Hi guys, need some help choosing a resistor. I have a 12v 7.5aAh SLA battery and would like to alter the voltage to around 4 volts or so I'd like to use a resistor - what amp rating (ie: 1/4 watt, 1 watt etc.) and resistance.

Cheers.

 

It depends on load current. The series droping resistor is connected in series between the battery and the load. The calculation is;

(Battery voltage - 4) / load current


4 is the desired voltage in your case.


With a resistive voltage divider like this, the voltage may not be stable depending on load current demands. Depends on what your trying to do with the 4-volts.

 

Originally posted by electro-man@Apr 9 2006, 06:37 AM
Hi guys, need some help choosing a resistor. I have a 12v 7.5aAh SLA battery and would like to alter the voltage to around 4 volts or so I'd like to use a resistor - what amp rating (ie: 1/4 watt, 1 watt etc.) and resistance.

[post=15999]Quoted post[/post]​

What is the voltage tolerance of your load before you begin to damage it?

 

You'ld be much better off with a voltage regulator, but again, need to know what sorta current your after...??