10 watt load resistors in place of 25 watt?

Miss_Man · 11-27-2001, 12:22 PM

In the PSU linking article, it was suggested to have a 1 or 2 ohm 25 watt load resistor on the 5v. However, I only managed to find 1 ohm 10 watt load resistors. Can these work as well?

Butcher · 11-27-2001, 01:39 PM

At 5V a 1 ohm resistor will have I = V/R = 5/1 = 5 amps through it, this gives a power rating of P = IV = 5x5 - 25 Watts, so yes you need a 25W resistor. As for finding them, it shouldn't be too hard I turned up a 600W resistor the other day (requires water cooling

)

Miss_Man · 11-27-2001, 11:58 PM

But I really can't find those. Can I just use the 10 watt resistors? Would anything bad happen if I did? It would still give the 5v some load right?

Miss_Man · 11-28-2001, 02:53 AM

Opps I've just discovered what would happen. The 10 watt load resistors get super duper hot! Ok, is it possible to use a load resistor thats maybe like 30 watt? If it has higher ohmage would it matter?

Butcher · 11-28-2001, 09:04 AM

Higher ohmage can work if you use them in parallel.the lowest you can use with 10W resistors is 2.5ohm. Following my forumla above this gives 10W at 5V, which is low enough to stop them burning out. If you use 3 in parallel thats 1/(3/2.5) which is 0.83 ohms, which should be fine for loading. Also as there are 3 of them the current is split so they'll get less hot. NB: make sure it's parallel, in series they'll work but won't put enough load on the PSU. If you can't find 2.5 any value close will work, or you can use more of a higher value, for similar resitors just divide by the number of resistors to get the resistance of them in parallel.

Miss_Man · 11-28-2001, 12:14 PM

Ok thank you! I roughly get this electrical stuff. I'll search around for appropriate resistors. So as long as the wattage rated is higher than the wattage calculated thru the formula, the resistor wont burn up, am I correct?

Butcher · 11-28-2001, 12:15 PM

yes, that's correct.

Miss_Man · 11-29-2001, 05:41 AM

Butcher, need your help again. I have with me 4 1ohm 10 watt resistors and 5 2.2ohm 15 watt resistors. What manner should I connect these to get a load that wont burn my resistors? I've tried 2 2.2ohm resistors in parellel and they burn. I've tried 1 2.2ohm + 1 1ohm resistors in series and they burn too.

11-27-2001, 12:22 PM	#1
Miss_Man Cooling Savant Join Date: Dec 2000 Posts: 151	10 watt load resistors in place of 25 watt? In the PSU linking article, it was suggested to have a 1 or 2 ohm 25 watt load resistor on the 5v. However, I only managed to find 1 ohm 10 watt load resistors. Can these work as well?

11-27-2001, 01:39 PM	#2
Butcher Thermophile Join Date: May 2001 Location: UK Posts: 1,064	At 5V a 1 ohm resistor will have I = V/R = 5/1 = 5 amps through it, this gives a power rating of P = IV = 5x5 - 25 Watts, so yes you need a 25W resistor. As for finding them, it shouldn't be too hard I turned up a 600W resistor the other day (requires water cooling ) __________________ Once upon a time, in a land far far away...

11-28-2001, 09:04 AM	#5
Butcher Thermophile Join Date: May 2001 Location: UK Posts: 1,064	Higher ohmage can work if you use them in parallel.the lowest you can use with 10W resistors is 2.5ohm. Following my forumla above this gives 10W at 5V, which is low enough to stop them burning out. If you use 3 in parallel thats 1/(3/2.5) which is 0.83 ohms, which should be fine for loading. Also as there are 3 of them the current is split so they'll get less hot. NB: make sure it's parallel, in series they'll work but won't put enough load on the PSU. If you can't find 2.5 any value close will work, or you can use more of a higher value, for similar resitors just divide by the number of resistors to get the resistance of them in parallel. __________________ Once upon a time, in a land far far away...

11-28-2001, 12:15 PM	#7
Butcher Thermophile Join Date: May 2001 Location: UK Posts: 1,064	yes, that's correct. __________________ Once upon a time, in a land far far away...

11-27-2001, 11:58 PM	#3
Miss_Man Cooling Savant Join Date: Dec 2000 Posts: 151	But I really can't find those. Can I just use the 10 watt resistors? Would anything bad happen if I did? It would still give the 5v some load right?

11-28-2001, 02:53 AM	#4
Miss_Man Cooling Savant Join Date: Dec 2000 Posts: 151	Opps I've just discovered what would happen. The 10 watt load resistors get super duper hot! Ok, is it possible to use a load resistor thats maybe like 30 watt? If it has higher ohmage would it matter?

11-28-2001, 12:14 PM	#6
Miss_Man Cooling Savant Join Date: Dec 2000 Posts: 151	Ok thank you! I roughly get this electrical stuff. I'll search around for appropriate resistors. So as long as the wattage rated is higher than the wattage calculated thru the formula, the resistor wont burn up, am I correct?

11-29-2001, 05:41 AM	#8
Miss_Man Cooling Savant Join Date: Dec 2000 Posts: 151	Butcher, need your help again. I have with me 4 1ohm 10 watt resistors and 5 2.2ohm 15 watt resistors. What manner should I connect these to get a load that wont burn my resistors? I've tried 2 2.2ohm resistors in parellel and they burn. I've tried 1 2.2ohm + 1 1ohm resistors in series and they burn too.

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