Increase in voltage, indicator lights stay the same

[bluemarshall]

I have a circuit that has gone from 12 VDC to 24VDC and i don't want to have to replace my indicator lights? Can I add a 2 ohm resistor in front of an indicator light to cut the voltage in half?

 

[davenn]

what current do the indicator lights need ?

using a single resistor isnt the usual way to go ... normally use 2 same value resistors to make a divide by 2 voltage divider. The value of those 2 resistors will determine the current

Dave

 

[bluemarshall]

The packaging did not mention the required current. Just that they were all 12VDC. Three of them are LED and one is bulb. How is the wiring with two resistors for the voltage divider? Parallel or series?

Thanks

 

[BobK]

You can use a single resistor, but you need to know the current that that the indicator draws at 12V. Once you know this, calculate the resistor that will drop 12V at that current (24-12), by Ohms low:

V = I R

R = V / I

For example, if the indicator is using 50ma (0.05A) then the resistor is:

R = 12 / 0.05 = 240 Ohms.

Then you have to calculate the power rating for the resistor.

P = V*V / R

And make sure you use a resistor with a power rating higher that that, at least double if you don't want it to get too hot.

Bob

 

[(*steve*)]

Probably best to replace the bulb with a 124V unit.

I agree with resistors to limit the current to the LED lights. I will also point out that measuring the current is absolutely essential. A mistake could leave you with very dead lights.

 

[JPU]

Hi

This may sound like a stupid thing to say. I was just wondering, why couldn't he use a voltage regulator to drop the Voltage down to 12V for his lights.

Forgive me nube-ness!

JP

 

[CocaCola]

Hi

This may sound like a stupid thing to say. I was just wondering, why couldn't he use a voltage regulator to drop the Voltage down to 12V for his lights.

Forgive me nube-ness!

You can it's just wasteful, and impractical... Incandescent lights draw some pretty high levels of current, take for example your time proven automotive 12 volt 1157 bulb, they are about 25-30 Watts @ 12-14 volts... That is about 2-2.5 amps each (sloppy math)... When most of your cheap regulators cap at 1 or 2 amps you start seeing how impractical it becomes without going into a full fledged power supply...

I have to agree with Steve on this one, probably best to just upgrade all the bulbs to 24v, it's a standard voltage in aircraft and military vehicles as well as other machinery so sourcing bulbs isn't overly complicated...