fit into the housing, matching the one you replaced.

Step 4: Putting It Back Together

Slide the circuit board back into place so that the top of the LED goes into the hole in the center, and put a drop of glue or silicone on the board next to the housing to hold it in place. Put the two pieces of the housing together and replace the 2 screws.

This is my first instructable, and I hope you found it useful!



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    Nice job! I've got the same ones and I was wondering how to pair up (or triple) the solar panels so they'll recharge sufficiently up here at 47deg N. Mine are only AAA, but I have some rechargeable AAA's to replace these "solar" batteries". I don't mind the lights - just enough to see my way ... but they die an hour after dusk. (Not sure if the solar panel will give enough juice for AA.) Time to experiment ...

    great job..simple enough for me to understand. but i had a question about your "braided wick" method of removing the excess not familiar as to what the wick is? i know its more of a preference but im new to the solder world.

    1 reply

    The wick is just a braided wire that when heated next to solder will pull it away very cleanly. it's commonly available at Radio Shack.

    Just what I was looking to do, thanks

    A question, is the panel big enough to power the light for say 6 hours, my house faces south so have good exposure but how long will it last for? Any idea how much long a NiMh would last? They are now 70c on Ebayyyyyy so will need to find a Radio Shack etc to get these LEDs

    1 reply

    Unless someone has done a real time test, mathematically solving this only works when the LED is on full till the battery dies. These devices use a trick to dim the light over time to make them last longer. However, lets do the math.

    The replacement batteries are 150 mAh, at 1.2v. Now, typically the way these devices work is they boost the voltage from the battery up to meet the forward voltage of the LED. This would be roughly 2.8 - 3.3v. The conversion process isn't perfect, so some power is lost. The cheap board on here is probably in the lower end of efficiency, so lets just assume it's 80%. If we take (100x1.2)/3, we get 40. In this case, that's 40% (1.2v is 40% of 3v). Lets take 150*0.4, which equals 60 (in this case, 60 mAh). Why we reduced the miliamp hours is due to converting to a higher voltage. We can't get power for free, we exchanged higher voltage for a lower amperage. The power is the same till we add in the drop in efficiency of the conversion. Normally, here we could say we have 60 mAh to work with at 3v, however we have to add in the drop in efficiency. So take 60*0.8, which gives us our final 48 mAh.

    If you are still with me, we have 48 mAh (roughly, really). Lets calculate the power to time. A typical LED at maximum current uses around 25 mA. From here we just take our 48 mAh and divide by 25, which gives us 1.9, or about 2 hours. This doesn't seem right though, does it? That's because these devices actually dim the LED using a Pulse-Width Modulation based on the amount of voltage reaching the converter. Towards the end of the night, the lights will appear very dim and will have a flicker to it. So sadly, there is no real way to calculate the longevity. It is far to complicated and requires a real time test.

    Thanks, glad you liked it! The yellow lights are much nicer and more natural to look at than those super-white LEDs

    Great idea! And I like yellow lights outside. Thanks for sharing!

    Good idea. I have a bunch of these lights. I might have to try this.