3310 LEDs in a car

[ifad]

Hi all, it's my first post here, but I've already read this forum a lot, because no other website can offer so much information to Nokia mobiles.

Recently I got some extra original green-yellow NHM-5 LEDs and my plan is to use them in my small car (Volvo 240) project - changing instrument cluster front bulb illumination to LED backlight. I've measured voltage at diodes' terminals - it's 2.2 VDC, but when jumpered "-" and PCB ground it's 4.0VDC with bright yellow color, which I find very nice.

Car power network voltage varies from 11.5V to 15V, so if I put 5 or 4 LEDs in a series, I get 2.3 to 3V (first case) or 2.8 to 3.75 V (second case) for each LED.

So, I would be happy if somebody can answer my questions:

1) Am I missing something in my plan?

2) If i put only 4 LEDs and get bright yellow color with ~4V voltage, how long would LED survive in such conditions (in compare to normal 2.2VDC life)?

3) I've got two white 3510 LEDs, but only two. And no information on it's electrical specifications. What voltage do they need and how do I find out resistor rating to include in the circuit to function properly?

Thanks in advance.

[danwood76]

I think your best bet would be to put them in parrallel running them from a voltage regulator

For example you could get an LM317T which gives out any voltage between 1.5v and 35v (depending on supply)
Then you will need to place each LED with its own resistor (to stop them blowing)

The LEDs from a 3510 will be same as ones in 3310 I guess

It would be a big mistake trying to run all the LEDs off of a 12v supply as as soon as you seitch on engine you would get a 5v increase on your supply and blow all the LEDs

regards,
Danny

[ifad]

danwood76, thank you, LM317 idea is great. But why should I put each LED with extra resistor if i can get "clean" 2.2V or something like that from a LM317 using just adjustment resistor?

[danwood76]

danwood76, thank you, LM317 idea is great. But why should I put each LED with extra resistor if i can get "clean" 2.2V or something like that from a LM317 using just adjustment resistor?

The resistors reduce the current flow

Basically your average LED will use around 2mA the LM317T can pump out 1.5A and if you had some changing grounding conditions you will quite easily blow your LEDs
You can use the LM317LZ as it only gives out 500mA but I still suggest the current limiting resistors
330 ohm resistors will be fine

You should probably use around 4.0v for your LEDs I think

regards,
Danny