Trevor Rymell
Member
I'm embarrassed to ask such a basic newbie question here.
Is there a reliable rule of thumb to choose a suitable resistor value for a single LED where the current and forward voltage are unknown?
Like I imagine a lot of hobbyists do, I have a drawer full of spare LEDs with no specs. or case markings. What I've usually done in the past is simply connect one up to a bench power supply set to the voltage I want to run the LED at, and with a resistor decade box in series. I then gradually reduce the resistance until the LED brightness looks about right and the device isn't overheating etc. It would be nice to do this without the guesswork however and to know I'm not shortening the life of the LED by using too low a value.
What I want to do is fit a 5mm, high-intensity green LED on a motorcycle which uses a 12v, 16Ah lead/acid battery. The intention is to provide a visual indicator on the handle bars when a certain micro switch opens/closes.
The LED I have seems to run ok at around 3 - 3.5v DC on my bench PSU (no resistor in series). I would like to feel reasonably I've got a value somewhere near correct for the 12v supply so I don't burn the LED and have to take the bike apart again.
I would be grateful for any advice.
Trevor
Is there a reliable rule of thumb to choose a suitable resistor value for a single LED where the current and forward voltage are unknown?
Like I imagine a lot of hobbyists do, I have a drawer full of spare LEDs with no specs. or case markings. What I've usually done in the past is simply connect one up to a bench power supply set to the voltage I want to run the LED at, and with a resistor decade box in series. I then gradually reduce the resistance until the LED brightness looks about right and the device isn't overheating etc. It would be nice to do this without the guesswork however and to know I'm not shortening the life of the LED by using too low a value.
What I want to do is fit a 5mm, high-intensity green LED on a motorcycle which uses a 12v, 16Ah lead/acid battery. The intention is to provide a visual indicator on the handle bars when a certain micro switch opens/closes.
The LED I have seems to run ok at around 3 - 3.5v DC on my bench PSU (no resistor in series). I would like to feel reasonably I've got a value somewhere near correct for the 12v supply so I don't burn the LED and have to take the bike apart again.
I would be grateful for any advice.
Trevor