Basic Resistor Question

Archiver

Hello again,

Most of my circuits I plan to build will use a single 9V battery or
maybe 12V. Should I be using the 1/4 watt resistors or the 1/2 watt
resistors? Does the voltage matter?

Thanks,
DJ

Archiver

DJ,

If any 1/2W resistor value is less than E^2 * 2 (volts squared times 2) or
any 1/4W resistor is less than E^2 * 4 then you should calculate actual
power dissipation (P = E * I or E^2 / R) and select the resistor
appropriately. The usual advice is to size resistors at least 50% higher
than actual continuous average power dissipated. If the circuit could fail
with higher average power dissipation, you must size the resistor to handle
it (worst-case) or add some kind of safety feature.

>Most of my circuits I plan to build will use a single 9V battery or
>maybe 12V. Should I be using the 1/4 watt resistors or the 1/2 watt
>resistors? Does the voltage matter?

Mike Hardwick, for Decade Engineering -- <http://www.decadenet.com>
Manufacturer of the famous BOB-II Serial Video Text Display Module!