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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

Troubleshooting a plasma cutter



 
 
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  #1  
Old April 16th 06, 05:27 PM posted to rec.crafts.metalworking
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Default Troubleshooting a plasma cutter

Esab 550. I had cut three holes in 1/4" plate when it just stopped cutting in
mid-stream. No spark. I checked the consumables, they're all new.

I still get air when I hit the trigger. The overheat light isn't on. It still
doesn't work the next day.

I checked continuity of the power cable with an ohm meter and it has continuity,
almost zero resistance. Is there some other way to test it? Could it have
continuity at rest but fail under load?

The trigger wires obviously have continuity because the trigger still works the
solenoid valve to supply air to the torch.

It just won't cut anything.

The book suggests replacing the HF unit. How can I test the HF unit and what
kind of money are we talking about to replace it?

--
Jack
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  #2  
Old April 16th 06, 07:55 PM posted to rec.crafts.metalworking
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Default Troubleshooting a plasma cutter

I'm not familiar with the Esab 550. Some other manufacturers models
have a pressure switch which will only allow an arc if air pressure is
present. If that switch goes bad you won't be able to initiate an arc.
Easy test is to jumper the switch.

  #3  
Old April 17th 06, 12:04 AM posted to rec.crafts.metalworking
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Default Troubleshooting a plasma cutter

On 16 Apr 2006 10:55:10 -0700, "Lefty" wrote:

Easy test is to jumper the switch.


I'll try that first thing in the morning. Thanks.

--
Jack

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  #4  
Old April 17th 06, 04:26 AM posted to rec.crafts.metalworking
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Default Troubleshooting a plasma cutter

Search google for high frequency arc starter. Sorry I don't have any
links, there on my other computer that is currently down. However,
there are a couple of sites that show you how to build one. Also, look
up Tesla spark gaps, same thing same parts. HF is commonly used with
tig welding and also tesla coil people.

I only have experience with older welders and plasma cutters. This
means no solid state HF stuff. I'm no electronic expert, however I
have fixed three HF circuits (which really means I simply changed out
the capacitor). An HF circuit has basically three things: 1) step up
transformer, 2) high voltage capacitor, and 3) an air inductance coil.
The only thing that can really go wrong is that the capacitor goes bad.
It seems to be a common problem.

Test the capacitor (it will look like either a small hockey puck
(called a doorknob capacitor), or like a rectangular block about
..5"Wx2"Lx1"D. I buy mines off ebay for about $10 to $20 each). Again
search for high voltage capacitor or tesla.

Aloha, Russell

  #5  
Old April 17th 06, 04:44 AM posted to rec.crafts.metalworking
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Default Troubleshooting a plasma cutter

On Sun, 16 Apr 2006 18:04:56 -0400, Jack Hunt wrote:

On 16 Apr 2006 10:55:10 -0700, "Lefty" wrote:

Easy test is to jumper the switch.


I'll try that first thing in the morning. Thanks.


I can't find instructions listed, "650" is not a complete model
number, is it...?

If you don't have the instructions, try looking them up at
www.esab.com - they might have a troubleshooting flow chart in the
back of the book that will lead you right to the problem. Either
that, or you find out you did something seriously wrong.

Failing that, you open it up (carefully!) and look. Make sure there
are no popped fuses, any safety switches (like the air pressure
failure switch mentioned above) are working properly. As in, connect
an ohm-meter across the contacts, apply air to the inlet as a function
test, and see what happens. And make sure the supply air pressure is
high enough - if the safety is set to cut out below 50 PSI, you have
to be running over that point...

DO NOT jumper switches or safeties randomly while you try to run the
machine unless you are sure of what you're doing, and you are sure
that the air pressure is in fact there - there is a good reason why
the safeties were put in there. If it wasn't totally blown before,
it will be after you jump the safety...

And you look and sniff for any components that have "gone all
melty." You'd be surprised how obvious that is sometimes...

-- Bruce --

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
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  #6  
Old April 17th 06, 04:52 AM posted to rec.crafts.metalworking
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Default Troubleshooting a plasma cutter

Jack Hunt wrote:

On 16 Apr 2006 10:55:10 -0700, "Lefty" wrote:


Easy test is to jumper the switch.



I'll try that first thing in the morning. Thanks.


What he said.

I once "fixed" a plasma cutter by telling
the machinist to turn up the air pressure
to it (:

 




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