KenK in TX

I searched "club blue" but didnt find any solid information - or at least in a format I can digest. Anyhow, I tore everything apart last night and have the factory red led in hand. (getting that led out of the assembly was a pain!)

Anyhow, I'm still in the dark about led selection. I think the size is T1/3mm as you mentioned, but Im lost after that. I'm guessing the factory led is "diffused" vs. "focused" because of the hazy vs. clear shell. I know my car is 12v, but I have no idea how to figure out what resistor to use to step that down to the appropriate led voltage (which Im guessing will be 3.6 maybe?)

Anyhow, if you how to calculate the resistor stuff I'd appreciate the help...otherwise I'll be relying on the guys at the electronics shop.

TIA!

Tsyndr

Hey there.

Sorry for the late response, if you still need...

Ok, you'll need to make sure what the specs on your LED are, cuz they are all different, depending on manufacturer and brightness. How familiar are you with wiring up circuits? I'll assume you don't know much and try to explain as much as I can, just skip if you already know.

I got my LED from www.digikey.com. You can get almost any electronic component from them. My LED is clear, cuz I wanted it to be bright, a diffused one will be more muffled and like the stock red one.

1. Check the voltage drop specification for your LED. For a blue one, should be from 2.5V - 3.7V.

2. Check the current draw for your LED. I'd guess it's between 20mA and 30mA

3. To choose the resistor, you don't want the current going through the LED to exceed the current rating for your LED (step 2).

Let's pretend your LED drops 3.5V and has a current rating of 25 mA.

So your 12V from your car, 3.5 is lost in the LED, and the rest (12 - 3.5 = 8.5) is dropped across your resistor. So you have to select a resistor that will give 25mA. So your resistor will be: R = V/I = 8.5V/.025mA = 340 ohms.

To be safe, I'd round up to the nearst resistor value available, but not too much, otherwise your LED won't turn on.

4. Now you have to check your power. You'll have to check the power rating on the resistor, most are 1/4 watt. In our example, since P = V^2/R, then the power is 8.5x8.5/340 = 0.2125W, less than 1/4, so you are fine.

However, as a general rule of thumb, I try not to exceed 2/3 the rating on resistors. Some would say using a 1/2W resistor is overkill, but since it's probably a few cents more, why risk starting a fire inside your door? I used a 1/2W resistor.

5. Lastly, hook it all up. If I remember properly, the BROWN wire was ground, and the BLACK wire was 12V (go figure those weird Germans). Anyway, the black wire should connect to the resistor, which should connect to the + end of the LED (longer lead), and then the - lead of should be connected to the brown (ground) wire.

I would wrap any open wire with electrical tape to be safe, don't want to short anything out and blow stuff up. Make sure the LED is secure in the holder, cuz you probably won't have that glue stuff like the OEM one. I just pulled OEM one out, came out like a popsicle!

Sorry for the long explanation, but i'll be gone the rest of the evening, and wanted to make sure you had the info you needed. Good luck! Hit me up on IM if you need anything else.

KenK in TX

...so I'll try a different approach. Can you tell me what kind of resistor I would need for part L120TPB1KN on the link below? (It's the only 3mm diffused blue led on the page)

I figure I'll just buy a bunch (since there's a minimum purchase) and a handful of resistors to pass along to other electronically challenged AW members like myself.

I think part of what was confusing me was that I assumed the resistor dropped voltage. My volt meter tells me thats not true, so I guess its dropping amperage? I dont know. Whatever the case it, I'm just got getting it.

BTW, I did track down a blue LED from Frys but it looks like ****. All it says on the box is 20 mA, and on the back it recommends a 5.1k ohm resistor for 2MA and 3.9k for 2.5MA. I wound up with a 4.7K ohm resistor and the led looks like **** - its barely lit. I hooked it up to the factory assembly and its a hair brighter but still looks like total crap.

Thanks for all your help! Hopefully I'll be able to pass it along to others...

I *think* I would need a 410 Ohm resistor for what I've selected, assuming 12v, 20mA, and 3.8 voltage drop.

I think I'm starting to get it. Lets say a 410 Ohm resistor was available in 1/8, 1/4, and 1/2 watt flavors. In my situation, they would all yield the same (brightness) results right?

I think I've been getting tripped up on terminology, big time.<ul><li><a href="http://www.ledtronics.com/ds/L120TR6N/default.asp">Ledtronics L120TPB1KN Blue Diffused</a></li></ul>

Tsyndr

Ok, looks like your part is:

3.6V and 20 mA current.

So from your 12V car supply, 3.6 goes through your LED and the other 8.4 is in the resistor.

So to get 20mA you need R = V/I = 8.4/.02 = 420

Lower the resistor and the LED will be brighter, but you risk burnin it out. Raise the resistor value and it'll be dimmer but it won't fail. 420 should be just fine, LEDs are supposed to last long.

As far watt rating for your resistor. 1/8, 1/4, and 1/2 will all do the same thing. The rating just means how much power it can take until it burns up.

P = IV = .02 x 8.4 = 0.168W. So a 1.4 resistor should be fine.

So you know how to hook it up right? I assume so if you got it to light already. Try using 420 ohms for your resistor.

Last thing is I would test it once you hook it all up and put your door back in, but before you screw it in. You can do this while the door is open by pulling the tow signal (the one above the trunk release). The LED should light for a few seconds.

Let me know if you have any questions, hit me up on IM if you can.

KenK in TX

We both came up with the same answer. I think 470 Ohms is the closest available thing to what I'll need. I'll snag one tomorrow to see how it looks.

Now that we have that project out of the way, can you walk me through building a Tesla coil or jacob's ladder?

Thanks again for all the help and patience!

Tsyndr

Grab a couple values 400 430 470 if possible, just in case 470 makes the LED too dim. Even if you use 400 the LED should be ok, it's MAX is 100 mA, but typical was 20.<ul><li><a href="http://www.amasci.com/emotor/vdg.html">http://www.amasci.com/emotor/vdg.html</a</li></ul>