How to Remove Radio Interference Using Ferrite Coils for HID and LED Headlights

Many people nowadays are installing aftermarket HID and/or LED conversion kits in their headlights and fog lights. These new conversion kits use an external power booster, called a Ballast for HID setups and a Driver for LED setups. Both of these external power supplies do similar functions, but technically they are quite different. Also, both of these products create RFI (Radio Frequency Interference); in fact every electronic device ever made creates RFI, but there are different types of this electrical interference. Sometimes when installing an LED conversion kit or an HID conversion kit in your vehicle the result can be better, brighter light, but also a side effect of AM or FM radio interference. This is characterized by where you once were able to pick up a radio station, with the new lights installed and turned on, now that same radio station is just white noise.

Here is an example of a DIY ferrite coil that can be used in lighting installs.
Here is an example of a DIY ferrite coil that can be used in lighting installs.

The solution for your problem might be what is called a ferrite coil, also known as a ferrite bead, a ferrite choke, or an RFI choke. All of these names mean the same thing. Ferrite beads prevent interference in two directions: from a device or to a device. A conductive cable such as the input power for the HID or LED headlight bulbs acts as an antenna – if the device produces radio frequency energy, this can be transmitted through the cable, which acts as an unintentional radiator. In this case the bead may be required to reduce RFI. Conversely, if there are other sources of RFI, such as an ignition module or battery charging alternator, the bead prevents the cable from acting as an antenna and receiving interference from these other devices.

Ferrite coils are already used in everyday household uses. You can find them on USB cables, power cords for your television or home stereo, and even on input power cables on your automotive satellite radio:

Ferrite coils are commonly used in household electronics to reduce interference signals.
Ferrite coils are commonly used in household electronics to reduce interference signals.

LED Conversion Kits Small Ferrite Coil:

For an LED Headlight conversion kit you can use a large ferrite coil and wind the input power wires around it, or you can use a small ferrite coil, and just clamp it over the power cable:

LED Conversion Kits Large Ferrite Coil:

 

HID Conversion Kits Small Ferrite Coil:

For the HID conversion kits you can put a smaller ferrite choke around the power input cable of the ballast like this:

HID Conversion Kits Large Ferrite Coil:

For the HID conversion kits you can put a larger ferrite choke around the power input cable where the small wires are exposed. This allows you to wrap the wiring around the choke for a better result. This is how to install the larger ferrite coil:

Sources for Ferrite coils:
Large style designed for looping wires around coil: RND-6 ( Wurtz number 7427151 ) snap on chokes
The inside hole size is 0.57″ (over 1/2″, 14.5 mm)

Small style designed snap onto power input cable: RCT2 RFI Radio Frequency Interference Ferrite Chokes – Black
measures approximately 1.25 x .75 x 75 inches

10 thoughts on “How to Remove Radio Interference Using Ferrite Coils for HID and LED Headlights

      1. I have installed a lot of ferrite chokes on my system and they do not work. Although I can stand outside of my jeep, place my left hand on the seat and put my right hand over the face of the radio and the interference goes away. Very frustrating…..

      2. Hi Greg, that means you have radiating interference, not inline interference. In order to solve radiating interference you either need to use a different product that doesn’t have this issue, or physically isolate the product from the rest of the vehicle by creating a ground field. One example is to wrap the HID ballast or LED bulb driver (whatever you’re using) with tin foil or wire mesh “fabric”. If this makes the problem lessen or go away, then you’ve confirmed the type of EMI you’re dealing with and you can come up with some other more permanent fixes.

        Ferrite coils only work on situations where the interference is inline, or called line EMI.

  1. I installed new LED Fog lights and strangely my radio was not working very well. This post was excellent in identifying the issue and providing a remedy for it. Thank you very much.

  2. I have since installed many ferrite chokes on the wires behind my led headlights. they still interfere with my radio reception. what next?

    1. James, if the ferrite chokes do not work then your interference is not “radiant” interference, not in-line interference. This means that you would need to shield the entire device as good as possible away from the vehicle electrical system, not just filter out the line. There are several methods for this, most include wrapping something around the product like tin foil, or building some sort of a wire mesh cage. Sounds silly, but basically you want to create a small scale version of a Faraday Cage. If you aren’t familiar with the term, just google it. There is a ton of info out there about it for other applications.

  3. HI.
    I having this issues.
    Ferrite cores, dont work and my led work ligth is full aluminium cage, and also i put a aluminium foil, but nothing.
    Any ideas?? Big thanks

    1. Hi Rodrigo, I think it all depends on the brand you’re using. We’ve never run into a problem that cannot be solved with GTR Lighting LED headlight bulbs… perhaps the ones you’re using are not possible to fix?

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