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View Full Version : 19inch Rack Enclosure - interference?



Washout
25-08-2012, 06:18 PM
Hi all,

I'm researching some electronics stuff for my CNC project and was looking at an enclosure to use with the following kit:

Zapp Automation Ltd - Stepper motors & Stepper Motor Drivers - Servo motors and Servo Motor Drivers - Ballscrews & linear motion products. : High Voltage Driver Kit Three (Three axis) [3axiskit3] - £412.38 (http://www.zappautomation.co.uk/high-voltage-driver-kit-three-three-axis-p-746.html?cPath=139_33)

Possibly I am fortunate in having a 27U rack I use for a few servers in my office/workshop and was thinking this might also be a perfect place to house the drivers and PSU's using something like:

Buy Rack Fitting Cases & Enclosures Rack Mount enclosure,6U 465mm Black RS PF-19 6U D4 online from RS for next day delivery. (http://uk.rs-online.com/web/p/rack-fitting-cases-enclosures/6657738/)

Question is, assuming I will have my VFD/Spindle unit and cabling well away from the rack (underneath the CNC machine workbench), will the driver and PSU stuff be OK in the same rack as my servers and not interfere with my servers? Also assume I will be getting decent quality shielded cables.

Cheers


Chris

Lee Roberts
25-08-2012, 09:30 PM
I canít see this being a problem, more so if you use shielded cables. I would try and keep the cable runs as clear as you can; I would maybe look to keep the rack under the cnc with the other stuff though.

I did a build in a pc case and had everything in that enclosure, including the pc stuff without shielded cables and didnít have any problems. I know others have done this as well, Iím currently working on an enclosure for the same again featuring an Atom based system so hoping all will go well with that, I cant actually recall anyone having an issues with the PC next to the drivers and so on but I think it does happen for some, may have to try it and see.

.Me

Washout
25-08-2012, 10:38 PM
Thanks Lee,

Sounds like my rack may be housing more than servers now and save me some workshop real estate.

Good idea on using drive enclosures for your stepper drivers. I have some of those spare, so will be "borrowing" that idea :-)

I guess the interference problems people experience (steppers skipping etc) come from the VFD and its cables being in the same cable run as poor quality unshielded stepper cables - Tesla vs Edison again? ;)

Cheers


Chris

Lee Roberts
25-08-2012, 11:24 PM
Hey,

Sorry didnt mean to post so many pics...i should have thought about it, the only problem i had doing it that way was the 542's are a little wider than a hard drive and as luck would have it the side of the rom bay lined up nicely with where the side of the hd bay needed to be. I did have a 4u nocking about i could have used and i did strip it down ready to start hacking it up but it was old and grey/cream and a new tower was only £20 and looked a better option at the time. I did plan to put the fuse holders, l.e.d extensions for the drivers and so on in the front bay panels but i nver really got that far, the case and bits are still sat on a shelf collecting dust.

I just used some ali angle for the side plates the drivers sit on, looked cool i guess.

Re the VFD cables, i've not got one or any experience using one so cant really comment sorry.

.Me

irving2008
26-08-2012, 12:26 AM
Shielded cabling, proper star-wired earthing and pull-ups on all inputs whether used or not, is all thats needed... a VFD is nothing more than a big switch-mode PSU. Problems that people have come from running unshielded power and signal side by side for long runs (> a few inches), creating ground loops by not wiring everything back to a common point (or grounding both ends of a shield), not grounding things at all, or in worst cases, powering different parts of the system off different ring mains on different phases (can induce huge ground offsets). Ok the latter is very rare but I discovered it in a commercial premises wired by cowboys (and it did have a P-certificate)

Washout
26-08-2012, 01:22 AM
Thanks Irving,

I didn't want anything guassing my precious server data and the VFD is not going in the rack, just the PSU, drivers and possibly the controller. Just wanted to check in case I was throwing the equivalent of a tesla coil in there ;)

I don't have 3 phase, so I don't think your latter scenario will apply (not yet anyway ;) ), although I was thinking of running a seperate wiring feed to the VFD (and possibly the rest of the machine's electronics) from my consumer unit (I have a spare 32A RCD), just to keep it isolated from the rest of my "stuff".

Cheers


Chris

JAZZCNC
26-08-2012, 03:29 PM
I don't have 3 phase, so I don't think your latter scenario will apply (not yet anyway ;) ), although I was thinking of running a seperate wiring feed to the VFD (and possibly the rest of the machine's electronics) from my consumer unit (I have a spare 32A RCD), just to keep it isolated from the rest of my "stuff".


Well actually you kind of do because the VFD is converting to 3 phase.? THE BIGGEST cause of trouble with electrical problems in CNC is incorrect or bad earthing creating ground loops or electrical noise.
Very important you use Star grounding and run all earths and shielding back to this star point. That includes the VFD and it's cable shielding.
What I do is have a mains pickup point in the control box with earthing block and pick the VFD power and earth from this point but still keep it outside the cabinet.

The separate feed is a good idea helping to keep the marriage out divorce courts after the Mrs puts Air drier on just when machines at full chat 10hours into a job and POP.:sorrow:

irving2008
26-08-2012, 04:18 PM
I agree with Jazz.

My own setup is:
- Consumer unit with dedicated 32A MCB, routed to
- 45A DP Isolation Switch (near work area), routed to
- Emergency Stop contactor, routed to
- Distribution point (small metal electrical cabinet, with 3 buss bars, I made it but a cheap 4 or 6 way domestic consumer unit would suffice too and give option of individual fuses/MCB).

