Hello again,
Well strictly speaking i wasnt talking about spikes really, i was talking about the normal fluctuation that occurs in an app like you would find in an automobile. Spikes are also of concern though, and a capacitor is often a simple protective solution or a zener and capacitor. The cap and/or zener is used with a series resistor to dampen the spike and protect the LED(s).
For the normal fluctuation though it could go from around 11.5v to 14.5v so you should analyze your circuit for at least those two extremes.
If you can afford the power and you dont have too many LEDs then a single resistor for each LED is a good idea. If you dont want to use as much power then you can start to string them in series. One resistor per series string works pretty well. You can put two LEDs in series or possibly even three, although the more overhead voltage you have the better the regulation between extremes will be (more constant light output with change in source voltage).
I wrote an article for the Washington Post a while back on a similar application where the voltage can change significantly (photovoltaic) and it also addresses the power dissipation with higher power LEDs. It's on the web somewhere too but im not sure where anymore.
Well strictly speaking i wasnt talking about spikes really, i was talking about the normal fluctuation that occurs in an app like you would find in an automobile. Spikes are also of concern though, and a capacitor is often a simple protective solution or a zener and capacitor. The cap and/or zener is used with a series resistor to dampen the spike and protect the LED(s).
For the normal fluctuation though it could go from around 11.5v to 14.5v so you should analyze your circuit for at least those two extremes.
If you can afford the power and you dont have too many LEDs then a single resistor for each LED is a good idea. If you dont want to use as much power then you can start to string them in series. One resistor per series string works pretty well. You can put two LEDs in series or possibly even three, although the more overhead voltage you have the better the regulation between extremes will be (more constant light output with change in source voltage).
I wrote an article for the Washington Post a while back on a similar application where the voltage can change significantly (photovoltaic) and it also addresses the power dissipation with higher power LEDs. It's on the web somewhere too but im not sure where anymore.