Recycling old xmas lights

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Getting the strings of solar powered Christmas lights out … and about half the strings don’t work. Hey, they are fairly cheap, so partner says just throw them out and buy new. But seems wasteful to not even try resurrecting or scavenged for useful parts.

Last year I found several youtube videos where some of the LEDs at the end of the string failed … but in my case I have left the solar panel in the sun for 2 days, hidden the solar panel to simulate night, pressed the power button … and still no lights.

I’m guessing the problem could simply be cheap thin wiring which has broken with being packed away; or could be the solar panel is faulty (unlikely); or maybe the battery didn’t like being stored away for 11 months. If the last, maybe a new battery would resurrect them cost effectively.

I will try taking a couple apart and see what I can see, though being an electrical newbie I don’t expect that will be much … so wondering if you guys have experiences you would like to share …

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Please check if there are breaks in the wires, particularly around the connectors.

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HI @Donald23173,

As Lia said, checking the wiring for breaks is a good place to start.

If you have a multimeter and are looking at opening the solar power supply, Checking if you’re getting voltage on the output to the LEDs will likely point to if the issue is with the string or with the power supply.

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I’ve opened a few of them (I now have 7 including some put aside last Christmas but didn’t get around to it at the time). They look rather similar inside using Ni-MH AA rechargeable 1.2V batteries, either 600 or 800mAh. Easy to check battery voltages:

  • In three, the batteries were fully charged (so battery and solar panel must be good).
  • One, the battery connector was corroded
  • In a couple, the battery was about half charge, suggesting that the solar panel or charging circuitry probably the issue.

I assume that placing multi-meter probes across the wires coming from the solar panels when they are in direct sunlight should indicate what voltage they are generating. I might need a 3rd hand … and a bigger desk … in the sunshine … :wink: One that I did test seems to be working OK.

I guess where the LED string wires go into the control box is the most likely point for broken wires, though there is no visual sign of damage. In some cases placing multi-meter across the wires going to the LED strings gives wildly changing voltage readings - which makes sense … the one circuit board will be driving the patterns on the lights as well as controlling the battery.

On one set, the problem seems to be the power switch itself. LEDs flash momentarily while the switch is being turned on or off, and continually if I hold it partway down - but when the power switch is turned ON the lights blink normally for about 5 minutes before stopping. Turning power switch off and on without moving any wiring starts the LEDs flashing again.

For broken wire I guess just cut off the first 10cm or so off the LED string, and solder the shortened wires back ? On one set I did cut the wires to the LED string - but that first 20cm to the controller has excellent continuity … suggesting that wasn’t where the the wire broken, and the problem is down in the body of the LED string itself ?

As I’m sure you’ve realised I am not into electronics so my goal is not to take the effort to find and fix faults - instead wondering if it is worth scavanging batteries and solar panels to use in other projects - and the answer seems to be … in many cases yes.

I expect there will be projects which require smallish amounts of solar power … such as my greenhouse … have 3 or 4 separate solar cells for different modules rather than one bigger battery to power everything.

However…

The single AA Mi-MH batteries are old tech and I may even have an AA battery charger from the old days. However charging them from a solar panel seems to be a different matter, especially in-situ.

I’ve looked on Core’s website, and see lots of cheap rechargeable Ni-MH battery packs but the only Ni-MH charger I could find is SkyRC iMax B6 V2 Battery Charger. Not only is it $57.20, but it requires that the batteries be removed from the device in order to charge.

In contrast, Core’s catalogue is filled with Li-PO chargers from only $4.80; some of which charge from solar panels.
Given that Li-PO is 3.7V and a pack of 3xAA Ni-MH is 3.6V, can one of DC-DC Charge Discharge Integrated Module (5V/2A) at $4.80, or Solar Lipo Charger (3.7V) at $8.05 be used with a 3.6v Ni-MH battery ??

If these christmas lights can do solar charging plus the twinkly lights and sell cheaply; the charging circuitry can’t be too complicated. Or is that it ? Is the recharge circuit actually so simple that no-one bothers to make a breakout board for it ?

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Often in these lights its the LEDs that cark it first. Salvaging the batteries and solar panels is certainly worth your time if you want to use them for other projects. Just test them to make sure that there isn’t any underlying issues with them and you will be fine.

I wouldn’t use a Lithium battery charger to charge NiMH batteries. These batteries charge differently. Lithium batteries charge with a constant current and voltage. NiMH batteries charge with a constant current but vary the voltage. Using the wrong charger could damage the batteries. I do own a SkyRC charger and can happily say it is my favourite charger I own. My ones designed for individual cells haven’t been used since I picked it up.

The circuitry in your lights could also be harvested for your project if you are really keen too. While the circuitry may be simple, lithium batteries dominate the hobbyist electronics world so there is a large focus on these.

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My intention in scavenging the solar xmas lights is to leave them in place in my greenhouse, but it seems that is not possible, at least not with Core Electronics products.

I think this diversion has already wasted too much of my time.

Thanks for your assistance.

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