Rods "Spaceship" Scratch built Plasma Cutter build

robertspark wrote:

Am I reading the resistance correctly.... 11k ohm?

Checked my notes. Should be 2.2 k ohm as per advised by PCW.

I've been ignoring my plasma build for a long time becasue I sold my Everlast to another forum member with the intention of buying a Hypertherm XP45 but other priorities have got in the road. But now my table is sitting in a shed with a 3 phase power point beside it and I really need to get it going now the new year is with us.

So a question for the plasma guys on the forum. I have found an older Brand new in box 120 amp Thermal Dynamics A120 machine with CNC interface and a SL100sv machine torch at a very good price from a dealer. Its not much more than what I was intending to spend and about half the price of a Hypertherm 125 amp machine.

This machine is coloured blue and the current model is green. The torch is the same. Did anything change other than the paint?



Would it be worth buying or is it going to be a headache?

Rod

Does the machine have the "full CNC interface board" with voltage divider or just the the ArcOK and Arc Start signals available on the CPC connector?

I think the newer machines have different controls and are closer to HT in features. The one thing I don't like is the cutting current setting knob. You are entirely dependent on TD's calibration being correct, no actual arc current feedback. I have pencil marks on my panel to aid in reproducible setting.

One thing with any TD machine is that the cut tables are really lacking compared to an HT. This is actually the reason I made my "Franken Torch" by grafting the Duramax parts onto the front of my SL100sv torch. Not really a problem for you with all the THC testing you did, the process for finding the correct cutting parameters is the same and the book does provide a starting point. I think I get better consumable life with the HT parts.

One strange to me feature is that if the SL100sv torch shield touches the material while cutting the machine will throw an error and stop cutting. This caused me no end of grief with my old commercial controller. So much so that I hacked the unit to prevent this from happening. This most likely isn't necessary with my new LCNC control with the good THC.

My TD power supply hasn't missed a beat in ten years of use. I am careful to feed it clean dry air and clean out the dust once a year. The ambient temperature here is much cooler than Oz. The front panel looks the same as mine accept for the A120 logo which is A60 on mine.

Make sure you get a really good deal from the dealer, plenty of consumables thrown in etc. This is an old stock machine and not the latest and greatest.

John

John, thanks for your input. I'm not sure if I want another experiment. I did note that there is no voltage divider as standard. That might not be a bad thing as the THCAD10 could be mounted on the machine and fed raw arc voltage.

The newer TD machines (eg. a40i/a60i) have a switch on the divider board to select between tip contact as being for ohmic sensing or an error signal and have ohmic sensing built in. I wonder if that error you had was by design?

I did have a good trawl through the plasma spider forum last night and some liked the machine but it was obvious you needed to set it up properly for each cut with correct pressure and tip.

So it sounds like I need to get them down under the price of a Hypertherm 65 to make it worthwhile considering.

I actually have my homemade voltage divider inside my A60 with the divided voltage on the correct pins of the CPC connector. My THCad is mounted in a small box that sits on top of my my A60 and also serves as the terminals for the Ok to Move and Arc Start signals. This way I am not trying to send an analog signal across the noisy shop floor.

I was told by TD customer support after a lot of questions that the shorted shield feature was a request from one of TD's OEM customers. It is only active when the SL100sv torch is used, when the hand torch or aftermarket machine torch is used it is not active. It works by sensing the presents of the second air solenoid valve in the torch.

Yes, you should get a significant discount to take that unit off the dealers inventory.

John

Well I bought it! I screwed them down another $500 so according to Google I paid about USD $3500 for it which in the Aussie Market was a steal for 120 amps of cutting power! Thats about what you pay for a Hypertherm 65 amp machine.


I pulled it apart to check the divider settings which were set on 50:1. I changed it to 30:1. Apparently, the maximum arc voltage is 260 volts so this will get it very close to the 10 V full scale of the THCAD-10 at 8.7 volts. It remains to be seen if the THCAD10 sees the divider board resistors as part of its resistor network or not.

Interesting that there is room to mount a board inside the machine beside the voltage divider board and it looked like this would be perfect place to mount a THCAD-10


Hmm, I better check that that wire is properly seated now I've seen this photo.

So a question for PCW... would it be OK to power the THCAD-10 from the Plasma inverter or should it be powered by the control panel? The manual says there is 12 volts on this board so it would be pretty simple to add a 12v to 5v Buck converter to step down to 5 volts for the THCAD-10.

I got as far as getting power and air to it today but still need to sort out the interconnect cable and revise the air supply before I can use it. Also, I need to add a larger drag chain to accommodate the much larger cable for the torch.

Grotius has been kind enough to provide me with some amperage settings for different materials as its a bit confusing becasue the machine came with a very generous starter pack of consumable with cutting tips for 30, 40, 60, 80, 100 and 120 amps and the cutting charts go right down to 2mm material for a 120 amp arc . (40 amps sounds like a much better amperage!)

Tommy, thanks, I suspected as such. I just realised they gave me a nice heavy duty 12 core interconnect cable so there are a few spare wires in it that could be used to power the THCAD.

In any case, its a bit of a plan B as the THCAD is already fitted in my control box but I'll give it a bit more thought. In theory, it should be more robust to send the frequency back to the control box as it should be more immune to noise then a divided arc voltage.

And if anybody has ideas for a simple DIY ohmic sensor circuit, it would be good now I have a machine that supports it.

Tommylight is exactly right, the THCADs main function is to isolate the
_very dirty_ ground of the plasma supply from the controller.

You dont want _any_ direct electrical connection from the plasma supply to the controller