mike_302

I've never made a circuit outside of grade 9 science. I'm in grade 11, and pumped to try my hand at an LED circuit using LED's I bought off of ebay just moments ago. I have read quite a few VERY simple "altoids box LED flashlight" tutorials, and I understand GENERALLY how to set one up with a battery. Here's the thing:

I want to make a simple LED circuit, probably hooked up into a small chunk of styrofoam, or possibly a "bread board" as you call them. The LED's are these (the specs):

http://cgi.ebay.ca/20-BLUE-10000mcd-...QQcmdZViewItem

and

http://cgi.ebay.ca/20-ULTRA-VIOLET-L...QQcmdZViewItem

And the big part of it all is that I want to make it SOLAR powered. Obviously I'm going to need to get myself a solar cell as well, but unfortunatly for a world moving to alternative enrgy sources, there are little to no sources on the net for how to wire up the circuit with simple cells such assssss.... calculator cells? So my question is this:

What are hte details on those cells? could I fully power a board of up to 20 of those LED's with an efficient set of those calculator cells (not 100 of them... hopefully more like 5 of them at the most)? Is there another source I can find for a cheap solar cell to power something as tiny as a board of LED's? I don't want a huge, 25 sq. ft. solar panel or anything like that. Anyone able to help me out on this? Thanks!

Nigel Goodwin

Probably 100 (or more) is what you would need, they produce almost no power at all.

You can buy much better solar cells, and you should'nt need 25 sq. ft. - but I do fail to see the point of solar powered LED's? - using bright sunlight to light a few dim LED's seems pretty pointless?.

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Torben

Hi Mike!

I'm assuming you want to use solar to charge a battery to run an LED? Otherwise, Nigel's right (and he probably is anyway)--why light a flashlight LED from existing light? Anyway, are you planning to leave the solar panel attached to the flashlight (or whatever it is you want to build--more information is needed!) all day in bright sunlight? Or do you just want to use rechargeables charged in a solar-powered charger?

If you want to run these things off of an easily charged single AA cell, then you might do worse than reading (carefully) the page at http://www.cappels.org/dproj/ledpage/leddrv.htm . Note that while I built one of the circuits here (the last one on the page: http://www.cappels.org/dproj/ledpage...d_Garden_Light ) and got about 7 continuous days of light out of a bright white 3V LED from a single fresh 1.5V cell, the charging thing didn't work out so amazingly well. It kinda worked but I never really tested it fully. YMMV.

What exactly are you trying to do?


Torben

mike_302

I am hoping to run the LED's off a battery that is recharged by solar.. Not power it by solar :s sorry if I made it sound like that. Anyways, I don't really have much of an objective for it yet, seeing as how this is mostly educational for me, with the added bonus of keeping a dark light in my bedroom (if it becomes effective like that). I guess I COULD make some sort of flashlight thing out of it, but for now, I think I just want to take a box or board of some sort (be it thin styrofoam, wood, or just the computer board) and wire a bunch of LED's to it, and have it light up at night.
Like I said, this is my first electrical project of this kind outside of grade 9 science... I wired a few simple circuits in a construction course, but thats all with common cables and household switches and plugs... Obviously this is a little different.
Anyways! Back to the point If I use a solar cell to charge a battery, what would be the simplest way to do it? I've read about diodes to stop the drain of the battery at night, and then I've heard of the issue of overcharging the battery. What kind of battery, solar cell, and diodes do I need to set this all up? I'm assuming I can get the battery, battery holder, and diodes at something like radioshack, but could I use a solar cell like this to charge the battery?:
http://cgi.ebay.ca/New-12V-Solar-Pan...QQcmdZViewItem

The major part of the battery charging is how fast it will charge based on the specs. of hte solar panel... Not that I can't comprehend it, but I haven't found much literature on it to tell me.

thanks again in advance for all your help!

Nigel Goodwin

I suggest you first buy a smallish solar panel and experiment with it - you will probably be VERY disappointed with the amount of power it generates.

Notice the panel you mentioned says "2W max" - this would be at noon in the sahara desert, with the panel perfectly aligned. In practice it will probably never get near this level.

But buy a panel (like you mentioned), and connect your multimeter set to an amps range between the panel and a 120 ohm resistor, and leave it running outside all day. Take a reading from the meter every 5 minutes or so and write it down. This will give you some sort of idea of the amount of power the panel can supply.

