Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: laugeo on October 07, 2016, 07:05:57 PM
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Hi, I’m wondering if you are able to offer some advice?
My home built cnc has been running flawlessly for 4 years but developed an intermittent problem with random stoppages for ‘Smoothstepper error’.
I changed the board to a usb board but to no avail.
I wondered if after 4 years there might be some cables starting to break down internally after all that movement.
So, the next step was a complete rewire and at the same time an upgrade. I have moved to a DMM Technology Breakout Board (DMB4250-8B) and to one of your ESS boards. During the rebuild I have added a contactor as the mains on and this highlighted that one of the 48v power supplies (I use 2 of these) had failed.
Of course, now I suspect that this had been the issue all along!
I have ordered 2 new power supplies from you to replace both of mine.
Anyway, I have pressed on with finishing the machine while I wait for the new power supplies and have installed the new ESS.
The question I am looking for some suggestions for is:
Although I am running on only one power supply at present – When I switch the machine on, the X and Y axis run perfectly but as soon as I touch the Z axis, the Z axis doesn’t move AND then both the X and Y axis become very ‘grumbly’ when I try to move them? This situation doesn’t change until I turn off power to the controls and then restart the machine. Also, when started up – although the X and Y move properly, if I leave the machine standing for a short period without any movement, then both X and Y will no longer move smoothly either, they grumble just as they do if I try to move the Z.
I have been back through the wiring multiple times and I’m convinced all is well. I am also running a quality 5v dedicated supply to both the BOB and the ESS.
Are these issues likely to be as a result of trying to run the machine on the single power supply and they may resolve themselves once the 2 new supplies are fitted?
Or is there anything else that you can suggest might be the issue?
I probably should have mentioned too that this machine is running servo motors not steppers on the X and Y but a stepper on the Z AND (although I know it is frowned upon) I have been running this machine for the last 4 years with the power supplies wired (properly) in parallel. I also run 3 drivers – 2 dedicated to X and Y and a lower powered unit for the Z stepper.
There is also a small Geckodrive unit to run my 4th axis occasionally.
I have attached my .xml in case that helps?
Any suggestions will be gratefully received – especially after the last 10 days of frustration!
Regards,
Colin.
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I am confused, will you end up with a usb ss or an Ethernet ss at the end of your rebuild?
The reason is because the uss suffers from ground loop issues potentially. You really need to check your wiring with the USBSS including the usb lead that connects to the pc.... make sure that there is no continuity between the outer sheild and the ground of your cnc case
The ess is less susceptible but can still suffer from secondary side ground loop issues.... use a separate 5v power supply for the ss and you should be fine but do not join all grounds or zero volt lines together
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To answer your question as I understand it, it would depend on the rating of the power supply and the current requirements for the motor/driver systems. I'm not too familiar with servo motor systems so I'm not sure if there is a driver for those but I'm sure there would have to be since most BOBs do not supply enough current to run motors directly. In any case, having two 48V power supplies would indicate to me that each one individually cannot supply enough power for all the motors (including the 4th axis that you use occasionally). In this case, the two power supplies should be dedicated to specific components in the system. In fact, even with one power supply it is recommended to run separate leads to each motor driver to reduce cross-talk potential. Depending on how your system is currently wired, this could be contributing to some of the issue if you've simply daisy-chained the power from one motor driver to another. But I suspect it is an issue with the amount of current the single power supply is delivering as compared to the current required to run the three motors - let alone the 4th one on occasion. And the fact the the X and Y motors do not operate smoothly after sitting a while indicates the possibility that the remaining single power supply may be failing as well.
If you have not already done so, make sure you have completely disconnected the failed power supply as this could be loading down the other one.
Otherwise, I think your new power supplies should help eliminate this problem as long as you have also made sure your motor driver power leads are not daisy-chained one to another. And as robertspark has indicated, make sure your grounding is proper and you do not end up with a non-isolated connection to your computer.
