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Making LEDs glow; the bare minimum setup?





quex
Long story short: I am trying to get LEDs, the tiny little nubby lights, on a kite.

The LEDs need a power source; I'm thinking button cell batteries.

Now, I understand that, unlike filament bulbs, LEDs do something weird where they get more efficient the longer they're running, so there's some sort of crazy second voltage limit you need to be aware of when you're pairing an LED to a battery, and you need to put a resistor in there somewhere...? Also, the visible angles on LEDs; how does that work? Is a sharper angle more focused and therefore brighter, or you just can't see it from the side?

...so now I'm talking about things I don't understand. -_- Can anybody put me straight, and maybe give me a "this common voltage of LED plus this common battery equals bright light" formula?

Thank you.
ocalhoun
Well, all you really need is a battery and a LED.
If they do become more efficient after running for a while, you can just connect them to a battery of the more efficient voltage, and let them 'warm up' with a less efficient voltage.

I would look at the available LED's and the available button batteries, and find some where the voltages match up without being very heavy.
(Oh, and you may already know this, but I'll point it out anyway, LED's are diodes; they will only work when they're attached in the right direction; if you connect the leads backwards, they will not work.)

The leads from the LED's could be attached to the battery easily with small rubber bands (the rubber bands that hairstylists use might work well).


If (as I think) you're trying to make a glowing kite, you might also consider using glow-in-the-dark paint.
It would be lighter, could make a wider variety of patterns, and would be more reusable.
Just keep the kite in a well-lit room before use.


*Other alternatives to keep in mind:
-Instead of using string for the kite, use a pair of wires, which would supply power to the lights. Without batteries, they would be more light-weight, so you could use more without making the kite too heavy.
-Consider using larger batteries and wiring all the LED's to a central power source. (Making battery replacement easier, and making it feasible to wire a small switch into the circuit.)
snowboardalliance
Other considerations:

Different colors will emit light at different voltages.
You probably want at least a small current-limiting resistor
And yes, make sure you connect them in the right direction, they are light emitting DIODES after all
FunDa
My advice, just connect an LED to a button cell, stick it onto the kite and fly it.

Make sure the polarity is correct or the LED will not glow.
weableandbob
With button cell batteries, you shouldn't need a resistor. Just hooking the LED up to the battery in the correct orientation should work fine and not cause any problems.
FunDa
weableandbob wrote:
With button cell batteries, you shouldn't need a resistor. Just hooking the LED up to the battery in the correct orientation should work fine and not cause any problems.


Yes, absolutely. But make sure it is not a 12 V button cell(they are a bit bigger and are rare) like I once accidentally used and bunred out an LED
quex
weableandbob wrote:
With button cell batteries, you shouldn't need a resistor. Just hooking the LED up to the battery in the correct orientation should work fine and not cause any problems.


Did this already in the experimental stage and ended up with a glow that lasted less than 12 minutes. That's why I'm trying to get a good pairing... 12 minutes isn't even long enough for me to get to 500 feet. ;_;
Asap170
quex wrote:
weableandbob wrote:
With button cell batteries, you shouldn't need a resistor. Just hooking the LED up to the battery in the correct orientation should work fine and not cause any problems.


Did this already in the experimental stage and ended up with a glow that lasted less than 12 minutes. That's why I'm trying to get a good pairing... 12 minutes isn't even long enough for me to get to 500 feet. ;_;


12 minutes?! that's really short. You can try doing like 2 AAA batteries and make the LEDs a rely makes sure you have more then the power source because you may blowup a LED. If not then get a resistor in there stat!
quex
ocalhoun wrote:
Well, all you really need is a battery and a LED.
If they do become more efficient after running for a while, you can just connect them to a battery of the more efficient voltage, and let them 'warm up' with a less efficient voltage.


Hard to do that from the ground. ;D

Quote:
I would look at the available LED's and the available button batteries, and find some where the voltages match up without being very heavy.


