Novice needs help

wicked demon said:

Hi. I have never really wired anything and a friend showed me some questionable stuff, and I have concerns.
I am making LED strips in parallel. example;
-
90 bulbs -30 rows of 3 x 3.5v+100ohm resistor
12v 1.5a dc power supply
I think your going to use 5mm LEDs with the legs right, looks like it will work
Your setting up a 3 Series x 30 Parallel array
+ ___________________
....|.......|........................|
..Res..Res...................Res
....|.......|........................|
..Led...Led...................Led
....|.......|......~repeat~.....|
..Led...Led ....~27x~.... Led
....|........|.......................|
..Led...Led...................Led
- _I____I______________I

How do I figure out how much light I am producing?
How much current are the LEDs seeing? I figure with the 100ohm resistor on each series of 3 the leds will see 15ma each
-
Is it ok to use any DC converter as long as I use a calculator and the appropriat resister?
Well best to use a switching converter not a transformer coil
-
If a spec says to use an 82ohm can a 100 be used?
Sure but you'll get less current at the LED since the resistor consumes more
A lower resistor would let more current thru but might overdrive your 5mm and burn them out
-
What limits the number of lights you can put in parallel?
The amount of current your power supply can deliver
Your setup shouldn't use more than 0.6A

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