Calculations
Calculations
Increasing Resistance
The wattage rating is how much energy the resistor can absorb and dissipate.
It is more important to have an accurate Ohm rating for your resistor than it is the wattage.
Resistors are solid state components that have a fixed internal resistance that cannot be altered which is listed as their resistance rating. The amount of circuit amperes they can handle is listed as their wattage rating.
While resistors are useful, I prefer rheostats because you are able to control the resistance of your circuit with the turn of a dial. With this ability you gain control of the circuit’s current flow (and temperature) when the voltage from the power supply cannot be altered. Visit the Fixed Voltage Power Section for more information on this topic as many concepts overlap.
When dealing with resistors and rheostats, there are a few points to keep in mind...
Consider the Wattage rating is a minimum,
and the Ohm rating is a maximum.
Calculating and determining a resistor is not all that difficult, but it does require a bit more in depth understanding of resistance wire circuits and their required heating current. If you have not yet visited the Circuit Theory Page, go there before proceeding further.
In days past, small electrical components had colored bands printed on them to designate their internal resistance. But discoloration from overheating, dirt accumulation and those that were color blind made it quite difficult to ensure proper reading. Advances in printing technology made printing the values on the small components more practical and some resistor manufacturers have abandoned the electronic color code.
The Electronic Color Code is used to indicate the values of electrical components including resistors, capacitors, inductors and others. More information available through wikipedia as Electronic Color Code.
Each color band on the resistor has a specific meaning depending on its location within the code sequence.
Brown, Yellow, Red, Grey
14 x 10 ohms
2
1400 ohms
or
Black, Green, Brown, Grey
05 x 10 ohms
1
50 ohms
or
Grey, Blue, Orange, Red
86 x 10 ohms
3
86k ohms
or
+/- 0.05%
+/- 0.05%
+/- 0.05%
+/- 0.05%
+/- 2.0%
+/- 2.0%