RE: Grounding the printer
"you must make sure that all metal casings and shields are tied to ground". To me that includes PSU case and frame.
I really think you would find American / European PSU cases grounded. Anyone have one to check?
I can certainly test an ATX PSU case.
RE: Grounding the printer
Data points:
Ultra ATX 650W PSU - case grounded to AC ground.
Meanwell 350W 24V PSU - case grounded to AC ground.
MK3S: Both front rails show zero ohms to frame. Rear rails, anodization prevents connection. It would take a bit of work during assembly to have a good connection.
Will any of this cause me to modify my MK3S? No. But I do think the PSU case should be grounded. I thought international standards required that.
RE: Grounding the printer
The printer gets by through a claim it is a low voltage instrument and thus needs no authoritative compliance testing.
On MK3 PS - Prusa adds a plastic shell and the power socket. The case is only incidentally grounded via the ECB.
The printer frame "might" be grounded via screws attaching the PS to the frame. But these are painted surfaces and are not adequate nor reliable grounds.
Proper electrical grounding for the MK3 design would be a fair bit of work. Also, the Einsy and LCD boards are sitting in free air, with only plastic shielding them. Then consider the LCD wires in plain sight. Pretty sure the printer exceeds any FCC 15 Type A and Type B emissions, and certainly doesn't meet the emission acceptance criteria. As for EC or UL safety? It's whatever the PS folks did, and for Prusa to mess up -- i.e., Prusa's power panic board touches AC, so whether they did diligence to ensure that board is safe (or meets any compliance specs) is a question mark.
RE: Grounding the printer
Lordy Tim - my Czechoslovakian is not that good.
Are both the silver case and the black one metal?
I would not worry about the 24V, but the PSU runs at 120-240V. That should have required testing.
Now if the case were plastic - that in itself should be enough. Power tools, since going to plastic housings, don't even use grounded power cords anymore.
RE: Grounding the printer
Well - if the PS case were plastic (it isn't) and were only two-wire (L+N) the term "double insulated" comes into play, and the definition of what constitutes the first and second levels of insulation become important (and are well defined at UL and IEC).
ps: As for languages? This is the part that I read:
The fun part is that the testing authority decided the product doesn't need testing to any of the standards listed above... gotta love that.
RE: Grounding the printer
Well I went through the Prusa MK3S Black construction manual again - and I can't tell what Prusa did.
The only user accessible connections are +V +V -V and -V, along with Power Fail. Line in is buried in the housing.
We know Prusa uses a grounded power cord. If power line ground is not used for case ground - why is it there? Just for show?
RE: Grounding the printer
I should note - I did not test either the Prusa silver or black PSU. I am going on the original OP report that the cases are not grounded.
I have to lean on that being a testing error or a defective unit.
Can anyone else confirm that the cases are not grounded? That just does not seem right....
RE: Grounding the printer
that would be crazy, I will check this evening
RE: Grounding the printer
My power supply case and frame are now connected to earth ground. There is an obvious difference in it's ability to handle static discharge, it's printing fine, so it's going to stay that way unless I hear a really good reason to change it back.
My unit is black, the PSU is PMZ-24V240WDAL. On either side of the two sets of V+ and V- connections are screws. Those screws are connected to the ground pin on the main plug. From my multimeter testing, the case was not connected to the earth ground.
I connected one of those ground screws to a screw that holds the PSU case to the frame. It's still hard to get a reading on the frame, but anywhere there's a screw in the frame, I can now see that the frame and PSU case are connected to the ground.
I didn't build this unit, I purchased it pre-assembled. I have no idea if what I found was typical or an error.
I hope this helps. The printers ability to take a static shock is dramatically better. It's really dry right now, and I'm shocking things all over the place, so I'm feeling pretty confident my issues are fixed.
Thanks
Scott
RE: Grounding the printer
I decided to do a sanity check - sanity lost. I pulled things apart and disconnected my wire, this time I made sure to touch one of the screws on the case, rather than the painted part of the case, and sure enough, it was connected to the ground pin.
