Retrofit Precix 3 Axis Gantry Mill

Hopefully this is following the forum rules when i open a new post.
This is more or less a follow up of a post from Randy: 
forum.linuxcnc.org/27-driver-boards/3649...t-of-precix-5x10-cnc
We got a precix 3Axis Gantry mail in our department (University of applied arts vienna), which i want to give a 2nd life as the controller was broken for years. The mill has 3 DC-Servos and a 2.2KW Colombo Spindle  
I Started it in Feb. 2023. Learned a lot over the summer and set up a new controller with new electricity but mostly relying on the old components (PSU, Motors, Spindle/VFD, Drivers are original). Controller is a mesa 7i77/7i92t. 
Also learned to draw electric/electronic blueprints with KiCAD which was a great help
With the help of the forum I managed to run first G-Codes on the plain setup board (disconnected from the machine ) last week.
While tuning the motordrivers i ran into issues constantly tripping the breakers in front of the servo psu which is a beefy toroidal transformer(1500VA). Tripping happens when turning off! the PSU 1 out of 3 times. Also my ssr was blown already - maybe not a good idea i found out already.
So here is my question:
Who has more experience with induction/overvoltage issues running an old psu?
Suggestions for improving the electrical layout is appreciated, as the machine will hopefully run in an university environment again and i am not a trained electrician #safety.
I also attached some images and a schematic of my current controller setup.

Thx,
Armin


 

ahess wrote:

Tripping happens when turning off! the PSU 1 out of 3 times.

 
[strike]If this statement is correct, the only thing i can think of that would remotely be able to do that is having all the motors and drives enabled and under load when you switch off the machine. Still to far fetched, and very, very low chances.[/strike]
-edit:
RMU reminded me that even this is not possible due to rectifiers not allowing back powering the transformer.
Thank you RMU
-end edit.
Tripping normally happens on power on, not power off.
-
Are the drive enables wired and set up properly in LinuxCNC?
The drives should only be enabled when pressing F2 or "machine enable" on the GUI. Othervise they should not be enabled.
Those are DC motors, so another question, does the machine have "extreme limit switches"? These should be separate from all other limit/home switches, and should cut the power to the drives if they are tripped.
These should be mandatory on brushed DC motor powered machines as any short on output mosfets inside the drive will send the machine at full speed in some direction.

You trip P15 when turning off? That is odd. Does P15 come from the original box, what type is it? Overvoltage should not trip a breaker, they trip on overcurrent, how quickly they react depends on overcurrent and type of breaker. But overvoltage will damage your SSR. Maybe get a beefy relais or a contactor ("Schütz") to switch the Trafo if you have to.

Also I would check the "Einschaltstrombegrenzer" is working properly.

In general it looks very clean, but you will have to put it into a box, main switch must be reachable without opening the box.

I would keep wires with line voltage separate from the low voltage stuff and mount some sort of shield over the open busbars (e.g. acrylic) or at least some isolating tape, to prevent nasty molten metal flying around in case somebody drops something...

Regarding safety: E-Stop button should be reachable by machine operator. From a "Maschinenrichtline" POV this thing will probably never be OK without a cage around it that inhibits any motion if door is open and some type of dust extraction, depending on materials you are milling. Dust from MDF and some hardwoods is nasty and IIRC cancerogenic.

tommy, that can't be. Even when all drives are running full power, they could rise the voltage on the DC side filter caps beyond their limit, but the DC bus can't back-feed into the transformer because DC doesnt go through transformers also there are the rectifiers.

I suspect wrong type of circuit breaker and or some fault with the inrush current limiter. Or maybe some miswiring but hard to imagine. 

rmu wrote:

tommy, that can't be. Even when all drives are running full power, they could rise the voltage on the DC side filter caps beyond their limit, but the DC bus can't back-feed into the transformer because DC doesnt go through transformers also there are the rectifiers.

You are right, it won't make it past rectifiers!
Thank you.
But transformers do feed back from DC, for a very, very short period, when powered on and off.
Still should not be enough to cause tripping, or anything.
The thing is, tripping on power off has never ever happened to me or anything/anyone in my entire life, so i was grabbing at straws.
Tripping on power on, that is a normal occurrence.

You might want to try a MOV across the input to the transformer. Something is going on if it took out the SSR.
MOV info:
components101.com/articles/metal-oxide-varistor-mov-overview