I have two LEDs and three batteries:
The typical voltage of one LED is 1.7V. The maximum is 2V (there is no data about the initial voltage) within 700mA.
The nominal voltage of one battery is 1.2V. The battery capacity is 780mAh.
When charging to full, the voltage goes up to 1.42V.
All I need is to link three batteries in series with two LEDs in series with suitable a resistance
- 3*1.2 =3.6V for nominal voltage of the battery
- 3*1.42=4.26V for maximum voltage of battery
- 3.6÷2 =1.8 when nominal voltage is on the LED
- 4.26÷2=2.13 wich is above the maximum voltage of a single LED
Is it OK if I just choose the resistance depending on the typical voltage of the LED and the nominal voltage of the battery, ignoring the maximum voltage of the battery?
Best Answer
If you want to play it safe, calculate the resistor using the highest battery voltage, and lowest LED voltage. LEDs work fine when run at below their maximum rated current, so they will still work if your calculation was pessimistic.
If you want as much brightness as possible, then measure the actual battery voltage when under load, and the actual voltage across the LEDs when on. Then re-calculate the resistor you need.