I put everything back together, and built up some static, and discharged on one of the frame screws. Once again, my display went blank. The frame screw is connected to ground, as is the case screw. I have no idea what's going on. But I guess I'm back to square one, with an ESD wrist strap on the way.
I'm feeling a bit confused ATM. It's late for me. Time for bed.
Scott
RE: Grounding the printer
The ESD discharge from the finger to the printer PS creates a huge current in the air that broadcasts a rather significant magnetic field outwards. This magnetic pulse passes through the LCD wires and creates a voltage that corrupts the data being transmitted; this wave also passes through the circuit board driving the LCD, and it also passes through the EINSY board - anywhere there is a wire the magnetic field of the ESD creates a voltage spike in unshielded circuits. Think of it as a mini-EMP.
On a larger scale, these magnetic fields kill entire regional power systems by the same method, and why EMP is such a problem if a nuke war ever breaks out. Unfortunately, EMP is not science fiction.
ps: the wrist strap doesn't prevent the discharge, rather, it adds resistance to the circuit so that discharge is over seconds and not microseconds, so that the currents involved are small and the magnetic fields generated are also small.
RE: Grounding the printer
I don't understand - are we worried about the printer building up a static charge, or the user? I really don't know, does the printer generate static electricity, e.g. through friction with the filament spool?
RE: Grounding the printer
I think the problem being discussed is users touching the printer and zapping the electronics hard enough it scrambles the CPU's. The belts are probably generating their own charge, too, but the scrambled display usually happens when a user walks up and touches.
RE: Grounding the printer
There are two aspects here. Grounding the frame is to protect the printer (electronics) from the user (static).
Grounding the PSU is to protect the user from the printer (line voltage).
Electronics are easily replaceable. Users - not so much.
RE: Grounding the printer
Grounding the frame won't protect the electronics... too many exposed wires and they act as antennas. It isn't only the electrical spark that does the damage: the magnetic field the spark produces is just as hazardous to the circuits.
Did you know sparks were used as early wide-band transmitters? https://en.wikipedia.org/wiki/Spark-gap_transmitter
RE: Grounding the printer
If I were to ground my frame (I won't), it would solely be to give me a place to ground myself before getting in range of the electronics.
Giving ESD a path to ground that does not pass through electronics is always beneficial.
RE: Grounding the printer
Not always ... you want to provide a path that 1) doesn't conduct through sensitive circuits; 2) you want to limit the current of the discharge to minimize EM effects.
Most grounding products use a megohm resistor to limit impulse currents and also the resistance limits the risk of electrocution should the person touch something else they shouldn't.
RE: Grounding the printer
After replacing 3 LCD panels, I finally addressed the issue of discharging my static buildup with a ground wrist strap. Most time I just make sure I touch the metal plate on the hanging strap or put it on if I'm working on the printer.
https://photos.app.goo.gl/LEynjfSp5Kxej2Q3A
RE: Grounding the printer
It is surprising that printer is not grounded and passed regulations on this matter.
Regulations are quite clear. If device is connected to mains and has any metallic parts exposed to touch, accessible metallic surfaces must be grounded. It is not just about regulations. it is common sense.
If PSU is physically separated from frame and 24 V is introduced by cable, that would not need grounding.
I believe printer is constructed in matter that it is fairly safe but anyways, 220V is in device and there is lot of metal exposed. Rings the bells. I've put grounding on the schedule for customization.
RE: Grounding the printer
In our environment right now, I'm generally assured of getting a static zap when I touch the printer to pull the plate off when a print is done. This makes the display go haywire for a second but it returns. Then it occurred to me that there is no ground connection between the frame of this printer and the AC mains here. The PSU is insulated from the printer frame by its plastic bottom. Should we consider running a ground wire from the printer frame to the PSU?
And come to think of it, there's no electrical connection between the main carriage and the ground either due to the steel rods being cradled in plastic. Should we consider running a ground under there as well?
If you are getting this problem its possible that some of the wiring on the extruder is starting to come away? Most likely the thermistor, extruder heater or print fan? Had this issue previously and it turned out to be one of those