Solar Power LED Array (Dead Simple)

**simoin** · 7th August 2006 04:41 AM

Hi Everyone,
I am trying to do something on a quite small scale here with:
* 2, 2volt, 500milli amp solar panels
* 2 Nickel Metal Hydride (spelling?) AA batteries
* A couple of super bright 5mm LED's, however many I can run off 2 AA's.
* A Light Sensing Diode
* A Schottky Diode
* An ON/OFF switch

Pretty much is a portable LED solar light.

What I am trying to do is hook up the 2 little solar panels in the best format (parallel or series?) posible to charge my AA batteries and then when I feel like it (probably at night) I can flick my little circuit on and have a little bit of light from my LED's. Could be handy when I go out and come home and it's dark and I want to find a light switch or something.

I will try to set the whole thing up in a little plastic box, and I was going to make the solar panels hang off it on adjustable storks, so that where ever the box is placed the storks could be moved to set the solar panels to face the sun. I imagine the storks, would be kind of like swivelley car areial things. A straight peice of metal rod with a swivel ball joint on the end.

I have yet to find a good circuit diagram or even any material that I can use to learn more about circuit's so I can build my own circuit. Any tips help with how to set it all up in the best way would be very appreciated.

Thanks

Simon

**simoin** · 7th August 2006 05:21 AM

Just to clarify, I have all the necessary parts to make something cool, but am very new to electronics and am not sure how to align everything. so am after help designing a circuit diagram. Thanks in Advance

Simon

**audioguru** · 7th August 2006 05:24 AM

The LEDs have a voltage rating which depends on their color. Red is about 1.8V and blue or white is about 3.5V.
The Ni-MH battery cells also have a rating about how much current they can delifer and for how long, measured in ma/hrs.
The light sensing diode has a rating and needs to control a switching transistor to switch the LEDs.

We can't help you until you tell us the LED voltage, battery ma/hr rating and light sensing diode's part number.

**simoin** · 7th August 2006 06:03 AM

Originally Posted by audioguru

The LEDs have a voltage rating which depends on their color. Red is about 1.8V and blue or white is about 3.5V.
The Ni-MH battery cells also have a rating about how much current they can delifer and for how long, measured in ma/hrs.
The light sensing diode has a rating and needs to control a switching transistor to switch the LEDs.

We can't help you until you tell us the LED voltage, battery ma/hr rating and light sensing diode's part number.

I have not purchased the light sensing diode, was thinking of getting it today, so you can either ignore it for the mintue, or just let me know which one I should get and I will go get it.

The batteries are,
2 AA size, 1.2V, 1600 mAh
Normal Charge is 15 hours at 160 mA
Quick Charge is 5 hours at 480 mA

And the Solar cells are
2 by, 2.0 Volt, 500Ma

so would I be right in guessing that it should charge both batteries when hooked up properly in about 5 hours of full sunlight.

I have 3 of each colour LED's in diffused and in water clear, I was going to use the water clear ones, probably I will use the Yellow ones, I bought them from www.jaycar.com.au I think they are pretty standard, and could be 2 or 2.1v? not sure though, can I check it with a volt meter or anything?

**simoin** · 7th August 2006 09:38 AM

Is that all the information you need, let me know if you want anything else. If you can help in anyway just post a quick reply, thanks heaps - Simon

**audioguru** · 7th August 2006 12:10 PM

A yellow LED is about 2.0V, so two battery cells in series will power some if each has a current-limiting resistor in series with it. A fully charged battery will power 10 LEDs for about 8 hours when they are bright.

Your solar cells are rated for noon on the earth's equator. If the battery is fully drained then I don't think your solar cells can fully charge it.

I don't know which parts you can get in your country, see what photo-detector they have. A photo-transistor would be best.

**simoin** · 7th August 2006 02:15 PM

would a photo transistor like this one be okay?
Quick view: http://www.dse.com.au/cgi-bin/dse.st...uct/View/Z1945
full detials: http://www.dse.com.au/isroot/dse%5Csupport/Z1945.pdf

What sort of current limiting resistor will I need? Just something to bring each LED in the series back down to 2v, rather than the supplied 2.4V from the batteries. (not sure if I have that right)

Would a 15 Ohms resistor for each LED sound right to you. I found a LED resistor calculator, pretty handy

here's the link if anyone want's it. http://ourworld.compuserve.com/homep...Bowden/led.htm

I was also wondering about putting a capacitor on there so that when a shadow passes by it won't interrupt as badly, or at least if you switch the light off it will take a few seconds to fade down rather than switch straight off.

I would love a little diagram if anyone out there has one, thanks very very much for your help thus far, hopefully I can repay the favour.

How is it that those 6 and 10 dollar garden lights can recharge one or two AA batteries but my larger solar panels cannot?

