Why is the printer not earted?
Hi, I mustn't be the only one getting static shocks from his printer now and then. But sometimes more than once per day.
I remember from assembly (bought the kit version) that there is an earth connection between the power outlet to the SMPS's ground, but then, it stays in the power supply. I don't see a connection between the PSU's ground and the machine. Also the machine powered by a floating power supply (aka V- is not connected to the earth), why? I find it strange, specially considering the machine as long cables connecting directly to sensors.
Today, I checked up the machine, saw no reason not to, and connected an alligator clip from a power socket's ground pin to the frame of my printer and everything was good, used the printer normally and all systems worked as intended.
Why isn't this standard? Surely Prusa Research must have a reason not to do this, considering there is no cons, and makes the machine safer and more reliable (and you don't get electrical shocks touching the metal 😉 )
Re: Why is the printer not earted?
The printer is earthed. Because you don't and sometimes your body get charged, you are getting a static shock once you touch something which is earthed.
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Re: Why is the printer not earted?
I verified on my printer the PS case is connected to earth; and the screws mounting the power do make an electrical connection (thinner paint?). But there is no intentional connection. The verification used in the CE documents appear to use low voltage as the reason for no formal electrical safety testing. But I don't even see a CE mark on the PS - which is NOT low voltage. Note to Prusa: This isn't a complaint so much as a question being asked by someone who has some experience designing electronic gear.
But cleaning paint off of an area under one of the PS mounting screws will ground some of the frame. But you'd need to do that at every mechanical connection - each frame piece needs a clean screw. Then, somewhere at the Einsy (Mk3) there is an earth ground available -- that if used -- allows a couple semi-floating grounds that let the board to float a few volts above earth ground for noise reduction. More work than I want to do ... but it could be done.
Going back to mechanical connections used as electrical connections: a generally bad idea.
The frame is NOT intentionally grounded to the PS. It is ACCIDENTALLY grounded on SOME printers if people have actually torqued screws down where they penetrate the paint layer. Not everyone does this. On some printers paint insulates the screw from making the bond.
This is a common problem in system design. Even when the PS gets bonded to the upright frame, the same issue can cause other frame parts to float. All screw interfaces must be DESIGNED to be free of paint and oxidization that can insulate the connection. Prusa didn't do this.
Re: Why is the printer not earted?
The printer is earthed. Because you don't and sometimes your body get charged, you are getting a static shock once you touch something which is earthed.
Where it is earthed?
Re: Why is the printer not earted?
Where it is earthed?
Plug - PSU - PSU frame - bolts to the printer frame
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Re: Why is the printer not earted?
Where it is earthed?
Plug - PSU - PSU frame - bolts to the printer frame
I check the continuity of the PSU's earth and the PSU's frame and it isn't.
Re: Why is the printer not earted?
I don't want to start a long thread again. Feel free to check this thread: https://shop.prusa3d.com/forum/others-archive--f66/ground-pc-boards--t15284-s40.html
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Re: Why is the printer not earted?
Please do no mod with this ! The printer is earthed with capacitors and high resistors via the PSU.
Look for EMI/RFI filtering
Thomas
Re: Why is the printer not earted?
Just checked with my multimeter on my MK3's PSU, the ground pin of the IEC input socket is indeed connected to the PSU chassis, so while the whole frame may not be earthed, the power supply is ground referenced.
This means that probing with other ground referenced instruments is safe to do (the voltages are not floating, so large differences from a different ground referenced source is effectively impossible), and connecting other ground referenced supplies to the common ground from the PSU will not automatically cause problems (like plugging in a USB connection from a desktop computer).
What possible benefit could come with an earth connection from the frame to ground? Are you concerned that RF is being picked up on your frame or axis rods and is being re-radiated because they're not earthed? The likelihood that could be an issue if you're not next to a powerful RF transmitter and are working with sensitive, unshielded electronics is extremely low - and would likely have a similar effect to a metal table leg on a non-conductive table (i.e., a negligible one).
EDIT: To elaborate, you can look through the slots to the silkscreen on the PCB to find it's a T-LED TLPZ-24-240 V2 model supply plus the integrated connectors and power panic module. From T-LED's datasheet, it is UL listed, even if the logo is not visible from the outside, and the CE mark is a certification to meet EU compliance standards, as an FCC logo or similar would be for the US. I don't know the exact regulations of selling the power supplies in EU countries (T-LED is Czech) without the compliance stated, but the UL mark means the PSU was independently tested for safety standards appropriate to the device.