I am looking into taking the power supply 12V output of my PrintrBot and plugging a very simple parallel circuit with some LEDs.
I know I can connect a parallel circuit similar to this Splitting a power supply between two circuits. And it would be particularly easy if they use the same voltage.
I also know that I could put 4 3V LEDs in series without a resistor (or add a resistor if the LEDs are rated for less voltage), and they should work properly with a 12V input… and I believe my power supply has enough juice for this (it is a 6A power supply).
My question is:
How to minimize the risks to my printrbot circuit? (I guess there is always a risk that an issue in my LED circuit would affect my printrbot circuit).
While a 4 LEDs in series circuit sounds like the most simple circuit in the world, I know little about electronics (and my experience is very limited). For instance, I am concerned that things like a short in my LED circuit would ruin my PrintrBot circuit or that a LED getting burnt while the printrbot is printing would cause an issue.
Note: I know some people powers the LEDs out of the BED port in the board, but that's too risky for me.
UPDATE after getting answers (2014-09-28).
As explained in the 3 answers so far, some of the asumptions related to the LEDs made by me in the question above are plain wrong. Please read the answers below and do not let my asumptions mislead you.
Best Answer
You need resistors to limit the current. This circuit should meet your needs:
simulate this circuit – Schematic created using CircuitLab
The resistors limit the current through each pair of LEDs to about 15 mA. The total current draw can be easily handled by your 6A supply. Provided you construct the circuit correctly, there will be no risk to your printrbot circuit.