Stephen "Highspeed" Kruse
EDIT: I re-read your original post and realized that you did mention drivers even for the servo motors. So definitely check that you are not daisy-chaining power leads between these and instead run power leads for each driver directly to the power supply. Again, make sure the total load (current draw) for all drivers connected to a given power supply do not exceed the rating for that power supply.
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How have you wired the two power supplies?
Please tell me you did not join the (+) and (-) together..... (that will kill one of you PSU's if they are SMPSU's as the voltage outputs are never exactly the same or align as load kicks in which means one will backfeed into the other)
How many drives do you have?
If you take my scenario.... I have 4 drives X, X' Y and Z .... I use a toroidal transformer with two windings.... one winding feeds two drives ... the other winding feeds the other two drives .... (my drives are ac input [so much easier!]) ...
essentially I'd feed two (and or your occasional extra drive) off one of the psu's and then the other two off one of the other PSU's
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Hi,
Thanks for the advice. I have used a dedicated 5v power supply BUT I have returned all earths to a din rail. Why is putting all grounds together an issue? Pardon my ignorance.
I have no ground loops that I can detect and I have tested everywhere I can think of.
Thanks.
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Because you create the ground loop as unfortunately the power supplies do not output zero volts but the zero volt lines are offset from each other...
Suggestion.... if you have a voltmeter... break the dinrail... so that all the zero volt lines are seperate... then test the voltages between each of the zero volt lines with respect to reach other, that is your offset voltage... and creates your ground loop (which the SS will be particularly unhappy about and the cause of much annoyance to you)
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Its the reason why we use optoisolators and optocouplers.... to separate the circuit out... by joining the grounds you are effectively getting ride of the main benefit of the optoisolator/ optocoupler (other benefits being dissimilar voltages interface)
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Understanding a little more! Ok, I will try that. Thanks.
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Also remember if you have a 5v power supply for example, when you measure the no load voltage it may be say 5.2v... then when you apply the rated load on it it now measures 4.9v.... those voltages are with respect to the power supplies vcc+ and vcc- lines... ie the voltage is pulled closer together under load.... now when you join all the zero volt lines together you will try to pull those zero volt lines voltages upward too and change the offset voltage with respect to the other power supplies vcc+ outputs
With simple electronics and electrical circuits this is not seen as a problem but with high speed data communication (usb for example ) where the data is offset and has high and low status voltages for the different state a change in the offset voltage that's different... it looses packets plus the controller (FPGA) may lockup because the voltages they work in are minute differences with very little current flow)
Edit: man this autocorrect is killing my messages!
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I have already removed the dead power supply hence trying to set it back up with just one temporarily.
This may sound odd but I have run each positive 48v out of the power supplies separate from each other but to a common junction, I have done the same with the negative (to another common junction).
I have then taken a line from those junctions to the power in on the BOB.
I have taken the positive and negative power out lines from the BOB to separate (insulated and covered bus bars) and have then taken respective individual positive and negative lines (each of the same length) straight across to the drivers.
So, no daisy chaining. I hope this makes sense - clearly there a some VERY knowledgable people on here!
Thanks
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I have attached a picture of the new panel I have put together for this upgrade.
They say a picture pants a thousand words? Hopefully it will explain more clearly the layout and connections I have been talking about.
As I said before, there are clearly some very knowledgable people on this forum so NO LAUGHING!
Thank you.
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Yes, sounds Ok... suggest maybe splitting your drive power supply from your bob.
I have 50v ac to each of my drives... 24v to my bob... then a 5v supply to my ess (when I ran an ess... now moved on... same principle applies). None of the zero volt lines are joined... plus because the bob has optoisolators within it it separates the 5v motion controller signals from my machine side 24v signals.... plus the dries have optoisolators in them.... hence the ability to feed them directly off their own power supply (which does just happen to be ac) ... but I did a similar thing when I ran lesser 42v drives too
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Looks neat... note... I've edited one of my previous posts as my autocorrect on this phone is killing my messages and changing the text to any old thing it thinks...
