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


 

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. 

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

tommylight wrote:

But transformers do feed back from DC, for a very, very short period, when powered on and off.

When powering on / off you have a changing current, that can go to the other side of the transformer, yes. But changing current means it is not DC in that moment

Usually with toroidal transformers powering on is the critical thing. The iron core can retain magnetisation and if polarity when turning off is same polarity when turning on the transformer looks like a short-circuit for up to a half wave (10ms) and that is what trips the fuse. This effect is particularly strong with toroidal transformers. wikipedia has all the details: de.wikipedia.org/wiki/Einschalten_eines_Transformators

That short-circuit type situation can't happen when turning off, so I'm puzzled. 

Thx for your time first, i really appreciate your attention.

We have frequent inrush current  issues with "B" rated breakers inhouse. our house electricians refused to put slower breakers.
So tripping goes down from my Controllber P3 (10A C-rated) then my Lab breaker (16A B-Rated) and the first house breaker ( 16A -B-Rated). All together. No FI t(guess RCCB in english) tripping, of course - walk of shame when it tripps. This ratings define how fast breakers trip A-B-C-D (not sure if you have this in US?

Old Powerbox was 110/230 mostly with 20A Fuses no breakers, a schütz for Vacuum else nothing special.

For now i just run the motor driver without Mesa Fieldbus and Logic Power
Checked the old setup in it was almost the same, also a very standard SSR to switch, but two NTC's instead of the P1 Current Limiter.
DC currents  are super low as there is no torque on the motors.
Thanks for your thought on backfeeding the toroid from the motors/Caps, this should not be possible right?

@tommylight
On the test setup the ssr is controlled by the red emergency button. This failures were mostly driven by switching via the ssr. Might be an issue switching when driver is still enabled. On Linux enabling works fine as you described.
The machine just had homing switches no min/max switches. The servo loop worked fine so far, inhibit/fault seem also ok Z-Axis has a break, X,Y run out  when driver gets disabled. But thanks, about the mosfet info . So i should put relays in between PSU and driver not! controlled by LinuxCNC?

@rmu
Also thx for your comments. My understanding so far: The primary side of the toroid induces  a voltage peak when turning it off. Maybe together with a high current? it flows backwards through the breakers. But how when switched off? The SSR must be faulty or too slow. Or only half of the sine is switched, one mosfet broken? Ok the Voltage kills the ssr, the current tripps breakers. With a mechanic switch there should be no way to flow back. But i liked the ssr And what i understand from your comments the secondary side has nothing to do with these issues. That helps.
The "Einschaltstrombegrenzer"- nice German should not have any effect as it should be switched through at the time.
Thought of using a NTC instead (switches with heat), not sure.

The safety issues are an ongoing issue in our lab.
We mostly do 3D landscapes on prototyping foam aka Sika stock is up to 300mm. We were forced to get a new filter extraction. Even though we hardly catch the chips/dust at the tip as any hose close  would mostly hit the stock. Also the machine is open on all sides - an issue - we separated the mill with a thicker curtain (transparent plastic) from the operator - what i am testing now is steel wire around the machine connected to estop switch (picture). Nothing which complies with safety standards - we also have a small robot standing around which is even worse



 

Would like to measure the voltage spike guess it must be huge.Thanks I will try this as I am still experimenting on my breadboard.