What's the best place to mount Load Resitors for LED bulbs? - BMW Forum

rockblock · 08-01-2009, 08:48 AM

I'm planning to get a set of LED bulbs to replace my P21W turn signal bulbs (F+R) + 4 resistors to put in parallel with each LED bulb to lower blinking frequency. I've heard that the resistors (6 ohms/50W) heat up pretty bad, so I'd like to know where have you guys mounted them (both front + back) and what your overall experience is? Any pics would also be appreciated. These are the resistors I've been told I should get:

rockblock · 08-02-2009, 11:20 PM

I've also noticed that most people use 6 ohms/50W resistors, but complain that they get very hot...I thought that a higher ohm value would solve the heating problem, but I haven't seen anyone use 25/50/100 ohms @ 25W...everyone seems to be using the 6 ohms resistors...

I could be wrong, but here's how I see things:

The LED bulbs + resistors are supposed to draw less amps than the stock 21W bulbs...based on the Power law equation (P=V*I), a quick calculation reveals that when signaling, the stock bulbs draw a max 21W/12V = 1.75A...while at night (when on all the time) they'd draw a constant ~600-700 mA (since they operate @ aprox. 30-40% nominal power).

So, if the Resistor goes in parallel, based on Kirchhoff's current law (I=I1+I2), I would have to look at ensuring that the total Amp draw: I1 (LED) + I2 (Resistor) < 1.75 Amps? So now, if I go with the 6 ohms/50W, Amp2 > 2A, so no good...if I use a 100 ohm/25W resistor, then I2 = 125mA, which is OK...so, basically, I1 (LED) would have to draw a max of 1.625A, which I think they don't... so wouldn't the LEDs actually put less stress on the LCM if we use a Resistor with a higher value (not to mention solve the heat problems)?

I'm still debating on this one...any electricians around?

Adam@theHoffmangroup · 08-03-2009, 04:42 PM

Have you thought about using an LED Flasher instead?

KEEP IT CLEAN NO LOAD FLASHERS

rockblock · 08-03-2009, 06:12 PM

Quote:

Originally Posted by kris@thehoffmangroup

Have you thought about using an LED Flasher instead?

KEEP IT CLEAN NO LOAD FLASHERS

They seem to be available only for LED tails?...will they work on just the fronts? I assume I'll have to replace the existing flasher? Will it work in a combination front LEDs + rear OEM bulbs? Which type do you recommend? Do you have any installation instructions? Thx

BimmerE39 · 08-03-2009, 06:43 PM

This is one area I'm not too sure about. You're obviously going to want to mount them where it's going to be dry. Mounting them in the engine bay for the headlights shouldn't be too problematic but it's the rear signals I'm not 100% sure where they could go.

rockblock · 08-04-2009, 08:20 PM

YEs, I agree...now there's another issue with the 6ohms/50W resistors that heat up pretty bad...some say use 25ohms/25W, some 100ohms/25W...I did some math (as described in post #2) and here's what I've concluded:

If I had a variable resistor (something like a rheostat with low ohms), I could connect it in parallel to the LED bulb and then increase the ohms value from 6 ohms -> up until I get the "bulb out" warning. Then I'd know exactly what resistor to put.

...but unfortunately, I don't have a low ohms rheostat

... so I'm hoping we can find someone that has one and will be able to shed some light to this topic...

BimmerE39 · 08-05-2009, 12:20 AM

Unfortunately, this is one area I have yet to explore too much to really give any answers. I decided to stay with halogen turn signals for a reason.

Adam@theHoffmangroup · 08-05-2009, 02:21 PM

In the engine compartment there is your flasher relay. Take it out and replace with ours. The BMW front and rear lights run off this one flasher. So yes it will work for either front or back.

rockblock · 08-05-2009, 08:59 PM

Quote:

Originally Posted by kris@thehoffmangroup

In the engine compartment there is your flasher relay. Take it out and replace with ours. The BMW front and rear lights run off this one flasher. So yes it will work for either front or back.

Kris, this sounds very tempting and simple...my signals also act as city lights at night (probably @ 30-40% power)...so in order to use my Xenons, I must also use the city/signals...so the following questions arise related to this Flasher:

1. Does the Flasher solve the fast blinking issue? - You already confirmed it does
2. Does this 1 flasher correct the "bulb error" - I believe it does
3. Does your flasher support a combination of LED (front) + OEM bulbs (back)... or do I need to change both F+R to LEDs in order to use the Flasher?
4. Does the Flasher have the right load to ensure the city lights don't burn out while on at night?
5. Which Flasher model do you recommend?
6. Have you had any BMW owners that have successfully installed the flasher and are happy with it?

This would be a slam-dunk as it would simplify matters considerably compared to resistors.

Thx

Adam@theHoffmangroup · 08-06-2009, 07:22 PM

The owner of Keep It Clean has it on his E21 BMW and it works great

rockblock · 08-06-2009, 08:36 PM

Quote:

Originally Posted by kris@thehoffmangroup

The owner of Keep It Clean has it on his E21 BMW and it works great

Thx for your response to question #6... maybe I should have been more specific and asked if you had any e46 owners that have successfully installed the flasher and are happy with it...there's quite a big difference between mid 70's and early 00's BMWs

Also, if you could pls respond to questions #3-5, I'd appreciate it. Thx

Adam@theHoffmangroup · 08-11-2009, 02:49 PM

Sorry our BMW tech has been on the road. I am awaiting the answers.

Adam@theHoffmangroup · 08-11-2009, 03:45 PM

Does your flasher support a combination of LED (front) + OEM bulbs (back)... or do I need to change both F+R to LEDs in order to use the Flasher?
** On flasher is all you need

Does the Flasher have the right load to ensure the city lights don't burn out while on at night?
** Yes

Which Flasher model do you recommend?
** FF552NLP

Have you had any e46 BMW owners that have successfully installed the flasher and are happy with it?
** Yes

rockblock · 08-13-2009, 06:01 PM

Quote:

Originally Posted by kris@thehoffmangroup

Which Flasher model do you recommend?
** FF552NLP

Hi thx for your response. According to the info on your page, the flasher you recommend, is for LED tail lights: "Keep It Clean’s No Load Flasher is great for LED tail lights!", while I'm looking for front signals...would the same work?

Also, other than the adjustable blinker rate, is there any other difference between the FF552NLP and the FF552NLF? I could not find a flasher in my panel that resembles the FF552NLP on my 325i/2001.

Thx

Adam@theHoffmangroup · 08-17-2009, 01:01 AM

Quote:

Originally Posted by rockblock

Hi thx for your response. According to the info on your page, the flasher you recommend, is for LED tail lights: "Keep It Clean’s No Load Flasher is great for LED tail lights!", while I'm looking for front signals...would the same work?

Also, other than the adjustable blinker rate, is there any other difference between the FF552NLP and the FF552NLF? I could not find a flasher in my panel that resembles the FF552NLP on my 325i/2001.

Thx

Our flashers may look different than your factory flasher. From our understanding from BMW techs the single flasher controls front and rear lights.

FF552NLF- Will work but most customers like to control how fast or slow the lights flash

FF552NLP- The best bang for your buck. This is our top selling flasher. You can control the speed of the flash.

Did you see the video we have on our site showing you what the flasher does?