Voltage Scale and Auto Volts

Hi all,

Thanks again for all the info. I have tried different things as per all suggestions from you all, but the main problem is still there and seems to be this : the machine starts cutting and after a undetermined time it just rapidly lifts up the torch and of course then it loses the arc. Sometimes it goes the other way around, the torch just dives into the material. On 25mm plate the feedrate is not very high, so the THC should be able to maintain height at its leisure. But it just goes awry in the blink of an eye.

The problem is that this happens very erratic, sometimes we cut half a meter without problems and then all of a sudden the torch decides to go whichever way it wants to go, buggering up a part. And sometimes this happens after say 50mm of cutting, and sometimes it doesn't happen at all. Something seems to trigger the torch to go up or down without a feedback loop to correct it.

Most of the time the THC works splendidly, it is very fast and is highly responsive. It's just this gremlin we are chasing and we can't put our finger on what it is.

Cheers, Peter

Try to catch what is going on with the voltage when that happens.
Seems like interference on the THCAD side, so first thing to change is the 5V going to it.

tommylight wrote:

Try to catch what is going on with the voltage when that happens.
Seems like interference on the THCAD side, so first thing to change is the 5V going to it.

On this note, it may be worth brining up halscope and watching the voltage at idle while not cutting.  I found that I had my shield connected to table ground, and it was actually making the signal noisy, even at idle.  I removed any connection to the shield, and the noise went away.  I had asked PCW about it, and the basic answer was that whatever makes it less noisy is the best option.  

Yes, plotting the voltage with halscope when idle and when cutting
should help pinoint what's going on. Normal operation followed by
crazy behaviour at random times sounds like a hardware issue of
some kind.

Hi all,

I had a look with Halscope and the voltage is fluctuating about 3 volts at idle. About the same when cutting. The fluctuations seem pretty consistent in time, I don't see spikes larger than 3 volt when at idle or cutting. Can a 3 volt fluctuation trigger this behavior ? The THC treshhold is set at 1 Volt.

Do we consider setting the voltage divider on the Hypertherm at 20:1 and make the relevant adjustments ? Will there be an advantage in doing that ?

I checked the cable and shielding for the arc voltage and that looks like it is grounded as per info I have been able to find here on the forum. The THCAD has it's own power supply, separate from the motor drivers and breakout boards. I am reasonably confident that is okay, but I will try to route a different cable from the plasma cutter to the controller to see if that makes a difference. On that note, we have the THCAD in the controller box, would it be better to have the THCAD mounted in an enclosure on the back of the Hypertherm, to minimize noise on the cable feeding the arc voltage in the breakout board ?

Cheers, Peter

If you look in halscope you will probably find there is an AC ripple at 50 /60Hz depending on your  supply.
As Snowgoer mentioned, try with  the GND wire from the THCAD removed. In most countries the Neutral wire is bonded to earth at the meter box so the AC ripple comes back up the earth wire. I found it added quite a lot of noise at the THCAD with this connected to frame ground.

Just let halscope run without cutting and remove the GND and see what happens at 0 volts. It may quieten down.

There is no need to move the THCAD. I've always had mine in the cabinet with a 120 amp machine.

If you can change the divider to 30:1 on your larger machine its 300 v full scale. Otherwise 20:1 is OK with full scale of 200V which is higher than cut volts except when piercing and the THC is not looking then!

Also,  the THCAD should be powered from the mesa card. From memory there are 5v signals on the encoder for this purpose.
Its coming back to me now, thefabricator03 had similar issues to you and I think the separate power supply is the culprit! Should be an easy fix.