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What is this and what does it do to prevent hum/buzz/noise?

Chinese finger torture - It's for torture, obviously.
- 1 (5.3%)
Stops electrical system noise from getting into your power amp
- 4 (21.1%)
Stops electrical noise inside your amp from getting out into the electrcial system
- 2 (10.5%)
Stops Triplen Harmonic Current Buildup in 3-phase electrical systems
- 2 (10.5%)
Prevents radio signals from getting into your sound system
- 10 (52.6%)

Total Members Voted: 19

Voting closed: September 30, 2013, 01:31:36 pm


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Author Topic: Name that gadget  (Read 9999 times)

Mike Sokol

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Re: Name that gadget
« Reply #10 on: September 24, 2013, 07:44:34 pm »

Also, the triplen harmonics generated by switch mode supplies have rapid energy drop off as you go up in harmonic order/frequency. The following is a typical graph:

So even if you could get a ferrite bead that would get down into the upper end of the audible band, it's not going to do much good unless it can work down to a pretty low frequency.

You might be right about the ferrite cores not attenuating the lower harmonics enough to be beneficial to reduce Triplen currents from motor speed controllers.  I do know that we added series inductors to reduce the harmonics of thyristor light dimmers and motor controllers, and that stopped the neutral overheating. Also, before a lot of non-linear loads were introduced, it was common practice to undersize the neutral wire in a 3-phase WYE circuit because the different phase currents were normally subtractive. So a 100-amp, 3-phase circuit might only have a 60-amp sized neutral simply because 3-phase motor loads would have no neutral currents at all. Fast forward to modern times and this same warehouse can now have dimmer lighting and all sorts of non-linear loads. That undersized neutral could be carrying way more than its 60 amp current rating, and that's when the real overheating problems start. 
« Last Edit: September 24, 2013, 07:51:14 pm by Mike Sokol »
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Jonathan Johnson

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Re: Name that gadget
« Reply #11 on: September 25, 2013, 05:42:19 pm »

Also, before a lot of non-linear loads were introduced, it was common practice to undersize the neutral wire in a 3-phase WYE circuit because the different phase currents were normally subtractive. So a 100-amp, 3-phase circuit might only have a 60-amp sized neutral simply because 3-phase motor loads would have no neutral currents at all. Fast forward to modern times and this same warehouse can now have dimmer lighting and all sorts of non-linear loads. That undersized neutral could be carrying way more than its 60 amp current rating, and that's when the real overheating problems start.

Sounds like we need a new type of circuit breaker that also measures current in the neutral, and when that current exceeds a safe value, disconnects the hot/live lines related to that neutral.
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Mike Sokol

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Re: Name that gadget
« Reply #12 on: September 26, 2013, 08:32:50 am »

Sounds like we need a new type of circuit breaker that also measures current in the neutral, and when that current exceeds a safe value, disconnects the hot/live lines related to that neutral.

I worked in an 1890's theater once, and ALL the neutrals had fuses. Guess that's how it was done back in the day. Of course, we now know that's a bad idea. If you're ever working around K&T (Knob & Tube) wiring, watch out for neutral fuses.
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Jonathan Johnson

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Re: Name that gadget
« Reply #13 on: September 26, 2013, 01:45:15 pm »

I worked in an 1890's theater once, and ALL the neutrals had fuses. Guess that's how it was done back in the day. Of course, we now know that's a bad idea. If you're ever working around K&T (Knob & Tube) wiring, watch out for neutral fuses.

That's why I didn't suggest interrupting the neutral -- bad idea (unless you can guarantee than any and all feeds that use that neutral are also interrupted). I probably could have made it more clear.
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Jonathan Johnson

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Re: Name that gadget
« Reply #14 on: February 20, 2015, 05:41:07 pm »

So what is it and what does it do? There's actually two correct answers (maybe three) but one of them is its most important function (IMHO).

Not to be confused with a Ferret Bead:

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Stephen Swaffer

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Re: Name that gadget
« Reply #15 on: February 20, 2015, 06:46:37 pm »

Sounds like we need a new type of circuit breaker that also measures current in the neutral, and when that current exceeds a safe value, disconnects the hot/live lines related to that neutral.

The NEC/NFPA has taken the approach of putting the responsibility on the electrician/engineer involved.  I had a friend that failed to follow through on getting his license when the state began requiring them-he wanted to cherry pick and take the high profit lighting upgrades at a mutual customer saying it was just replacement.  The state (Iowa) allows non-electricians to do repairs-but not installs.  I posed the question to the state inspector and his response was that since the load was changing an electrician had to be involved.

Many people think wiring is simple "anyone can do it"-but things like this are brought up in required continuing ed classes for electricians for a reason.  And an electricians rate reflects the time and money invested in classes, of course, there is no guarantee that the electrician you hire will be conscientious enough to do it right-and if the job is bid without engineering specs and really needs a neutral upgrade, then the electrician that includes that will likely not be the low bid.   
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Frank Koenig

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Re: Name that gadget
« Reply #16 on: February 21, 2015, 12:16:29 pm »

Triplen harmonic frequencies are well below the RF range in 3 phase power systems, . I don't see any evidence that ferrite beads of a conventional nature are able to operate anywhere near there. And the most problematic harmonics are the lower frequency harmonics closest to the fundamental.

I agree. A quick look at the Digi-Key catalog shows their ferrite beads' impedance rated at 25 and 100 MHz, well above power line harmonic frequencies.

As a circuit element a ferrite bead on a wire behaves more-or-less as a frequency dependent resistor with the resistance increasing with frequency. The resistance at operating frequency is in the range of a few hundred Ohms. The beauty is that as the series element in an EMI filter their lossy (low Q) nature avoids sharp resonances over a large range of external variables making for a robust filter. Unlike an ideal inductor, power is dissipated in the ferrite. Pump enough RF into one and you should be able to blow it up, or at least cook it, although I've never seen this done.

If your filter design needs higher series impedance or has to operate at lower (power line) frequency, use a coil, along with all its fiddly trade-offs.

--Frank 
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Mike Sokol

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Re: Name that gadget
« Reply #17 on: February 21, 2015, 05:20:52 pm »

If your filter design needs higher series impedance or has to operate at lower (power line) frequency, use a coil, along with all its fiddly trade-offs.

I've used these Neutrik EMC connectors with an integral ferrite bead and RF capacitors to knock out AM radio stations. See the full specs at http://www.neutrik.com/en/xlr/emc-series/nc3mxx-emc
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Tim McCulloch

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Re: Name that gadget
« Reply #18 on: February 21, 2015, 07:12:30 pm »

I've used these Neutrik EMC connectors with an integral ferrite bead and RF capacitors to knock out AM radio stations. See the full specs at http://www.neutrik.com/en/xlr/emc-series/nc3mxx-emc

Yes.  The Mackie VLZ radio station removal XLR.

We serviced a house of worship that replaced their old Peavey 700 series with a new Mackie.  You had your choice of sports talk, country/western or oldies rock depending on which of the affected channels you raised.  New wire had been pulled, the workmanship was good, but the Mackie was happy to demodulate the AM.  Ferrite beads were applied and chicken bones were cast.  The AM was rebuked.
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Mike Sokol

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Re: Name that gadget
« Reply #19 on: February 21, 2015, 07:49:38 pm »

Yes.  The Mackie VLZ radio station removal XLR.

Yup, sort of like your own crystal radio set. Remember those?
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Re: Name that gadget
« Reply #19 on: February 21, 2015, 07:49:38 pm »


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