dimming leds?

[SpaceRangerJoe]

im going to be making a rheobus soon, and i was wondering if anyone knows where i could find some led's that dim according to the applied voltage (between the 7-12v range). also, what might even be better, is if i could get some that change color according to voltage. i know they have some that will be 2 colors, but are at certain voltages. I was thinking of more of a fade from one color to the next. if these exist, and someone knows where i could find them, i would really appreciate it. thanks a bunch.

 

[Wolfe]

you can use leds, but they dont work very well. you eitherr have to use pulse width modulation, screw around with specific resistors and voltage converters, or use a little christmas tree lights.

 

[Diggrr]

Those tiny Mag-Lite flashlite bulbs would dim nicely (though not changing colors. They're also smaller than led's too, and come in different voltage ratings (most commonly 3 volts), and are cheaper.
A dab of color from a sharpie works good on them too.

You can add a resistor like you would with a diode, and it should dim at the same rate as the fan speed would. There's also no pos/neg to sort out.

Just a thought.

 

[SpaceRangerJoe]

hmm.... what about those dual color leds they use in some baybuses? like it will be red at 12v, and green at 7, or something like that? how does that work?

 

[Wolfe]

dpdt switches.

 

[SpaceRangerJoe]

dpdt switches.

sorry?

 

[Mpegger]

double pole, double throw switches. Bascially, its like having 2 switches, each with one off, and 2 on settings, but only 1 toggle to switch both from one setting to another.

And dimming LEDs doesn't work well or at all just by reducing voltage. The LEDs need the voltage thier rated at to run. The mA applied is what controls the brightness. Run the LED at its rated mA, and that will be its full intensity. Reducing the mA will reduce the intensity of the LED. Reducing the voltage a couple of tenths (2.5V -> 2.4V -> 2.3V -> etc) may reduce the intensity of the LED, but after a certain point the LED will just cut off completely.

I'd go with Diggrr's idea. So long as you have a 3V source, those mini light bulbs will dim with reducing voltage.

 

[SpaceRangerJoe]

ok, thanks guys. i had a feeling that leds would only work at a certain voltage, give or take a little, but i just thought i would check. thanks for the help.


oh yeah, if i was to use flashlight or christmas tree bulbs, dont you think those would get a little hot if they were on all day?

 

[Diggrr]

In the flashlight, they're surrounded by a polystyrene plastic reflector that fits around the bulb very closely. That's the same plastic that's in your computer cases' front bezel.
Christmas tree bulbs are also in a plastic holder and socket, and run all day without melting.

Yes, they feel hot, but it's not in the range of melting the plastic. 100F feels hot to us, but the plastic can usually take twice that and then some.

 

[SpaceRangerJoe]

ok good, thanks. also, dont christmas tree lights 120v ac? will it light up on 12v?

 

[Mpegger]

Well there are 12V flashlight bulbs available, but they are much bigger as compared to the mini-mag light bulbs. I know the mini-mags can take a couple of more volts, but thier life will be quickly reduced if you run it all the time at high voltages.

I dunno about the christmas tree lights. Their wired in a series parrallel circuit (one bulb burns out, a whole bunch of them turn off), so they dont run at 120V each. I never bothered to count how many lights are in series, but they probably start around 12V (12V x 10 lights in series = 120V), and are a better size to use as compared to a flashlight bulb.

 

[jadams]

Does it matter than the Christmas lights use AC current and you want them to run on DC current? Just a thought.

Jeff.

 

[Diggrr]

AC or DC doesn't matter in incandescent lights (bulbs with filaments). They are just resistors, and light wether the electricity is traveling in one direction (DC) or in two alternating (AC).

LED's on the other hand must have DC only.

Oh, and Christmas tree lights can be found with differing voltage ratings. Some light sets put 100 bulbs in one series (1.2 volts per bulb) and some will have 3 sets of 35 bulbs in series (3.4 volts per bulb). The bulb refill package should have the voltage rating on them.
If you're scavenging an old set, just count the bulbs per wire and divide into 120.

Have fun!

 

[Paxmax]

Those tiny Mag-Lite flashlite bulbs would dim nicely (though not changing colors. They're also smaller than led's too, and come in different voltage ratings (most commonly 3 volts), and are cheaper.
A dab of color from a sharpie works good on them too.

You can add a resistor like you would with a diode, and it should dim at the same rate as the fan speed would. There's also no pos/neg to sort out.

Just a thought.

Thoose MAG lite bulbs last about for 30 hours of operation. So, not so cheap in the long run! A LED will last you around 7-10 years.

 

[Paxmax]

dpdt switches.

sorry?

DPDT switches= Dual Pole Dual Throw

DP switch = A switch that has two "channels" with 3 connections. 2 connections are conected at one lever end of the switch, switch it over and 2 other connects instead. LOL! hard to explain without paper...

DT switch= a switch with three lever posistions. Middle=off, Up = 2 connections are made, down=2 other connections are made instead. sort of ON 1 - OFF - ON 2

SPST switch= Single Pole Singel Throw = a plain ordinary switch that connects 2 connections together or disconnects the connections. Lever has two positions on or off.

 

[Paxmax]

AC or DC doesn't matter in incandescent lights (bulbs with filaments). They are just resistors, and light wether the electricity is traveling in one direction (DC) or in two alternating (AC).

One difference is that with AC, bulbs tend to live a bit longer.

 

[SpaceRangerJoe]

DPDT switches= Dual Pole Dual Throw

DP switch = A switch that has two "channels" with 3 connections. 2 connections are conected at one lever end of the switch, switch it over and 2 other connects instead. LOL! hard to explain without paper...

DT switch= a switch with three lever posistions. Middle=off, Up = 2 connections are made, down=2 other connections are made instead. sort of ON 1 - OFF - ON 2

SPST switch= Single Pole Singel Throw = a plain ordinary switch that connects 2 connections together or disconnects the connections. Lever has two positions on or off.

ok, i know what your talking about. i just hadnt seen it called that before.

 

[Diggrr]

Those MAG lite bulbs last about for 30 hours of operation.

Not according to my package. You shouldn't drop your flashlight so much.

 

[palee72]

The way that the multi color LED's work is by changing the direction of the current through the LED. + to - = red and - to + = green (your colors and polarity may vary)

There is no real way that you can change the color by changing the applied voltage. (except maybe red to orange as you drop power...but it isn't pretty)

 

[Blueacid]

I've got one of those LED flashlights - runs off 2x 1.5volt button cell batteries (like in a watch) - for bout 20hours a set of batteries.

The led *should* go for 100,000 hours, which is about 11 years or summat.

Most important thing - it goes dim as the batteries start to run down - Voltage drop!


Another thing I found - flashing LEDS. They run at 1.5volts, and flash every second. Don't know where you could get 'em from, though.