**simoin** · 7th August 2006 02:18 PM

by the way, dick smith and tandy electronics are about the same, in Australia as I imagine they would be in the states... So I should be able to get just about anything and everything

Thanks again for your help so far, much appreiciated.

**audioguru** · 7th August 2006 05:13 PM

Originally Posted by simoin

would a photo transistor like this one be okay?

It has a very narrow angle, so it won't work if it points to something dark or a shadow. It is very expensive. Farnell in Australia have it for a much lower price.
An additional normal transistor is also needed to drive the LED.

What sort of current limiting resistor will I need? Just something to bring each LED in the series back down to 2v, rather than the supplied 2.4V from the batteries. (not sure if I have that right)

We don't know how many volts the LEDs need. I just guessed at 2V. If a current-limiting resistor is calculated for a 2.0V LED, then it will burn out if it is actually 1.8V or will be dim if it is 2.2V. The rechargable cells are actually 1.25V each at the low current used for an LED.

Would a 15 Ohms resistor for each LED sound right to you. I found a LED resistor calculator, pretty handy

here's the link if anyone want's it. http://ourworld.compuserve.com/homep...Bowden/led.htm

15 ohms would create a current of 47mA if the LED is actually 1.8V and it will quickly burn out.

I was also wondering about putting a capacitor on there so that when a shadow passes by it won't interrupt as badly, or at least if you switch the light off it will take a few seconds to fade down rather than switch straight off.

Good idea.

I would love a little diagram if anyone out there has one

There are lots of ways to do it, some of them wrong. Google probably has both.

How is it that those 6 and 10 dollar garden lights can recharge one or two AA batteries but my larger solar panels cannot?

The ones I've seen work only for a couple of hours and are very dim. They have cheap old Ni-Cad battery cells rated for only 500mA/hrs.

dick smith and tandy electronics are about the same, in Australia

I joke that Dick Smith sells war surplus stuff and old car parts. Very high prices.
Tandy had something to do with RadioShack in North America but RadioShack is gone in Canada now and sell only appliances in the USA. Their prices are much more than anyone else.

**HarveyH42** · 7th August 2006 09:33 PM

Originally Posted by simoin

by the way, dick smith and tandy electronics are about the same, in Australia as I imagine they would be in the states... So I should be able to get just about anything and everything

Thanks again for your help so far, much appreiciated.

In the United States, Tandy is also know as 'Radio Shaft', for obvious reasons...

**bryan1** · 7th August 2006 09:56 PM

Eh Simion,
Take a look at www.oatleye.com as they have led's far brighter and better than jaycar or dse at much cheaper prices. Also checkout some of their led kits . The price of the kits would be cheaper than just buying the led's at jaycar. I got some 8mm white led's rated at 3.6 volts and 80 mA and off memory they put out about 8 lumens of light. I'm sure once you check out oatleys you be buying from them in no time.

Cheers Bryan

**simoin** · 8th August 2006 12:01 AM

Do Oatleye have a store in Adelaide? I'm down on the flats.

I will pick up some form of photo transistor today.

diagram is under - Solar Powered Walk Light
http://www.repairfaq.org/sam/samschem.htm#schras5
Not sure if the guy made it or just pulled one apart he already had...

Anyway am having fun learning about electronics and doing it this way rather than just following the instructions on a kit and not learning quite so mayn fundamental's...

What sort of computer based programs does everyone use when they do sketch up a wiring diagram?

Thanks

**audioguru** · 8th August 2006 12:25 AM

The Solar Powered Walk Light has a good idea to use the solar cell as the light detector. Then just two transistors turn on the LED. The author recommends adding a current-limiting resistor in series with the LED. IF the yellow LED is 2.0V and the rechargable battery is 2,5V then the resistor should be 0.5V/25mA= 20 ohms. 18 ohms would also be fine.

I use Microsoft Paint to make schematics. Straight lines are made with the Shift key down. I copy and paste parts of schematics and symbols from other schematics and datasheets.

**bryan1** · 8th August 2006 11:11 AM

Originally Posted by simoin

Do Oatleye have a store in Adelaide? I'm down on the flats.

Oatley's are based in Sydney and are a web based company also with a store in Sydney. I order stuff off them all the time and on most occasions I get the package within 4 to 5 working days and I'm up in the Adelaide Hills. Just for an example they have brought out a new project based on 24 high brightness led's for only $9. Now you go and try and get 24 10,000mcd led's from jaycar for under that price and don't forget that $9 includes a pcb and all the components all be it a few resistors and a cap. Here's the link to that kit http://www.oatleyelectronics.com/kits/k238.htm
For a cheap 12 volt led light you won't go past this one for value.

Cheers Bryan

**mathsgene** · 25th June 2007 10:51 AM

hello everybody,
I'm trying to manipulate a simple solar powered street light and it has been time taking. I'll use something like 50 LEDs in series and in parrallel to have a maximum illumination, but the problem i have is how to get a well designed and customise reflector. I need someone to put m e through.

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