Solar panel LED - How does this work?

[johankj]

Was a bit unsure of which category to put this in, but here goes:

I took this LED solar-panel garden light apart, to see how it works, and maybe use it for some micro project.
,
Is anyone interested in explaining/discussing how it works? I've taken some photos, and attempted to reverse engineer it (schematics). There could be some errors in it...

In the Schematics: Vcc is connected to a battery (rechargeable 1.2V 600 mA AAA), and V+ is connected to the positive pole of the solar panel. The solar panel has a <2.1V voltage across it when under a lamp.

In the photos: WYSIWYG

Comments are much appreciated.

 

[audioguru]

Hi Johan,
Google has links to hundreds of solar garden light circuits.
I think yours has two "470" inductors to multiply the voltage from the battery cell and is this circuit:

 

[johankj]

I think yours has two "470" inductors:

Would that be the two thru-hole axial components?

I've been looking at google, thanks for the tip, (Google is your friend), and the ones I saw all have inductors. I found a simple circuit here https://www.siliconchip.com.au/cms/A_30709/article.html

So, when the solar panel generates current, the battery is charged, and the rest of the circuit is of. But when the solar panel is not generating enough current, the circuit switches to the battery, which voltage is doubled through the oscillating bit.

Anyone know how much current such a panel generates? And if I understand this correctly, you can charge the battery directly of the solar panel?

 

[audioguru]

Garden lights glow dimmly with about 10mA for 6 hours. That is only 60mah. The voltage doubling circuit also doubles the mAh and adds its own operating current, the rechargeable battery cell wastes some current so the average current from the solar panel is about 200mah.
A solar panel rated at 400mAh (in the sahara desert at noon and following the sun) would work. The solar panel limits its current.

 

[johankj]

I think the panels could be 2-2.25V at 40mA, judging from this site: **broken link removed**

I'll do some measurements when I get home.

I also found some entries on the same topic by you, audioguru, which I will be reading thru now.
(https://www.electro-tech-online.com/threads/solar-power-led-array-dead-simple.23242/)

 

[audioguru]

Hi Johan,
One of my red, green and blue fading garden lights stopped. It was full of rain water which rusted away its on-off switch and a diode was a dead short. I sketched its circuit:

 

[johankj]

Thanks for the sketch. I will do mine properly, maybe later today, because It's a different design.

They all seem to be based on the same building blocks: Light detection to select either to charge the battery or to run of it, and an oscillating/resonating part to jack up the voltage.

I measured my solar cell under a lamp, and I got 14mA@2.15V at a maximum. I will try again under daylight. (P=30mW).

Sorry about your bust garden light, maybe you could do one of these? https://www.instructables.com/id/Jar-of-Fireflies/

 

[johankj]

Just measured the panel in the morning sun, and it was about 20.5mA. I guess that's okay at this latitude (60.3 degrees north), and it's past autumn equinox too.

 

[audioguru]

I fixed my solar garden light by draining the water, cleaning and drying the pcb, replacing the rusted away on-off switch with a jumper wire and replacing a shorted diode. The others I have glow for about 2 hours each night now in Autumn after charging all day (about 6 hours) in the sun.
But the one I fixed has a fully-charged 600mah Ni-Cad cell and it glowed all night and is still stong this morning when I shade it.

Therefore the solar panel has a very weak current now a days.