Identifying Resistors – Resistor Colour Chart. 10/08/19 Holding the resistor with the “GAP” to the right.

4 band – top.

1st band = the first digit.

2nd band = the second digit.

3rd band = the “multiplier” – how many “0s” to add to the                   first two digits.

4th band = the tolerance in %.

The example is a “yellow” for 4, “purple” for 7, “orange” for 3 “0s” and red for 2% bands equals 4,7,000 a 47,000 ohm 2% tolerance resistor, commonly called a 47K resistor.

5 band – bottom.

1st band = the first digit.

2nd band = the second digit.

3rd band = the third digit.

4th band = the “multiplier” – how many “0s” to add to the 3 digits.

5th band = the tolerance in %

The lower example “green” for 5, Blue for 6, Black for 0, Red for 2 “0s” Brown for 1% bands equals a 5,6,0,00 a 56,000 ohm 1% tolerance resistor, commonly called a 56K.

Resistors are manufactured in a range of values and wattages (power).

Resistance values: the two common ranges are:

·       E12 series that comes in twelve values per decade - 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68 and 82. The above two 47K and 56K resistors fall in this range.

·       E24 series comes in twenty four values per decade - 10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 72, 82, and 91.

Wattage:

·       1/4, 1/2 and 1 watt carbon or metal film resistors

·       5, 10 25 etc watt wire wound resistors (high power types).

Wattage is the rating of the resistor. When current flows through a resistor like in our LED and Incandescent headlight examples, the voltage that has to be dropped will be converted into heat. The higher the current, the more heat generated.

Power, therefore heat, that has to be dissipated by the resistor equals Amps x  Amps x  ohms.

When using 1,000 Ohm resistor with 14 volts DC at the Function Output Common, there will be at maximum .0125 Amps or 12.5 mAs to flow through the LED. While this is less than the desired specified current for the LED, it will give plenty of light and the brilliance is only marginally affected. You won’t notice the difference. Operating at the lower current, allows for a higher voltage at the track that some DCC systems have, mainly the Entry Level systems.

Using 1,000 Ohm resistors with your LEDs, as I do, the heat dissipated is .0125 x .0125 x 1,000 = .156 Watts. A 1/4 or 1/2 Watt resistor is suitable.

For Incandescent 10 to 20 mAs 1.5 volt lamps use a 1 watt resistor.

For 40 to 60 mAs 1.5 volt lamps, use two resistors, twice the required value connected in PARALLEL would be MUCH better. Two similar value resistors connected in parallel, make a resistor HALF the value of each resistor with TWICE the wattage. E.G. Two 1,000 ohm 1 Watt resistors in “parallel” makes a 500 Ohm 2 Watt resistor.

For hobbyist and the like (us model railroaders), the E12 values are close enough and because of the greater tolerance, makes them really cheap. Most electronic stores carry this range.

The later surface mount resistor like the ones used on our decoders etc, have markings like 473 (47,000 ohms), 272 (2,700 ohms) etc that are converted using 4 band resistor colour code markings.