Power supply sizing

[perry]

So, my Masso is arriving today, a full 4 days early, according to the original tracking estimate. This means I need to think fast about the power supply, which I was going to order over the weekend.

My Stepper drivers will be powered by the 48V/400W PSU that came with my Millright Mega V. I will have the following devices connected to the Masso:

1. X, Y, Z homing switches (currently I have mechanical switches but I'm going to use optical switches instead. I bought these: https://www.amazon.com/gp/product/B07PMW2QMT/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
   
2. Masso Relay module (I will likely use this to power on and off the cabinet lights and the cooling pump for the spindle).
   
3. IOT power relay (this is temporary, for the DeWalt router, until I can get the spindle installed). I may also connect the shop's vacuum to this eventually but I haven't decided. I have this: https://www.amazon.com/gp/product/B00WV7GMA2/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
   
4. Door Switch (I'll probably re-use one of the megaV door switches, or a similar simple mechanical switch
   
5. E-stop on the control box
   
6. Masso MPG pendant
   
7. 12vdc PC cooling fan for control box
   
8. VFD for spindle: https://www.amazon.com/gp/product/B01N1EJEQ1/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
   
9. Coolant: I will either have a coolant mister or I'll use a vortex cooler for the end mill when cutting aluminum. So it'll either need to power a pump or a solenoid. Haven't spec'd these yet.
   
10. potentially a tower light or other LED indicator.
    

Pretty sure that's it for now. Let me know if there's something else I should plan for.

I have a 12v PSU that I'm not using (12V 1.67A), which I'd think would be enough.

In terms of planning out the wiring, I should expect to share (DC) grounds between the PSUs, correct? If so then I'll place them close together in the box to keep the wiring neat. Otherwise my current layout has the DIN-Rail mounted 12V supply in a different location for space reasons.

Thanks!

 

[breezy]

Perry,

In terms of planning out the wiring, I should expect to share (DC) grounds between the PSUs, correct? If so then I'll place them close together in the box to keep the wiring neat. Otherwise my current layout has the DIN-Rail mounted 12V supply in a different location for space reasons.

You need to connect "grounds" together at one location. But there is no need to have the PSUs next to each other, just choose a spot for the common connection point that is convenient to your current layout.

Also consider VFD location in your wiring arrangement, because you need to ground the shield of the VFD -> Motor cable at the VFD end only. Another point to consider is spindle earthing, some spindles come without the earth pin connected to the body of the spindle.

Regards,

Arie.

 

[perry]

Quote from Breezy on May 2, 2020, 12:46 pm

You need to connect "grounds" together at one location. But there is no need to have the PSUs next to each other, just choose a spot for the common connection point that is convenient to your current layout.

I just prefer to minimize the amount of wiring inside a box when I can. so I'm thinking if they're together I can just jumper the two together, rather than running a wire from one end of the the box to the other. just a cosmetic thing, really.

Also consider VFD location in your wiring arrangement, because you need to ground the shield of the VFD -> Motor cable at the VFD end only.

thanks. I'll make a note of that.

 

[Ross]

Here is a Quote from a forum. It talks about ground loop noise and Star Ground. Plus i have attached their diagram for you.

Don't forget AC EARTH is different to DC GROUND and needs to be separate from each other.

(AC to mains supply) (DC to ground rod though the floor)

Ross.

http://www.mycncuk.com/threads/9135-Grounding-help-UCCNC-UC300-and-connection-loss



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Hi Gabi,

Ok well you could have a few issues going on here.?

The Uc300 is USB and some USB cables are better than others regards there shielding and ground. So use a good quality cable and keep it short has possible.
Then you have the VFD which is most likely the cause. The Shield of the Spindle Cable should connect to the VFD ground. Some say Ground both ends of the cable and others just one end, the VFD end. Personally I only ground the VFD end and never have any troubles.

Then you have the fact your control system is spread over several areas meaning your probably not using one Central Star ground point. This leaves you open to introducing ground loops.
The cables in your total system act like huge antenna sending or receiving signals so if they are not shielded or there shields not grounded correctly to single point then stray signals will be received and wrongly seen then acted upon. Which is why your getting troubles because the VFD is a Bad boy when it comes to making noise and infecting any poorly shielded or grounded cable.

So ideally you want one Earth point that all earths are taken from and shields etc run to. Also run a Earth lead from the machine Frame to this same point.
Make sure you run all High power cables separate from Signal cables, so don't run spindle or power cables next to limit or E-stop or drive signal cables.

Ground issues are always hard if not impossible to track down with certainty in situations like this where spread over several places so My suggestion is to get everything BUT the VFD into one box. Keep the VFD separate away from signal wires.
This will make it much easier to use Star ground setup. It will also allow you to get rid of the extension cables which don't always help matters.

Edit: Here's a quick knock up to show principle of Star ground. Notice only one path back to the Earth pin on Wall socket.!
Also Notice how the DC power supply's Ground drawn has black wire is different to Mains Earth. Very easy to mix up DC Ground with AC earth when they are completely different things. DC Ground finds it's path to Earth thru the DC supply so not be confused with AC earth.
We are only taking about AC Earth here and Signal Shield paths to Earth often mistakenly called Ground.

 

[perry]

Thanks. I was planning to put my VFD in the same enclosure as all the other stuff (Masso, stepper drivers, power supplies, etc). Is that a bad idea? I'd prefer that because it's cleaner to have it all in one place, self-contained in a single enclosure.

 

[breezy]

Perry,

I did the same thing and regretted it when the VFD went faulty and I had to pull the whole control box apart to get it out. So while it was out I rearranged the control box & wiring and moved VFD outside the box.

The VFD is now mounted where the white box was on the black board with the spindle coolant reservoir. Haven't got a photo of the rehashed control box.

Regards,

Arie.

 

[Ross]

Keep the VFD probably 2 meters from the Masso. Out side the control box.

Stepper drivers and power supplies to the far side of the box away from the Masso as well.

Use shielded wiring as much as possible.

Just my thought, cause it puts out lots of noise, From Ross.

 

[perry]

Thanks. I had wanted everything in one box to minimize wiring should I have to move (it's set up in a basement storage space/shop in our office building, so if we move, it moves). As the setup is in a corner, I think I'll put the VFD on one wall and the controller box on the other. The box I got is substantial since it was sized to fit the VFD as well, so there's plenty of room. Everything will be shielded wire. I'm redoing all the stepper wires (currently unshielded, as far as I can tell, but I haven't taken them apart yet) from the controller to the motors, as well as the homing switches, so I have plenty of shielded 18/4 cable to work with.