Solar Powered LED light string - not working

Submitted: Monday, Mar 13, 2017 at 15:33
ThreadID: 134456 Views:2589 Replies:3 FollowUps:5
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I have a cheap solar powered light string that now doesn't work. I should just buy another, instead of trying to fix it, but that defeats the purpose of being retired.

I have previously cut the lead from the solar panel to the lights and inserted a waterproof joint plug (50% of the value of the lights). Soldered joints and shrink wrapped. Allows the lights to remain in place and the charging panel put in the full sun. Worked well for the last 3 months.

Replaced the battery and left on charge for a full day in the sun. No result.

Checked the continuity of the leads from the solar module to to end of the light string. All good. Checked battery voltage, 1.28 and had the same voltage at the end of the light string but no lights. Checked on/off switch all good.

So what am I missing? If I have 1.28V at the end of the string why are the LED's not coming on. Does the small module in the solar panel unit do more than just act as a battery charger?

I know I should just spend another $10 and forget about this problem. But.....

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Reply By: Member - mark D18 - Monday, Mar 13, 2017 at 16:05

Monday, Mar 13, 2017 at 16:05
John

Can't help with the technical stuff , but good on you for trying to fix it .
I try to fix things as well sometimes I succeed and sometimes I don't , but at least we try .



Cheers
AnswerID: 609360

Reply By: qldcamper - Monday, Mar 13, 2017 at 17:01

Monday, Mar 13, 2017 at 17:01
Hi John,

Your description of the set up is just a little confusing.

What is the rated voltage of the battery? Most led lights operate a bit higher than 1.2 volts, but have seen some cheap garden lights with just one rechargeable.

The plug you put in, is it polarity conscious? Meaning can only be plugged in one way around, if it plugs in either way and you have it the wrong way round you will still have volts at the string, but they will only work if it is the right way round.
AnswerID: 609361

Follow Up By: Member - J&A&KK - Monday, Mar 13, 2017 at 18:07

Monday, Mar 13, 2017 at 18:07
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
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FollowupID: 879249

Reply By: AJC - Monday, Mar 13, 2017 at 19:56

Monday, Mar 13, 2017 at 19:56
Hi John,
Agree with previous comments, and you seem to have covered all the bases. In my experience replacing the cheap NiMh battery, like you've done, usually does the trick.
As well as regulating charge to the battery, the module behind the solar panel also acts as the day/night switch, so if this is covered to simulate night-conditions then I'd have thought 1.28V would be enough for the lights to work.
I've also found some of the soldered connections are not done that well on these cheap ones, so might also help to look there (wiggle wires, tap the module, etc).
And I second the commendation for trying!
Cheers,
AJC
AnswerID: 609367

Follow Up By: Member - J&A&KK - Monday, Mar 13, 2017 at 21:50

Monday, Mar 13, 2017 at 21:50
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
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FollowupID: 879257

Follow Up By: RJ5023 - Tuesday, Mar 14, 2017 at 12:02

Tuesday, Mar 14, 2017 at 12:02
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."
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FollowupID: 879272

Follow Up By: Zippo - Tuesday, Mar 14, 2017 at 12:36

Tuesday, Mar 14, 2017 at 12:36
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).
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FollowupID: 879274

Follow Up By: Member - J&A&KK - Tuesday, Mar 14, 2017 at 14:24

Tuesday, Mar 14, 2017 at 14:24
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
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FollowupID: 879277

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