LED headlights destroy FM reception

Thread Starter

Ac2OB

Joined Nov 2, 2017
11
I just installed aftermarket LED headlights in my Mazda 2. The low beams wipe out my FM reception. High beams, no problem. What's happening? Can I fix it? I assume the power module is some kind of switch mode regulator. Why would increasing the power output for the high beams reduce the noise output? Does the frequency change or is it the wave shape? Would a heavy duty torroid help? Series resistor? Shielding? Maybe this weekend I can get my Oscope on the job.
 

drc_567

Joined Dec 29, 2008
714
Is there a wire of some sort that goes between the power module and the two low beams? ... If so, the suspect wire might be acting as an antenna, causing the interference.
 

PatM

Joined Dec 31, 2010
86
I just installed aftermarket LED headlights in my Mazda 2. The low beams wipe out my FM reception. High beams, no problem. What's happening? Can I fix it? I assume the power module is some kind of switch mode regulator. Why would increasing the power output for the high beams reduce the noise output? Does the frequency change or is it the wave shape? Would a heavy duty torroid help? Series resistor? Shielding? Maybe this weekend I can get my Oscope on the job.
I would try some toroids.
 

BR-549

Joined Sep 22, 2013
4,936
I would try the cheapest, fastest and easiest solution first. Clamp on ferrite beads, on LED power module INPUT.

220px-A_collection_of_Snap-On_-_Clamp-on_ferrite_beads.jpg
 

cmartinez

Joined Jan 17, 2007
6,469
I just installed aftermarket LED headlights in my Mazda 2. The low beams wipe out my FM reception. High beams, no problem. What's happening? Can I fix it? I assume the power module is some kind of switch mode regulator. Why would increasing the power output for the high beams reduce the noise output? Does the frequency change or is it the wave shape? Would a heavy duty torroid help? Series resistor? Shielding? Maybe this weekend I can get my Oscope on the job.
Most likely, the LEDs are being PWM'd to decrease their intensity. The circuit in charge of that function is not properly filtered and it's causing severe EMI.

The solution would be adding some filtering to mitigate the effect. Either a ferrite (easy, but no guarantee) or an RC filter, which would be best, but a bit more complicated to implement.
 

BR-549

Joined Sep 22, 2013
4,936
The reason I made the suggestion was not base on probability of success. It's because of embarrassment.

It's just that I have seen many hours and money spent with lousy results.......and then someone comes along and does something simple and obvious......and bingo......problem solved. Usually for a dollar. And 2 minutes.

Very embarrassing.

Always check the simple and convenient solution first. It always paints you as a genius and you never get painted as a fool.........at least to where the client understands it.

Always try all the easiest solutions first....it reliably reduces the solution list.
 

Picbuster

Joined Dec 2, 2013
982
I just installed aftermarket LED headlights in my Mazda 2. The low beams wipe out my FM reception. High beams, no problem. What's happening? Can I fix it? I assume the power module is some kind of switch mode regulator. Why would increasing the power output for the high beams reduce the noise output? Does the frequency change or is it the wave shape? Would a heavy duty torroid help? Series resistor? Shielding? Maybe this weekend I can get my Oscope on the job.
This is an EMC problem and should be solved by producer.
Fail to apply to EMC contradict the law and punishment could follow. ( in Europe for sure)
Advice: go back to supplier.

Picbuster
 

DickCappels

Joined Aug 21, 2008
5,897
If it is possible to return these, that might be the best solution. Clearly, the lamps are not compatible with your car and your intended use.
 

Thread Starter

Ac2OB

Joined Nov 2, 2017
11
You can get clamp on ferrites if you can't cut or disconnect a lead.
I can always cut the power lead and insert filtering components but I don't want to go down that road. I have ordered clamp on ferrites that have maximum effect in the 100 Mhz frequency range. Price about $3 a piece.
 

cmartinez

Joined Jan 17, 2007
6,469
Why on the input? I work for Rockwell Automation and I noticed that when they use torroids they put them on the input of the VFD.
The ferrites are normally used on the input to prevent the electric noise generated by the circuit in question to travel back into the power source and induce further anomalies in the rest of the circuitry.
 

cmartinez

Joined Jan 17, 2007
6,469
I can always cut the power lead and insert filtering components but I don't want to go down that road. I have ordered clamp on ferrites that have maximum effect in the 100 Mhz frequency range. Price about $3 a piece.
I doubt the LEDs are being PWM'd at such a high frequency. Most likely they're being pulsed at a 20 to 40 Khz range. Those ferrites might help a little, but I doubt they'll completely solve the problem.
 

Externet

Joined Nov 29, 2005
1,411
Is it one single light emitter per headlamp ? Or there is two for high and low beams ?
Unplugging only one (left or right) erases the problem ? That could tell one has a defective driver circuitry... Have you tried a choke coil in series to the offending lamp ?

Edited- added: On a vehicle parked next to it, or other FM receiver, shows the same interference ?
 
Last edited:

BR-549

Joined Sep 22, 2013
4,936
Ac20B.......There are two probabilities. It could be one or another....or both.

Control frequency harmonic from LED controller could be transferred to FM radio by the auto power bus......OR could be emitted from LED controller leads......and picked up by FM antenna.....OR BOTH. Square waves generate multitudes of harmonics.

There are two possible routes. It might be BOTH routes....we don't know yet.

The reason I said INPUT......is because of "the cheapest, fastest and easiest solution first" procedure.

The DC side of LED controller is easier to check. To filter the OUTPUT of LED controller......requires equipment, measurement and study. The DC side of controller requires no bandwidth. Easy to filter. The output of controller has and needs bandwidth. I am assuming a PWM output. That might be wrong. I'm guessing.

If I am right about PWM......the output of controller(IF this is problem).....will need an rf filter........but not interfere with control frequencies. Hence equipment and measurement for a low pass filter. Again, square waves generate multitudes of harmonics.

A 50 kHz square wave can generate harmonics all up thru the RF band. It was used for years to calibrate radio receiving frequency dials. It might be swamping the FM radio IF.....who knows?

None of us will really know....until you solve problem. Have you got a SDR dongle and laptop? If your interference is being emitted.......the dongle should easily show it.
 
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