i want to lower down the voltage from 13.8v to 8v. i already try using 33ohm 10watt resisitor,but the voltage is still the same,only the ampere got lower down.

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make me sick with project

 

You can make a voltage divider out of two resistors or a potentiometer.

Heres the formula to calculate the resistors values.

Voltage Out = (Voltage In) x R2/(R1+R2)

Since I don't know what value of resistors you have you can mess around with them and see which values you can use.

The 13.8v is the input voltage I don't know why I put it in the schematic but anyone else that would just be the voltage in value.

And ofcourse if you use a potentiometer you can make it variable.

Attached Thumbnails

 

 

Try using an LM7808 voltage regulator

 

be carful uysing the voltage dividor method, because (as I discovered), as soon as you put a load accross the bottom resistor, it puts a resistance in parallel with the resistor, and changes the voltage completly.

Use a regulator, it will not have these problems, and will add a few extra nice features aswell

Tim