Re: 180 BPS synch? (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Sat, 14 Jul 2007 16:25:37 EDT
From: FIFTYGUY@xxxxxxx
To: tesla@xxxxxxxxxx
Subject: Re: 180 BPS synch? (fwd)

 
 
In a message dated 7/14/07 9:05:52 A.M. Eastern Daylight Time,  
tesla@xxxxxxxxxx writes:

>The VFD itself is wired up to accept a 0 to 10mA signal that  controls 

>the speed from 0 to 500 Hz.
 
    Shouldn't that be 4-20mA? One of the advantages  of a 4-20mA current loop 
signal is to avoid the noise of zero mA meaning  "zero signal". Hence the 
minimum 4 mA...
 
>I use an Altivar 31 VFD by Telemecanique. Telemecanique was once  known 

>as "not the greatest of VFDs". That has changed in the past 4  years. The 

>company actually was revamped. Nowadays, their drives are probably  the 

>easiest to use and are now very reliable. Especially the Altivar 31  

>series (versus the old Altivar 28 which was pure Telemecanique of  old).



Now that I've finished laughing so hard that I  had to pick myself up the 
floor, I find myself wondering if you're actually  *serious*! 
    I finished replacing the fourth ATV 31 drive  (from 2kW to 15kW) in a 
brand new installation. Four drives in less than a  year of operation? I 
cannibalized all of them. Most failed due to the "brick"  having bad connections. They 
went to a design that clamps down, so  the brick leads spring against pads on 
the circuit board, instead of  bolting or soldering to connections to it. One 
had a blown input rectifier,  which when replaced allowed control and display 
power but the output was still  dead as a doornail (even though the display 
told me it was running  OK).
    "Easiest to use"? Are you kidding??? Where do I  start... no local keypad 
jog function, no local/remote key on keypad, no  easy-to-replace keypad 
(without disassembling the drive), no parameter storage  in keypad, no built-in 
line or load reactors, no provision for external  powering/switching of cooling 
fan, no built-in macros for common user  applications, a *very* primitive LED 
display (three letter codes derived from  7-segment LED's, and the codes are in 
French/IEC abbreviations), no standard  provision for encoder interface, 
included hard copy manual is minimal.
    IMHO the only thing I like about Telemecanique  is their cable safety 
switches (which they pioneered). If it's Tele, you name  it, I've worked with it. 
I tried to get an Alitvar 41 (IIRC) which was a very  cost-effective drive. I 
needed a 20kW for a fan application, and they  don't make 31's bigger than 
15kW. We got a great price break from our vendor  on Tele crap, and I wanted to 
keep things standardized. But apparently  although they list that product on 
the Tele website, they only offer it in  Europe.
 

>when it comes to motor control, 3-phase is industry standard  and VFD's are 
>their industry standard control module.
 
    Depends very much on the industry! I've seen two  brand-new printing 
presses built and installed at two different local  factories in the last two 
years that both had 40+ HP *DC* motors as the main  drive! I've worked on all 
brands and vintages of those things, and can say  with no reservation that a DC 
motor is a complete waste (and liability!) for  that application. But it seems 
that's all the "old" engineers will trust.  Shame, I've seen tiny AC motors run 
big presses, and spec'ed and installed a  big 60 HP AC motor and C-H SV9000 
drive on an old press. Both run  flawlessly...
    Some places still use a lot of single phase  motors for smaller loads and 
machine automation. Steppers are popular for  slow-speed positioners. On that 
note, I've seen plenty of brand-new DC servos  on new equipment. 
 
> In motor control, Allen Bradley is still top of line for  VFD's.
 
    Are you trying to kill me with laughter, Bart?  :)
    Their new Powerflex line is interesting, but you  can keep your 1305's 
and 1336's. Too many problems with those in too many  applications to list here.
    OTOH, A-B is the "Dark Side" of Rockwell  Automation. Reliance has always 
made very tough stuff. I've seen old Reliance  drives, of all types, 
soldiering on long after they've become obsolete. They  still seem to make a very 
tough AC drive with a good reputation. I wish I've  had more than a passing chance 
to work with modern Reliance AC drives, so I  could confirm my good 
impression.
 
> But the others now are right there with them in capability. The  main 
difference is that industries are >tied into a particular breed by the  code they 
write. It would be an expensive task 

>to change over to something else. So, they stick with what they are  

>familiar with. I do the same. I understand that situation  completely.



    True, and nothing can make or break you like  being tied to a particular 
brand by nothing more than a salesperson or  engineer's inconsiderate 
preference (usually a kickback).   
 
  IMHO the Cutler-Hammer SV(X)9000 drives have given me the best  luck over 
the long run, although the manual is a bit difficult in places.  Sumitomo 
drives were built like a battleship. ABB makes a very nice and  affordable AC 
drive, but their DC drives are a nightmare. Baldor drives are very  user-friendly, 
but always seem to have issues with control power supplies.  Eurotherm drives 
are *way* over-engineered for programming options (difficult to  commission), 
and not robust enough. Hitachi and Mitsubishi AC drives are about  the 
cheapest I've found, and seem to do fine. 
 
-Phil LaBudde
Center for the Advanced Study of Ballistic  Improbabilities



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