Solar powered LEDs - technology after my time.

[Martino]

Here's a question for all you electronic geniuses out there.

We have (don't ask - I blame the lady wife) a set of 6 clear plastic dragonflies, each containing an LED and powered by a sort of mushroom with a solar panel in it. The idea is that the mushroom on a spike goes in the ground and you connect this to a wire from which dangle the dragonflies which you hang in a tree. It was dirt cheap.

The solar panel charges three internal (replaceable ) 1.2 volt batteries during the day and at night, the dragonflies light up and change colour. All very nice if you like that sort of thing!

Any way, some of the LED failed, some of the wires broke and the thing was about to be consigned to the scrap, but ended up in my junk box.

I now have some buildings I want to illuminate.

Now, I'd like the light in the buildings to be a yellowy sort of colour, and don't want them flashing or anything like that.

What sort of LEDs do I need to acquire to hitch up to that solar panel thingy? What voltage? How do I hook them up? I have no knowledge of LEDs!

Also I have some garden lights, also with solar panels and rechargeable batteries. These are globe things, with the solar panels and batteries in small box attachments to the stakes that go in the ground. These also have colour changing LEDs. Again it occurs to me that these could have the LEDs swapped out and replaced with white or yellow LEDs, which could then be inserted in (semaphore) signal lamps, so that they come on when it gets dark. Again, how do I work out what sort of LEDs I need and how do I hook them up.

The solar power bit is no problem here in NW Florida as it's the Sunshine State, I just need to keep the tropical rain and hurricanes out of the gubbins, which isn't a great problem as we're used to that too!

Any suggestions?

 

[Neil Robinson]

I suggest you use standard 5mm leds. Some of the brighter ones achieve high brightness by focusing the light into a narrow beam, O.K. for headlights but for building lights lower intensity wider angle ones are better.
The three 1.2V cells are most likely wired in series so the nominal voltage on your led circuits will be 3.6V
Most leds have a D shaped base where the wires enter the plastic, the flat edge is nearest the negative lead.

I suggest you find a supplier of leds who publishes their characteristics. The important ones are the typical forward voltage, the typical forward current the light intensity and viewing angle.
Then just experiment, leds aren't expensive so if you destroy a few as you learn it's no big deal.
Also use the links in the quote below, taken from a similar topic on here.
You can run many simulations with them. Choose whichever display format you understand best.

Dave Hub - 4/11/2009 11:19 AM
1) I got to ask some questions. I got some of those resistor things free with my LED, will they work without?

2)the seller said need them for 6-12v power, is this ok for track power or do I need different ones?

3)If i do attach resistors I take it I solder them, do I solder them to both pins of LED or just one?

4) I remeber an old physics lecture for about 15 yrs ago about series and parallel, what difference will it make to voltage supplied, and brightness of LED if I link five of them together. will I need lesser resistor.

1/ Yes they will work, but only for a short time, just a few seconds in some cases!
You'll also do damage in most cases even with resistors if you connect them to DC the wrong way round.

2/ In short yes. The optimum resistor value depends on the voltage, the number of LEDs and the manner in which they are connected.

3/ Just one and it doesn't matter which lead or which way round the resistor goes. (it des matter which way round the LED goes, see 1/. If you wire several LEDs in series you'll only need one appropriate resistor for all of them.

4/ It can make a big difference. I recommend that you choose the arrangement which takes least current, especially if you use battery power as the batteries will last longer.

DON'T PANIC, the link below makes it all very easy.

http://led.linear1.org/led.wiz

I suggest you experiment with that site to start with. If you're unsure of anything just click on the adjacent question mark on the site.

First try the following values,
Forward voltage 12, diode forward voltage 2, diode forward current (mA) 20, number of LEDs in your array 6 and
View output as wiring diagram.
You should get one answer.
Now repeat, keeping all of the above the same except the number of LEDs in your array which increases by just one to 7. You now have a choice of six circuits (numbered 0 to 5)! Three only take 40mA of current, two take half as much again, one takes twice as much and the last 3.5 times as much.
Now experiment as much as you like, but keep the diode forward voltage and current to the values in the data for your LEDs, or, if you don't know, use those suggested by the question marks in the links.

If you only want to use one LED then use the link below, which is also mentioned in the previous link.

http://led.linear1.org/1led.wiz

If you still have questions after you've explored the above links just ask, either on here or via a P.M.

 

[Martino]

Fantastic Neil, Thank you VERY much.

 

[Madman]

I purchased my LEDs from this outfit. Very good results all around.

http://cgi.ebay.com/20X-5mm-LED-Lig...420?pt=LH_DefaultDomain_0&hash=item3f028e0c9c

The LED driver is also well worth the cost.

http://cgi.ebay.com/Waterproof-LED-...558?pt=LH_DefaultDomain_0&hash=item19b62ab116

 

[trammayo]

Interesting - great value - they say they ship to Europe and then go on to exclude most of it (including Ireland or the UK). Most frustrating!

Mick

 

[Madman]

Interesting - great value - they say they ship to Europe and then go on to exclude most of it (including Ireland or the UK). Most frustrating!

Mick

Thats rather odd. I could buy them for you, and send them to you. They ship rather strangely. No matter how many packages of LEDs you buy, from the same auction listing, they treat each one as a separate sale. They arrive in separate packages on the same day. You are sent separate emails all saying the same thing, about shipping and so forth. I would be willing to re-wrap them into one package which would save you some postage cost. Since they are so light in weight, I can't imagine that it would cost too much to send them to the UK.