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Ok, last dumb question (unlikely!) if you don't take all the earths to one place what do you do with them. I thought the whole point was that (ultimately) they all do end up in one place?
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Ahh.... earth's are a different matter...
People get very confused by earth's... vcc-.... 0v..... gnd.... and think they are all the same.... they are not!
Ask yourself what is earth?
It is essentially the 0v with respect to everything else...
Electrically.... mains voltage side... it is created at the substation transformer by grounding the centre tap of the transformer.... the transformer will be in one way or another a star wiring configuration.... so as the three electrical phases move 120 degrees out of sync the star point provides a common 0v point.... and because this is grounded at the transformer literally by driving earth rods or more correctly laying an earthing mat in the ground this provides the earth point.....
Now the next problem is your wiring arrangement... they vary across the world... but essentially you need a live (hot wire) and another wire... in the rest of the world (non 2 or 3 phase) this is called the neutral phase.... and it is essentially the centre tap of the transformer..... same as the earth.... sort of.....
These two wires are required .... now there is a choice by the local electrical requirements... with a separate protective earth can be sought by laying of an earth mat... and or driving earth rods into the ground (same as the mat) .... or connecting onto the neutral or a combination of the two....
...2 phase (common with USA 110v and remote uk supplies plus others I suspect too) and 3 phase are a little different...
.....I need to do this over a few posts as I have children demanding lunch (uk time)
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I didn't finish this one off.... 'll have a go here, but I've kind of lost my chain of thought...
There is a bit of waffle over here on the UK earthing arrangements..... basically although the nomenclature is UK based, if you consider the wiring arrangements it kind of covers every possible permutation of the incoming earth....
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwj2o6ycm9DPAhXKJsAKHZUuDeMQFggfMAA&url=http%3A%2F%2Felectrical.theiet.org%2Fwiring-matters%2F16%2Fearthing-questions.cfm%3Ftype%3Dpdf&usg=AFQjCNGgVmZa42MaWWheFH0je93n2TQVdg&sig2=12kT_2cmztOW93h4-zaNaA&bvm=bv.135258522,d.d24
Because cnc systems work on lower voltages, we have step down transformers or switched mode power supplies.
Both of these allow for electrical isolation of the primary (mains) and secondary (lower voltage) sides and all use some form of transformer (two / more coils of wire wrapped around a ferrite [iron] core).
Because of this electrical isolation, you really want to separate out the secondary side 0v, Vcc- or ground connections because they will never be at exactly the same zero volt potential as the primary side because of the load characteristic trying to reduce the potential differences between the two wires when under electrical load. ...... its this electrical isolation that means that the are not true "ground" voltages but can be offset slightly which will lead to some current flow
Lots of people just join them all together and in some cases link them to the earthing point which makes it even worse.... because it can create earth leakage currents.
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I'm probably going out on a limb here and slightly disagreeing, ok maybe not disagreeing but raising a few points... :)
In theory the secondary 0v rails can be joined to chassis ground/supply earth quite happily - no current can flow between this link *unless* there is a path from the +ve supply rail back to the chassis ground somewhere - this should never happen.
Now, i say "in theory" because the chassis ground may possibly contain all sorts of nasty things like RF from a plasma supply, spikes from other sources and generally some noise. The level of this electrical muck can depend on how good or bad your supply earth is - if it is good then the muck gets drained rapidly to safety, if bad then it can raise the earth potential above where you think it should be for the duration.
Next - suppose I have my low voltage supplies floating - this is what you describe - "floating" because neither rail is grounded, and there is a short from +ve to chassis - what will happen? Nothing will happen apart from all the muck on the earth will now get injected into the +ve supply rail and forwards.
So, say i ground my 0v rail to chassis and there is a +ve short to chassis - what will happen now? It *should* blow the fuse alerting me to an issue, after tearing my hair out for a few hours or days trying to find out why it stopped ;)
As you can see, grounding can be a nightmare and can cause issues if not done correctly, I am not saying that 0v should be grounded, especially when a PC is involved UNLESS there is 100% opto-isolation on all signals and the 5v rail is not being pulled outside the PC to power a BOB or the MP3 player etc :)
Its all about loops, interference, safety, shielding etc and sometimes - take a CNC plasma cutter, probably the worst case scenario, it can be a nightmare to get right.
