Taken in high res so you can see the parts etc and markings

 

The round plastic thing is the old garden lamp. I cannot remember the make, but I think it was Grand Solar or similar. It has two LEDs and two rechargeable 1.2V batteries (AA). It also has, somewhere, a light sensitive switch (maybe on the panel itself?) so the light only comes on at night. I still have 10 of these, intact (without PV panel)

 

Hello,

The following circuit might interest you:
http://talkingelectronics.com/projects/SolarLight/SolarLight.html

Take a look at no.2

Bertus

 

Thanks so far. I did look at the link to resistors etc. - unfortunately it makes no sense at all to me.
I also looked at the link above, but again, it is too technical for me.
Sorry about that - I didn't do any of this at school, or if I did, it is long lost in the recesses somewhere!

 

Took mine apart and took photo's, but mine looks allot more like the circuit provided in the link.

Now, as far your problem goes, there is no problem to wire up a couple of led's with 3 cells in serie. However, charging them with these tiny solar panels in that configuration is for some of the other experts to comments on.

However, sometimes the best solutions are the simplest. It might be allot simpler to take a piece of hardboard and glue the solar panels from the broken lights, along with their circuitbords together. Extend the wires to the led's to allow you to get them closer together and arrange them such, that together they can give a descent light?

As for the components that you got donated, perhaps some of the other nice people here could assist with a workable circuit. I have the setup to make circuit boards at home, I will gladly make the boards and send it off to you, as a donation to your charity.

 

Thanks. Your donation offer is gratefully accepted. Just waiting for someone to help with the circuit.

 

One PV cell is too low in voltage to charge a 3.6V battery, so try 3 cells to charge 2 batteries, which then will light 2 LEDs in series with 1 or 2 27 ohm resistors. Open SW 1 before sun down to prevent discharging batteries back into PVs. Turn on SW 2 for about 2 hours of light.SW1 may be replaced with a Si diode. Open SW2 when light starts to dim to prevent over discharging battery. Try one unit & test, then
it can be expanded.
Have you figured out resistor color code? Attachment management is not working , will try later.

 

Running realy slow.

 

Some form of light or charge current sensing will also be needed otherwise the leds will be on all the time and the battery won't charge properly. Connecting the solar panels in serie will result in the batteries potentially taking twice as long to charge, but it is perhaps something that must be test, since we know very little information about the solar panels capacity.

 

Most of my solar garden lights use a single Ni-Cad cell and a simple voltage stepup circuit.
The few that use two Ni-Cad cells use a solar panel with an output of only 60mA when in bright summer sun and a load that is 2.8V (two ni-cad cells in series being charged).
The two cells have a voltage that is too low to light a white LED without a voltage stepup circuit. if three cells are connected in series and produce 4.2V then the 27 ohm current-limiting resistor in series with 3.5V white LEDs make a current of 26ma when the battery is fully charged then the LEDs dim slowly as the charge runs down.

But How will you charge three cells in series? They need at least 4.2V. The solar panels produce 4.2V only at noon and only when there is no current.

 

He has 17 solar cells. He will have to parallel 2 and series them 8 sets. This will give you the most bang. You will have ~8v for each set of 2 and then connect each set in series to get a higher current for charging.

Make 1 main charging station, using all of the panels.

Take 2 cells and combine them + to + and - to -.

After you have all 8 sets (and 1 left over due to having 17 to begin with)

Connecting them in series (+ of one set to - of the next set), will give you the ability to charge a bank of batteries.

This bank will power the LEDs at night.

I would use a low drop diode to keep the batteries from draining into the solar cells when the sun goes down. You should have one on the circuit board for the old garden lamps.

[ed]
I just saw Bernards post. So 3 cells for two batteries can work, I think we should build one main power source for possible future use.
[/ed]

 

One PV cell is too low in voltage to charge a 3.6V battery, so try 3 cells to charge 2 batteries, which then will light 2 LEDs in series with 1 or 2 27 ohm resistors. Open SW 1 before sun down to prevent discharging batteries back into PVs. Turn on SW 2 for about 2 hours of light.SW1 may be replaced with a Si diode. Open SW2 when light starts to dim to prevent over discharging battery. Try one unit & test, then
it can be expanded.
Have you figured out resistor color code? Attachment management is not working , will try later.

Use two 27 Ω resistors in series for the 3 shown pg 28. Monitoring two freshly charged batteries, 8.09V, one R dropped .75V the other .738V, LED 1 [bright white ], 3.27V, LED 2., 3.30V, @25mA. I a little above rating of 20mA but of no consequence, as I have built many LED flash lights with 3 either N 0r AA cells, no resistors-no failures.

 

Thanks. I am trying to follow the advice, although there appears to be two methods here.. Have made eight PV chargers (2 in panels in parallel for each). Connected them in series to each other. Have connected all the batteries in parallel. I have placed a switch from one of the old garden lamps between the PV chargers and the cells to switch off at dusk.
So now I have a charger (PV panels) and a bank of batteries. I now need to connect them all to the LEDs. Where do I put the resistors, how many, or can I connect direct to the LEDs without resistors (see above post) I can put another switch between the battery and the LEDs to switch them off during the day when charging the batteries. How many LEDs, should they also be in parallel? Is there a right and wrong way to connect the LEDs (is there a (+) and (-) side? Is there a wrong way to connect the resistors ?

 

Just to clarify: I used 16 PV panels to make 8 "cells". I have used 8 batteries (1 per cell). I can wire up the LEDs in groups of 2 with a resistor like the diagram on page three of this topic forum. I am a bit confused on the diagram given - there are three squares on the left of the PV panels labelled (+) and (-), but I don't know what they represent. I am not sure whether to make a whole batch of the systems shown in the diagram, or to make a large single PV charger and a bank of batteries.

 

I have found another old PV panel, making it 18 in total. With this I can made separate units as per the diagram on page 3 of this forum.
3 panels to charge 2 batteries. I am not sure of the diagram given if there are six LEDs in the circuit or only 3?

 

An LED is a diode so of course it has a (+) wire and a (-) wire. If it is connected backwards then it will not light and it might be damaged because its max allowed reverse voltage is only 5V. Solar panels also have a (+) and a (-) wire.

An LED or a few LEDs in series must have the current limited. Usually a resistor is calculated to limit the current to an amount that is less than the max allowed current. Use 20mA to 25mA for most ordinary LEDs.

LEDs should not be connected in parallel unless you test them all and match their forward voltages which is different for each LED.

 

Can you tell me which terminal on the LED is (+) and which is (-)? Looking through the bulb, one wire is attached to an "anvil" shaped piece of metal, and the other wire is attached to a "zig zag" thinner piece of metal. There are no markings to tell me the difference

 

The wide piece of metal inside the LED where the chip sits on is the (-) wire.
The outside rim of the case has a flat spot beside the (-) wire.

 

Some LEDs also have a long lead and a short lead.

See if this helps: (Notice the long lead, the stuff in the LED and the flat spot on the lens rim.)

Image is part of a LED tutorial located at:
http://www.societyofrobots.com/electronics_led_tutorial.shtml

You can get a lot of good information about LED from an article written by one of our members here, Bill_marsden:
http://forum.allaboutcircuits.com/blog.php?b=378

 

With 18 PV panels suggest making two units 0f 9 each; easier to troubleshoot two than one big one. Each string of 3 PVs in series produces about 36 mA X 3 = 108 mA X 5 efective hours of sun = 540mAh. X 75% , battery charging efficiency, = 405mAh . One string of LEDs draws on average 20mA so 405 / 20 = 20 hours of light per string, so for 5 hours of light we can use 4 strings.