I've got a few matchups, but there's such a swing in the voltage they want to begin and what they use after a while, I fear I'm wasting my diodes. That is, by just taping the diode onto the battery, I get light.... but about 10-20 minutes thereafter, having secured them to a kite and sent them up, they start burning out. Diodes aren't THAT cheap... I'd like 'em to last a few hours each, at least.

Quote:
(Oh, and you may already know this, but I'll point it out anyway, LED's are diodes; they will only work when they're attached in the right direction; if you connect the leads backwards, they will not work.)


Yes. I like this quality about them :D

Hey, do you know if it harms the diode to trim down the two spurs that extend from the glass? I've been afraid to try it, but I could make better connections if I cut the positive end down so it doesn't extend over the rim of the battery...

Quote:
The leads from the LED's could be attached to the battery easily with small rubber bands (the rubber bands that hairstylists use might work well).


Tape seems to work best for me... helps insulate the battery, too, as the temperature on high is considerably colder than ground level, especially at night.

[quote]If (as I think) you're trying to make a glowing kite, you might also consider using glow-in-the-dark paint.
It would be lighter, could make a wider variety of patterns, and would be more reusable.
Just keep the kite in a well-lit room before use.[/quote}

I effing love this idea. O.O Now I need to find glow paint... but I have never seen it before. ;_; Could also recharge the glow from the ground with a good focused flashlight beam...?


Quote:

-Instead of using string for the kite, use a pair of wires, which would supply power to the lights. Without batteries, they would be more light-weight, so you could use more without making the kite too heavy.


I think the ultimate line weight would take too much of the kite's lift away, plus there is the trouble with bridling the kite in wire (lots of strain on the wire)... but a cool concept, nonetheless.

Quote:
-Consider using larger batteries and wiring all the LED's to a central power source. (Making battery replacement easier, and making it feasible to wire a small switch into the circuit.)


How do I divide the draw of the LEDs over the voltage of a larger battery? Just like normal bulbs, or is there some extra effect to consider, like a variable voltage drop...?
Asap170
If I remember correctly you just take your AAA Batteries(maybe get a battery pack to put them in). Then you do: battery(-) + - + - + - battery(+)

Probably should add a resistor, but don't know which one you need. Or you can always go and make a solar powered light up kite! Not sure how heavy it would be though :/
ocalhoun
quex wrote:
ocalhoun wrote:
Well, all you really need is a battery and a LED.
If they do become more efficient after running for a while, you can just connect them to a battery of the more efficient voltage, and let them 'warm up' with a less efficient voltage.


Hard to do that from the ground. ;D

I think you misunderstand me...
Suppose the LED warms up best with 6V, but after warming up, runs most efficiently at 5V.
In that case, I'd simply use 5V, let it warm up inefficiently, but run more efficiently after the warm-up period.
Quote:

Quote:
I would look at the available LED's and the available button batteries, and find some where the voltages match up without being very heavy.


I've got a few matchups, but there's such a swing in the voltage they want to begin and what they use after a while, I fear I'm wasting my diodes. That is, by just taping the diode onto the battery, I get light.... but about 10-20 minutes thereafter, having secured them to a kite and sent them up, they start burning out. Diodes aren't THAT cheap... I'd like 'em to last a few hours each, at least.

They burn out quickly?
Definitely too much voltage applied then.
Or, actually, could also be too much current... If the resistance value for the LED's is very low, they could be allowing too much current to flow, and overheating.
Quote:

Hey, do you know if it harms the diode to trim down the two spurs that extend from the glass? I've been afraid to try it, but I could make better connections if I cut the positive end down so it doesn't extend over the rim of the battery...

