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Offline laugeo

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Any help / suggestions please?
« on: October 07, 2016, 07:05:57 PM »
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.
Re: Any help / suggestions please?
« Reply #1 on: October 08, 2016, 03:32:21 AM »
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
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”
Re: Any help / suggestions please?
« Reply #2 on: October 08, 2016, 04:19:52 AM »
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.
« Last Edit: October 08, 2016, 04:22:43 AM by Highspeed1964 »
Re: Any help / suggestions please?
« Reply #3 on: October 08, 2016, 04:35:18 AM »
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
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”

Offline laugeo

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Re: Any help / suggestions please?
« Reply #4 on: October 08, 2016, 05:20:59 AM »
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.
Re: Any help / suggestions please?
« Reply #5 on: October 08, 2016, 05:26:00 AM »
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)
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”
Re: Any help / suggestions please?
« Reply #6 on: October 08, 2016, 05:29:44 AM »
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)
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”

Offline laugeo

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Re: Any help / suggestions please?
« Reply #7 on: October 08, 2016, 05:39:02 AM »
Understanding a little more! Ok, I will try that. Thanks.
Re: Any help / suggestions please?
« Reply #8 on: October 08, 2016, 05:46:17 AM »
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!
« Last Edit: October 08, 2016, 05:55:51 AM by robertspark »
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”

Offline laugeo

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Re: Any help / suggestions please?
« Reply #9 on: October 08, 2016, 05:50:55 AM »
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