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OLi

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Reply with quote  #1 
So I play with the new system and get no work done and suddenly I look at the DC motor Yankee drive bearings and it got almost no 300Hz compared to the press drives where one have a normal level and the other maybe a little to much, but near nothing? Have you heard of the sparkys inventing something new gadgetry so the 300Hz is no more? It would for sure be possible technically but cheaper than a rectifier? It is a old machine but things get replaced when they break so you never know. If not is the rectifier whacked totally then? Normally I would guess there would be something else, 50Hz, 100Hz but at a first look, not so much. Yes the motor is still a DC motor and we had problems with the drive. Do they feed it with AC? What would that look like?
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electricpete

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Reply with quote  #2 
Quote:
Have you heard of the sparkys inventing something new gadgetry so the 300Hz is no more?

If you have no 6*LF vibration in the dc machine than you probably have no 6*LF ripple on the dc voltage. 
You can reduce the 6*LF ripple in the voltage output of a three phase full bridge rectifier by adding a low-pass filter to the output of the rectifier. It may be a large capacitor in parallel, and possibly an inductor in series.   Also they may use feed to rectifier output to a DC-to-regulated-DC unit that uses something fancy like PWM.  I wouldn't consider lack of 6*LF on a dc machine to indicate a problem (although I understand it is logical to question a change). 

Danny Harvey

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Reply with quote  #3 
I would wonder about it too but do we really need to worry about vibrations that are not there in addition to the ones that are?[wink]  Does it work?

I'm not really on top of the variable speed drive technology but I don't know of any innovations in DC drives. They are mostly full-wave rectified and on a 50 hz supply will generate 300 hz. Half wave rectified makes 1/2 of that.  Most development has been in AC VFD's.


OLi

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Reply with quote  #4 
Most peaks are 200 and 400 Hz in that range, it can't be good, it can't be normal to feed it with a triangle wave or what it would be. I doubt that they put in a capacitor battery for fun they used to be expensive, we did that at another site where motors had a resonance at 300Hz and they rented it to start.


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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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OLi

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Reply with quote  #5 
Well rectifier fuses blew 05.46 yesterday morning on one of the DC drives for a press drive and it would not restart. Machine is now running much better with the press as a undriven slave. I will try to extract some very squiggly lines that someone may recognize somewhere else. I sent the warning email 2 hours to late as I don't look at data every minute but it was a interesting case where I emailed and warned for drive problems likely rectifier and the answer was, yeah it just blew up...... Not always just in time. You always learn.
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Danny Harvey

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Reply with quote  #6 
I wouldn't be too hard on yourself for not immediately reporting what was not there.  Reporting on things when all you have is the absence of something and an hunch is a big risk to your credibility but this case does show how keen your instincts really are. I haven't looked but I don't think that call is on the wall chart.
OLi

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Reply with quote  #7 
Well, looking for 300Hz or 6xLF on DC motors is something I eventually always do and that is on the chart but the other way around may not be in charts and maybe it should but it is really rare so maybe not. We have worked on this site for 25+years so they allow a slip up now and then, every 5 years or so..... So if I had the system running more than a few days so I got some more to look at i would have screamed earlier but it may not made that much difference any way. We collected data using at least 3-4 brands of collectors etc. so they are used to having funny things around their machines. We normally collect data 3-4 times per year and that is stretching it during the time I remember I got 1 fan bearing fail just before the next measurement and one one off measurement that showed nothing due to no balls left in the bearing.... So getting data every 2 hours is a strange luxury and hey what variations, no wonder why the route data trend goes like a roller-coaster.
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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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