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GB: Round #2; Fo-Felix EMI Filter for AC mains 120/230v; By Folsom

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I have the latest pcb's and am placing an order at mouser. I am looking at the bourns common mode chokes. None of my equipment will draw more than 3 amps. Is there better filtering with the higher values like the like the 8112, or should i just stick with the 8120-21 and allow for a higher draw?

I am planning to use 4 in parallel after a balancing transformer with +60 -0- -60 on the secondary and I am assuming their is no required orientation of the H & N pads for both input and output?
 
Finally finish 1 of 4 rear panels using a PowerCon input connector, fuse, and three Fo-Felix EMI filters.
 

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Coilcraft vs Bourns

Nice, individual sockets.

If my load is say 10A, then I have a choice of either the Coilcraft 10A or the Bourns 20A.

Has anyone any feeling which one may perform slightly better?

Could the coilcraft with its combo common mode / differential mode in one design be somewhat better?

I know it's tough to tell. But Destroyer has alluded to much experience working with common mode chokes.

Best rgds,
Denis
 
Load capacity of cmc

I wouldn't run a load at 100%. There's problems with saturation running like that.

hmmm! Here's another thought:
Differential mode currents comprise of a large load component of mains AC (say several Amps) and a tiny component of noise at a wide frequency spectrum but at the micro volt level.

The DM current take the usual circular flow across the live side and return via the neutral side of the circuit, alternating in direction according to AC mains cycles. However, for DM currents, the windings in the CMC produce opposing flux in the core and thus mostly cancels out - thus magnetic saturation does not easily occur. Hence, it's possible to carry normal (i.e. differential mode) load current fairly close to the rated capacity of the CMC. There is no need to scale down the load factor by a large discount like 75% or even 30%. A 4x ratio of CMC current to Amplifier current is perhaps excessive.

I would think the primary current capacity of a CMC is determined mainly by wire size, heat dissipation and frequency (skin effect) rather than by the core saturation of the CMC.

Common mode currents (the major noise component, but still in the micro volts) on the other hand flow in the same direction on the live and neutral side of the circuit and thus see a combination of the inductance of both windings, which thus provide higher attenuation of CM noise.

Just a thought!
 
Ah, so that's 600wpc, not 600W total load. Much better.

BTW, I think you gave 510W for 17A, not 600W.

Reactance for these millihenry CMCs are negligible @ 60Hz. But shoots up to kohm range above 100kHz to block high freq CM and DM noise.

Which also points to a similar outcome - that power capacity at AC mains is mainly determined by wire size and power dissipation, not core saturation.

Core saturation could occur in rare situations of high inrush current, DC currents in only 1 winding due to unbalances like small differences in switching times of SMPS, or due to large high freq CM current.

For a typical power line CMC rated for say 100A max DM current, max CM current is likely around 0.1-0.2A, a ratio of 1000 or 500 to 1. Since CM noise current in AC mains is in the range <100 microvolt, saturation is unlikely for CMC rated in the Ampere range, unless one lives in a horrible environment.

Here are a couple of references:
Murata - Differential and Common Mode Noise
Schaffner - EMI Filter Design with Common Mode Chokes
 
I still recommend our numbers. We accounted for behavior of transformer, and full power with the amplifier. And disagree with your conclusion. We aim to keep your amplifier within a margin of undetectable changes in internal voltage (dynamics, or coloration as many people hear it). If there is saturation information included we use it, and our ratings reflect the average saturation rating if none where given.

You seem to be saying the CMC is rated for current in CM, but that isn't how they work. Leakage flux from the DM current causes saturation. I've demonstrated this with an amplifier before. The amp uses about 4.25A max (no peak), and a 10A COMOCO wasn't enough. It causes audible problems. As you may have noticed the COMOCOs are rated a bit lower than the Bourns. The amps draw current in pulses, which can be pretty big, and are more likely to saturate. When I say saturate it may only be for a split second, but that can be audible.
 
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A DC trap prevents DC from getting to your equipment. If you have DC on the line it can make transformers hum. Certain trashy electronic things can generate DC onto the house's power.

I know shattered dream has had an issue with humming related to the Fo-Felix in some way, but he's the only one so far out of hundreds. The reason is likely some mix of attributes, not a defective design of common mode choke. The simple answer might be to just use a larger CMC.
 
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