miller 451 power supply running away with the amps

[drozone]

hello!
this p.s. is controlled by a 1DW-1 wire feedspeed/voltage controller. luckily the robot has 5 torches so i can swap parts. i've swapped every board, relay, and component with no success. i tested the feed rate and it changes when i change the input value.i've checked all the cables and plugs for continuity and traced lots of the wires. the timer board is going through its sequence so i know it is sensing the arc.
i figure that if someone can tell me HOW the controller knows the arc length is changed(therefore needing an amperage change)during the weld, it might help me to look more efficiently for the problem.
in this application the output should be about 225 amps at 21 volts and 500ipm. the p.s. is putting out 21 volts, but at 550 amps.
the guages were certified only a month ago and yes, i swapped the amp guage with one that was reading 200+ amps in the next station with essentially the same perameters.
further, i know the power output is controlled by the pulse width to the scr's but does this translate to voltage control, amperage control, or both? i know it's actually watt control but is one component "adjusted" more than the other? since the p.s. is "constant voltage" i would think that the amps are changed more but i could be fooling myself.
thank you in advance for any threads of wisdom that would be thrown my way,
drozone

 

[mcprofusion]

What type of robot is it ? (MotoMan, ABB, Fanuc, etc..)

I had a similar problem like this once. A control parameter might be switched, so your actually typing in AMPS required and not WFS ?...EVEN IF YOUR SREEN SAYS WFS INPUT

Your PS is CONSTANT VOLTAGE = Current adjusts to maintain a constant voltage (arc length) when you change electrical stickout (contact-tip-to work distance). When welding current will rise if you decrease you stickout, and drop when it is increased.

Marc

http://www.mcprofusion

 

[drozone]

thank you mark (allj258)
so, then, as the gap (arc length) gets larger the amperage would decrease in order to maintain the set voltage. this then means that as the arc length changes, if all other parameters stayed the same the voltage would change, getting larger as the gap gets larger in order to jump the gap?
perhaps i was misleading in my robot statement. the unit is made by a company called melton. they make custom fabrication equipment and call this thing a "5 torch, two slide welding robot" it is a rather loose use of the term robot.it was also made back in '85 so the term may have applied better then.
the input is simply the dial settings on the wire feeder/voltage control unit (this is a remote unit).
so it must be controlling the power supply by monitoring the voltage feedback loop. therefore, it is either not getting the feedback or the control signal is not getting to the power supply.
also, if the controller reduces the amperage as the voltage rises, then if it saw lower voltage it would raise the amperage. therefor if it saw an abnormally small voltage it might just run away with the amperage. perhaps then there is a continuity anomaly in the feedback loop that my meter won't see but would affect the controller.
forgive me for thinking out loud, but sometimes it helps, and if the analisis goes astray, then someone may knock it back on the track.
thank you again for your feedback. can't wait for monday to see where this leads me
drozone