🚀 go-pugleaf

masterov@chiller.ecn.purdue.edu (Michael Masterov) on Dec 15 12:10 1992 posted:
|
|
|For anyone out there - I need help.  I am currently running a volta arc
|from a welding power supply which is supposedly current regulated.  To
|measure the current I am using a scope and a shunt (the supply is not
|filtered so there is a waveform to observe ) with a shunt resistance
|of 5 milliohms.  Specified current is 20 Amps.  The waveform I am
|getting is non-sinusoidal and has an rms value around 300 milliVolts.
|
|Note - I am not an EE.  I am lost.  Anyone out there with a clue?
 
 
	I would suggest using a larger shunt, perhaps 4x (?) the
present. Then use the following ckt.
 
          shunt
---------/\/\/\/\/\---------
        |          |
        |          |
        |          |
  |------------------------|
  |     ~          ~       |
  |   (BRIDGE RECT.)       |
  |                        |   Br1
  |     +          -       |
  |________________________|
        |          |
        |          |
        |    C1    |
        |----||----|
        |          |
        |          |
        to scope
 
	C1 5uF might be good...experiment to get a good smooth DC waveform
        If there is a polarity on the cap MAKE SURE IT IS CORRECT!
        electrolytics are polarized, if you get it backwards it might explode
	also observe the MAX voltage indicated on the cap and make sure it
	can handle about 2x the voltage coming out of the bridge
 
        shunt: 4x might do the trick. Try to get approx. 5-10v across the
        shunt. Keep in mind too, the diodes in a bridge rect. have a .6-.7v
	drop accorss them while conducting
 
	The Bridge rect. will convert the ac/dcsp/dcrp to what you KNOW
	is DC. Then the Cap. will smoothen the DC. 
 
	Also, if you run DCRP or DCSP it wil keep the polarity 
	consistent at the scope end.
 
 
	This is off the top of my head and you did not say if this was a 
TIG,MIG or SMAW welder.
 
 
	Lincoln Electric or Arco might have some Ideas. They make many of
the welders out there.
 
-- 
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  also known as   | your face, it reveals what the rest of us see. It conceals
   WHITE  ROOK    | what you'd like you to be."--Blue Oyster Cult
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