PMX1250 cnc interfacing

[steve_p]

I've just replaced my Powermax800 (+ PAC121 machine torch) with a used 1250 (+new T80M machine torch $$$!). I'm getting arc start, but no movement... the arc stays on for about 10 seconds before the control (Burny 2.5) gives an arc fault. I've tried on various thicknesses up to 8mm and it does the same.

The 800 has the same 4 terminals (2 for start, 2 for xfer), and I just wired it the same. The 1250 came with a hand torch, are there any links or jumpers that need changing when switching torches?

I'm wiring the cnc control lines directly into the terminal block on the 1250 main pcb rather than the rear panel socket, but the socket just connects to the terminals anyway.

Seems odd that it might be different. (While I'm on the subject of strange things, why did Hypertherm move from a nice all-in-one mig welder-style torch connector on my PMX800 and old max100, to the strange push-the-wires-and-air-connector-through-the-panel-and-push-in-a-plug system? It's a bit of a shame when, like me, you want to be able to switch over at will- it feels like the wires will get pinched or abraded at some point.)


UPDATE

I just tried linking the xfer wires at the plasma machine end of the cable manually, as a program was run, and it was fine (it waited until I shorted them, and did a cut, then waited till I opened them to begin the next cut) So it seems my 1250 isn't operating its internal relay. Is this likely to be a fault, or is there something I need to do to put it in some kind of 'auto' mode?

[jimcolt]

I would suggest talking with Hypertherm tech service directly. I cannot remember if we use exactly the same circuit on the 1250....but some of our units have a capacitor across the arc transferred relay contacts that in some cases needs to be removed from the circuit. Th tech service guys can help you out with that. You can also transfer an arc to the plate and monitor pins 12 and 14 to see if they are closing when the arc transfers.

We switched to the 1250 style torch quick connect for reliability reasons.....the earlier style had its share of failures in the field, mostly mechanical failures (things being dropped on the connector, machine being pulled around by the connector). The new system that will replace the 1250 (Powermax85) has a new quick disconnect that is very easy to use, and is protected and more rugged than the original 800 style design.

Technical Service
technical.service@hypertherm.com
800-643-9878 Tel - Toll Free in USA
and Canada

Jim Colt

[steve_p]

thanks Jim, I'll speak to tech support tomorrow (I called today but missed them, and as it was only 4.10pm I was pondering on the wisdom of a company being owned by its employees, until I realised the tech department is in Holland, so it was 5.10 there!)

I tested the xfer terminals on the PCB, they don't close when the arc transfers, so it looks like a fault, unless there is an optional removable component like you mentioned. If it is a fault, I guess I can either trace the fault (the arc ok circuit seems pretty easy to see on the board, there's a current transformer and a few discrete components and the relay, so it shouldn't be too difficult.) Otherwise, I could just add another current transformer such as the ones they sell with THC kits for a few dollars. Do you know if the Hypertherm circuit is much different/better than these?

By the way, the cuts the new T80M on the 1250 did with finecut tips when I was manually triggering the xfer signal are noticeably better than I was getting before- I did a 150mm dia flange with bolt holes, the disc came out at 149.95mm and the 10mm holes were within 0.1mm circularity. When I first bought the machine, I was disappointed at the results- I assumed the mechanics were worn out, since my small holes were badly eliptical, but I realise now how much difference the power source/torch makes (as you said in another thread of mine Jim)

must get a THC on there now!

[steve_p]

For anyone else ever in the same boat as me, I'll post here how I fixed the problem- I called Hypertherm as Jim suggested, but they said it was definitely a fault in the arc transfer detection circuit, and the only fix was a whole new circuit board. I didn't bother asking the price, because I'd use a separate current transformer rather than do that.

But I guessed I had nothing to lose by having a look, so I removed the pcb (the 1250 is much better designed internally than the previous generation 800, all the large components are mechanically attached to the chassis, but aligned so that the pcb just bolts onto their terminals- hardly any cabling) which took about 15 minutes. The xfer circuit is quite easy to locate, and nothing seemed burnt or discoloured, so I thought the first thing to check was the relay. I desoldered it from the board (the hypertherm tech tried to put me off a board-level repair, saying it was multi-layered, but it just looks double-sided to me, which isn't a problem) and sure enough, the coil was open-circuit. I happened to have another pcb-mount 24v relay kicking around (I checked the coil resistance to make sure it didn't draw more current than the original), but the pin-out was different, so I just glued it to the board and wired it in.

Half an hour later it was all back together and... success! Works perfectly. Cost me nothing, although a relay would have been about $2.. a bit less than a pcb.

Anyway, I've been running it all day today, cutting 10mm mild steel. I've attached a picture of a part, it was drawn at 100mm, but it came out the wrong size- you can see by how much in the image...

that's 0.0004 inches, for you americans.. However the bottom surface was 0.5mm bigger