What has gone wrong????

[EddyCurrent]

So why did the 24v PLC power supply not work ?

[Davek0974]

Well, from what I can guess, it was a poorly filtered smps that was allowing all sorts of muck through. Simply replacing it with an old style iron transformer and simple components fixed the issue.

it was not just that smps either, I had tried four different units but all were smps', seems it just does not like them.

[m_c]

Given that the BOB in question also has a SMPS built in, it may not of liked being powered from another SMPS, especially once you threw in a few spikes from interference coming in from elsewhere.
I would of tried connecting an extra capacitor across the input of the BOB to provide a bit additional filtering before I went to the hassle of rigging up another power supply.

[Davek0974]

Yes a large cap might have helped out, but was not suggested in time :)

it could well be that the intelligent regulator did not like the output from smps as you suggest, it's a pretty advanced little board.

still, it's going now and that's all that matters, notes will be made for future use.

[tommylight]

To late but still, get RID of all that grounding, stars etc. Computer ground = power supply minus rail, BOB = no ground never ever, drives = no ground = grounded through power supply or not at all, Plasma gound clamp = POSITIVE power rail on plasma. Also using the same PS for Z axis drive and BOB = no good unless you know exectly the inner workings of both and the said PS = short between PS in some cases.
As a rule for plasma: short wires, no wires going paralell with torch ang clamp wires, and a good clamp to workpiece contact.
Regards,
Tom