a low value wattage resistance

[walid1]

hi
in many many circuits u faced a wattage resistance
for example in a PC monitor i see a 1 ohm 5 watt and in a low cost inverter in our project section you can see a 6 0.5 ohm 10 watt
also in many car batt charger you find one directly before the batt

why this resistance
can i replace it with a thick long wire
thanx

 

[audioguru2]

Hi Walid,
Power resistors are much smaller and cost much less than 0.5 ohm or 1 ohm of long wire.
Copper wire increases its resistance with heat, most power resistors don't.

 

[walid1]

hi guru
we all know that resistors are used to limit current to some value
can a 0.5 ohm resistor limit current and to what level
secondly: why it so big 10 watt, what if i use a 0.5 watt regular resitors

no no, i'll ask my question another way:
what exactly i want to know that: what should i think when i see say 0.5 ohm 10 watt resistor in any board

MY ANSWER:
power = I*I*R
10 watt = I*I*0.5
I max= 4.5amper
so i shoud expect that this R can safely pass a 4 A of current

is it true guru

thank u guru

 

[audioguru2]

Hi Walid,
I never use resistors at their power rating. Look at their datasheet, the temperature is hundreds of degrees C at the rated power. Their power rating is "the absolute max do not ever exceed" amount.

Power resistors are big and take time to heat up. So they can pass pulses of current much higher than they can pass continuously.