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mike_302

So are you saying that this panel won't charge the battery properly if I have this light running up to 20 LED's (as mentioned originally) for.... max. 1 hour a night? Like I said, the charging of the battery via solar power: I don't know how to do the math so, you might need to do that for me thanks! And, for the sake of calculations, lets say I was powering this array with... 2 AA batteries.

Nigel Goodwin

For a start you don't have your location filled in, so we have no idea where you might be, and how sunny it is there.

However, if you're getting a good few hours of bright sunshine, and depending on how bright you run the LED's, it should be possible to manage an hour per night fairly easily.

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HarveyH42

This is similar to a 'solar garden light', just a slightly larger scale. First, you should decide your power needs for the number of LEDs. You stated 20 early, but you might decide to use less.

http://led.linear1.org/led.wiz
This is a site where you can experiment with your LED array, and figure out the best configuration for your needs. If you wire your LEDs mostly in series, you will need a higher voltage, which means more batteries (assuming AA rechargeables). In parallel, they'll drain the batteries faster. So, you need to balance the number of LEDs and batteries you want to use, with how long you want to keep them lit.

Next, you need to decide on the solar panel that will provide the needed power to charge your battery pack. Ususally, the panels stated output works fairly well here in Florida, but not so good in Canada , depends on your location, and how much sun you have availiable for how long. If you plan on just sitting the panel in a window, it won't get a full exposure, maybe a few hours of direct sunlight. So, you would need a larger size. You'll want to go a few volts higher then your battery pack, and the amperage will determine the charge rate. Normal AA rechargebles need slow charging, other wise the get hot and damaged. Think its about 20 percent capacity, so you don't want too exceed that by much. The solar panel won't be giving it's maximum all the time anyway.

mike_302

I'm in Canada, Southern Ontrio to be more specific. Fairly bright but, as you say, I will have it in a window so it won't get max. sunlight full time. But those last two posts helped a LOT I must say. I will be using rechargeable AA's-- two to be specific. So... I don't know if anyone here is able to do it for me but... Since there are so many differnt specs out there on ebay, can anyone point me in the direction of a reliable seller on ebay for a solar panel that would work in this config. ?

audioguru

Haven't you seen solar charged garden LED lights? They have a solar panel much bigger than a calculator and they glow a single LED extremely dimly.

I bought a 12V/150mA (1.8W) solar panel on sale for $10.00. It is supposed to trickle-charge a car battery. It is as big as a big book.
I don't live in the Sahara desert so i never got its rated power, I got about half the power at noon nearly in the middle of summer with it pointing directly at the sun.
Then it would charge a battery with about 75mA for 1 hour a day and maybe 40mA for 4 more hours.

So the total charge of 235mAh would operate a single bright LED for 9 hours or 20 LEDs for half an hour.

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audioguru

Windows block a lot of sun power. My solar panel produces about 1/4 its rated power behind a window at noon nearly in the middle of summer with it pointing diectly at the sun IN SOUTHERN ONTARIO! Half the power as outside.

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HarveyH42

Two AA batteries won't be enough for 20 LEDs. You only get 2.4 volts. Your blue LEDs need at least 3 volts to turn on (3.2-3.6 volts). Even if you use a boost convert like the suggested Joule-thief, you couldn't get enough current for 20 of them.

I'd go with 12 LEDs, 8 AA batteries, and a 12 volt panel. The 12 volt trickle charge panels Audioguru mentioned, are cheap and easy to find surplus, and at many auto parts stores. They are cheap, because they are basically useless for charging a car battery, as intended. I have several, about 12 inches long, 6 inches tall. A diode is built in to block reverse discharge through the panel.

Anyway, 2 LEDs in series and a 180 ohm resistor, 6 of these in parallel.

mike_302

Perfect! I'm already able to see this going together. I mena, with the last post, I understood the terminology and I'm sure I'll be able to draw it out in my head when I get the chacne to really think about it. 8 AA's is fine... I'll just see if there's anyways I can piece this togehter to hide all of this stuff . On that topic: COULD I use a thin piece of styrofoam almost like a bread board? or would it ignite/melt?

Nigel Goodwin

Nothing should be running hot - but you should solder the connections together.

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mike_302

Ya, definatly.. I planned on soldering it all together... And I guess that would be a concern with the styrofoam too...