13-04-2014, 08:35 AM
(12-04-2014, 11:23 PM)richard296 Wrote: Thankyou for that refugee. I hope i understand what your saying. So therefore if the higher wattage number doesn't count. You would then only need 1 value then you can work the other 2 values of the equation needed. Or should i stick to to being a mp and robbing you all blind. thank you richie
Richie, you might be getting confused between the wattage (power) rating of a resistor and the wattage (power) that the resistor is dissipating.
The wattage rating is the maximum power in watts that the resistor is designed to dissipate while maintaining it's specified resistance value.
The power dissipated by the resistor is dissipated as heat as a result of the current flowing through it.
The wattage rating of the resistor should always be higher than the power the resistor is dissipating for safety and long term reliability.
The power (in watts) that the resistor is dissipating is a product of the current squared (in amps) that is flowing through it and the resistors value (in ohms)
The current flowing through it can either be determined by connecting a test meter in series with the resistor and set to measure current or the current flow can be derived by using ohms law by measuring the voltage across the resistor in volts and dividing that voltage by the value of the resistor in ohms.
Lawrence.
