THC - It can't be this difficult !!!!!!

[bad-rat-57]

To set the tone, level of frustration = 11/10

Learning mach,sheetcam and CAD from scratch were easy compared to this THC-300 unit.

Doing test runs with my table, all the thc wants to do is drive the torch down. Voltage readout is 169. Any time I adjust either of the adjustent knobs I can't get it to go up. Turning either CCW I get no reaction, either CW as soon as I pass midpoint I get a fault light. I have adjusted the limits from small to crazy big and it just drives the head down farther.

I am unable to get an arc ok signal using the current transformer. The only way I am able to do this testing is to jumper the orc ok terminals and fool the system.

During initial calibration, the unit must be adjusted to read 100v on the readout. I'm on my second unit now and still can't get any better than 90v

I must be missing something in the mix here, it can't be this difficult.

Anybody with any help would greatly be appreciated.

[Torchhead]

Of course it drives it down with a 169V torch reading.

You "initial calibration" was not needed since there is nothing to calibrate. You probably have the volts reading off. The unit faults when you go above 200VDC or below 50

Have you setup and done a test cut with the THC turned off in MACH? What does the readout show when you manually cut with the gap at the specified distance? Can you adjust the controls to make the up and down indicators on the THC300 change? Finally is your UP and DOWN moving the Z in the correct direction. If you jog your Z up/down manually does the DRO increase in value as you go up?

When the head dives down is the DOWN LED on? Voltage reading is way off but may not be the actual voltage the THC circuit is seeing.

You don't list the plasma type or model so it's hard to take it further. You were given direct answers on the CandCNCSupport forum and via e-mail from me. While we don't make/sell the THC300 we offer support since it's based on one of my earlier designs.

Learn to run your table without the THC on in MACH to understand the dynamics of plasma cutting.


I am including the content of an e-mail you were sent yesterday with specific tests to run on the Arc Okay. You also were given a solution for your Z motor stalling in another response. I assume you fixed that since it's not in the content of this post.


Clip from E-mail:

The ARC Okay circuit operates on the principle that a Current Transformer (CT) transfers current to the seconday winding from the wire you pass through it (primary) divided by the turns ratio. For the CT that comes with the 300 that ratio is 40:1 (for one COMPLETE wrap of the secondary) if you pass two turns it would be 40:2, etc) So if you pass 20A of current through the secondary at 40:1 you get 1/2 (500ma) of secondary current. To transform that to voltage you place a resistor across the secondary. Ohms law (E = I * R of Voltage = Current times resistance) says that 500ma passing through a 15 ohm load (resistor value) your voltage will be 7.5 Volts.

.

The first test is to make sure the resistor provided is across the CT and with an AC volt meter across the resistor and the torch cutting metal you should see a minimum of 7.5 volts AC. If you get no AC voltage across the resistor, check the resistor with one end disconnected (15 ohms) With the ressistor still disconnected read the resistance across the CT terminals. Should be a few ohms. Make sure the resistor is making good connection on both terminals of the CT.

There is a sensitivity pot on the sensor card for the Arc Okay. If you put in 12V DC into the Arc Okay Voltage pins (not the Arc okay J4 and J5 direct pins) and rotate the ARC Okay opt to about mid range you should hear the arc okay relay click and it should show up in MACH as the THC ON input changing.

I don't know what size or type plasma cutter. Some small plasma units running on 220 or higher do not pull very much primary side current or on the inverter types draw current in short bursts (that don't work well with the 50/60hz CT transformers).

You can short across J4 - J5 and just bypass the ARC Good and get the other parts working.

Which DRO are you talking about? There is no DRO for the TH300 in MACH for tip volts. The meter on the THC displays the actual tip volts while cutting. The course and fine controls control the tip gap and tip gap changes the tip volts in proportion (more gap = more volts)

[bad-rat-57]

Got some great help from the THC-300 guys. The initial problem with the torch driving down was due to the fact that my tip was way too close to the plate during the tests and instantly put the THC out of limits.

The second issue was the speed THC % setting on the program was set at 80%, reset to 10% for initial testing and worked not bad. Needs some fine tuning.

Arc OK signal still an issue. Working on some testing with the mfg to determine why relay is not responding.