Understanding Resistor Limits

It depends on their resistance ..

Power dissipated in the resistor is I^2 R.... so they would need to be very very low R values to avoid burning out.....

At 5amps... I^2 is 25 therforr for 0.6w dissipation the resistor would have to be 0.6/25 ohms which is stupidly small.

So the short answer is NO.....

thanks, but your answer doesn't make much sense to me.

if you were to say, 0.6 = I²R and R = 1 ohm, then the max current would be 0.6 *0.6 =0.36... So I guess that when one speaks of dissapation factors, one speaks of maximum power handling capability. It's a valuable question to me, and all the other folk who like things simplified.

How about this?

At 10 amps, you need the following size resistors:

for 1 Ω, 100w

for 10 Ω, 1,000w

for 100 Ω, 10,000w

for 1kΩ, 100,000w

for 10kΩ, 1,000,000w

for 100kΩ, 10,000,000w

At 0.6 watts, you can accommodate the following currents:

for 1 Ω, .77A

for 10 Ω, .24A

for 100 Ω, 77mA

for 1kΩ, 24mA

for 10kΩ, 7.7mA

for 100kΩ, 2.4mA

Does that help?

Thanks, but I think its better to underwork your resistors.

Gees, post 5 & 6 are a waste of ink. obviously intellectual heavy weights:? Now thats the real joke!

No doubt. In my work, 50% derating is standard. But that wasn't the question.

.

I must have missed something here but it wouldn't be the first time. If P=I²R with P=0.6W and R=1-ohm, isn't the current 0.77A? One of the posters who gave the table of max current with a 0.6W resistor even had 0.77A limit for a 1-ohm.

Your resistor for 5A has 24mOhm, that for 10A only 6mOhm for the rated power.
Thats only some cm of wire of a selected material, perhaps wound up to a small coil.

If you need small resistors of these values you should look at some SMD-parts of
ISABELLENHUETTE.DE.
Regards Uwe

He He he I'm going to throw a spanner in the works by asking...

What about 0.25watt zero ohm links then??

I bet they have a maximum current rating???

John.

I was asked once by the buyers at a company what tolerance are the zero ohm links I wanted to use.... LOL

I bet they have a maximum current rating???

Yes but it's probably much more than the pcb track...

Tolerance.. that'd be zero +/- 8000%

Del

Actually, fuses are low-value resistors. I know resistors can be fuses from experience.

Mathematically yes, they can be be used in 5 to 10 amp circuits if their resistance is between 0.006 and 0.024Ω.

R = W / I²

R = 0.6 / 5² or R = 0.6 / 10²

R = 0.024Ω or R = 0.006Ω

Practically, however...no.

It should be obvious, now, that you can't get any commercial resistors of these values from any store. Sure, you can connect resistors in parallel to get these resistances but what circuit would use these values?

Then again, when you deal with such small resistances, other resistances can affect the final value. Things like, a hook up wire, a Printed Circuit Board trace or a solder pad. These also have very small resistances and will add to your "resistors" and affect the circuit.