how is the lil black THC box connected?
Black wire goes into torch plug, red wire goes into Clamp plug.
Cable to the machine is plugged into raw voltage plug.
Unfortunately, presumably to keep the cost down, Langmuir really did not use enough galvanic isolation in the controller. For this reason it is highly susceptible to grounding problems which are particularly hard to avoid given the presence of the water table. Ideally, the IHS wiring would be galvanically isolated from the control board (easily done with an opto isolator, but requires an additional isolated power supply ($)) and the voltage sense would also be isolated from the controller (less easily done, but can be accomplished with a voltage to frequency converter, opto isolator and another isolated power supply ($$$)). Doing it right, might add $100 to $150 to the cost of the controller, which is significant considering the cost of the Crossfires, but would probably be worth it to anyone who really wants THC.
so, basically theres nothing LS can do about my problem. starting to get real bored with chasing the metal around holding it down so the head doesnt hit the metal from it rising.
working with a lot of .090 aluminum right now and it loves to rise.
Unless you actually have a faulty component, probably not assuming you’ve carefully followed Langmire’s detailed THC troubleshooting instructions. One might hope, given the significant level of issues reported on this forum, that Langmire might reengineer the control system to incorporate proper isolation. While clearly some people get the system to work as it is, it is really not a robust system.
given also the number of systems sold there are not any problems is the other side of looking at it…
sure there may be some problems…but you will always hear from people with problems…and never hear from people who have perfect running machines…
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I would agree with you except for the fact that because of the lack of proper galvanic isolation, the problems many are experiencing are hardly a surprise.
To design a system which requires the work piece and control computer not share a common ground is simply asking for trouble. There are also potential safety issues with everything floating wrt. ground.
For my part, I will not buy a THC from Langmuir but will build my own and do it right.
you are a lucky person to be that experienced and have that knowledge base to take that on.
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Is there a way to tap into and make a common ground between the two things you mentioned?
any LS tech guys want to have a stab at it?
Not if you want the THC to work. The problem is the torch runs negative with respect to the work piece. The THC can only measure positive voltages with respect to its ground (which is also the PC ground because of the USB connection). Thus, the torch voltage sense is connected to THC ground and the workpiece sense is connected to the THC ADC input. Because of the way the voltage divider works, this puts the workpiece a few volts above THC/PC ground potential. Anything which provides any kind of ohmic connection between the THC/PC ground and the workpiece will disturb the voltage sensed by the THC and result in erratic behavior of the THC.
Because it is difficult to ensure the workpiece and water table have no stray connections to ground, you will see in Langmuir’s trouble shooting guide that they suggest running only with a laptop and running off batteries if you have issues. This should ensure there is no connection between THC/PC ground and any other grounds although if your laptop has a metal case there is a possibility that touching it could cause problems.
Dude, bro’ …you are wayyyyy above my ohmnastic pay grade…
But I do understand the most basic reasoning 
Thank you 
Do you know this for a fact? Have you traced out the circuit?
I’m not asking because I know different. I have no idea how their THC circuit is designed, however, just because the circuit only has a positive power supply, doesn’t prohibit it from measuring a negative voltage with respect to ground.
I have traced out the circuit sufficiently to know this is the case. It is not hard to verify with an ohmmeter.
@KSiegel Just so we understand if you run the THC Test wizard in FireControl you are getting somewhere around 95 cutting volts? And then when you made a cut smart voltage was set to around 4V? We think that you are experiencing a ground loop issue between the DC voltage of your plasma cutter and the DC side of the MCB. Please shoot an email over to support@langmuirsystems.com and we can send you out a USB voltage isolator to try and see if that fixes your voltage issue. Are you running a PC desktop or a laptop. If a laptop have you tried with the charger unplugged?
Another thing that you can try is to remove your electronics box from the leg of the machine. The first batch of PROs shipped without a plastic isolator bracket and if you are one of the first customers then you may not have this. If you can remove the box from the leg and prop it up on something and try to cut again and see if that fixes your issue we can send you out the plastic bracket as well (assuming that you don’t alraedy have one).
0ne last thing that I would try is to unplug your IHS cable from the electronics box. Then make a straight cut program with IHS/THC toggled off and run it. Your THC won’t be active but you can watch the Live Voltage while it’s cutting to see what’s going on. If you are getting anything other than 80-120V cutting then something is still wrong.
yes, test gave me something like 95.4V. then when its on smart it only get about 4 volts and rams the head down, so i have to stop the program immediately, its hard to get an accurate reading when youre packing to make the machine stop.
i dont think i have a voltage isolator, i have the little plastic thing that clips onto the usb cable, that you guys sent me months ago.
running laptop, set on a tool box about 8 feet from the table. tried it while unplugged and still made no difference.
i dont have the plastic isolator bracket. i was in batch one, its just rubber grommets that mount the box to the frame. ive ran continuity tests between the frame and usb and a bunch of other points and have not gotten anything.
ill try the removal of the control box and the other thing this weekend when i get time.
thanks for the help.
removed the box from the frame. made no difference. head still jams down.
then tried the straight cut feature and it starts at like 85v and climbs to about 103 by the time the 12" cut is finished.
so my voltage seems correct, right?
usb voltage isolator installed, and plastic bracket for the case installed.
on smart voltage, machine still rams the head down.
set voltage to 100 or 120 or 130, machine still rams the head down…
i dont get why this doesnt want to work…
You might find this users solution with the IHS will solve your problem.
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