Putting mesa cards and PSUs in the same enclosure – yay or nay?

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22 Jul 2021 00:08 #215537 by Twizzlermill
Hello,

so, with all the cables having shielding ( is that the right word? I mean the metal mesh/foil wrapped around the wires to prevent electromagnetic interference), I wonder where exactly to start with this. I know, it's supposed to eventually go back to ground, but if I want to connect up drivers and card, I need to untangle the wires at some point, to get them in their respective sockets/pins. Also, I guess if the other cables are a problem, the stuff that they are there for seems like a problem as well, no? Like PSUs, mainly. Getting a metal housing for the electronics rather than a plastic one seems like a good start, but after that, I'm not so sure. Should I isolate the Mesa card from the PSUs? Or does it not matter that much? If yes, should I go for a separate enclosure? Is there an established way of doing this? Am I overthinking stuff?

TIA,
Twizzler

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22 Jul 2021 01:46 #215544 by BigJohnT
My Mesa cards are in the same enclosure as the drives and power supply. Shielded cable should be grounded only at one end to prevent a ground loop. Power supplies 0vdc should be tied together so no floating ground voltages are present.

JT
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22 Jul 2021 20:19 #215614 by Twizzlermill
Thanks for the answer. Yeah, not grounding the shields at both ends is something I've heard of, thanks for giving me an explanation as to why.

However, I'm not sure I understand this part:

Power supplies 0vdc should be tied together so no floating ground voltages are present.

Maybe it's a language issue (I'm a non-native speaker, mix in technical jargon and it's… worse), but I'm not sure which part 0vdc refers to and what floating ground voltages are exactly.
 

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22 Jul 2021 20:55 #215616 by bevins

Thanks for the answer. Yeah, not grounding the shields at both ends is something I've heard of, thanks for giving me an explanation as to why.

However, I'm not sure I understand this part:

Power supplies 0vdc should be tied together so no floating ground voltages are present.
Maybe it's a language issue (I'm a non-native speaker, mix in technical jargon and it's… worse), but I'm not sure which part 0vdc refers to and what floating ground voltages are exactly.
 

The power supplies common or 0v should be tied together so to have a reference so they are at the same potential.
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23 Jul 2021 10:08 #215659 by Twizzlermill
Thanks, but I think I need a bit more clarification. If I have a power supply with three cable in (L, N, Ground), does the 0v/common refer to the ground there? Or is it something else?

In another built somewhere, I've read that you should always "collect" all your ground cables at a central point (i.e. tie them together?). Is that what is meant here?

Sorry if I'm asking basic questions.

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23 Jul 2021 10:48 #215663 by rodw
I had my power supplies in the same cabinet and put a fair bit of thought into cable layout to separate mains, 48V steppers, and 24v logic as I laid it all out so that each voltage was kept apart from the others

I thought best practice with mesa was not to connect 0 volts to the frame ground and therefore to keep the field power isolated.
I did have issues with noise and I fixed that by replacing my IEC mains connector with one that had an EMI filter built in as the noise seemed to be entering via the mains ground. But my machine is a plasma machine so noise abounds!

My  next enclosure will feature 60V AC toroids and I am thinking of adding a steel partition between the mains power section and the rest  of the enclosure.
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23 Jul 2021 10:49 #215664 by tommylight
Ground is the power grounding wire, usually green and yellow, and it literally has to be tied to a ground rod somewhere around the shop/house.
0V or common is the -V on the picture, so if using multiple power supplies the -V should be tied together, although that is not always the case, when using isolated electronics like Mesa 7i76 or 7i77 the 5V logic and 24V field should not be tied together as that would void isolation.
Also some power supplies will have the -V tied to ground and that is in most cases ok for the field side.
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23 Jul 2021 10:51 #215665 by rodw

Ground is the power grounding wire, usually green and yellow, and it literally has to be tied to a ground rod somewhere around the shop/house.
0V or common is the -V on the picture, so if using multiple power supplies the -V should be tied together, although that is not always the case, when using isolated electronics like Mesa 7i76 or 7i77 the 5V logic and 24V field should not be tied together as that would void isolation.
Also some power supplies will have the -V tied to ground and that is in most cases ok for the field side.


Except if you are using the Mesa MPG's on say a 7i76e, and you do power the 5v side seperately, you do need to tie the 5V and 24V grounds together...

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23 Jul 2021 11:29 #215675 by tommylight
7i76E has different power options than 7i76.
And there are cases when that might be required, but to many examples make for a confusing post and has nothing to do with how i explain things ! :)
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23 Jul 2021 12:03 #215678 by Twizzlermill
Thanks guys, this helps clearing up some questions – and raises others. I do indeed plan to use a 7i76E card. My steppers are JMC, so there won't be any drivers in the enclosure for now. I guess I still have some more figuring out to do before I can ask the right questions.

Just for reference, this is what I need to connect up right now:

Mesa 7i76E card
4x JMC closed loop steppers
2x 36V power supplies for the steppers
1x 24v power supply for the card and maybe fans for the enclosure
1x 5v power supply for the card
fans (here I'm not sure whether I want to put another 12v PSU in there just for them, because 12v fans are way more common, or get 24v fans)
2x wall power sockets for shop vac and spindle

Also:
Endstops
tool length sensor
Power Button/Emergency off

For now, I won't fuss with relays for the vac and spindle, but it's planned down the road.

So really at the moment, in the enclosure will just be a bunch of PSUs and the Mesa card I guess.

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