Problem with lowering voltage in a car wire using resistors

[rmasu]

Hi,
I am trying to lower the voltage form 12V to 8V in one wire in my car. I thought I could run about 5-6 1Kohm resistors in series, but when I checked the output with my multimeter it still read 12V can some one help me on what to do next?
Thanks
Ross

 

[A.Anand Srinivasan]

Re: resistor help

measure the current through the wire and then put resistor by calculating the IR drop (4V) that is required... or use a voltage divider because the current used seems to be so low and hence it would be easy to use voltage divider....

 

[flatulent]

Re: resistor help

It would be safer to use a three terminal voltage regulator. That way you would get 8 V out at any load current.

 

[rmasu]

Re: resistor help

thanks for the help,
I don't understand what you guys are talking about, I;m really a noob in electronics. So what resistors would I use to get an automotive 12V line down to 8V I;m not too worried about current changes, or should I be?
Would 5 or 6 1K ohm resistors in series drop the voltage down to around what I want?
Thanks!

 

[RDRyan]

resistor help

If you use a resistor in serial, and then use multmeter to check the output, the circuit is open, So the output is still 12V.
If you want to low the voltage, you should check the resistance of the load first, and choose the right resistance for serial in.
as flatulent said, use a three terminal voltage regulator is the best choice.

Ryan

 

[A.Anand Srinivasan]

Re: resistor help

find the current I required to drive the load that you desire to drive with 8V then find the resistor R such that IR=4V... else use a voltage divider with resistance in 2:1 ratio say 10k and 20k in series from supply to ground and take output at the junction...

else use a voltage regulator as flatulent said... it is a very good solution...