My Bridgeport CNC conversion has multiple PSU's - one is grounded and powers the control signals into and out of the CSMIO controller, it needs to be grounded because i use a touch-plate which uses ground through the machine as a return path.
The other PSU is NOT grounded and only powers the CSMIO controller itself, this controller has fully isolated inputs and outputs so this lack of grounding ensures there no possible path for any muck to get into the controller. The PC will be grounded of course but it uses ethernet which is isolated so no loop there. The servo drives are grounded via the chassis (bolted down) and the AC supplies but internally who knows?
;)
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Gents
Don't get your PE and system earth mixed up keep them separate
With 50 years at the Sparks game you do learn a bit , last job 27 years looking after a large Uk banks main computer centre (facilities engineering) you can imagine the havoc with data and high power stuff not to mention some 400hz stuff in the mix the main PE was dirty odd order harmonics all over the place
Keep them apart , no loops , only star point earths
I wish you luck to calm it down , shielded cable from the bob to drivers are recommended but only connect the shield to system earth at on end only .
In my book PE is only for the mains power side be it 240vac ( uk ) or 110vac for the guys across the big pond
Stuart
PS if your machine is in a garage/workshop consider putting in a good copper earth rod at least 6 foot long for the main PE that will calm it down that's what I have done even that we have a PME system
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Haha... Nothing more emotive than equipotential bonding....
The bit that I was trying to sort of get to is keep the earth and secondary side separate.... but if you have optoisolators.... desperate the power supplies unless you're using the optoisolator for dissimilar voltages interface.
Like most things in life... do whatever you want... if it works for you happy days...if not try something else..
But the smooth stepper is particularly susceptible to ground loops and the usb one electrical noise too (which is what was part of the original posters post)
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That's easy to sort out Robert just bond everything with some 6mm or bigger :) :) :)
Agree is a mine field what work in one situation fails elsewhere
I was brung up on the 13th edition nice little blue book
Stuart
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... yellow 16th... now consultant on the dark side... mechanical ... I could tell you some funny house bashing tales... of moving meter boxes as foreigners using an electric drill on a bit of bell wire wrapped round the tails.. when there was a knock at the door.... "come to read the meter mate." .... "oh F!".... "hmmm... ill come back later mate should I?" .... "yeah nice on mate..."...
Not me you'll understand....
Them that can do... them that can't ... consult...
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PS if your machine is in a garage/workshop consider putting in a good copper earth rod at least 6 foot long for the main PE that will calm it down that's what I have done even that we have a PME system
:) :) It's a fascinating subject for sure.
I am in a garage and was advised not to run an earth rod when i fitted the plasma table. We are PME and was advised it would not be good as the earth was exported from the house supply then it got technical :)
It all seems to work ok so i have not questioned it ;)
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Dave
As my play pen is remote from the house there was a chance that the Earth at the end would float up in respect to the actual earth it's self so I bunged in a rod now I am confident that I have a true Earth in the play pen as well as the Earth rod fo the house.
Dave not done much house bashing I was more to heavy power and high voltage , as I was a SAP and did live line working and underground live jointing it's a different world , we were the supply authority for a village owned by the firm I served my time at I have seen most of the meter work but best not tell how here :)
Earth testing is a major field in its self not a simple matter well that's what my paper was about the other was lightning
I have polluted this thread to much so I will now go quiet
Stuart
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Hi,
Thanks for the advice. I have used a dedicated 5v power supply BUT I have returned all earths to a din rail switching mode (http://www.wattcoenergy.com). Why is putting all grounds together an issue? Pardon my ignorance.
I have no ground loops that I can detect and I have tested everywhere I can think of.
Thanks.
I can't detect either