The earth buss in that cabinet is my star point. Power to everything comes from there.

Lathe VFD is wall mounted and fed from there
Control box under desk is fed from there,
PC is fed from there.
Mill starter contactor fed from there.

Lathe and Mill chassis are earthed back to there.

Mill (currently non-VFD) motor and mill head individually earthed back to mill chassis (star of stars) so I dont rely on bolted joints to make earth connections

There is a seperate 'normal' spur off the main Consumer unit for powering other intermittent stuff like soldering irons, the bench grinder, and the fan heater!


When I eventually finish my new workshop I'll transfer this pretty much as-is except everything will come from the distribution point which I will replace with a 6-way RCD consumer unit to provide local isolation/fusing. The existing Isolator will stay in the garage and the armoured cable to the workshop will feed from there.

Washout
26-08-2012, 09:50 PM
Thanks guys,

Sage advice as usual.

BTW - if you have time I have a couple of other areas I'm looking into:

1. I have a spray gun (also powers my airbrush) compressor and was thinking of using this for tool cooling/chip blowing - I notice Jazz you mentioned misting in another thread and am guessing this is just essentially atomising lubricant/cooling fluid into the air stream? I should be able to whip up a suitable nozzle if that's the case.

2. I'm also looking to run a 2.2Kw water cooled spindle with an arrangment of PC cooling rads (2xdual 120mm left overs from PC watercooling), which should bring the water in the curcuit+tank down to ambient air temperature. The tank will likely be somewhere around the 10-15L capacity mark, dependant on the room I have left under the workbench.

JAZZCNC
26-08-2012, 10:17 PM
1. I have a spray gun (also powers my airbrush) compressor and was thinking of using this for tool cooling/chip blowing - I notice Jazz you mentioned misting in another thread and am guessing this is just essentially atomising lubricant/cooling fluid into the air stream? I should be able to whip up a suitable nozzle if that's the case.

Yep but warn you it can use plenty of air so if it's a small tank then expect it to be going all the time and watch for it overheating.? With a bit of playing around with nozzle sizes you can get a nice flow and limit the CFM used. Can't help on the nozzle size has I now use dedicated misting unit which is a fancy spinning thing-a-mi-bob with loads of tiny nozzles.!


2. I'm also looking to run a 2.2Kw water cooled spindle with an arrangment of PC cooling rads (2xdual 120mm left overs from PC watercooling), which should bring the water in the curcuit+tank down to ambient air temperature. The tank will likely be somewhere around the 10-15L capacity mark, dependant on the room I have left under the workbench.

These things don't get very hot even after hours of use so don't get silly with the cooling and rads etc.? My simple submersible pump dropped in 20ltr drum works a treat, it can and does run for 20hrs+ continuous without any trouble.! . . But if you read about my Mister you'll probably seen I've posted that before as well.? . . Keep it simple.!!

Washout
22-09-2012, 11:44 AM
Chaps,

Mulling over the option of putting my control box into my 19" rack with the servers, I think I have a snag with that, but could use an opinion:

I was intending to run a seperate 32A RCD spur for sole use of the CNC machine and all its electronics (including the PC that will run Mach3). Taking the advice above, if I run all the shielding and earth points back to a star point in the 19" rack mounted case and then onto the 32A earth feed, am I creating a ground loop with the existing 15A feed's earth supplying power to the existing rack mounted windows servers via two rack mounted distribution bars? i.e earth will have two paths back to the consumer unit 1. through the 32A spur's earth and 2. through the 15 Amp ring's earth?

If that's the case I see a few options:

1. Buy a new control case (not a problem but does mean I use some valuable workshop/office real estate
2. Use the existing rack mount server case but isolate it from the rack, so that the two earth paths (15A and 32A) are seperated - tricky to do, as the case is bolted to it rails and hence the 19" rack itself.
3. Up the rating on the 15A circuit and run the servers and the CNC off of the same circuit - risks dirty power to my precious data/server hardware
4. Stop drinking Redbull at night and conjuring up problems where they might not exist ;-)

I'm about to order the shielded cabling, e-stop button, limit switches this weekend, so any help would be most appreciated, as I can add a new control box to the order if its needed.

BTW - what do you guys normally use for limit switches - RS has some pretty exotic looking kit, but if I can use a suitably rated momentary single pole then I'm all for shaving a little cost.

Cheers


Chris

irving2008
22-09-2012, 09:47 PM
Hmmm... as long as the 15A and 32A are on the same phase, from the same consumer unit, I dont see any issue with taking the earth from both of them to the star point. It won't create a ground loop within the downstream equipment and thats the main reason for the star point - to avoid differential ground voltages impacting the sensitive signalling.

Washout
22-09-2012, 10:10 PM
ah thanks Irving - they are both from the same consumer unit on the same phase, so the "earths" are going back to the same point in the office/workshop.

That's good news then as I have gutted the antiques I found in the unused rack mount server case and already made a mod to the 5-1/4 drive bay so it can accomodate my drivers and have a 120mm fan to cool them. Just waiting for my shielded CY 16A rated cable to arrive on Mon/Tues to start hooking stuff up and doing the cable runs. I think it may be time to start a build log :-)

Cheers and thanks again


Chris