L.E.D. questions

[erxloes]

I am making some custom lighting for my motorcycle and i need to know what kind of resistors i would need.

if i have in series with 12 volts and all L.E.D.'s are 5 mm.
1 L.E.D what kind of resistor would i need or
2 L.E.D "
3 L.E.D "
4 L.E.D "

 

[SABorn]

You have not given data to what leds you are using, but on an average for a basic led a resistor of 560 ohm to 1K would do for a 12v supply, it only needs to be 1/4 watt but anything bigger will work to.

The calculation is.............

12 volt - led voltage / led current (amps)

Example........

12 - 2.2 = 9.8v

9.8 / 0.020 = 490 ohm resistor

So a 560 ohm would be safe for this.

But as the charging voltage of the battery may get as high as 14 volt than the calculation should be done for 14 volt

14 - 2.2 = 11.8

11.8 / 0.02 = 590 ohm so as you see 560 ohm is a bit low.

 

[erxloes]

ok the with 14 volt's comming from the bike and the 2 L.E.D's are 3.6 volt, 20 mA

so if my math is right the resistor should be 340?

 

[Reloadron]

14 - 3.6 = 10.4 so 10.4 / .020 = 520

I get a 520 ohm series resistor for each LED based on a Vsupply of 14 volts and a Vfwd of the LEDs of 3.6 volts and the Ifwd of the LEDs being 20 mA. That assumes two individual LEDs with their own series resistors running on 14 volts.

Ron

Ron

 

[audioguru]

Erxloes calculated the correct resistor value for two 3.6V LEDs connected in series but he didn't say so.
But 340 ohms is not a standard resistor value. Use 390 ohms.

17mA will not make the LEDs bright. They won't light anything but if they shine directly at you at night then you will see them glowing. If they don't shine directly at you then you might not see them.

 

[erxloes]

thanks guys this helps a lot