When using a string of LED's with the inline resistor, would you reccomend using a 12v Regulator because of the jump to 14.4v with the alternator?
If not whats another way to do that? And i don't want to just calculate the resistance for the resistor based on 14.4v because i still want the LED's to work even with the engine of
Don't panic too much about the voltage most LEDS have a 10% tolerance anyway so just base it on 12v and usually use 1 resister to 5 LEDS I can't remember the impedence right now but most electronics stores will be able to tell you
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WOW Sight and Sound
Maroochydore
Nothing is impossible!
Do it right the first time or don't do it at all.
The proper way to do it is to not worry about voltage at all.
Calculate the current your LEDs will need based off of a 14.4vdc power supply (worst case condition). The resistor you will then be good up until 14.4. Anything above that and you'll be pushing the limits of the LED, but unless something major happens you should be alright.
The LEDs will still work with the engine off, they just won't be as bright. Depending on the LED you might not even notice the difference.
Example:
If you're looking for 10mA at 14.4vdc you would use 1440 ohms
at 12vdc flat you would still have 8.3mA to power the LEDs, which should be more then enough (although over a 10% difference).
Technically, a 12vdc regulator wouldn't work for your application anyway. To maintain the voltage you need to keep the 12vdc regulators input voltate 1-2 volts higher then the regulated output. If you input 12vdc to a 7812 you will NOT output 12vdc, it will be closer to 10vdc.
To fix this, select a 7805 and run all your LEDs at 5vdc if you are really worried about these small differences.
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Kevin Pierson
Alright, but if i set the resistor to work with 14.4v and i drop to 12v with the engine off... then I will probably fall out of the acceptable forward voltage range... so will that affect whether or not the LED's actually turn on?
Run them all in parallel and it won't matter.
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Kevin Pierson
Ehh then i get problems with some LED's being more or less bright. I think i will just run them in series and calculate the resistor with a source voltage for about 13.2v. So then there will a balanced change.
They are just for "decoration." But most sources I've read claim that LED's in parallel do not have an even intensity (i don't need EXACT but i don't want so much that your looking at it and wondering wtf). And I want them to work at both 12v and 14.4v. Im not concerned about a huge difference in intensity between the 2 voltages, as long as the LED's stay on at 12v and don't blow up at 14.4v.
I might be being a little too picky, but before i go spending money on buying the mass amount of LED's and resistors, i just want my design to be right.
Run them in series and calculate the resitor value so that each led will have about 30ma. That way they will be a little overdriven at 14.4v and just above 20ma at 12v. And don't worrie about cooking them at 30ma, they will be fine.
If you want ps me and I'll send you a little program that let's you calculate the resistor value based on the amount of led's, desired current and foward voltage.