Help with LED load resistors / protectors
 

OK... I kinda have my answers but I'm looking to get more information.

There are so many "solutions" for LED turn signals and brake lights, and I for one would like to expand my electrical knowledge and figure out how it all works. Last time I did this was high school physics class so it's a bit far :)

Let's start with this: Here are 4 "choices" for turn signals

1) 6Ω 50W (vleds recommends 1 per bulb for turn signals)
2) 3Ω 50W (vleds recommends 1 per side -- hence 1 for 2 bulbs on the same side -- for turn signals)
3) 25Ω 25W (vleds recommends for bulb out warnings, but not for turn signals)
4) 10Ω 25W (RR recommends 1 per bulb -- from my PMs with him -- for turn signals)
etc...

Now there are also 2 methods to install them:
1) For a "load resistor" (parallel install): (See: http://superlumination.com/images/leds/installation.jpg)
2) For a "led protector" (series install): (See: http://superlumination.com/images/au...otector_wm.jpg)

Now I will give you my take on this, granted it could be wrong, but this is what I understand: The parallel installation is to add load on the circuit and simulate the draw of a filament bulb, used mostly to get rid of annoying dash lights. The series type of installation is used to protect LEDs from voltage spikes, but can also result in dimmer LEDs.

I'm also going to toss this in: (See https://www.rx8club.com/rx-8-discussion-3/leds-rx8-161725/)
According to the other thread we have going, it seems that replacing all 3 brake lights with LEDs will cause an ABS warning light. The solution was a 10Ω 2W resistor wired in parallel.

Now I know I've opened up the possibility for this thread to go in all directions so I'll summarize with two questions:

1) How would you determine the proper resistor (Ω & W) to use to ensure that LEDs are at their full brightness, will not burn out and will not cause bulb warnings (for all lights: turn signals, brake lights, any other light)?
2) How do you choose whether to install the resistor in series or in parallel?

I know these are both "classroom questions", and I would love to simply be able to take a class to learn all of this, but I just need a jumpstart :)

For anyone else interested, this article explains the wattage rating on resistors and how to calculate the min. wattage requirements of any resistor. This partially answers #1 :)

http://www.helium.com/items/618789-w...-what-it-means

I am guessing that, by playing with the resistance of the resistor, you will alter the amount of power going through the circuit. Question remains: how to decide how much power you want to draw :)

I can give you a partial answer. I don't use LEDs for my turn signals, so I don't use any resistors in parallel. But I do use resistors on all my 194 bulbs (parking lights, corners, plate light, etc.) in series.

When I started using LEDs the little 5 LED refractor bulbs were about the highest output bulbs you could get from V-LEDs (or autolumination). After having several burn out in only a couple of months I decided to try the "LED protector" that autolumination sells. Problem solved, no more burned out bulbs and the little refractor bulbs were at full brightness.

As V-LEDs started putting out brighter bulbs with more LEDs or higher wattage LEDs, I noticed that either not all the LEDs in the cluster would light up (like with their 11 mini-SMT refractor bulbs) or they would all light, but not at full brightness (4 x .5 watt LED bulbs I'm currently using). I cut open the autolumination "protector" and found it to be a 100Ω 1W resistor. I picked up some 10Ω 1W resistors and made my own and now the LEDs run at full brightness and still no burnouts.

Yea I noticed that part... I had a concern there:

Running on 12V, your 10Ω resistor draw 1.2A, which equates to 14.4W. If you have a 1W resistor, how has it not burnt out?

This is partially a guessing game because the LED bulbs that you buy from V-LEDs or autolumination already have resistors in the base of the bulb. I don't know how you would calculate the exact resistor to use unless you knew both what components were in the base of the bulb and what the specs of the individual LEDs were. I can tell you that with the 10Ω 1W resistor all my bulbs run at full brightness, even my 68 LED fog bulbs. Not one LED has failed since using them either.

I'd also like to point out that I know zero about electrical engineering. I just grabbed the next closest resistors to the 100Ω at Radio Shack, which ended up being 1000Ω and 10Ω. The 1000Ω made the LEDs even dimmer. The 10Ω worked perfectly. So I made a bunch more and they seem to be doing the job.

Yes 10Ω will let more current pass through... just pointing out it was likely not a 1W resistor :)

Sure is. I can take a pic of the package that they came in when I get home if you like. The colored bands on the resistor itself also identify it (and also the 100Ω from autolumination) as 1W.

Not saying I don't believe you... but how does a 1W resistor not burn under a 14.4W load? Perhaps I am not understanding something?

Sorry to rehash this, but assuming there are 12V running to the bulb then the 100Ω 1W resistor by autolumination would also burn out, since it's getting 1.44W.

What that tells me is that there's either
a) another resistor somewhere down the line thats taking up some V
or
b) it isn't a 12 V line to begin with.

I don't have a multimeter, but maybe someone who does can check the input voltage to ground?

grab a multimeter and check the resistance across the led bulbs in question. if there is a built in resistor then you end up running resistors in series with each other. current across both resistors will be the same, but voltage across the resistors wont. also depending on how exactly you guys are wiring in your resistors you could be running into voltage division