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Re: 180 BPS synch? (fwd)
---------- Forwarded message ----------
Date: Sat, 14 Jul 2007 16:25:37 EDT
Subject: Re: 180 BPS synch? (fwd)
In a message dated 7/14/07 9:05:52 A.M. Eastern Daylight Time,
>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
> 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.
Center for the Advanced Study of Ballistic Improbabilities
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