Originally Posted by greasefingers
I am thinking of buying separate LEDs and potting them in a container, with my own resistors, and wiring. This is to save money and learn more about this. The difficult part is mixing serial and parallel circuits together. I need to investigate or spend some hours reading first.
Coming up with a LED/resistor network for 12V should be fairly straight forward... Assuming the values you gave in your earlier post... here's what I would do:
Arrange 3 LEDs in series (3.6V *3) for a voltage drop of 10.8V.
Then you estimate your highest expected voltage ~ 14V
Take the difference = 3.2V
Calculate the required resistance: 3.2V/.03A = 106 Ohms
Calculate Power = 3.2 * .03 = .1W
So based on this scenario, I would think a 100 - 120 Ohm 1/16W would work great. You may want to parallel up as many as these networks as you need to achieve the desired light output. You could ultimately replace the individual series resistors with a single larger resistor equal to the combined parallel resistance and power of the resistors in the individual nodes. The only pitfall to this circuit would be that if the battery voltage drops below approx. 10.8V the LEDs won't illuminate. Maybe I'm telling you stuff you know already. If not I hope this helps.
Regarding LEDs in general...
While LEDs have advantages, there are some drawbacks. As noted, an LED based lamps cause problems in traditional bimetal type flashers. This is because a prescribed amount of current needs to heat up the bimetal actuator in order for it to "click". Since a replacement LED based lamp uses 10-20% the current of a traditional incandescent lamp the bimetal never gets hot - thus no click. Load resistors can be added which can solve the problem. However, you lose the efficiency advantage of the LED when you do this.
Also, most LEDs are somwhat directional as opposed to the omnidirectional standard bulb. There are various manufacturers offering different versions of LED based replacement bulbs. Some do a better job than others in emulating the original incandescent design. Many manufacturers add the disclaimer "for show or off-road purposes only" on the packaging of their LED based lamps. This is because many LED based replacement lamps currently available don't meet SAE and DOT applicable standards. So, keep this in mind if you decide to change your lamps (you don't want to set yourself up for a lawsuit).