Quick electronics/powersource question...

[DeNguyen]

So I have an LED light source that runs off a 9v battery. The thing is I want to put that light in my car and power it via cig lighter. cuttin and splicing is easy, but my question is, will the light fry itself because its running off of 12v now instead of 9?

I was thinking of possibly wiring a resistor in there, but im not sure what ohm resistor I should get. all i remember from circuits class is v=I/r. No idea what the current is. anyway, any help would be good.

Thanx in advance

 

[NSX-Racer]

Yes, 12 V can kill your LED. You can use a resistor if you know the Ampere (or better milliAmpere) of your LED. You can calculate it if you know the Watt number or you can measure it with a Multimeter. Example for a 50 mA LED:
12-9=3
3 divided through A (0,05)= 60 Ohm for the resistor.

 

[Tom239]

Bear in mind that you get more than 12V from the lighter
outlet, more like about 14.5V when the engine is running.

Does it matter to you that you get full brightness no
matter whether the engine is running or not? If so,
a 9V regulator is a better choice than a resistor.
See http://www.electronics-lab.com/projects/power/020/
(you won't need the capacitors if you're just running a LED).

 

[Briank]

I am sure there is resistor in series with the LED already. The question is at 12-14 volts will the current be to much for the LED. Considering a 9 volt battery can not supply much current the resistor has a large value already. I would think that it would work fine on 12 volts. Do you have way to measure the current with the 9 volt?

 

[D'Ecosse]

I am sure there is resistor in series with the LED already. The question is at 12-14 volts will the current be to much for the LED. Considering a 9 volt battery can not supply much current the resistor has a large value already. I would think that it would work fine on 12 volts....

I agree