• Welcome, Guest! We hope you enjoy the excellent technical knowledge, event information and discussions that the BMW MOA forum provides. Some forum content will be hidden from you if you remain logged out. If you want to view all content, please click the 'Log in' button above and enter your BMW MOA username and password.

    If you are not an MOA member, why not take the time to join the club, so you can enjoy posting on the forum, the BMW Owners News magazine, and all of the discounts and benefits the BMW MOA offers?

  • Beginning April 1st, and running through April 30th, there is a new 2024 BMW MOA Election discussion area within The Club section of the forum. Within this forum area is also a sticky post that provides the ground rules for participating in the Election forum area. Also, the candidates statements are provided. Please read before joining the conversation, because the rules are very specific to maintain civility.

    The Election forum is here: Election Forum

L.E.D. Resistor Help

J

jr44

New member
I have 2017 R1200R

Recently installed a Puig fender eliminator kit that also has a L.E.D. license plate light replacement.
Everything works and looks great. However, the new L.E.D. light is tripping my dash warning light for bulb malfunction.

Since the L.E.D. is not canbus I believe I need a resistor to match the previous bulbs load, voltage, etc.

Does anyone have any experience and/or fixed this issue? I do not know how to determine wich resistor I need to install. Puig has been no help.

Thanks in advance!
 
Welcome to the forum! There are a couple of threads in the Similar Threads pane at the bottom of the screen that seem to touch on the issue. Good reading while you wait for more current answers.
 
It's All Math

Hi,
Using Ohm's law where current (amps) = voltage divided by resistance, you only need two of the values to figure out the 3rd. Once you have all three values multiply current (amps) times volts to get watts. Again if you know two of the values you can calculate the third. Calculate your original load, using the formula's figure out how much resistance is needed to equal the original load than calculate the wattage of the resistor needed.
Later,
Norm
 
Welcome to the forum!
I did some looking around and any cures past purchasing a whole aftermarket specific LP light ended up either not working or only working a short time.
I guess to really attempt to get this to work, you would have to get a few LED’s and some lab grade resistors and make up a perfect match.
OM
 
gloucesterman said:
Hi,
Using Ohm's law where current (amps) = voltage divided by resistance, you only need two of the values to figure out the 3rd. Once you have all three values multiply current (amps) times volts to get watts. Again if you know two of the values you can calculate the third. Calculate your original load, using the formula's figure out how much resistance is needed to equal the original load than calculate the wattage of the resistor needed.
Later,
Norm
Click to expand...

Thank you for your the info!
The original bulb and wire, I'm unable to locate and test for the above values.
Far as I can tell from the bulb itself from online, is 5watts-12 Volts.
Is this enough to go on?
 
Yes

Hi,
Yes, 5 watts at 12 volts using Watt's law and basic algebra will give you .42 amps draw per bulb which you can now plug into Ohm's law to get the resistance of each bulb, 5.04 ohms.
Later,
Norm
PS
Watt’s law - 5 watts = amps X 12
Algebra – amps = 5 / 12 or .42 amps per bulb
Ohm’s law .42 amp = 12/resistance
Algebra – resistance = 12 x .42 or 5.04 ohms per bulb
 
Last edited:
Correction: R=V/I so 28.8 Ohms for the resistor. Or, P=V2/R so R=V2/P 144/5=28.8 ohms
 
Close however keep in mind the resistor must be placed in Parallel. so this changes some values.
Gator
 
Omega Man said:
From the Department of Keeping it Simple-

https://www.electricalsafetyfirst.org.uk/watts-to-amps-calculator/

OM
Click to expand...

What, we can't do simple math anymore?! ;)

Now if you want to get picky, there may be a more complex impedance at play here so you would need to look at inductance and capacitance too. Then there is the fact that the voltage varies from about 12.6 to 14 as load changes on the bikes electrical system, and then of course, the phase of the moon has to be considered...
 
sharsman said:
I have 2017 R1200R

Recently installed a Puig fender eliminator kit that also has a L.E.D. license plate light replacement.
Everything works and looks great. However, the new L.E.D. light is tripping my dash warning light for bulb malfunction.

Since the L.E.D. is not canbus I believe I need a resistor to match the previous bulbs load, voltage, etc.

Does anyone have any experience and/or fixed this issue? I do not know how to determine wich resistor I need to install. Puig has been no help.

Thanks in advance!
Click to expand...

If Puig can't supply a light that works and is compatible with your bike I would send their junk back to them. We shouldn't need to buy stuff and then find work-arounds for their crap not working.
 
????

