Re: IGBT long life at 3X rated Ip?? Re: 15kva 14.4 kV Transformer.. (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

Moderated and approved by: Gerry Reynolds <greynolds@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Sun, 24 Dec 2006 17:12:20 EST
From: FIFTYGUY@xxxxxxx
To: tesla@xxxxxxxxxx
Subject: Re: IGBT long life at 3X rated Ip??  Re: 15kva 14.4 kV  Transformer..
    (fwd)

 
In a message dated 12/24/06 12:14:40 P.M. Eastern Standard Time,  
tesla@xxxxxxxxxx writes:
 
>Automation Direct has a large selection of PLC controllers --- some under  

>$200.   These work great for control  applications.


 
    Not to rain on D.C.'s post, but I work with a  variety of PLC's every day 
as my job - very common in industrial  machinery.
 
    The Automation Direct PLC's are made by Koyo. In my  experience with 
their modular PLC's:
 
    1) Power supplies fail. Some sort of bad solder  joint problems. But I've 
had problems with *all five* of the ones I've ever  dealt with, and they were 
of different ratings. They might last a few  years, but eventually they will 
die. And as they mate into the PLC modular  rack, they are proprietary. 
 
    2) Software/capabilities are a bit weak compared to  the other industry 
standard PLC's. Timer values are limited, inputs/outputs  assignment are 
limited and somewhat idiosyncratic. Just makes things more of a  pain to casually 
play with them.
 
    3) I've had one of their "com interface" modules  die (the thing that 
allows connection between the programming PC and the  PLC).
 
    4) Tech support is iffy quality.
 
    You get what you pay for. While I'm sure  Automation Direct must have 
some decent deals, I never found them to  be worth the gamble for any components 
I was willing to install in machinery I  was tasked with building/maintaining. 
    FWIW, I'd go with either a Siemens or Allen-Bradley  micro PLC. Siemens 
has micros that are incredibly compact and powerful, and they  love to *give* 
you all the support and software you need. Allen-Bradley has the  better 
programming software, but they are very "snooty" about tech support  unless you've 
*bought* a support package.
    Just be careful about running too much current  (especially with 
inductive loads) through the PLC's outputs -even relay  outputs. I've had Siemens 
micros "bounce back" after their contacts "stuck" from  too much current, but best 
to include a separate glass fuse for each and every  output. Saves 
programming time spent on re-assigning an output to a  spare...
    Also hard to find a Siemens micro PLC with  120VAC inputs. A-B still 
makes those, tho. Most micros, except the very cheapest  models, have the 
capability for expansion modules if you find you run out of I/O  for some reason.
 
-Phil LaBudde