<span class="highlight">Solar</span> Powered LED light string - not working

Sorry did my best with the description of the setup.

Supplied battery was 400mah 1.2V NiMh rechargeable. Replacement battery is 1000mah 1.2 V NiMh. Fully charged it is showing 1.28V on the Fluke.

Connector is polarity conscious. Only goes together one way and has not been a problem up to now.

Thank you for your response. Appreciated

Cheers John

Many thanks AJC

Have done the wire wiggle etc to no avail. Covered up the light sensor when checking continuity etc. I have no knowledge of electronic circuit boards so no point in trying to check if any of the components have failed.

I fail to understand how I can have the same voltage in the wires at the end of the light string, as the battery, and have no lights. That's why I asked if the electronic module did more than just regulate the battery charge. Does it also boost voltage?

All a mystery.

Cheers John

Many (most) LED strings are not driven by DC, even if they are using a DC supply. The PCB does tricky things and produces an output that allows a very long string of LED's to work for hours/days using very low power.
Other wise, if you have a string of 20 (or more) LED's - such as used on Xmas trees etc, they would flatten a small battery pretty quickly.
I went through this process about a year ago, and found a bunch of references on the Interweb about the technology used in those PCB controllers, but don't have those references any more.
In the end and despite best intentions, the LED's went in the bin.
Suggest you have a beer instead. :-)

edit:- Found one. This is the text that most likely applies to your LED string (even a cheapie).

"The buck converter (step-down) is a very simple type of DC/DC converter and the most common. It produces an output voltage that is less than its input. The buck converter is so named because the inductor always “bucks” or acts against the input voltage. The components used in a buck converter are relatively simple and inexpensive making it a favorite of cost sensitive applications. The output voltage of an ideal buck converter is equal to the product of the switching duty cycle and the supply voltage. The buck converter can obtain its DC input from a DC supply or a rectified AC signal. In the case of an AC rectified signal isolation from the AC source may be obtained through use of a flyback topology that employs an isolating transformer between the AC source and the input.

The switch at the VIN position of the buck converter continually switches between ON and OFF at a high frequency. Energy is stored across the inductor while the switch is ON. The reverse-biased diode ensures the capacitor and VOUT are in the circuit. Energy is released from the inductor and used at VOUT by the load during the time that the switch is OFF. The diode is now forward-biased and is part of the circuit path. The inductor-diode-capacitor combination in this circuit bears analogous similarities to a mechanical flywheel providing regularly spaced energy in a smooth and continuous fashion. The result of this is that any load at VOUT experiences a small ripple waveform that is determined by the timing frequency of the circuit design."

Buck converters are used to reduce the supply voltage, but they haven't made a production LED yet which will operate directly on 1.28 volts. (If you understand the physics behind the light emission you'll realise they are unlikely to without having some completely new materials).

Invariably these single-cell LED drivers step UP the voltage (boost).

Many thanks gentlemen.

The decision has been made. Electronic module in the bin, waterproof connector ( will be recycled in the replacement) and light string salvaged( you never know when you may need it) and $10 to be spent.

Whilst the last lots of info are contradictory it appears that the electronic module does do more than just act as a battery charger. So as usual have learnt something via this forum.

Thanks to all of you for your responses.

Cheers John