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crwdns2944351:0crwdnd2944351:0Solar garden led light with dimming along the stringcrwdnd2944351:0crwdne2944351:0

crwdns2933797:0Dave Empsoncrwdnd2933797:0crwdne2933797:0

crwdns2936043:0crwdne2936043:0 crwdns2933505:0crwdne2933505:0 Dave Empson

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Solar garden led light string
Type
technique
Title
Solar garden led light with dimming along the string
Introduction
This repair requires a thermal imaging camera (typically about £400)
I have a generic, 4 years old, 50 led light string powered by a small solar panel with one standard AAA NiMH battery to hold charge collected while the sun is shining. The coloured lights (green blue yellow red) come on automatically when dark, either steady or flashing depending on switch position.
A few of the lamps were not working, but the real problem was that the lamps got very noticeably dimmer as the distance from the power supply increased, such that the end ones were not lit at all. All the led's were in parallel running off what should be a near constant 1.3V, but clearly something was causing a voltage drop.
I examined the string of led's with a Topdon thermal imager (which is sensitive to about 0.1C) having left the lights on for about 15minutes. One of the lamps (one of the many that wasn't working) showed it to be hot relative to the others, so I cut this led out and all the other working light came to full brightness. (my fingers weren't sensitive enough to notice it was hotter than the rest.
Normally led's fail open circuit (high resistance) but the above problem led failed with a low resistance of 200 Ohms so was taking enough current to drop the surrounding voltages
Image shows opened solar panel assembly with battery and circuit board
Time Required Min
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Time Required Max
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Imageid
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Difficulty
Moderate
Conclusion
You don't have to reattach the section that has been cut off, but the string will of course be shorter. Just make sure the exposed ends cannot touch (ie cut one wire shorter than the other and insulate with tape or shrink-fit.)
Normally led's fail open circuit (high resistance) but the above problem led failed with a low resistance of 200 Ohms so was taking enough current to drop the surrounding voltages (and thus heating itself up to be visible in the far infra red imaging camera).
Open circuit failure was due to corrosion and breakage of the led arms due to rain ingress. Close circuit failure was probably due to corrosion product bridging the power lines. Which failure occurs depends on build quality ie the amount on water ingress, how much corrosive flux was not washed away, the insulation between the power lines etc. etc
Garden solar lamps are often of poor quality material and build and seldom last more than 3-6 years. Perhaps they would last longer if sealed with silicone rubber or similar?
Author
Dave Empson
Public
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  • thermal camera x1 added.

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  • In Progress added.
  • Community-Contributed Guide added.

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