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Author Topic: Any help / suggestions please?  (Read 5526 times)

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Offline laugeo

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Re: Any help / suggestions please?
« Reply #10 on: October 08, 2016, 05:58:26 AM »
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.
Re: Any help / suggestions please?
« Reply #11 on: October 08, 2016, 06:02:25 AM »
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
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 #12 on: October 08, 2016, 06:04:19 AM »
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...
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 #13 on: October 08, 2016, 06:44:28 AM »
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?
Re: Any help / suggestions please?
« Reply #14 on: October 08, 2016, 07:06:26 AM »
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)
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 #15 on: October 10, 2016, 08:33:23 AM »
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.
Rob

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

Offline Davek0974

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Re: Any help / suggestions please?
« Reply #16 on: October 10, 2016, 09:51:43 AM »
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?
;)
« Last Edit: October 10, 2016, 09:57:21 AM by Davek0974 »
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.

Offline Stuart

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Re: Any help / suggestions please?
« Reply #17 on: October 10, 2016, 10:47:33 AM »
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
« Last Edit: October 10, 2016, 10:51:42 AM by Stuart »
Re: Any help / suggestions please?
« Reply #18 on: October 10, 2016, 11:21:45 AM »
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)
Rob

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

Offline Stuart

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Re: Any help / suggestions please?
« Reply #19 on: October 10, 2016, 12:05:48 PM »
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