# Thread: 12VDC to 1.7VDC and 2.4VDC

1. ## 12VDC to 1.7VDC and 2.4VDC

I am wireing LEDS to a 12VDC source..The leds are rated 1.7 to 2.4 VDC..anyway to convert this? There will be 50 LEDS wired together...I need help
-Dan

2. LEDs can run fine off 12V. The voltage ratings are the forward voltage required for the diode to conduct. The only issue is selecting the right current limiting resistor(this must be wired in series with the LED) for the input voltage. I'll dig up the formula for calculating it for you(I can't remember every formula in my head. We can't all be that good damnit).

3. wire a few in series, and WHAT do you need 50 for???

IE:

+ -0-0-0-0-0-0- - == 12v stable

Else if you want to wire them like this;

+ -0- -
+ -0- -
+ etc -

you would need to cut the voltage line down to 2v. Try using a few diff resistors with a volt meter till you find one that works and cuts it down..

BTW, I said this before, but WHAT do you need 50 for???

Scott--

4. Here is the formula. You will need to know what drive current the leds will require(20mA is a safe bet usually).

R(Ohms)= (Vin-Vforward) / Current in Amps

for for an LED with a forward voltage of say 2.2 Volts and a drive current of 20mA running of 12 Volts it would be:

R= (12-2.2) / 0.02
R= 9.8 / 0.02
R= 490 Ohms

So you could use a 470 Ohm resistor (490 Ohm resistors don't exist. You may need to use the next highest value resistor as using a lower value will increase the current. It's unlikely a slight increase in current will damage the LED). The circuit is like this:

-&gt;|- is the LED
-/\/\/\- is the resistor

+12V -------/\/\/\-------&gt;|---------GND

I hope this helps

5. I wouldn't recommend connecting LEDs in series straight to 12V. If you do it this way the current through the LEDs will increase greatly when the engine is running (battery up to 13.8V or higher). The recommended way to connect LEDs in series is the add up the forward voltages of all the LEDs and use the same formula I gave earlier (with the total forward voltage) to get a value for a series resistor. It is recommended when using LEDs in series that the total forward voltage be a maximum of 80% of the supply voltage as a general rule. This means you will only probably get away with 4 or 5 LEDs in each series.

so for 5 20ma LEDs each with a forward voltage of 2.0 Volts it would be.

R= (Vin - V(total)forward) / Current
R= (12-(5*2.0)) / 0.02
R= (12-10) / 0.02
R= 2 / 0.02
R= 100 Ohms

This would be wired like this:

12V----/\/\/\---&gt;|---&gt;|---&gt;|---&gt;|---&gt;|----GND

6. Originally posted by DarkWolf:
<STRONG>wire a few in series, and WHAT do you need 50 for??? </STRONG>
maybe building a new spoiler taillight assembly....?

7. Maybe we will never know...
I'm sure we will though...

8. They are just for some tailights on a blazer.. I will run the LEDs in a series with one resistor per 5 but one more question....If i give the Led more Milla amps will the leds get brighter? Cause i gotta have them get brighter when i hit on the brakes

9. you can't "give" the leds more current. they will pull the most current that they need when you have no resistors attached. now my knowledge of electronics is limited, and i dont know if this is sounding right at all...but you would have to set up some kind of switch so that when you brake the leds switch to a power source without a resistor, enabling them to be their full brightness. you could accomplish this with a relay of some type.

10. Yes I know...On my car there are 3 wires...ground, postive light, brake light. So...correct me if i am wrong...but ((connect 5 leds with one 100 resitor)*10) and connect a diode before the resistor and then connect it to the postive light wire...Then I would do the same thing but put a lower resistor like 50...and hook that up to the same 5 leds like this... Here is a pic to explain what i am saying and what i want to do...

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