Most online calculators for LED current-limiting do not have any common sense.
I tried it with a low voltage across the current-limiting resistor and the calculator gave a NEGATIVE current when the LEDs have 10% high forward voltage so they become a GENERATOR!
Then of course when the LEDs have a 10% low forward voltage then they burn out because the current is too high.
I posted about the problems with the LED current-limiting calculator because many nOObs do not know the details that the calculator should say.I dont see the point of your post unless its just to find fault with some else's work.
I posted about the problems with the LED current-limiting calculator because many nOObs do not know the details that the calculator should say.
what 'useful' additions would you like to see included in the calaculator that would make the output easier to understand???
Thanks for this, I get people asking me to calculate a dropping resistor for an led all the time.
Might be helpful to show resistor wattage - lots of people want to run one red LED (1.7V) off a car's 12V supply (which can go to 15V) at the full 30ma the led is rated for. This requires a half-watt, not a quarter-watt resistor. Additionally, there's these new high-current white LEDs that can require something even bigger.
I think it would be FAR more useful to show the equations that these calculators were based on and describe what and why each variable in the equation is important so that users can actually eliminate the need for the calculator itself. The Thermistor calcutor throws up a bit of math but no explanation, how is a newbie going to even know what beta is, or how to determien what the reference values for their thermistor are?
I don't think these calculators are a good addition to ETO, simply because there are hundreds if not thousands of them already available via a simple Google search, many of which have a description of their methods much better than the ones I've seen posted here.
I am not a teacher and I don't want to be one.
A calculator should be able to be used by an "idiot" who knows nothing about mathematics or electronics.
Anybody with a small amount of common sense can calculate the simple value of a resistor to limit the current for a few series'd LEDs.
Calculate the current of some low forward voltage LEDs then calculate the current if their forward voltage is high. Then re-calculate so that all of those LEds will be bright enough and/or will not burn out. Simple.
The resistor calculator would benefit from showing the nearest standard value resistor that will work within specs rather than just the idealized value.
Provide a mention of this on the LED calculator page and provide a link to the second calculator then? That kind of cross referencing will be extremely important for new users.
What about wattage derating of the resistor? The example that pops up when you load the page shows a resistor that's being run at it's fully rated power right from the start, this is bad practice.
When a person suggests operating a resistor at its rated power then that person should try holding the hot resistor (250 degrees C?)on his tongue or on another very sensitive part of his body (you know) for a few minutes. Or watch the hot resistor melt a nearby plastic cased capacitor or wire insulation.
The maximum power in a resistor should be HALF its rating.
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