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Most through hole (wires on the ends) resistors are rated for 1/4W (0.25W) maximum. But remember that it is highly recommended to keep them below 1/8W (0.125W).
- You can get about 10mA (0.01A) through a 1,000Ω 1/4W resistor without it getting hotter than desired.
- 2 parallel 1,000Ω 1/4W resistors can pass a total of about 20mA without getting hotter than desired. Each one is still passing about 10mA, but their currents add up as far as the rest of the circuit is concerned.
10V across a 1,000Ω (1k) resistor will pass 10V/1,000Ω = 0.01A (10mA) of current through it. Which gives us 10V x 0.01A = 0.1W (100mW) of power that the resistor must be able to dissipate. Therefore, that’s almost the limit of power you want to ask of a 1,000Ω 1/4W resistor.
20mA though an LED is a bit high. That is the maximum current you want to put through the the 3mm and 5mm sized through hole indicator LEDs. Adding another series LED will drop an extra 2 or 3 volts from the current setting resistor(s). If each LED drops 2 volts, then a total of 4V will be dropped from the current setting resistors
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