Resistor color code

Status
Not open for further replies.
There is no color code for wattage

There is no color code for wattage

The size of the resistor determines its wattage Wattage ratings are:7 watt, 10 watt, 2 watt, 1 watt, 1/2 watt, 1/4 watt and a 1/8 watt.
 
EEC said:
How can you determine the wattage rating of small color coded resistors?
Click to expand...

Well its a resistor that can be measured in ohms and is only one aspect of determining wattage :)

The colors band equates to a multiplier thats on the resistor, Here is many color charts that explain in various ways to determine what a resistor color bands represent.
 
The only absolutely certain way of determining the wattage rating of a small resistor is by enquiry of the supplier.
In practice though the wattage is related to the dimensions, and a fair estimate may be made by comparison with a resistor of known wattage.

In many circuits the power disipated is minute and well within the capacity of even the smallest resistors.
If however appreciable power is involved then care should be taken that the wattage rating selected is sufficient. If useing components of unknown wattage, then estimate the rating from the dimensions and allow a generous margin of ignorance.

High power resistors normally have the wattage and resistance written on them for example "147 ohms, 25 watts" small ones have the resistance indicated by color code, and no marking as to wattage.
 
Last edited:
For the smaller resistors, 1/8 through 1/2 watt, the physical size of the resistor determines the rating.

Steve
 
I recently bought a 100 watt resistor. It is rated for a whopping 2.7 watts in free air. To actually dissipate 100 watts, looks like it would need to be submerged in liquid nitrogen!
 
sgunsel said:
I recently bought a 100 watt resistor. It is rated for a whopping 2.7 watts in free air. To actually dissipate 100 watts, looks like it would need to be submerged in liquid nitrogen!
Click to expand...
No, just cooled the way the manufacturers state.

That's the rule with pretty much every electronic component. Moving electrons generate heat, and the heat has to go somewhere, and prevention of self destruction (or, more correctly, ensuring the device remains within the envelope of it Safe Operating Area Region) is what a designer or implementer has to do.
 
sgunsel said:
I recently bought a 100 watt resistor. It is rated for a whopping 2.7 watts in free air. To actually dissipate 100 watts, looks like it would need to be submerged in liquid nitrogen!
Click to expand...


I once had a radio power meter that measured 5 or 10 watts, or maybe even more. It had a single 1/4 watt resistor immersed in oil.

So, yes, cooling makes all the difference. It could be immersed in liquid, or forced air, or even a heat sink.
 
Status
Not open for further replies.
Top