Small non laser tube arcing issue

[Graham Facer]

Hi all,

So this post is half information and half a question.

I've had an arcing issue on my Shenhui but unlike the bad arcing issues, this one is from the laser emergency cut off to the LCD panel. Until I realized that (as the switch totally failed/melted) I'd freak out when I heard it, find nothing, reset the machine and carry on. As it is, the cutter never stopped cutting, the program was fine, it just blanked out the lcd screen until reset.

I have replaced the switch and then I used some of the extra 3m high voltage sealing tape, left over from sealing the tube connection, to cover the connections but it seems to like to fall off and so I still have the issue once in a blue moon. It would only ever happen every so often with no rhyme or reason though never right at the start of cutting for the day.

I suppose I should silicon the connections rather than taping but... haven't.

Anyhow so the information is that if you have an arcing noise but cannot find the source at the tube, this is another place to look (and it is easy to overlook - especially if you have soot in the machine). I took off the tube cover several times trying to find the arc mark so maybe this will save someone some time.

The question is should I be more concerned about this (other than frying the LCD panel - which is an obvious risk)? Anyone else have this issue and solved it?

Cheers, GF

[Dan Hintz]

Should you be concerned about 30kV arcing to the case you continually touch during operation? Really?

What happens when your grounding system fails? You're going to light up like a Christmas tree.

Fix it, and fast.

[Bill George]

Trying to understand the question. Your 120 volt emergency shut off switch is arcing to ground? Pretty much impossible unless you have a high voltage grounding problem in the PS to your tube. It can't find a ground and is seeking one.

[Graham Facer]

Well the case is grounded direct to the panel and I've had my hands on the case when it happens, practically right above it and feel nothing. But Bill is right, its a 110v arc on the same circuit that I want to interrupt on my fire detection project.

I've not had it happen lately but since I was posting, I decided to put it out there too. I'll try silicone on the connections and some tape again.

Bill - why do you think it must be related to a high voltage issue? Thanks, GF

[Bill George]

As an electrician I can safety say I have never seen 120 volts ac arc to ground, (on its own) UNLESS it has arced before, like from moisture and left a carbon track. Or you have a non rated switch, as a low voltage one on 120 volts.

High voltage and especially high frequency voltage does weird things at times.

BTW don't assume the grounded outlet you are using, is actually grounded.

[Clark Pace]

Hi all,

So this post is half information and half a question.

I've had an arcing issue on my Shenhui but unlike the bad arcing issues, this one is from the laser emergency cut off to the LCD panel. Until I realized that (as the switch totally failed/melted) I'd freak out when I heard it, find nothing, reset the machine and carry on. As it is, the cutter never stopped cutting, the program was fine, it just blanked out the lcd screen until reset.

I have replaced the switch and then I used some of the extra 3m high voltage sealing tape, left over from sealing the tube connection, to cover the connections but it seems to like to fall off and so I still have the issue once in a blue moon. It would only ever happen every so often with no rhyme or reason though never right at the start of cutting for the day.

I suppose I should silicon the connections rather than taping but... haven't.

Anyhow so the information is that if you have an arcing noise but cannot find the source at the tube, this is another place to look (and it is easy to overlook - especially if you have soot in the machine). I took off the tube cover several times trying to find the arc mark so maybe this will save someone some time.

The question is should I be more concerned about this (other than frying the LCD panel - which is an obvious risk)? Anyone else have this issue and solved it?

Cheers, GF

Hello. I have had the problem with a Gweike and my first Shehui laser($600 dollar ebay special). My solution was 2 fold. First ask shenhui if they have a rubber insulated sleeve that fits over the back of the tube. Some laser come with one. If they don't or you want a quicker fix. What I did is purchase some ceramic squares and lined them around the metal chase on back part of the laser helping insulate the tube. That is electricity want to go to the least path of resistance. So If you can insulate the metal it will help. That solved my problem.

[Dave Sheldrake]

If the HV is tracking to earth check the tube, it may be on it's way out, the second biggest cause is failure / leakage on the HT connection between the PSU and the main RED power line going to the tube.

While 35mA is unlikely to kill a fit and well person, across the chest it can cause fibrillation of the heart that will end the same way unless treated VERY quickly. Masking the issue with added insulation could make the situation worse, have a good look round and find the leak then treat that rather than trying to treat everything and possibly missing the actual problem

cheers

Dave

[Graham Facer]

Sorry to be clear - THERE IS NO ARC FROM THE TUBE. I've checked the tube many times and never a single trace of an arc at the tube and lots and lots of traces (ie it melted) on the old switch. The ground is direct to the sub panel (not to the outlet) and wired directly into the ground bus on that panel from the machine (where it is bolted on to a painted stripped section at the power in area in the back.

The arc was strictly from the 110v emergency laser cut out (which is just a switch that interrupts the hot on the laser power source before it is converted to high voltage). The clearance from a connection on the switch to the LCD housing is only about 1.5-2cm at its closest so I while I agree it shouldn't be happening with 110v, I doubt it beyond the laws of physics. I did notice that it seemed to happen more in summer so I think humidity and maybe moisture from the compressed air might have played a part and helped enable the arc.

Anyhow, I'll goop some silicone on the connections and hopefully forget it used to be an issue.

But I gather its not that common unlike arcing at the tube - which unfortunately is (but not for me). Here's the old switch - you can see the melted bit on one side.
IMG_20150223_150536.jpg

Cheers, GF

[Bill George]

I will say it again, I bet that switch is not rated for line voltage. If its even rated at all. As I recall its a push to stop and twist out to reset switch. Moisture will do it on a marginal switch, look for a UL rated USA made switch. Kind of looks like that spring metal clip is very close to the line voltage terminals.

[Graham Facer]

This is the old and new switch side by side (old is partial disassembled - I wanted to try and use the mushroom on the new switch).

IMG_20150223_154636.jpg

So maybe I should switch to a brand name...

[Dave Sheldrake]

Wish I could say it's the first time I've heard this Graham, it's not, outside of tube / HV the dead stop switch seems to be an issue on some Chinese machines. That said a 20mm leap is HUGE for 110v (although my understanding of mains electrics is lacking to say the least) Bill is the sparks and what he is saying sounds accurate to my unqualified mind for sure, even 240 over here won't leap much of a gap

cheers

Dave

[Wilbur Harris]

It sounds like some higher voltage is bleeding to the switch somehow. A centimeter is really a big gap for 110V to jump.

[Dan Hintz]

Wish I could say it's the first time I've heard this Graham, it's not, outside of tube / HV the dead stop switch seems to be an issue on some Chinese machines. That said a 20mm leap is HUGE for 110v (although my understanding of mains electrics is lacking to say the least) Bill is the sparks and what he is saying sounds accurate to my unqualified mind for sure, even 240 over here won't leap much of a gap

cheers

Dave

Yeah 120V is not going to leap nearly 1", even in moist conditions... but I see a LOT of carbon build-up on that old switch, and that will happily allow a large spark gap.

Also, seeing "push bhtton switch" on the new one doesn't give me any warm fuzzies... I would question the rating on that one, too.

[Graham Facer]

Ok on this last issue it seems the power supply was at fault. I had another issue (laser did not go next day) and so swapped power supply and found it under the board where it was arcing to the case. replaced with another power supply (with interesting enough, a bump out to give more space in that area...) - added some extra insulation there and we'll see if it remains an issue.