How to Remove Radio Interference Using Ferrite Coils for HID & LED Applications

Many people nowadays are installing aftermarket HID and/or LED bulb kits in their vehicles. These 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 bulb kit or an HID bulb 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.

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 bulbs acts as an antenna – if the device produces radiofrequency 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:

LED Kits Small Ferrite Coil:

For an LED 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 Kits Large Ferrite Coil:

HID 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 Kits Large Ferrite Coil:

For the HID 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:

You want to find a section of the power input harness with the 2 smaller wires exposed so they can better wrap around and through the ferrite coil to form a loop.

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