Members agedhorse Posted April 21, 2012 Author Members Share Posted April 21, 2012 Don't they run a tone signal test on all speakers before they ship? How did that one get by QC. Not always, though they will certainly sample and test from each production run. IMO, it was just one of those flukes which happens sometimes in spite of the usual care excercised. Link to comment Share on other sites More sharing options...
Members Art Flood Posted April 21, 2012 Members Share Posted April 21, 2012 Anybody here old enough to ever have to polarize an automobile generator? My first job as an apprentice was to rebuild automotive generators. Part of the testing process was to 'motor' the generator by applying power to it so it would run like an electric motor. This of course effectively also polarized it. Polarizing was important because the residual magnetism was needed get the generator started. Once the generator reached the system voltage a relay would kick in effectively connecting the generator to the battery. It was common for generators that sat around for a long time to lose their residual magnetism and need polarizing before putting them into service. Link to comment Share on other sites More sharing options...
Members Dogoth Posted April 22, 2012 Members Share Posted April 22, 2012 Part of the testing process was to 'motor' the generator by applying power to it so it would run like an electric motor. I think there were several cars in days gone by that used the generator as a starter motor as well (not super efficient at either job but neither were cars in general back then :-) Link to comment Share on other sites More sharing options...
Members W. M. Hellinger Posted April 22, 2012 Members Share Posted April 22, 2012 I think there were several cars in days gone by that used the generator as a starter motor as well (not super efficient at either job but neither were cars in general back then :-) My first car was a 57 Chevy... straight 6, 3 on the tree, carburetor, point ignition, generator, and no computer. It made dead-on 20 mpg combined highway and city (town) driving. My Chevy Astro van weighs about the same as my 57 Chevy did... the Astro is fuel injected and computerized to the hilt and makes approx. 20 mpg highway (I dunno what it makes in-town). Even 40 years ago, my 57 Chevy turned more heads than my Astro van does today. Today I think it would even be less of a contest. One thing I know for sure is I'd trade working on that 57 Chevy in a heart-beat over working on my Astrovan. I'm not convinced of the "progress" made in the automotive industry over the past 60 years. Link to comment Share on other sites More sharing options...
Members sailorman Posted April 22, 2012 Members Share Posted April 22, 2012 Anybody here old enough to ever have to polarize an automobile generator? Not quite the same thing but... I have an '82 Suzuki GS1100. One day hit the starter button and the starter wouldn't turn over. Took the starter apart and one of the 4 permanent magnets had separated from the case. Since it was an EXPENSIVE starter, I removed all of the pieces of magnet (took quite awhile) and it's still working fine today. As a curious kid, I remember finding speakers with coils instead of magnets in an old TV. Couldn't make it work for some reason..:-) Link to comment Share on other sites More sharing options...
Members glepko Posted April 22, 2012 Members Share Posted April 22, 2012 worked on the floor in the DC department of an electric motor manufacturing facility for a few years, various sized motors (smallest for treadmills and paint sprayers) up to unit some four times larger/heavier. don't remember the ratings, it's been 20 years. anyway, i do remember the magnetizing process creating great noise! always intimidated me watching those meters build then plunging the 2nd button to charge. definitely vibrated the floor. the force would sometimes break the magnets, or loosen them from the frame if not glued properly. i often wonder how harmful that blast of energy was to any of us working through a pallet of shells for an entire shift. we had an occasional motor make it through assembly and onto the run-in line without being magnetized. thankfully we had a run-in time and audio inspection of each motor before shipping. Link to comment Share on other sites More sharing options...
Members agedhorse Posted April 22, 2012 Author Members Share Posted April 22, 2012 Magnet failure (physically coming apart from the case) is not uncommon. Corrosion gets in between the epoxy and the metal surfaces and breaks the bond. The forces can be really large. Link to comment Share on other sites More sharing options...
Members WynnD Posted April 23, 2012 Members Share Posted April 23, 2012 Is it possible, albeit unlikely, that something de-magnetized the driver en route. Old ferrite magnets would lose strength quickly if subjected to sharp impact. I think Andy would have gotten something if the magnet had just suffered a sharp impact. Don't think the magnet would have gone the entire way to nothing and any magnetism would have resulted in a little sound. This has to be a magnet that was never magnetized. It's my understanding that at least one of the factories where they magnetize magnets puts out so much magnetism that it shows up on aeronautical charts. Link to comment Share on other sites More sharing options...
Members agedhorse Posted April 23, 2012 Author Members Share Posted April 23, 2012 There is enough hysteresis in the mag. curve on ceramic that it would be hard to end up with zero magnetic strength by accident. Link to comment Share on other sites More sharing options...
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