Power controlers... on another note. - relays

Jim Lux James.P.Lux at jpl.nasa.gov
Tue Jun 4 10:16:23 PDT 2002

At 11:40 AM 6/4/2002 -0400, Alvin Starr wrote:
>alvin at Maggie.Linux-Consulting.com wrote:
>>hi ya
>>relays are bad .... very bad ....
>>         - all kinds of mechanical failures
>>         - all kinds of inductive currents
>>use an SCR instead .... and it can be turned on and off with
>>a simple +5v circuit on the gate and turned off with a negative
>>pulse ...
>>         -- same thing as a relay only 10x better ??
>>c ya
>>>all you need is a 5A 110V DC-control relay.  the way this works is 
>>>essentially wire the relay + outlet like so:
>>>it's quite straightforward.
>Has anybody played with the X10 controller stuff. I have been thinking
>of that for our computer room but I am not sure if we would have problems.
>The hardware is cheap and readly available and can be easly computer 
>controlled. The prduct line is intended for home use and is not your usual 
>industrial quailty. There is also an upper limit of 255 devices and some 
>possible issues with external interferance.

The "wire your own" using solid state relays or SCRs has the disadvantage 
in many environments of not being certified to meet various and sundry 
safety requirements (UL, CSA, etc.).  It works just fine, but, if bad 
things should happen, and they start on a "blame hunt", the maker of that 
homemade power controller is going to have a big red target painted on them.

There are numerous commercial vendors of power controller components 
catering to the industrial market (e.g. Allen-Bradley, Square-D, etc.) and 
a bit of time spent with the appropriate catalogs might be well 
spent.  There are a number of industrial controls companies selling 
Ethernet and/or RS232 controlled devices for installation in appropriate 
enclosures, etc.  Look at the color pages in the Newark catalog.

Really, things like grounding, fault protection, overcurrent protection, 
and electrical codes are important.

As far as X10 goes, there are "commercial" quality components available 
from Leviton.  Lots of discussion over the years on what precisely is 
different between the consumer and commercial parts (other than the factor 
of 3 price).

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