correct resistor help

Discussion in 'General Electronics Discussion' started by gizmo13, May 12, 2011.

1. gizmo13

2
0
Apr 20, 2010
Hello all,

I am making a chaser light unit for my car and I am planning on using a 3w led.
I have used a website called ledz.com which has an automatic resistor calculator.
I typed all the info: 14v, 2.2 voltage drop with 700 mA and it gave me a resistance
calculation of 16/857 ohms.
Is this correct??????

Craig

2. Laplace

1,252
184
Apr 4, 2010
The formula is R=E/I = (14-2.2)/0.700 = 16.857142

3. nbw

48
2
May 8, 2011
Just be aware that if your battery voltage is down a bit; e.g. you have lights on, or the battery is just getting old - you won't be seeing 14.4V but a little less. Might also be worth considering some form of protection in case the odd higher voltage spike comes through...!

4. BobK

7,682
1,688
Jan 5, 2010
Hopefully, the calculator also told you that the resistor will dissapate 8 Watts. It's going to get hot, and if you use less than a 10W resistor, it's going to melt.

Bob

5. (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
Using a resistor to drive a high powered LED is generally not the best idea. You are far better off finding a constant current driver, and preferably a switchmode device so that you can get high efficiency as well as constant brightness as the voltage fluctuates.

6. gizmo13

2
0
Apr 20, 2010
Thanks all.
Will do some more research.

Craig