Hi,

Im in the mid of doing some leds projects for my car. Just wondering can I just connect a 1k resistor to the leds and connect it to the door lightings, so that the leds would light up when I open the door? Would the 1k resistor help to light up the leds?

Cheers!

 

Yes, you will need a resistor to limit the current. Your lighting systems works off of 12V. A 1K resistor will cause about 10mA of current flow through the LED, which if fine.

Reese

 

It is a function of the applied voltage and current used by the LED, and how they are wired, series or parallel, that determine what resistance is needed.
Check the specs of the LEDs you will be using.
In general red and orange consume 20ma and will reach this point with 1.5 to 1.7 volts applied, although some will get to 2 volts. Yellow and green requires a bit more current and will run at around 2.5 volts. Blue and white will use 30ma, sometimes more, and will achieve that at about 3 volts. Infra-red generally have a maximum of 1.5volts at 20ma. Ultra-violet will function like the blue ones although run as high as 3.5v.
Three red will run easily in series from a 5 volt source.
You need to be more specific, how many, what color, high brightness or standard, get the specs, and you may get a more appropriate answer.
There is no standard resistor value, it depends on the supply voltage. Use Ohm's law.
Say you are trying to drive a yellow LED from a 12v source. The LED draws 25ma at 2.5v. So you need to drop 9.5v. 9.5v / .025A = 380 Ohms.
Remember with series circuits current is equal at all points. 2 or more LEDs will draw the same current as a single one.
Also remember if you are doing this with a vehicle that the battery produces 12v while the alternator produces around 14.
You could build a driver circuit with a transistor or two, that's the best method.

* 1 day ago
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COLI

http://www.electro-tech-online.com/n...ote=1&p=336691

 

Thank you for all the replies guys! Is there a schematic which I can refer to if I want to construct a 6 x 4 rows of blue or white leds?

Cheers!

 

Attached is a circuit I made for my UV box... it's a bit bigger than you need but it will give you an idea of how to do it.

Attached Images

UVCircuit.JPG (225.1 KB, 42 views)

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Thank you! What's the value of the resistor that you are using? My supply is 12V from a car.

Cheers!

 

That will depend on the fwd V and rated ma of the LED's you are going to use. Once you decided on the LED's let us know what they are, and we will assist in working out the value of the resistors.

The LED's I used was reated 3.3V and 20ma, so I used 430R resistors on a 12V power supply.

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Why didn't you use two LEDs connected in series?

You could've halved the power consumption, the number of resistors and made it easier to assemble.

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Because I read about some problems using them in series... assembly was easy enough and I have a 13A 12V psu lying around doing nothing.

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What problems?

I think you might be confusing that with connecting them in parallel?

It's perfectly acceptable to connect LEDs in series providing there's adequate voltage headroom and two 3.3V LEDs give 6.6V which is plenty of head room. Indeed you might be able to get away with three in series which would give 9.9V but the LEDs might have a large Vf than 3.3V, they could be 4V which would make them very dim.

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By the way, can I tap the LEDs to different ground from the source that I am tapping from, which means, I just take the +12V from the source but for the ground, I just tap to any grounding point in the car. Would this be alright? Any problems?

Cheers!

 

The chassis of an automobile is like one big wire going back to the negative post of the battery. You can ground to any point that adequately completes the circuit.

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Thank you guys! So let say I want to tap 2 LEDs from a 12V from a source, would it be alright to tap 3 wires together?

Cheers!

 

Draw a rough schematic of what you are planning, attach it here, and we'll give some comments.

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Try this site for a calculator for series parallel connection that also produces a schematic

http://led.linear1.org/led.wiz

Or This one for single LED's

http://led.linear1.org/1led.wiz

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