Voltage Scale and Auto Volts

I think I would try and log the encoder velocity in halscope and a few other variables that work on this. just in case something is happening in software between reading the frequency and converting it to a voltage.

Probably watch these
plasmac.arc-voltage-in float in arc voltage input [mode 0 & mode 1] see Notes above
plasmac.arc-voltage-offset float in offset to set arc voltage to 0 at 0 volts
plasmac.arc-voltage-scale float in scale to convert arc_voltage input to actual volts

Hi Peter, I'm not on this forum much / don't have much time to reply or follow threads.

However I took a look at yours and it's got me wondering.

You have a hypertherm 125, and the problems you experience are when you are cutting very thick material (32mm), at 125A and your machine is struggling to maintain voltage.

Just to think outside of the box here for a minute.....

The hypertherm plasma cutters are quite intelligent so.....

I suspect maybe your power supply is not up to cutting at 125A as they will try to compensate to maintain a consistent cutting current.

(happy to be told that I'm talking out of my rear here, but I'd suggest you consider it, and maybe go back to basics and investigate a little before twiddling more settings IMO).

xnet.hypertherm.com/Xnet/library/library...HYP116922&format=pdf

I don't own a 125 (but do own a 45 (nonXP)).

There seems to be 4x variants of the 125 and I'm not sure which one you have:
480V CSA
600V CSA
400V CE (European Market).
380V CCC ( Chinese specification)

each of the machines will require the following current (I'll igore the ccc one as I don't think its that common or one that you'll have).

480V CSA - 50A
600V CSA - 38A
400V CE - 55A

These amperages are rated at ARC STRETCH, i.e. when you fire the torch at pierce height...... or if the torch is rising up to it's maximum cutting height)...... your machine is presently trying to do that.

Yes, the actual cutting currents are rated at
480V CSA - 31A (21.9kW)
600V CSA - 24A (21.9kW)
400V CE - 36A (21.9kW)

the interesting thing to note here is regardless of the actual voltage and cutting current all the machines have the same kW (power rating) so the machine will try to maintain that same current rating when its cutting.

Also of note is on PDF page 30 (page #28) of the linked Operator manual above there is a +20%/-15% voltage tolerance parameter.

When you are trying to cut at 125A, it may be simply that your machine is compensating for undersized supply cable (or a long way from the source of supply) by lowering its cutting voltage to try to maintain the cutting current setting, the CNC is seeing this and rising the machine up which is making the situation worse.

I would suggest you measure the supply voltage at the machine with the machine OFF.

I would then suggest that you measure the supply voltage with the machine cutting and see what the actual supply voltage is when the machine is cutting at 125A. When you do this I would suggest that you set the machine to operate with THC lock (ie the machine will not try to compensate for a falling voltage).

Please note, you are best to measure the voltages between PHASES or between each PHASE and NEUTRAL so that you end up with 3x readings minimum when you are in both OFF and 125A cutting mode.

I would also suggest measuring the voltages say first thing in the morning / before you start cutting as I suspect that once you have been cutting at 125A for a while the cables are probably going to be getting warm and their resistance is changing.

It is also worth checking your electrical connections along the whole supply to ensure that you do not have a loose joint somewhere that could be causing you the agro.

Please note that 600V and 480V or 400V can obviously kill and you need to be mindful of that when removing covers to check electrical joints are secure and you've not got a loose joint and also when you are taking supply voltage readings.

If in doubt get an electrician to do it for you (or wear your big boy pants and take responsibility for your actions & omissions if something goes wrong..... you probably won't be here to argue about it).

a 5% voltage drop in my opinion would be acceptable + good (it would fall within the UK design guidance).  However you are actually allowed a bit more if the manufacturer of the equipment allows it.... and in this case hypertherm do with a -15% (from the rated voltage, not the measured voltage).  However that to me would indicate that your cable is probably overheating and its resistance is rising over time as it gets hotter ...... 

It is worth noting that a cable as it gets warmer, it's resistance will rise:
www.cirris.com/learning-center/general-t...%20C%20(room%20temp).

which may be something you are experiencing cutting at 125A if your supply cable is undersized (or your supply is undersized or you have a joint problem).

I have access to a thermal imaging camera and they can be useful to check for potential overheating issues once things have been running for a little while to show where you may have issues and are sometimes (quicker and safer) than isolating the supply to check joints / bolted connections.


good luck, let us know what you find or how you get on.

I had a similar problem with a H 65 that was in a workshop on single phase but with a long run of cable. upgrading the under sized  cable fixed the problem.
Just saying 

Hi all,

Thanks a lot for the suggestions and interesting thoughts. As regard to the power supply, I will check that or get it checked. There is a lot of machinery hooked up to the main supply board in the shop, it might very well be that the voltage drops when we are cutting and some machines are running or starting up. That would explain the erratic nature of the problem too.

Firstly I will change the THCAD to a fresh one that we have as a reserve, then we rule that one out as the culprit. If that board still shows the same voltage as the current one then we will certainly investigate the power supply.

Thanks again for all the info !

Cheers, Peter

Hi all,

It looks like we have finally solved the riddle that has been bugging us. I had the THCAD jumper for frequency dividing set at 1/64 as per user guide. I changed that to 1/128 and changed the necessary settings, and that works. At 25mm the machine reaches the voltage as per Hypertherm manual, and the THC works beautifully. I use a configuration with lower acceleration as per Tommy's suggestion, increased the THC delay but other than that most settings are similar to the recommended settings. I have also cut 16mm and 2mm without any hiccups. On 2mm I have used a FineCut nozzle very close to the material and the THC follows the material no worries, even when it buckles a bit.

I thought I share the good news with all of you who have given time and thought to this, we really appreciate it. I also hope this might help if anybody ever gets the same issue.

Cheers,

Are you using a Mesa card or a parallel port with your THCAD-10?
Most of us with Mesa cards would be using 1/32 divider so I suspect you are not using one.
 

Great news Peter, thanks for letting us know.
 

CFE wrote:

I had the THCAD jumper for frequency dividing set at 1/64 as per user guide. I changed that to 1/128 and changed the necessary settings, and that works. 

I will add a note in the doc about your experience with thicker material.

rodw wrote:

Are you using a Mesa card or a parallel port with your THCAD-10?

It is in the config that was posted forum.linuxcnc.org/plasmac/44512-voltage...olts?start=20#229583