Hi all...been a member here for quite a while but not posted before....so be very grateful for any help offered......
I am currently using 3 SD-2H044MA stepper drives in my small home built plasma CNC machine. I am having problems with one or other of the axis 'freezing' in mid program and the red fault light coming on the drive. I have to stop Mach3 and turn off the power to the stepper drivers even have to reboot Mach3 sometimes to get going again. I am using 1.7NM Nema 23 drives and running them from two separate PSU's - one a 27volt 13amp for the Z axis and the other a 36volt 10 amp for the X and Z axis. The current setting for the motors is only set at 2.2 amps. The Nemas run cold. I have everything shielded and grounded. I have capacitors on all the BOB inputs. I have a very large and expensive mains filter on the electronics and I have the debounce setting at 400us on Mach3 but still I have the axis freeze...not the same one but random X Y and Z. It seems to happen mostly, but not always, whenever the plasma cutter 'stutters' at the beginning or end of a cut. I have the plasma cutter on a separate mains supply to the PC and drive electronics. It is ruining a lot of my work and I wonder if I should change my drivers or is something else causing the problem? I would be grateful for any ideas on this.......cheers Gerry
Last edited by gerrymoore; 29-08-2013 at 12:50 PM. Reason: mistake in text
Certainly sounds like an interference issue, which is causing the drives to trip on a fault.
Google turned up the following manual extract about what could cause issues.-
To improve reliability,the driver incorporates some built-in protections features.
When power supply voltage exceeds +45VDC,portetion will be activated and power indicator LED will turn red.
Coil-ground Short Circuit Protection
Protection will be activated in case of short circuit between motor coil and ground.
Attention:Since there is no protection against power leads(+,-)reversal,it is critical to make sure that power supply leads correctly connected to the driver .Otherwise,the driver will be damaged instantly.When power supply voltage is lower than +20VDC,the driver will not works properly.
If it's near any of the control/motor wiring, try moving it away, even it means tying it to the roof and letting it dangle just to try it.
How have you connected the plasma cutter to the controls?
Also, you do only have the cable sheilds connected to ground at one end?
Thanks for your response....
1st the voltage..cant go more than 36 volts so not that
2nd coil ground short...not sure how this would happen but sometimes the machine behaves perfectly, other times it a real PITA..and it's different axis hence different motors.....so don't think it's a coil short.
The plasma 'wiring'? If you mean the mains input it's well away from the machine and electronics on it's own 30amp supply.
The 'switch' for the plasma...I made a litlle circuit - fully enclosed in a metal box - that takes the 5volts output from the BOB 'spindle enable' signal and thru a ULN relay driver to a relay that switches the plasma torch....my BOB doesn't have a relay fitted.
Most of the cable shields, but not all, are grounded both ends.
As I said, it seems to be whenever the plasma cutter (RTech P40 - which I'm not impressed with) fires or ends a cut....but not always!! It has a habit of stuttering the pilot arc and the drive electronics really don't like it. I've fitted an expensive mains filter to the drive electronics and I have a spare one. I could fit this to the plasma (it's rated at 55amps)...other thing I thought was a UPS for the PC and electronics...or different drivers??
Just because the voltage supply is a 36V, doesn't mean interference from the plasma won't cause a spike on it, however I'd expect that to of damaged something by now.
The stepper motor fault detection will be a reasonably sensitve system, which is what is probably causing the fault. I doubt there is an actual fault, but noise on the stepper wires may cause the driver to think it's dected a fault. Or even just noise in general may be causing problems in the stepper drive. Have you tried putting a additional capacitors on the power inputs to the drives?
By plasma wiring, I mean the torch cable. Is it routed near the stepper/control wiring?
Cable sheilds should only ever be connected at one end!
By connecting them at both ends, you create ground loops which are far more likely to cause noise issues. I'll try and dig out a link to the usually recommended earthing/grounding guide.
Hiya...and thank you for your time over this. The spikes you talk about I thought would be taken care of by the very large mains filter I've fitted recently but I must say it hasn't helped at all....just glad I didn't pay the £185 price tag on it!!!
I agree that the drives must be very sensistive and I am considering different drives but not sure which ones...they are not cheap and I can't afford to waste money.
When you say additional caps on power inputs to the drives...the only caps I have fitted are a few little 0.1uf to the limit switch inputs on the BOB...I don't have anything on the driver inputs...can you explain more on this please?
Torch cable goes up and away from the machine although it does go close to the Z stepper ...strangely the Z stepper hardly ever faults!!
I'll check my shields and remove any 'duels'.
At the moment, I suspect that the drivers are too sensitive and the plasma is too noisy....aarrgghhh...why did I get into CNC :-))
Noise/interference can come from two sources.
Either wire bourne, i.e. noise from one source travels through common wiring and into another device, or air bourne, i.e. something unsheilded generates electromagnetic interference (EMI) which then creates a voltage/interference in any nearby conductors.
The mains filter should stop any interference from entering via the mains, however your system will still be susceptible to EMI. The point of sheilded wiring is to stop the EMI from reaching the wires within the sheild, and drain any generated voltage to ground. If you connect both ends of the shield, if whatever either connect to is at different voltages, even a very small difference, then current will flow through the shield start producing EMI.
The big issue with plasma, is they're a very good EMI generator due to the high voltages when striking an arc, and any metal nearby will absorb that causing a voltage to be generated in it.
Which reminds me of one thing, have you ensured the plasma table/frame itself is well grounded?
If the table isn't well grounded, then that could be the source of your problems, although I can't decided what would be the best grounding technique. If you use a ground other than via the control box, then you'd have to ensure nothing connected to/within the control box also connected the table to ground, otherwise you'd end up with one very large ground loop. And if you grounded it via the control box, you'd have to ensure all the connections were perfect.
Have you tried over on CNCZone to see what's suggested to combat noise on plasma tables?
Hello..and thanks again for your input. I cut quite a few parts out yesterday without a single problem. They were quite large figures so the plasma only had to 'start' once for each figure andit's the initial start of each cut that usually causes faults...especially if there are a large number of holes to cut...I have learned to do them in small batches. Only thing I changed before cutting was the current setting to the drivers which I reduced from 2.37amps to 1.91amps...made no visible difference to the performance of the machine but may have helped?
Re the table earthing...The only 'earths' to it are where I shouldn't have them...in other words the shielded cables earthed both ends. The plasma cutter has a large bolt on the back...wonder should I conncet this to the table and ensure all the other earths are removed? A curious thing happened the other day...I had forgotten to put the earth clamp from the plasma cutter on to the steel I was cutting...the plasma cutter stuttered badly and the other PC in my workshop started up!!
Yesterday I removed all the earths from the cables and connected the plasma via its earthing bolt to the table. Cut load of things and it froze the Z axis once..but not cutting holes yet so can't be too optimistic.
On Monday, I'll try cutting a load of holes on some scrap and see what happens.......
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