What does the ring on ESC do? – The Ferrite Ring

by Oscar

Occasionally ESC signal wire is wrapped around a little doughnut ring, for example on the Hobbyking 30A ESC. So What does the ring do and is it necessary? 

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Published on 14/02/2014, last edited on 04/05/2016.

What is Ferrite Ring and What does it Do?

This mysterious ring is called ferrite ring or ferrite bead. It is used on ESC to reduce noise caused by the long signal lead. ESC signal leads can behave like an antenna and picks up all sorts of noise, the longer the worse it gets. By using a ferrite ring, it suppresses both conducted and radiated noise and interference. Don’t forget noise can also potentially come from power supply and BEC which may cause issues as well.

So how does it work? The ring is basically an inductor which adds inductance to the wire and substantially reduces the ability of the wire to act as a noise receptor within a small band of frequencies. However to make the most of it, you really need to know which band of frequencies you are trying to suppress, as the ferrite bead are designed to attenuate noise in different ranges of frequencies.

So is the Ferrite Ring Necessary? How to use it?

If your ESC doesn’t come with a Ferrite Ring, then don’t worry about it. That means the manufacturer has probably done enough testing to ensure it’s not needed.

However if your ESC comes with a ferrite ring, then you better keep it. You might get away with it not using one, but one day if you have an unexplained crash, and you probably know why.

The more wraps round the ring, the more inductance it creates. I normally see 3 to 5 wraps on the ESC if there is a ring come with it.

Place it closer to the ESC for more effective result.


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Mark D 28th September 2020 - 3:46 pm

I disagree. You need it regardless of the throttle wire length. Think about it – if the problem were primarily radiated noise, then EVERY wire would pick it up, not just the one going to the ESC. Radiated means radiated. You would need the same on every long wire attached to your receiver, regardless of its destination. The fact that these are used ONLY on the wire directly attached to your ESC is your clue that the problem is primarily conducted, not radiated, noise. Shortening the wire will not reduce conducted noise.

DW 7th July 2016 - 6:02 am

So if I cut off most of the length of the signal wire, because I don’t need that much wire to reach FC, do I still need to keep the Ferrite ring?

Jacob Carr 19th February 2019 - 11:27 pm

no you will not need it

Charles 2nd March 2014 - 10:37 pm

Good information. Lucky me I discovered your blog by chance (stumbleupon).

I’ve book-marked it for later!