alright, so here's what I'm trying to do...

last time i tried doing this mathematically and stuff i blew the led and the HVAC fuse. tell me if this will work please. if it doesn't, can you please tell me what i'm doing wrong? Raptor's FAQ was helpful, but just not enought for people like me



just hoping you guys will help me out on this one... oh, and don't hate on my ms paint skills. lol.

~Cole

got me on that one lol

why a 220 ohm resistor? im so lost... try asking viper he knows alot about 'lectronics

A better way to go aobut this... instead of using resistors... use 5 volt voltage regulators

I promise they will have them at a store like RadioShack.

Its got three pins: 12v in, ground, and 5v out

The ground from the regulator and the 5v device (led) go to your cars (12v) ground.

The input can be anywhere from like 5 to 38 volts, and the outsput will always be 5v. So whether your car is on or off, you'll have the same voltage output.

One note though, voltage regulators give off the extra voltage (7v in your casse) as heat, when you but it you will notice it has a samll heatsink on it. For your application, i would suggest mouting it with a screw to metal (not plastic!!!) or at least put some sort of larger (1 inch swuare) metal peice on the back of it for a heat sink.

And on a note to my note.... the heatsink that is built-in to the regulator is also a ground for the regulaotr, so if you mount it to the body of your car, you wont need to wire the ground of the regulator (the middle pin).



 
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Hopefully I can help out those of you who, like me, prefer using LEDs for their main & accent lighting in thier cars. First off, and I'm not saying you're wrong as there are specialized LEDs with different requirements, but most colored LEDs require around 3.3 - 3.5V to operate with the exception of the common red LEDs, which require 1.8V. Most of us using LEDs bright enough for lighting purposes will be dealing with 20mA (0.020 Amp) devices. The most common (& easiest) method for powering LEDs is that shown in the original post. the Resistor value is easily calculated as:

Supply Voltage -( LED voltage x # of LEDs in series)
Resistor = -------------------------------------------------------------------------
LED current (typically 0.020A)

I personally rebuilt the domelight in my '94 using 12 blue LEDS, 18 UV (blacklight) LEDS, & 6 white LEDs. These were wired in groups of 3 in series (see figure) and powered by a 7810 regulator (10 volt). The UV LEDs also used a 7810, but with a diode connecting it to ground to give approx. 10.6V.

A word of cAuTiOn on powering LEDs:

1) LEDs which draw 20mA can be pushed to about 25mA, but doing so will decrease thier life; you should NEVER push them at currents higher than this as they will overheat & burn out.

2) LEDs have an exponential relationship of Voltage to Current. This means that when you go from 3.3V to 3.35V, you will go from 20mA to say 25mA; at 3.4V however, they may pull close to 40mA!!!

3) 78XX series regulators have a minimum required voltage typically 2V higher than their output voltage. This means that a 7805 requires around 7V to run, and a 7810 requires about 12V to operate.

4) 78XX regulators disippate the extra voltage as heat... this means that they can get HOT when driving several groups of LEDs, and therefore require a medium to large heatsink to operate.



Shown here are the pin configurations for standard 3mm & 5mm (T1 & T1 3/4) LEDs, 78XX regulators, and a schematic of the system I used for my dome light.

NOTE: several groups of 3 LEDs may be connected to a single regulator, each group would connect to ground and then to the regulator. The limit is determined by the current handling of the regulator. (a 2A regulator can power a maximum of 100 groups each pulling 20mA)

As a note, I purchase my LEDs bulk through an Ebay seller from China.. high brightness LEDs cost about $0.25 purchased in quantities of 50 or more.

^^ Good explanation of a voltage regulator. This is what I was talking about in the psot I made previous.

They are much more reliable then resistors. And will always give you the steady output voltage they are rated for.

A few things that arent described very well in the diagram...

-- The center pin of the regulator (ground) is also that top tab. I know he has this labeld but it may be unclear to some people. That top tab (with the hole in it) is also ground. If you have this tab connected to your cars frame for example, it will ground the regulator and the center pin is not needed. If you do this, do make sure you are using your cars power source for this circuit (i dont see why you woulnd't be, jsut thought id mention it).

Also, this tab is where to connect an extended heat sink that is much recommended. Any peice of metal will do. I would recommend a peice about the size of a baseball card, unless you are mounting to your car... your car will make a big enough heatsink

-- The diagram shows a diode on the ground of the voltage regulator to give you an increase in voltage. In my opinion... If you have 5 volt LEDs with a 5 volt voltage regulatr... you probably DONT want those extra .5 volts. Just watch what you're doing and addapt to your application.

And as he said, LEDs on EBAY are CHEAP!!!! My friend made is own LED underbodies... 5,000 5volt high-output red LEDS cost him $12.46, including shipping.


-- The The One One --
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