Repairing solar powered garden lights

[Bloogoo]

Is there any way that I can use my 55x55mm solar panel (**broken link removed**) to light up these 8 LEDs effectively? It seems that my solar panel can only put out 2-2.5V in direct sunlight, but there are 8 LEDs to power ...

What can I do about that?

 

[audioguru]

I see no detailed.datasheet for the little Chinese solar panel. Its max voltage of 2.5V is not high enough to charge two Ni-Cad or two Ni-MH cells that need 3V.
The max power rating of the solar panel is only 0.2W.

If you are using 3.5V white LEDs at 25mA each then they use 0.7W.

Use four Ni-MH cells to make 4.8V. 2500mAh AA cells will power the LEDs for 12 hours.
Replace your little solar panel with a 6V/400mA one.

 

[Willbe]

BTW, sunlight puts out 60 W/sq. ft.; solar cells are ~10% (?) efficient.

 

[audioguru]

The intensity od sunlight changes throughout a day. it is max at noon if the solar panel is pointing at the sun. in the morning and in the afternoon the intensity (and the output current of a solar panel) is much less, especially if the panel does not move to follow the sun.

 

[Willbe]

60 W/sq. ft.

Might be a max at the equator on the equinoxes at noon.

I saw a clip on the TV how a guy much improved solar cell efficiency by using a thin flexible Fresnel lens curved over the cell.

Bulky, but it worked. Probably made for very hot cells.

 

[mneary]

Is there any way that I can use my 55x55mm solar panel (**broken link removed**) to light up these 8 LEDs effectively? It seems that my solar panel can only put out 2-2.5V in direct sunlight, but there are 8 LEDs to power ...

What can I do about that?

You can try running the LEDs for only 15 minutes after sunset. Or charge all week and only run them on Saturday.

You have a fixed amount of energy unless you get bigger cells.

 

[Bloogoo]

You can try running the LEDs for only 15 minutes after sunset. Or charge all week and only run them on Saturday.

You have a fixed amount of energy unless you get bigger cells.

The thing is, I know this can be done with the equipment that I have. I don't want to have it run only on batteries (unless I can recharge them), and I ' don't want it to have more pieces than what I have now (because there's no room for any more! It doesn't run very well, mind you, but it can be done. This project that I'm working on has 8 LEDs being powered by two Ni-Cd batteries and the 55x55mm solar panel. The lights stopped working, and I'm assuming it's because the battery case wasn't completely waterproof, and water got into it.

I'm just trying to recreate the circuitry, but unfortunately I had to destroy it in the process of removing it because it was "glued" in there.

 

[audioguru]

You said the original circuit lighted 8 white LEDs very dimly for 1 hour to 2 hours at night.
Fix it and it will do the same.

Or use four AA Ni-MH cells , a much bigger 6V solar panel and recalculate the current-limiting resistors so that the LEDs are very bright. Then it will light all night.

 

[Willbe]

but it can be done.

The smart money seems to be saying, "No, it can't."

You realize we'll have to report you if you violate the laws of physics.

 

[Bloogoo]

The smart money seems to be saying, "No, it can't."

You realize we'll have to report you if you violate the laws of physics.

HAHAHA! I've got two sets of these. One works, one doesn't. They're the same, so it must work. I'd love to just take the second one apart and build another system like it, but it's impossible to do without ruining the circuitry.

 

[audioguru]

I have about 24 solar garden lights. They are too dim to light up anything but they look nice in my garden at night.
When they go dead then I rotate the single rechargeable AA battery a little because the contacts corrode or something that makes poor contact. I did one an hour ago. They each have a single amber or white LED or a fading 3-colours LED.

 

[mneary]

I'm just trying to recreate the circuitry, but unfortunately I had to destroy it in the process of removing it because it was "glued" in there.

We seem to be going back and forth between "repair as original" and "make it brighter and last 3-5 hours".

With the solar cell you have with the LEDs you have, the result will be the same regardless of the circuit. Dim, for only 1-2 hours.

There are some good and some bad circuits on the net for garden lights, and we can help you get one working. Do you want to do this?

 

[Bloogoo]

We seem to be going back and forth between "repair as original" and "make it brighter and last 3-5 hours".