It won't harm them at all, as long as you don't cut the leads so short that you can't attach them anymore. They're intended to be trimmed, usually.
Quote:

I effing love this idea. O.O Now I need to find glow paint... but I have never seen it before. ;_; Could also recharge the glow from the ground with a good focused flashlight beam...?

http://glowinc.com/
I like this place's products especially, since they claim to be brighter and longer lasting.
Supposedly, many of their paints will glow for 8-12 hours, so there should be no need to recharge it.
(I was investigating painting a car with it at one time, but opted for cammo instead.)
Quote:

Quote:

-Instead of using string for the kite, use a pair of wires, which would supply power to the lights. Without batteries, they would be more light-weight, so you could use more without making the kite too heavy.


I think the ultimate line weight would take too much of the kite's lift away, plus there is the trouble with bridling the kite in wire (lots of strain on the wire)... but a cool concept, nonetheless.

*shrug*
Worth a try; get a bit of twisted pair wire from a phone or ethernet cable, then weigh that, and compare it to the weight of the same length of kite string... I doubt it would be that much more, and that thin wire should be enough for a few LED's (I think)... Perhaps use two twisted pairs, depending on how many lights you're using.
Also, take into account that you'd be removing the heavy batteries from the kite, and the lower it is, the less wire it will be supporting.
Quote:

Quote:
-Consider using larger batteries and wiring all the LED's to a central power source. (Making battery replacement easier, and making it feasible to wire a small switch into the circuit.)


How do I divide the draw of the LEDs over the voltage of a larger battery? Just like normal bulbs, or is there some extra effect to consider, like a variable voltage drop...?


In the series circuit, the voltage that R2 gets will be: (the battery voltage - voltage used by R1). The current will be the same through both.
In the parallel circuit, both R1 and R2 receive the same voltage. The current will be shared between the two; each will get 1/2 if their resistance values are equal.
The series parallel circuit may be your best choice; have R1 be an actual resistor to limit the voltage/current to the two LED's (R2 & R3).

Yes, it should work the same as normal light bulbs / normal resistors.
(Not sure about your warming up effect though.)
If your LED's don't have a resistance value labeled, you can find out how much they use by building a simple circuit, then using a multimeter set to DC voltage to measure the potential between the two leads of the LED (while lit).
Like so:

(Where 'shunt' is your LED. Oh, and also, the multimeter pictured is testing for AC voltage, presumably I stole a picture of an AC circuit; since your circuits are DC, use the DC voltage measurement.)
FunDa
quex wrote:
weableandbob wrote:
With button cell batteries, you shouldn't need a resistor. Just hooking the LED up to the battery in the correct orientation should work fine and not cause any problems.


Did this already in the experimental stage and ended up with a glow that lasted less than 12 minutes. That's why I'm trying to get a good pairing... 12 minutes isn't even long enough for me to get to 500 feet. ;_;


COuld you check the voltage in the buttn cells that you have.


I usually light up LED's in small DIY projects with two 1.5V batteries to get a steady light for hours.

Looks awesome in a fake security camera. (Just a box shaped and painted to look like a security camera housing and a single LED with two 1.5V batteries.
lasted for many many night till I got bored and dismantled it)
ocalhoun
Ah, something I just thought of...
Tiny little LED keychains like this one:

I disassembled one once.
They're made with nothing but one LED and a button-battery; the spring-loaded button simply presses the LED lead onto the battery to complete the circuit.

This means two things:
1: Yes, you can make a simple button battery + LED circuit that works fine.
2: You might simply be able to cheaply buy a bunch of those, bypass the switches, and remove the plastic housings. Keychains like these are often given away as marketing gimmicks.


Edit:
here's one disassembled; you can see how simple they are.

Looks like this one had a side-mounted switch, which pressed that copper plate onto the negative side of the battery, completing the circuit.
(Also, looks like this one is using a 5V battery. What voltage are you using?)
gangi
Yes, you can make a circuit with only a LED and a button battery, but if the LED is supposed to be ON a lot of time its a bad idea. The example above is ok because the LED only works once in a while (only at night when you dont have enough light to use your key), but if the LED has to be ON a lot of time is better if you put a resistor in series to limit the amount of current that go throw it.
theAngele
For most applications, a resistor of 820 or 1000 Ohm is good.
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