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Old 28th January 2014, 07:59 PM   #47561
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Quote:
Originally Posted by jcx View Post
again - EM in nonmagnetic metallic conductors is extremely Linear - Skin/Proximitty/Eddy Current loss is Linear - just not "simple" integer coefficient in s
Actually, it is related to current slew rate. All the big switchmode guys work out some extrapolated dissipation formula's, but they do not care about distortion, just dissipation.


Edit: to be even clearer, it is related to the absolute value of the current slew rate.
jn

Last edited by jneutron; 28th January 2014 at 08:06 PM.
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Old 28th January 2014, 08:05 PM   #47562
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George, the discussed paper shows pickup of 13 kHz frequency. Either very poor amplifier (demodulation) or poor instrumentation. Names do not count.
My guess is consistent with both you and George. They did not control loops, and they picked up neutral currents from something that was pulling a 13 KHz current from the neutral conductor in the building.

Variable frequency motor drives can certainly do that. We use them for water pumps, we use them for HCAV fan drives. In both cases, we are trying for about a 1 degree C control, and a bang bang control cannot support that.

George, as I said, that table is an ampacity chart. When the wire resistance of a 12 gauge has doubled, it's still only 3.4 milliohms per foot. Bad for a run of #12 romex, of no concern in an 8 ohm speaker circuit.



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Old 28th January 2014, 08:06 PM   #47563
jcx is offline jcx  United States
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1st order the loss should be Linear - when you get heating coupling thru tempco to give time varying R then you can have some harmonic distortion production

I assume all practical XO inductors are order(s) of magnitude more massive than voicecoils so their dT and dR are much smaller


any refs to this |dI/dt| effect would be good

Last edited by jcx; 28th January 2014 at 08:13 PM.
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Old 28th January 2014, 08:11 PM   #47564
a.wayne is offline a.wayne  United States
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Originally Posted by jneutron View Post
From the looks of it, that wafer thin pc board has lots of copper on the back. The coils flat to the board will have lower inductance and will go resistively non linear at close to half or a third of the intended crossover frequency.

Sheesh, don't they read Maxwell, or even lenz?

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Old 28th January 2014, 08:16 PM   #47565
PMA is offline PMA  Europe
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Old 28th January 2014, 08:17 PM   #47566
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Originally Posted by jcx View Post
any refs to this |dI/dt| effect would be good
It's actually quite simple. The eddies are related to the rate of change of the field. That occurs during the current zero crossing, in both the positive and negative directions of a sine. The dissipation is proportional to the absolute value of the cosine.. It can never go negative.

It's obvious by simple inspection.

edit: be careful, I'm not talking about integrated loss, I'm talking about time dependent loss.

I'm working on a test solenoid as we type..The ITER fusion guys have a similar problem, but their solenoid is 30 feet tall and about 24 feet wide.

My solenoid is about 2 inch ID, using what appears to be #10awg magnet wire. And, room temp.

jn

Last edited by jneutron; 28th January 2014 at 08:22 PM.
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Old 28th January 2014, 09:30 PM   #47567
gpapag is online now gpapag  Greece
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Originally Posted by PMA View Post
George, the discussed paper shows pickup of 13 kHz frequency. Either very poor amplifier (demodulation) or poor instrumentation. Names do not count.
Now that you mention freq.
One more bell ringing that should have attracted their attention: The ‘mysterious’ frequencies are not the same in all screenshots
In Fig.6.10.d ~ 45kHz
In Fig.6.10.f ~ 13kHz
In Fig.6.11.a and Fig. 6.15.a ~ 28kHz
I can not read the freq scale of the FFTs

Pavel, have you noticed with older DSOs aliasing effects, showing on the screen signals of much lower frequency (and unstable amplitude) than the real input?

VFDs as jn suggests maybe the offender. And they can spit-out noise much higher in freq than that (MHz)

Quote:
poor amplifier (demodulation)
You mean the driving amplifier?
Demodulating the HF signal picked-up at the input or through the feedback network from the output?

George
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Old 29th January 2014, 04:27 AM   #47568
RNMarsh is offline RNMarsh  United States
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I suggested once that a speaker designer (drivers and systems) use the German made ceramic/ferrite white color cores for winding the speaker XO coils on them. Because they were very linear over a wide freq range and could take very high power levels (currents) and stay linear. he tried them and told me they cost less than the air cores he used and had lowered the distortion measurably from his speakers.

I never see them used... wonder why? Building and maintaining Q vs freq is important to proper XO operation.

[no I dont remember the mfr name]

Thx-RNMarsh

Last edited by RNMarsh; 29th January 2014 at 04:33 AM.
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Old 29th January 2014, 04:41 AM   #47569
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Really easy to skip all the crappy coils and go active.
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Old 29th January 2014, 04:51 AM   #47570
RNMarsh is offline RNMarsh  United States
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yes it is. Very tempting. But the ceramic/ferrite core is excellent and that is why I wonder why they are not universally used - at least in high-end.

The Q of the inductor holds up much better than air core or even laminated iron. Just do a Q vs freq test and if it isnt near 90 degrees at and near the XO freq the over-all response will not be what you predict it to be. From test experience, they rarely are at 90 degrees (pure L) even at the 1kHz they are spec'ed at. And, if you use them at any other freq than 1KHz the phase angle is very different.. even in air core coils. You actually have to test them for Q and L at the freq they are to be used.

Thx-RNMarsh
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