With the solar cell you have with the LEDs you have, the result will be the same regardless of the circuit. Dim, for only 1-2 hours.

There are some good and some bad circuits on the net for garden lights, and we can help you get one working. Do you want to do this?

It's true, we are going back and forth, and I have gladly accepted everyone's input. I have tested two of the ones that I've listed so far, and only one has worked. Now I'm working on modifying it so that I can use more batteries, or a higher powered battery (1.2V, 2100mA, say).

I would love to have a more efficient/better circuit, so if anyone could propose one that would suit me, I would truly appreciate it. With my lack of knowledge, it would have to be trial-and-error to find the right circuit

 

[audioguru]

My solar garden lights are awesome!
They are dim most of the night following a full sunshine day in July (I am in the upper hemisphere) and they are dim for only half an hour at night following a full sunshine day in winter.

 

[Bloogoo]

My solar garden lights are awesome!
They are dim most of the night following a full sunshine day in July (I am in the upper hemisphere) and they are dim for only half an hour at night following a full sunshine day in winter.

The winter scenario sounds like how mine are all year.

 

[audioguru]

My solar garden lights were either free from my electrical utility comppany or were on sale at half-price. One dollar each (peanuts) when I was asked to pay for them. Cheap Chinese junk.
A few of mine lasted a few months.

 

[mneary]

Most circuits we've discussed are probably pretty efficient (80% or better). Improving an 80% efficient circuit to 100% would take running time from (e.g.) 60 minutes to 72 minutes. With all the other variables present in the garden, you can't measure it.

A more powerful battery such as 2100mAh still relies on your 0.2W (noon at the equator) solar cell. If your solar cell produces 0.5 W-h in a day, it doesn't matter if the battery is 600mAh or 2100. At the end of that sunny day the bigger battery will give back about 0.4 W-h, no matter how big it is.

Now I'm working on modifying it so that I can use more batteries, or a higher powered battery (1.2V, 2100mA, say).

You need to grasp that as long as you use those 55mm x 55mm solar cells nothing will increase the total energy you have available.

 

[Bloogoo]

You need to grasp that as long as you use those 55mm x 55mm solar cells nothing will increase the total energy you have available.

The reason why I'm sticking with the 55x55 solar panel is that there is a depression in the base just that size for a solar panel. Any bigger and it would make it too ugly to be weatherproofed. So I'm stuck with the 55x55 as a limitation.

I've just built circuit 1 (http://www.talkingelectronics.com/projects/SolarLight/SolarLight.html) to light my LEDs (we're now down to 7 due to an accident), and the lights can run off of one (partially charged) battery, 1.2V, 900mA. Everything seems to be great, and to be honest, I was surprised that it would work, given that *I thought* the LEDs would need more power than the battery could put out.

If I switch the NiCd batteries (in the case of using two) with NiMH ones, I find that the lights are always on, but are just brighter when there is no light hitting the solar panel. I think I'm going to stick with the NiCd's, but I worry that they might be overused if they're at full charge. I haven't got that far yet (that's tomorrow's work), but what can I do if either a.) the NiCd's, at full charge, cause the LEDs to be illuminated all the time, or b.) I want to switch NiCd's for NiMH's (and I'd have the same issue)?

I am satisfied with this setup, and I'm happy with the results. I guess one remaining question that I have now is, should there be a resistor connected in series with the LEDs? If so, what should the resistance be?

 

[audioguru]

The circuit is designed to drive one LED safely. Its output current is not much and is divided among your 7 LEDs so they will not need a current-limiting resistor.

The circuit is designed for one battery cell. If you use two cells then the circuit should have some changes.

An AA Ni-MH cell has exactly the same voltage as a Ni-cad cell. The Ni-MH cell just holds 2.8 times more charge.

The solar cell is supposed to turn on the BC547 transistor when there is light. Then the BC547 turns off the voltage-boosting oscillator the BC338. Maybe the battery powers the LEDs directly through the coil connected to the switch.

 

[Bloogoo]

The solar cell is supposed to turn on the BC547 transistor when there is light. Then the BC547 turns off the voltage-boosting oscillator the BC338. Maybe the battery powers the LEDs directly through the coil connected to the switch.

The LEDs just get brighter when there are two batteries and there's no light hitting the solar panel. I'll just run it with one battery.