easy question?

[high lord jah]

Hi, hoping some body would be able to tell me whether substituting .25 watt resistor for a .5 or 1 watt equivalent would do the same job.
Thanks alot any one who can help. John

 

[HarveyH42]

It's usually better to substitute a 1/4 with a higher rating, but seldom the other way around, unless you like smoke and flames (pretty cool). The price of resistance, is usually paid in heat...

 

[high lord jah]

Oh thanks, thats good. hmm smoke and flames.....

 

[philba]

do you know the actual current and voltage through the resistor? if so, calculate the wattage - V * I. Then you will know the appropriate wattage resistor to use. note that if you are close to the limit (say .24 watts, for example) you might want to move up the next size (.5 watt in that case).

 

[Don Hawley]

O.K quick while we are on the subject of resistors (I know back to basics)what is the best way to test them.(philba hey neighbor.) THANKS Don

 

[dknguyen]

Measure the voltage across the resistor.

Power = I*V = R*I^2 = (V^2)/R

The last equation is the one you want since all you need to do is know the resistance and the voltage across the resistor (easily obtained without breaking the circuit, unlike if you measured the current). So if the voltage squared divided by resistance is larger than the power rating, you need a larger resistor.

Easiest way to test a resistor?
Step 1. Eyes. See smoke or fire?
Step 2. Nose. Smells like burning resistor material?
Step 3. Finger. Does your finger burn?