Re: Using SCR's For Regulating Input Current (fwd)

["High Voltage list" <hvlist@xxxxxxxxxx>]

Original poster: <sroys@xxxxxxxxxxxxxxxxx>



---------- Forwarded message ----------
Date: Fri, 4 Feb 2005 06:01:03 -0500
From: Bob Paddock <bpaddock@xxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Using SCR's For Regulating Input Current (fwd)

On Thursday 03 February 2005 05:28 pm, you wrote:

> Would someone please explain how the brick-like high current 'power
> module' blocks containing 2 SCR's are used to regulate current?  We are
> interested in pursuing this as an alternative to heavy/bulky variable
> inductors.

> We have been given to understand that such a module may be placed in 1
> leg of the AC input line (along with a potentiometer and such) to
> regulate the input current as a sort of pulse width modulator. 

Go to http://www.unusualresearch.com/ , then under the Application Note 
section look up "A couple of sections from the GE SCR Manual, mostly the 
section on Phase Control."

The "GE SCR manual" is the bible for this kind of work.   Very rare book
to come by these days.

> We would appreciate a brief description of such a control circuit or a
> link to the explanation and/or a schematic.

In a nut shell the time that the SCR is turned on lets more or less of the AC 
line current to pass.  Simple in concept, but at the current/voltages levels
you mention it is very easy to make an expensive fuse tester, that eats
SCRs.  Turning the SCR on at the wrong time can short the AC line.

For high power systems there are usually three, six, or eight SCRs
on a three phase line.  Depends on what you are trying to accomplish.

IGBT's maybe a reasonable alternative to SCR's in some cases.

-- 
                          http://www.softwaresafety.net/
 http://www.unusualresearch.com/ http://www.bpaddock.com/