Hi,
azgman your confusing me, ohm law is I = V/R, that’s a formula, so when you move a value from one side of the equal sign to the other the function that took place on the original side is reversed, ie was multiplication, now division, was addition now subtraction???? The same with Watt's law W = I x V. So when I plug in his values to Omega Man’s link it comes up .42 amps draw per bulb. And resistance per bulb is 5.04 ohms. His resistor will be based on the difference between the stock bulb and the new LED's. Also Gator using these formula's the fact that it is being wired in parallel which is needed will not change the values??? The bike is spec'ed at 12 volts so that is what all of the electrical spec's are based on. Inductance and capacitance, yeah let's keep it simple!!!
Later,
Norm
 
gloucesterman said:
Hi,
azgman your confusing me, ohm law is I = V/R, that’s a formula, so when you move a value from one side of the equal sign to the other the function that took place on the original side is reversed, ie was multiplication, now division, was addition now subtraction???? The same with Watt's law W = I x V. So when I plug in his values to Omega Man’s link it comes up .42 amps draw per bulb. And resistance per bulb is 5.04 ohms. His resistor will be based on the difference between the stock bulb and the new LED's. Also Gator using these formula's the fact that it is being wired in parallel which is needed will not change the values??? The bike is spec'ed at 12 volts so that is what all of the electrical spec's are based on. Inductance and capacitance, yeah let's keep it simple!!!
Later,
Norm
Click to expand...

I = V/R, to find R, multiply both side by R this gives I * R = V * R / R. R/R = 1 so I * R = V. Next divide both sides by I, so I/I = 1 and gives R = V/I. To prove this, take the equation I = V/R If V=12 and R=5.04 Ohms then I = 12/5.04 = 2.38 Amps, not .42 Amps. 12/28.8 = .416 Amps
 
PGlaves said:
If Puig can't supply a light that works and is compatible with your bike I would send their junk back to them. We shouldn't need to buy stuff and then find work-arounds for their crap not working.
Click to expand...

^^^this^^^
Unless, of course, the description (not the fine print) indicated something else was needed...AND they told you what it was. I'm becoming a "find a good dealer and build a good relationship with them" kinda guy; to the point where they might even advise me on aftermarket ideas that they may not sell (in exchange for your ((my)) willingness to pay the briksandmortar premium.

ok back to the thread...
 
The warning light is tripped by the current draw in that branch not being within the computer's "spec window"; it can be either too high or too low to cause the warning light to come on.
So the first step is to determine if the replacement light is drawing more or less current than the stock setup.
If it draws less current, then a resistor in parallel would fix that; you need to know what the difference in current is - the stock vs. the Puig - to figure the resistor's value.
If the Puig lighting draws more current, put a piece of black tape over the warning bulb.
Ohms Law Pie Chart Formulas.jpg
 
gloucesterman said:
Hi,
Also Gator using these formula's the fact that it is being wired in parallel which is needed will not change the values???
Norm
Click to expand...

The value of the LED and the resistor in parallel will be different. When you have two devices in parallel the combined resistance is measured at the point where the two devices connect. Since you will now have two paths of current flow the resistance will be lower. Also, this means that it will always be lower than either device by itself.
 
Hi,
You're right. My bad. That is a per bulb value. His resistor for each bulb will be the difference between his original load and the new led load. Once he has that difference he can figure out what wattage he needs for each resistor. I would up the wattage rating on the resistor to take into consideration overall voltage fluctuation.

https://www.rapidtables.com/calc/electric/watt-volt-amp-calculator.html

5 Watts
12 Volts
.42 Amps
29 Ohms

Later,
Norm
 
So a couple of people caught what I was saying about parallel resistance. There is also the whole what does the canbus actually look for?
Lastly I have to say as usual I completely agree with Paul if the vendor sells a product that requires you to design and engineer a work around send it back. What I do know about canbus is depending on where you tie in you can effect any and everything on that part of the bus. IE if you tie in at the wrong spot you can cause all kinds of gremlins!
Gator
 
It Is Simple

Yes Gator,
But we are not talking about a parallel circuit here, and yes it is different but this is a simple series circuit. All he is trying to do is mimic the load that the computer originally saw on that circuit. I can't even imagine what might happen if you wired a resistor in parallel on a BMW!
Later,
Norm
 
You must log in or register to reply here.

Similar threads

TGA57589
R1250RT 2019 headlight problem: both low beams out at startup
2
Replies
23
Views
2K
veefore
veefore
S
Trailer wiring (yes, again) for 2022 R1250 GS/A
Replies
11
Views
607
jandhumphreyme
J
I
Installing Auxiliary Brake Light on 2023 R1250GSA - How to Run the Wires
Replies
5
Views
1K
trvlnt
T
J
Help with choosing led driving lights for my 85 r80rt
2
Replies
29
Views
3K
Omega Man
Omega Man
glenfiddich
Collision repairs
3 4 5
Replies
95
Views
6K
riderr1150gsadv
riderr1150gsadv
Back
Top