Chinese Plasma Fault!!

peterd51 · Nov 28, 2007

Hi,

thinking on about that voltage...

my Berlan will cut 12mm (I've tested it on 10mm and it cut cleanly) where the equivelent size Clarke is rated at about 5 - 6 mm. Could it be that the Chinese cutters get the extra thickness by upping the voltage out of the inverter?

All I can say is that I've had that particular digital meter for some years, it's not a cheap set and it's never had any problems before, but I reckon it's a bin job now.

I changed the fuse and the battery light stays on with a few extra 'dots' on the display.

As for sending the cutter back, I reckon I'll keep mine as I now know the danger (well this one anyway!) and I reckon I can make it safe for me to use.

Regards
Peter

shiftyseamus · Nov 28, 2007

Hi, I plan to turn up a ptfe sleeve to cover the connections(as per pic in the other thread). Once I have made one I will post pics and should be able to make them for other members for the cost of postage.

Perhaps Peter could have one to test as well?

Seamus

oddball90 · Nov 28, 2007

This has just put me off of a chinese plasma cutter big time. Think people should think long and hard about this. If the main power conecter is this dangerous, what is the build quality like inside. Just proves weldequip's rants are spot on.

MrFluffy · Nov 28, 2007

peterd51 said:
Hi,

thinking on about that voltage...

my Berlan will cut 12mm (I've tested it on 10mm and it cut cleanly) where the equivelent size Clarke is rated at about 5 - 6 mm. Could it be that the Chinese cutters get the extra thickness by upping the voltage out of the inverter?

Youve actually electrocuted your meter with a hf pulse, which is designed to intially set up the current path for the plasma arc to follow. The crack crack noise is the clue to whats going on, its the same sort of principle as a car ignition coil, short bursts of lots of energy designed to fire the spark across the air gap. With the same sort of voltages and stuff. I havent looked at my connections as I intended yet, but Ill take a look using a scope with a high impedance probe. Id imagine theyre very high voltage circa 20-40,000v the same but of short duration to set the arc up, which will bloody hurt if you get shocked by it instead. If its modern cdi levels I dont know, but your better treating it as such and thus do everything you can to avoid a shock. That includes not grabbing the torch and earth and starting the thing up too.

I cant see how hf start could work any other way as somehow you have to have enough energy to spark across a airgap to energise the plasma which ever way you look at it takes significant energy, so I imagine the miller sets etc do exactly the same thing.

MrFluffy · Nov 28, 2007

oddball90 said:
This has just put me off of a chinese plasma cutter big time. Think people should think long and hard about this. If the main power conecter is this dangerous, what is the build quality like inside. Just proves weldequip's rants are spot on.

Yes, perhaps we should all stop buying ALL hf start equipment

irondarren · Nov 28, 2007

HF equipment is ok as long as its safe, I guess this is where the problem lies though, during start up the machine may attempt to strike a current between the torch and the casing. If its anything like my IFL unit that will strike and arc to the nearest earth, often me when i press the torch button by accident. And yes it bloody hurts

oddball90 · Nov 28, 2007

Trouble is it is not only the hf it will be the main 40 amp current also. The adverts on ebay states that the seller takes all responsibilty for selling the plasma cutters. Think ebay are covering the'r corperate arses with that statement.
I've got a Portamig 206i tig welder with hf start, haven't had a shock off of that yet. Mind you it is a well built machine with a good quality torch.
Yes you can shock yourself with hf but you should only be able to do it at the torch not at the machine.

MrFluffy · Nov 28, 2007

So, we're saying you could get a shock off a connection on the machine, if a fault condition exists (connector has come adrift) and then you start the cutter up and touch the faulted area, that you could get in normal use anyway?

irondarren · Nov 28, 2007

Exactly only shock yourself at the torch, and thats through being a dumb ass like me and not looking grabing the torch and touching the start button, with my fingers to close to the tungsten. You most likely right about the amount of current i did post on another thread i think that the figures for power consumption didn't add when the TIG unit was in MMA mode

oddball90 · Nov 28, 2007

No, the connecter on the machine is not insulated. The pipe fitting carries the current, so the torch fitting that screws onto this connector should be insulated. This fitting is live when the trigger is pressed.

Wozzaaah · Nov 28, 2007

irondarren said:
Exactly only shock yourself at the torch, and thats through being a dumb ass like me and not looking grabing the torch and touching the start button, with my fingers to close to the tungsten. You most likely right about the amount of current i did post on another thread i think that the figures for power consumption didn't add when the TIG unit was in MMA mode

I've seen it on American Hotrod where some guy sticks a filler rod in the torch and zaps his mate on the @rse. I've also heard of people getting trainees to listen to the gas flow and get a zap on the ear.

HughF · Dec 4, 2007

Thought i would show some folk what the inside of a chinese cutter is like before you all think that they're crap and are a waste of money...

http://picasaweb.google.com/hugh.frater/PlasmaCutter

I work in electronics engineering in a very high tech field, that build quality aint too bad for the money.

BTW, I have a MAO's electric 125amp MMA inverter from the same inporter. They both use Fairchield Semi SMPSU IC's and are of similar design.

Had this since april, used extensively but not abused. All in all, pleased with it...

Hugh

weldequip · Dec 4, 2007

I work in electronics engineering in a very high tech field

How high-tech Hugh... aerospace, military?
weldequip

irondarren · Dec 4, 2007

just been and stripped the casing off the pico 140, so you can see inside that.

Case off

the tiny transformer

230volt mains end, with insultators on

my goodness its almost 8yrs old

are all the numbers next to each component bingo numbers

irondarren · Dec 4, 2007

second set of pics

dont think dropping something on it did it any harm

front view, think it needs a dam good clean up. Still welds as good as the day i bought it.
Not a plasma i know but if we are looking at the insides

HughF · Dec 4, 2007

Weldequip,

The company I work for manufactures underwater survey equipment.

Hugh

irondarren · Dec 4, 2007

One thing i am curious about, insulation class. most chinese stuff is grade B, thing most of my inverters are grade F, just noticed one of the butters is insulation class H. Anyone know what these insulation classes mean?

Wozzaaah · Dec 4, 2007

http://www.engineeringtoolbox.com/nema-insulation-classes-d_734.html if that makes any sense to you? :confused:

rusty69bus · Dec 4, 2007

the higher the letter the better it can deal with temperture changes

irondarren · Dec 4, 2007

makes good sense, it seems class A is only suitable to lower temperatures, B to slightly higher temperatures F to even higher and H is the highest. Its the point at which the insulation melts and the whole thing fries, bearing in mind welding equipment is subject to internal heat, the higher the class the better, or shall we say the safer

Chinese Plasma Fault!!

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