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Author Topic: Plasma Grounding Help  (Read 5647 times)

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Offline Shuey

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Plasma Grounding Help
« on: April 21, 2008, 08:34:46 PM »
Hey Guys,

I'm having an issue eliminating the HF noise out of my Plasma table. I'm using a Jim Cullin's THC300 system and a cheaper Chinese type plasma machine (at the moment anyway) and have followed the guidelines outlined in the Campbell Designs user manual, but still seem to have a a problem.

Hoping someone may be able to give me a few tips on what I should be doing.

This is my current configuration:

Plasma table is grounded to the body of the Plasma Machine then grounded to an earthing stake driven into the ground (1 meter into the ground measuring 1/2" Dia). the cable linking this is 5mm.

Interestingly, the system works sometimes and other times the PC simply freezes up.

I'm considering buying a Hypertherm PowerMax 1000 or 1250 should someone be able to convince me that the HF noise is alot less.

Any comments or solutions are welcomed...

Should I isolate the earth to the plasma machine and run it to the earthing stake? Feel free to describe the fix like you are talking to a 2 year old, so I get your point.

Marcus

PS... I have just re-read the Grounding section of the installation anual again and I wonder whether the earthing lead inside the Plasma machine box should be removed from the power cable and re-routed to the grounding rod???

I have tested the DB9 Shell and have an 0.00 ohm reading from the plasma machine box and the DB9 shell.
« Last Edit: April 21, 2008, 09:21:51 PM by Shuey »

Offline Whacko

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Re: Plasma Grounding Help
« Reply #1 on: April 22, 2008, 06:33:10 PM »
The Powermax range machines do not employ HV HF to initiate the arc. It uses a plunger style arc lifting mechanism in the torch. It is very well suited for PC based systems. I am a OEM business partner with Hypertherm and we fit these machines to CNC flatbeds all the time.

Things to do to try and kill the HF on your current system.

1.) Use a star configuration to ground the cutting table, plasma POSITIVE (Work lead), and the rails and your gantry.
2.) Keep cables away from torch and ground leads where possible.
3.) Fit a braided screen over the machine torch leads all the way and ground it on one side only.
4.) Use twisted pair shielded cables for your interface and limit switches and ground the shield on one side only, preferably on the PC side.
5.) Use common ground for all grounding, and the earth spike is not so efficient, that we've found through experience since 1984 in the industry.
6.) Check inside your plasma power pack. If the HF generator has open electrodes with a spark gap, adjust the gap as small as possible without loosing arc initiation.
7.) Most important, check your factory/home ground. Bad ground connections can even call ET! Beware!
8.) Keep in mind the Faraday cage.
9.) Best, chuck the yellow and fit a Powermax.

Whacko
Nothing's impossible
Re: Plasma Grounding Help
« Reply #2 on: April 23, 2008, 05:43:21 PM »
I have tested the DB9 Shell and have an 0.00 ohm reading from the plasma machine box and the DB9 shell.

The THC 300 manual doesn't say anything about the plasma machine side, but it does say this about the control panel side:
"The DB9 shell needs to be insulated from your cabinet chassis. DO NOT MOUNT WITHOUT
INSULATING IT FROM THE CABINET GROUND. It will form a ground loop and cause possible
noise problems. Mount it where you can access it externally. Check it with an ohm meter to make
sure after it is mounted. Measure between the metal of the shell and the cabinet. It should be a very
high reading."
Re: Plasma Grounding Help
« Reply #3 on: December 02, 2009, 09:51:21 AM »
I was wondering if you ever solved your hf problem we also have similar problems.
and have the same thc and are finally switching machines.
We have tried for over a year to get rid of the noise, many different ground rods, copper pipes, and finally
grounded to a well casing.  I am interested to see what you did.
Thanks

Offline Shuey

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Re: Plasma Grounding Help
« Reply #4 on: December 02, 2009, 10:13:40 PM »
I did solve the problems in the end... I changed my plasma unit over to a Hypertherm. I tried to get out of it cheaply with a chinese unit to start with, but in the end, there is just no comparison to a true plasma unit.

Part of this was the hypertherm was purchased as a 3 phase unit rather than a single phase, which meant that I could have them on a separate curcuit for one and two, the Earth curcuit is also separate. yep, it cost me a small fortune, but in the end it was worth it.

My only issues that I have had recently is that me PC has died and the Mach Driver seems to slow the hell out my PC sometimes.... restart sometimes fixes it and sometimes not... I've optimised Windows XP, but doesnt fix it... apart from that all good.

I haven't needed to use the table for some time and I was thinking of selling it...

Re: Plasma Grounding Help
« Reply #5 on: December 07, 2009, 02:05:31 PM »
Are you selling the hypertherm ?
Send me a personal message if interested.

Thanks