simulate this circuit – Schematic created using CircuitLab
I inherited the top circuit from a previous designer on my robotics team. The circuit uses two ferrite beads, a zener, a TVS and a capacitor to filter incoming power. The incoming power comes from batteries. Along with the digital circuitry the batteries have large motors connected to them making for a very noisy environment. My understanding is that with the help of the ferrite beads the zener and TVS suppress any spikes. Then the large capacitor holds up any droops. This circuit has worked well so far.
My question is whether replacing the ferrite beads with a common mode choke improve the filtering or if it's not broken don't fix it?
(I just used generic components to give the general circuit layout, the top is the current circuit and the bottom is my proposed change)
Additional info
The circuitry is going into a robot. The robot is made out of extruded aluminum (not grounded) and the whole thing is clad in clear acrylic. The whole thing is powered by a 24V 8 cell lithium iron phosphate 20Ah 10C battery. The digital circuitry draws about 1A. The motors are two wheel chair motors. The motors are rated at 60A max but they are never driven that hard, usually around 50% or less. The motors are driven by Vex Victor H bridge motor controllers.
Best Answer
Even though this questions looks like very specific, it can be treated indeed as a much more general case filtering question: "How can one filter out electrical noise coming from power electric motors?".
The first information data we need to gather in advance is the type of noise our circuit is exposed to. Sometimes it is really difficult to get this data in advance, sometimes it is even harder to measure the noise without prior experience and high-end laboratory equipment.
In general, we can assess our noise sources in terms of:
The above is a partial list, incomplete, which may serve as a starting point only.
Then, there are a lot of techniques, I mean literally hundreds of tricks and broader approaches depending on the case.
Delving into the specifics of the original question, this is my best guess on the sort of noise that may be originated by the system,
Some practical hints and techniques for dealing with the noise in the system above:
Returning to the circuit you posted, my initial approach would be:
Last but not least, devise a simple way to measure your circuit at critical points, in order to verify the effectiveness of the different approaches. Do, please, try to test under similar circumstances as the real device will operate under.
If neeeded, I can provide more references (books, articles) to the approaches aboves. If you can specify in greater detail some parts of your system, additional filtering techniques will surely apply.