The alkaline cells are capable of providing 200mA for several minutes. Without any resistor, I expect the current to be larger through the diodes (even if the voltage drop is 3.5V). The LEDs would probably be bright enough with 20mA. Most LEDs with a rating of 20mA will have a maximum current rating below 100mA, so this configuration is plain idiotic.That's common, if not the rule. The batteries are the limiting resistance.
You need to adjust your expectations. Consider what the I-V curve looks like.Without any resistor, I expect the current to be larger through the diodes (even if the voltage drop is 3.5V).
Often, LED flashlights come with "heavy duty" carbon/zinc batteries. I assumed that they were just using the carbon zinc batteries because they were cheap.The alkaline cells are capable of providing 200mA for several minutes. Without any resistor, I expect the current to be larger through the diodes (even if the voltage drop is 3.5V).
I also used to think it was idiotic to run the LED's well beyond the specified current. What if an LED lasts for 100,000 hours at the rated current and "only" for 1000 hours at the abusive high current? Well, that might well be dozens of sets of batteries! I doubt that most flashlights will last that long before breaking in some other way.The LEDs would probably be bright enough with 20mA. Most LEDs with a rating of 20mA will have a maximum current rating below 100mA, so this configuration is plain idiotic.
Ahhh, I see, planned obsolescence.I also used to think it was idiotic to run the LED's well beyond the specified current. What if an LED lasts for 100,000 hours at the rated current and "only" for 1000 hours at the abusive high current? Well, that might well be dozens of sets of batteries! I doubt that most flashlights will last that long before breaking in some other way.
by Jake Hertz
by Aaron Carman
by Duane Benson
by Jake Hertz