THC And Live Voltage issues

Will keep this short and sweet as I can.

Hypertherm 45xp - No CPC port - Laptop charger unplugged - USB isolator installed.

Still having trouble with my THC after 2 months of fighting it. One day it started raising itself up terribly, and has not been the same since. Before the issue happened I was cutting 12ga at a 110v nominal and it was great. Then “something” happened. I am now forced to rely on smart voltage as ANY nominal setting is wrong and causes weird raising as well. The smart voltage it selects is about 46v, although it still will raise itself up sporadically as it wishes anywhere between 1/8" and 1/2". I have been in contact with Langmuir over the 2 month period and have had some parts warrantied but also thought I would post here for more ideas because I am stuck.

One major issue I am having is that my raw voltage measured at the pigtails is about 98v and my live voltage is around 45v. Hypertherm tech support says that it is impossible for the arc to initiate at 45v.

I have followed the THC troubleshooting guide and everything checks out untill step C4. I have voltage here although about half as much as should be expected according to the troubleshooting guide. I don’t really understand how this talks to fire control but one thing I notice is that I am also getting a live voltage report (46v) of about half of my raw voltage (98v).

Langmuirs trouble shooting guide suggests I have a grounding issue, here is a copy paste from step c4 on the guide.

" If you are getting DC voltage between these two pins while cutting but the voltage is much less than what was found in step A3, it is possible that you have a grounding issue between your electronics box and the machine frame. Please check out our following guide as you most likely have a DC grounding issue: "

I have tried everything I can think of to help isolate things, including running the machine with the enclosure box removed from the table let set nicely on a cardboard box as well as a brand new computer plus the warranty parts from Langmuir. I am not really wanting to drop the cash on a new 45xp just to see if it fixes the problem.

Please help!

@langmuirsystems @langmuir-daniel @langmuir-mike

Hi Kyle,

Firstly I just wanted to check and see if you have had time to swap in the new MCB and THC chip and see if that fixes anything.

One other thing that I would check is to make sure that your electronics enclosure is plugged into it’s own outlet or power strip with nothing else connected but the machine. If there are other things plugged in, can you unplug these and try the voltage test again?

With the box now removed, what resistance reading are you getting between the machine frame and the USB shell plug on the MCB?

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Hey Mike, thank you for responding. I can confirm that the new MCB and THC are installed with no change in behavior. I have also ran an extension cord from another wall socket that I believe to be on a separate breaker for testing and observed the same behavior with the THC.

I will have to remove the box again and recheck resistances to answer your last question. Are you hoping to get a different reading that before now with these new parts installed? Will update asap.

Based on the low voltage readings that you are getting I don’t think that the MCB or THC is defective. It looks like clearly a ground loop issue between your DC voltage on the THC and the DC voltage in the plasma cutter through the VIM.

I would recommend removing the electronics box and removing the extension cord that you are using on this plug. Plug it directly into the outlet and don’t plug anything else into this outlet. Keep your laptop on battery power and try the THC test.

If that still is reading lower than expected voltage take a resistance reading between the USB plug shell and the slat bed. What are you getting here?

Another thing that you might want to check is continuity between the USB plug shell and the metal case of the power supply. If you are getting continuity here it’s possible that the USB plug is rubbing against the enclosure. I would recommend removing the 4 screws that hold the MCB into the enclosure and let the MCB kind of float in the enclosure without touching anything and try again. Once we get to the root cause of the issue it should be easy to get you buttoned back up again!

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Hello Mike,

I have removed the electronics box, and have it plugged into a power bar all by itself. I cannot reach a wall outlet without it. I no longer am using a laptop but ran an extension cord for my desktop and monitor from across the room from a circuit I believe to be separate.

I preformed the steps outlined in C4 in the troubleshooting guide and got a voltage of .7v.

With my meter set on 2000K OHMs I read a fluctuating resistance between 1330 - 1380.

The usb plug shell and metal case of the power supply were not continuant. I checked several spots on the power supply both on the case and on the screws that hold the power supply case together.

@langmuir-mike @langmuir-daniel @langmuirsystems Hey guys, I hate to be keep bugging you but I am turning down work because this thing isn’t working correctly. I sent you a PM Mike, please have a look. Hoping you guys can give me some more guidance on what more to try? I’m between a rock and a hard place and considering spending the cash on a new 45xp because I need this machine up and running.

Did it work for a while, then start acting up? I only ask because I fought with THC issues (low voltage when cutting, torch going to the moon) for months. What I found was that I was getting continuity between the Z axis lead screw and the IHS switch, caused mainly by grit and splashing water. I used a borax solution at the time which probably contributed to the continuity issues. I gave everything a thorough cleaning with isopropyl alcohol, added a funnel splash guard and blow the Z axis out before each run. I have not had an issues in the past month or so. I also added taller Y axis rail plates to raise the Z axis higher above the water table.


Why does having my laptop plugged up to the charger cause an issue? Seems kind of crazy to me. To note:My electronics enclosure and laptop are plugged into a three-way extension cord

I’m in the same boat as @ktice here. I’m using an Everlast powerplasma 50 instead of hypertherm but exact same issue. Table and thc will cut beautifully for weeks then all of a sudden the thc live voltage goes from 100+ volts to 10. Torch shoots through the roof and continues through on every subsequent cut. I’ve had to resort to just running with thc off most of the times which definitely sucks for longer cuts.

I have been through the troubleshooting guide numerous times and everything checks out. Figures right when I get in touch with langmuir systems it fixes itself out of nowhere haha.

So far I’ve verified it’s something happening either at the vim box or after. With the banana plugs that read the raw voltage plugged into my multimeter everything is normal 100% of the time. Checked every possible ground issue and found no smoking gun. Really lost where to go now

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From everything I have learned from all the help langmuir has given me I would suggest waiting for your live voltage to drop and cause issues and then immediately after you notice it acting up check your voltage at the banana connectors while cutting a straight line test. I was able to narrow my issue down to fluctuating voltages at the plasma cutter it self causing improper signals to be sent to the THC and firecontrol via the vim box.

Thats exactly what I did this most recent time that it started having issues. As near as I can tell it appears to be something happening after the VIM itself. Both when acting normal and not the voltages check out per the THC troubleshooting guide. It’s very strange for sure.

The very strange thing I found was on a whim I checked for continuity between the usb port at the box and machine frame and got continuity. This makes no sense as my control box is mounted over a foot away on the wall. After unplugging the cord and reconnecting the continuity no longer was present but THC still non functional.

Langmuir is currently having me check some resistances inside the control box. We shall see where it leads.

They had me check the voltages inside my cutter while cutting and then again on the pigtail coming from the vim box. The VIM is a 73:1 reduction so with math you can figure out if you’re roughly where you need to be after the VIM. I also had to use a adapter to rid my laptop of the ground, which was an earlier issue but unrelated to the current one.