# Is a 2W resistor sufficient to dissipate 0.6W of power?

I'm looking at reducing the power of a 24V 0.1A fan by half. I've calculated that I need a 240 ohm resistor for this purpose. But I also need to choose the wattage.

I'm using the following website for my calculations:

https://www.blackfiveservices.co.uk/fanspeedcalc.php?Voltage=24&Current=0.1&Target=12

It summarizes:

Power dissipated by resistor: 12V * 0.05A = 0.6W

I've read that when choosing a resistor I should double the required wattage on the part.

Is a 2W resistor sufficient?

I'm trying to do this as inexpensively as possible as high watt resistors are expensive.

• You can use series / parallel combinations of 1/4 W resistors as well. Then you'd have the option of going for 1 W, 1.5 W, etc. as required. Commented Oct 26, 2020 at 18:15
• Fans are not resistive loads : you can't assume it takes 0.05A at 12V (you might want to measure it). That affects both the value and power rating of your resistor.
– user16324
Commented Oct 26, 2020 at 18:16
• I think, rather than "can this resistor survive wasting a bunch of power and generating heat", perhaps you should be asking "how do I reduce a fan's power using PWM, which is both common and efficient"? Commented Oct 26, 2020 at 18:20
• It's also worth noting that - depending on a lot of things, including the resistor's derating curve, expected ambient temperature, airflow, heatsink contact and thermal resistance - if your resistor is in the air flow path of the fan, you might get away with a smaller resistor. But resistors are so cheap that it's generally a better expenditure of engineering time to simply over-spec the resistor. Commented Oct 26, 2020 at 18:30
• I've read that when choosing a resistor I should double the required wattage on the part. So you're saying that when a manufacturer states that a resistor can dissipate 1 W, we can only use it up to 0.5 W? In 35 years of dealing with electronics, I've never heard that one before. Because it is nonsense. If you want to have some margin, then yes, take a higher rated resistor. But always doubling the figure is silly. Next time: ask yourself why that would be needed. Commented Oct 26, 2020 at 20:38