Question on working with LED's...

I wanted to do some under dash LED's and searching eBay I found user "ectrend" selling:
"20pcs x Ø 5mm Red Round LED Super Bright 10k mcd
with 20pcs resistors (Free of Charge)" - $1 + $1 S&H so I thought cool, right?

Judging from this link: http://led.linear1.org/1led.wiz

I require 390ohm resistors. I received (100) 22 ohm (red, red, black, gold) resistors. AND, not only did they send me resistors I might not be able to use, they also forgot to send me the LED's that the Auction was up for :thumbdwn: . I'd hate to wire them in a series because like MustangP51 said in his posts that if one goes out, the whole series will go out. The only thing I can think to do is to combine resistors. Anyone have to do that?
If anyone can give me some advice, I'd appreciate it.

Also: Has anyone tried to make custom fog lights using LED's or even Luxeon's? I've got some gutted (what I believe are) stock fog lights from my Mountaineer. The metal inside rusted and the glass covers cracked. I'm going to use Plexi as a cover and possibly Luxeons for the bulbs.

 

[willindsay]

Just hit up RadioShack for some resistors. There like a dollar for 5 IIRC.

 

[inh]

mouser.com will be much cheaper. you want 390 ohm resistors? I'll get you a link

 

[Mountaineer1113]

WOW. Quick responses. Yeah, you guys are right. They're cheap enough to just buy again.

Hm... what should I use these 22ohm resistors for then? lol

 

[03 Explorer XLT]

You're going to be pushing right at 1/4 watt with a 390 ohm resistor. I'd go up to a 1/2 watt resistor.

 

[inh]

How did you figure you needed 390 ohm resistors?

390 ohm resistors, 1/2 watt $0.016 each when you buy at least 100:

http://www.mouser.com/ProductDetail/Xicon/293-390-RC/?qs=sGAEpiMZZMu61qfTUdNhG%2fFGN%252b%252bgFgzu3qZTZiujHHM%3d

 

[03 Explorer XLT]

How did you figure you needed 390 ohm resistors?

390 ohm resistors, 1/2 watt $0.016 each when you buy at least 100:

http://www.mouser.com/ProductDetail/Xicon/293-390-RC/?qs=sGAEpiMZZMu61qfTUdNhG%2fFGN%252b%252bgFgzu3qZTZiujHHM%3d

That's a fine question. A 390 ohm resistor assuming a 2V drop is going to be about 25mA. That doesn't sound like much for 10K mcd, but then I don't know what LED you're using.

 

[Mountaineer1113]

<---This guy is clueless.

You're going to be pushing right at 1/4 watt with a 390 ohm resistor. I'd go up to a 1/2 watt resistor.

Thanks! Any sites to school me on this? I haven't the slightest clue when it comes to Volts, watts, ohms, amps... etc.

How did you figure you needed 390 ohm resistors?

390 ohm resistors, 1/2 watt $0.016 each when you buy at least 100:

http://www.mouser.com/ProductDetail/Xicon/293-390-RC/?qs=sGAEpiMZZMu61qfTUdNhG%2fFGN%252b%252bgFgzu3qZTZiujHHM%3d

I used the calculator on the site that I posted. If wiring them up individually, I'd need 390 ohm per LED. In MustangP51's thread, he used 470 ohm resistors I believe.

 

[Mountaineer1113]

http://cgi.ebay.com/20pcs-x-5mm-Red...331?pt=LH_DefaultDomain_0&hash=item27b3162c43

Here's a link to the auction. Who knows what's actually going to be sent to me.

 

[OneLever]

Sounds like that seller doesn't have his act together. I just purchased LEDs from cece718 on ebay. They shipped quickly and everything was bagged neatly, properly, and with specifications on each bag.

I got an assorted pack of 1/4 watt resistors from Radio shack, 5V voltage regulator, 1Amp diode with 600 PIV, and 0.25A in-line fuses. Wired up the input line to the diode then the regulator which output to ground and two 22 Ohm resistors. Each resistor powered four LEDs in parallel. Which then went to the common ground for the circuit on my perfboard. One circuit for each dome light with the ground for each circuit going through the in-line fuses, and then to the stock common ground. Total current through each dome light circuit was 0.20 A stock bulbs there ran 0.35 A. Wattage through each resistor was about 0.20 W.

I used a voltage regulator to keep the LEDs at maximum brightness regardless of whether the engine is off or on. Because there is a two volt difference and that's a lot for LEDs whose operating voltage is three volts.

Edit: Corrected units for two values above.

 

[inh]

Voltage regulators waste a lot of power as heat though. While a good idea in theory, I would probably just wire up 4 LEDs or so with no resistor, or a very small resistor, thus wasting as little electricity as heat as possible.

Also, with white LEDs, the voltage drop is higher, usually 3-4 volts per LED.

 

[OneLever]

I don't see how, that measured total current was for eight (8 x 0.024 A = 0.192 A) leds in each circuit. The current increase was marginal which is the only source of power from the nearly constant battery voltage. Resistors also burn off energy as waste heat, but I do not know the emission differences. Any clarification is appreciated.

Since I use my dome lights to see mainly when I'm getting in and out at night it was important to me for them to be bright with the engine off. For a beginner you are right a regulator is a bit too much.

 

[03 Explorer XLT]

The LED wizard you started with has some useful information on another page:
http://led.linear1.org/category/led-basics/

You do need the resistor to limit the current through the LED. There are a lot of different ways to connect the LEDs and resistors so it's hard to say what's best. I can understand using a regulator because if the battery voltage varies, the current draw will vary too. If you end up close enough to the power rating of the resistor, a little more voltage might burn it up. If you use a high enough power rating that shouldn't be a problem. The light output would vary too, but I don't have any idea how noticeable that would be.

 

[LessThan8]

If you want some functioning fog lights...

http://www.dealextreme.com/details.dx/sku.1302

Plus

http://www.dealextreme.com/details.dx/sku.13557

Plus

http://ledsupply.com/10203.php

On some angle aluminum with a plexi front

=

I made an light bar with those materials and its brighter than my headlights!!

~2000 LM's (12 Q3 Leds)

Pics to come...

 

[Mountaineer1113]

If you want some functioning fog lights...

http://www.dealextreme.com/details.dx/sku.1302
Plus
http://www.dealextreme.com/details.dx/sku.13557
Plus
http://ledsupply.com/10203.php

On some angle aluminum with a plexi front
=
I made an light bar with those materials and its brighter than my headlights!!
~2000 LM's (12 Q3 Leds)
Pics to come...

Post them pics here! I'm anxious to see how it turned out. Thanks for the links too. I've been looking to see if someone posted where they bought "drivers" from. Post us up some How To pics while you're at it