Solar garden lamp repair

[Ale458]

Hi! I am trying to repair a garden solar light and hoping someone can help as I’m not so knowledgeable with electronics.

The light works but the battery is not charging. I removed the battery and charged it with a mains charger and the light worked for a night but then it would not charge again from the solar panel. There was a bit of corrosion on the battery terminal which I removed, but it still does not charge from Solar.

could it be a problem with the panel or is it worth just changing the battery and seeing if that fixes it? I thought as the battery took charge from the mains it might be ok?

when testing the solar panel should I see a voltage coming directly off the panel?

when I tested the circuit I got a voltage which was steadily dropping down to almost nothing. Is that incorrect?

hope someone can advise. Thank you!

 

[kellys_eye]

The panel should produce a voltage proportional to the amount of light falling on it i.e. you should be able to see it changing if you cover/uncover the solar cell.

Some of the 'exceedingly cheap' solar lamps might not even have a solar panel at all - a charged battery could keep the light working long enough to convince someone it was a genuine device but.......

If you get any replacement solar lights you should use some 'good' clear tape to cover the solar cell to stop water ingress and check for other areas of water entry as well as ensure their is a drain hole should any get in.

 

[Harald Kapp]

As the battery gets charged in an external charger, it is unlikely that it is the culprit here.
Check the battery terminals of the lamp (without battery inserted) for voltage when the solar cell is brightly lit. It should show a steady voltage. You can also check directly at the panel's output after opening the lamp:

• If you have voltage at the panel's output but not on the batttery contacts, the issue is with the charger circuit between panel and battery.
• If you hve no voltage at the panel's output, the issue is with the panel. Or with the connections to the panel. Check all solder joints. Re-solder bad joints using some new solder with a flux core.

My guess is a defect in the charger circuit.

 

[Alec_t]

In the garden light I tore down the 'charging circuit' was very simple, so not much to fail except for corroded connections :-

 

[Audioguru]

A modern solar garden light is still inexpensive but uses an IC to boost the voltage and sense darkness to turn on the light.
The IC has a Schottky diode between the solar panel and the battery so that the solar panel does not discharge the battery at night.

Old poor quality solar garden lights used an LDR to sense darkness and turn on the light but the LDR had a cheap plastic case that soon got sunburned then the LDR failed to work. The cheap solar panel also had a plastic cover that got sunburned and failed to charge the very poor quality battery cell that soon rusted away.