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Losing arc

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Largemouthlou
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Losing arc

Postby Largemouthlou » Tue Jan 02, 2018 6:36 pm

Hey gang, trying to track down a gremlin that just showed up last weekend. Was cutting an in the middle of the code I lost flame. Arc ok not lit in mach or on the PWM module. If I turned the torch off file started running again so I would turn torch back on and it re fired.
Had it happen a few more times and it would cut on of the same file fine then it would happen again, a few times it was on the M03 and a few times it would be in the middle of a cut.

I have run the basic filter checks, have air drier going, no faults on the 1250 hypertherm, consumables looked fine, didn't notice any power surges and checked all connections.. Im just wondering what else to look for and is there a possibility of my 1250 having an issue. After checking everything I cut several files with only one pierce and one of the files I had issue with and all cut fine.. Guess I'm trying to get a jump on next weekend if I have the same issue..

Thanks
1250 hypertherm
4 X 8 Precision Plasma
CandCnC electronics

tcaudle
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Joined: Tue Feb 28, 2012 6:47 pm

Re: Losing arc

Postby tcaudle » Wed Jan 03, 2018 5:56 pm

arc ok shows the presence of arc current. it is a signal that comes from the plasma (aka "transfer" and "Ok to Move") naturally thre will be no arc ok if the torch is out. So which comes first? Well if you lose the ARC OK signal (because the cut current is below the trigger point ) then two things happen: Motion stops then if you have the option checked for Torch off with loss of Arc it instantly turns off the torch, If its not checked (default) the torch will shut off after about 2 secs (done by the plasma) . When you turn it off and back on the THC turns off and ignores the ARC OK. So what causes loss of ARC oK? well cutting too high, cutting into a void, too lang a pierce delay or too slow a plunge rate on thin material and of course the torch going out.

You need to determine which is happening first. One thing you can do to see if its the loss of acr versus the torch actually turining off is to jumper across the arc ok pair into the PWM module and turn it on all of the time. It may cause some timing issues where you get motion on a pierce BEFORE you get a valid arc but it will let you determine what is causing what. Also the motion will NOT stop even if you do lose arc for any reason.

Largemouthlou
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Re: Losing arc

Postby Largemouthlou » Wed Jan 03, 2018 7:05 pm

tcaudle wrote: So what causes loss of ARC oK? well cutting too high, cutting into a void, too lang a pierce delay or too slow a plunge rate on thin material and of course the torch going out.


Thank you for the reply Tom, Hope your Christmas and New Years Celebrations left you ready for a new yr!! LOL

Out of the reasons I quoted above only the torch going out or not firing fit here. There were two occasions where the the torch went down to pierce height and the M03 code line was read and the torch never fired at all. Mach dro torch on was lit up but nothing happened. These are all the same settings I have been using with no issues for a long time. Not sure if this is part of the issue or a material quality issue but I have been cutting a lot of .090 alum over the yrs and all cuts have been excellent quality.Since this problem (and a new batch of material) I have had excess bottom dross where in the past there was just a fuzz.
One other thing I observed was the green light for the arc volts on the PWM was flickering (dull to bright) while the torch was on and cutting.

I won't be back in front of machine till this weekend to try any other tests.
1250 hypertherm
4 X 8 Precision Plasma
CandCnC electronics

Largemouthlou
Elite Contributing Member
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Posts: 1372
Joined: Mon Aug 30, 2010 5:56 am
Location: Palm Bch Gardens Fl
Contact:

Re: Losing arc

Postby Largemouthlou » Mon Jan 15, 2018 8:00 pm

Okay,,,,,,, not real sure what changed.. At this time I have to think my issues were due to power coming in to the shop (or lack of from the hick power company).. Cut quality on same stock back to good, only lost arc once and this time was due to a bad lead in on a skinny font. I changed that and file cut fine. I cut 4 of the same file I had problems with last week with no issue..

Only thing happening now is if I cut big files/sheets I get a touch off that don't seem to come up to pierce height and the fault bar say "requested home axis, home switch is active, please fix then home.. wondering if there is a problem with the micro switch? all the other touch offs seem to work after this happens.. have the feather touch hooked up, micro switch not hooked up for e stop if z raises to high..

I may be just time to upgrade this dinosaur!! LOL Been eyeballin the new stuff and new Z ya have Tom!!
1250 hypertherm
4 X 8 Precision Plasma
CandCnC electronics


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