Non squeal VFD

Martin Eastburn fired this volley in news:myfRt.40876$ snipped-for-privacy@en-nntp-16.dc.easynews.com:

They weren't 'coated' to begin with... they were vacuum-varnished.

Knowlegeable and judicial 'wedging' is the way the noises are settled in a real motor shop/lab. Occasionally, you'll see an entire frame go back into the vacuum pot.

Lloyd

Reply to
Lloyd E. Sponenburgh
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15,734.34 Hz for color, 15,750 Hz for B&W. The reason for the difference is to eliminate a color beat, but allow existing TVs to see color broadcasts.
Reply to
Michael A. Terrell

"Michael A. Terrell" fired this volley in news:zZednQl02IFkq4vPnZ2dnUVZ snipped-for-privacy@earthlink.com:

yep, flipped a couple of digits.

And... it was back in the BW days, when I was young enough to hear that frequency.

We didn't have color TV until about three years after I got married! (don't say it... no, I didn't know Marconi, except by reputation!) Lloyd

Reply to
Lloyd E. Sponenburgh

"Michael A. Terrell" on Thu, 22 Aug 2013

12:06:15 -0400 typed >> "Bob La Londe" fired:

Some people are more "perceptive" than others. The effect of fluorescent light bulbs for some folks is not "illumination" but "disco strobe light" - which makes concentrating in school or at work "difficult".

Tangent question - AM radio reception in a pickup truck. ('98 Mazda, EFI, manual 244000 miles)

I leave 'near' Everett WA, twenty miles as the seagull flies from Paine Field (a bit farther if the seagull is driving and stuck in traffic.) I cannot believe that I live so far out in the boonies, that I can't pick up local radio stations. (At night - the two strongest stations are in Calgary and Vancouver BC. Kind of tough to figure the local weather from their reports - in Celsius, no less. But I digress.) Regardless, and I realize diagnosing electrical troubles by mail is right up there with getting financial advice on the radio and other forms of occult prognostication, I have noticed a couple things. I get over the ridge - and past the high-tension power lines - and I can generally get the Seattle Stations. But sometimes, especially when I tune to ~550 AM, I get a "sound" - sort of like a marlin Brando clearing his throat on sideband. a sort of 'pop' - gargle, 'pop' - gargle, 'pop' - gargle,'pop' - gargle', pop' - gargle. It isn't (as far as I can tell) related to engine speed - in fact I can shut off the engine, energize the circuit and the radio is clear, then pop the clutch, resume engine running - and no pop-gargle. Also, on occasion I have "joggled" the key - returning it back to the proper detent for "engine is running", not part way to "engage starter solenoid!" - it has cleared up. For a while.

Now with that collection of wonderfully accurate set of technical descriptions, no doubt you can channel the mighty psychic powers of the Late Great Carnac and know exactly what is the source of my woes. (Aside from the County PUD.) And what the solution is, aside from "Plug the ipod in and listen to that instead."

thanks in advance.

pyotr

-- pyotr filipivich "With Age comes Wisdom. Although more often, Age travels alone."

Reply to
pyotr filipivich

Try removing your instrument fuse - see if it goes away. Don't know what kind of instrument regulator they are using theses days, byt they used to use a thermal unit that could (and often did) make terrible noise on AM radio. I replaced quite a few with solid state regulators over the years. (no, the dash instruments do NOT work on 12 volts) If the BZZ POP BZZ POP goes away with the instrument (not instrument lighting) fuse pulled, you know where to look.

Reply to
clare

[ ... ]

Well ... the usual figure given is 20 Hz to 20 KHz.

I have had poor high-frequency hearing at least since it was discovered in high school. In particular, things pretty much drop off about 2.6 KHz -- though I remember playing with headphones and a signal generator and discovering that I could hear a little just above 20 KHz, though I don't know whether the system was generating sub-harmonics.

I did a lot of things at a kid which could have damaged my hearing.

But I also remember, shortly after the high-frequency loss was discovered, sitting in my room with a pair of Koss Pro-4A headphones (pretty good sealing around the ear), and with a frequency sweep test record (LP for those who remember older technology). As the frequency was increasing, I was turning up the gain to try to keep hearing it. A friend, sitting about 10 feet away, screamed "How can you stand it!" about the time I was losing it totally.

While I am a man, I don't think that I am in the "high frequency range" in any sense -- but my hearing in the high frequency range was lost quite early, as I mentioned above. :-)

The makers know the range of the clock frequencies. Whether they will be *audible* depends on whatever they are driving, because there is nothing in the VFD itself capable of acting as a transducer from electrical signals to audio signals.

The *motor*, however, can quite easily do this, depending on how well it is made. The stator is made of a stack of laminations of a thin metal selected for its magnetic properties, which forms a number of poles around which is wound many turns of enameled wire. As the current increases, it generates a magnetic field. If there is a gap between any two of the laminations, it will attract the two pieces together closing the gap, and making a "tick" as they touch. When the current (and field) decrease (this is AC after all), they separate again, and are set for the next cycle. A really loose lamination could cause a buzz at normal line frequency. That does not carry very far. But if the VFD is running at a mid audio frequency -- say 400 Hz up to 12,000 Hz, you will get a quite audible sound.

And it is possible that the free length of the lamination might be just right to resonate at or near the frequency of the VFD -- which is why shifting the frequency can make a big difference.

The wires can move too -- but usually the proportion of current required and the short lengths and heavy gauge of the wire means that they will not move enough to generate significant sound in the typical motor.

Power transformers (once commonly used in electronic equipment) have the same construction as the motor stators, but typically a wooden wedge used to be driven in between the coil and the center pole of the laminations, thus minimizing the freedom to vibrate. (Really good ones in the early days were put in a metal can and the can was then filled with melted tar, so no chance of lamination vibration there. But later and cheaper ones have produced enough noise at 60 Hz so I could hear them.

*Most* motors are well enough made (stator dipped in a coating which hardens, both to hold the windings in place, and to keep the laminations together).

And a bit more information added, showing how a motor can generate sound -- and why it is more audible with a VFD than with the power company's 60 Hz (or 50 Hz in the UK).

Enjoy, DoN.

Reply to
DoN. Nichols

snipped-for-privacy@snyder.on.ca on Thu, 22 Aug 2013 16:21:00 -0400 typed in rec.crafts.metalworking the following:

Thanks, an option to follow up on.

-- pyotr filipivich "With Age comes Wisdom. Although more often, Age travels alone."

Reply to
pyotr filipivich

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