When using multiple LED's and a 12 volt power source. Is it best to hook up in series or parallel? I am using these to light up some buildings. Also in series if one goes out do the others? Thanks
In my experience, the best way is parallel with each LED having its own current limiting resistor in series with it. I prefer about 470 ohm resistors. If that is too bright I go with more ohms.
Parallel is always best in my opinion and experience and less prone to problems. If you want to put LEDs in a series array, check out the LED Wizard Calculator, which will show the best solutions for resistors and matrix (you'll need to know the LED's forward voltage and current draw)
I always found this site helpful when needing a refresher on LED's LED Circuitry tutorial: how to hook up LEDs.
Neither method is necessarily better, they both have advantages and disadvantages. Also realise that unless it is just a few LEDs you likely won't be able to put them all in series, but you can certainly use a series/parallel array(the link that RBrodzinsky posted is good for determining how to do that). Parallel advantages: If one LED goes out, the others stay lit. Since each LED has it's own resistor, you can vary the brightness of each LED individually. Parallel disadvantages: Since each LED has it's own resistor, it requires more resistors and more connections. Higher current draw and more heat dissipated by the resistors. Series advantages: Fewer resistors and fewer connections. Lower current draw. Series disadvantages: Since all LEDs wired in a series draw the same current, they can not be individiually adjusted; however, if they have varying specifications, they will have varying brightnesses. If one LED goes out, all LEDs in that series will go out.
Don't really have anything to add but more questions. The LED going out in series sounds real nasty to trouble shoot. Do all LEDs go out or just from the bad one down the line? So if I have 10 in a line and the 5th one burns out do 1-4 go out as well? Also how often do LEDs actually go out? They should last a lifetime of the RR correct?
In series, all LED's go out. Then you have to test each one to find out which has gone. LED's last longer the less current goes through them, i.e. higher resistor value, but ths reduces the lumens (brightness). An LED burns out quicker with a lower resistor value, thus higher current. They are supposed to last a heck of a long time given the correct resistor and power supply voltage. Angie
Speaking of LEDs and power supplies- does anyone know the spec of the LEDS for a Digitrax BD4 as I want to make an indicator panel. Cheers Simon
Unlike filament lamps which always (near as dammit) fail open circuit, LEDs can fail short as well. If one in a string fails short then the current through the string will increase slightly - depends on the Vf of the remainder and resistor values. In the extreme the higher current could cause another to fail thus making things worse still and eventually cascading the failure to the whole lot. But provided each LED is only dropping a smallish proportion of the supply volts and you aren't running them close to their maximum current it shouldn't be a problem in the short term. Obviously finding the faulty unit in this case is easy enough, but OTOH, depending on the way they are used, it may not be immediately obvious that one has failed at all.
