Prusa i3 MK3 PSU shuts down  

RE: Prusa i3 MK3 PSU shuts down

It is the old PSU, the silver colored to the right. According to the manual it is no longer produced so I should just ask for a replacement PSU.

RE: Prusa i3 MK3 PSU shuts down

I've not read about this one before, but the power supply has a shutdown feature for protection when overloaded. 

It is common for the bed heater to begin having problems, and shorting and melting things when it overheats.  Check the einsy board power screws - remove all the wires and look very closely with a magnifier - ensure they are not overheating - discoloration is one sign.  Also, check the screws on the bed heater - make sure they also are snug and not overheating.

RE: Prusa i3 MK3 PSU shuts down

As for power supply replacement, make sure you get a PS that has the ability to parallel any multiple outputs since some don't like being wired that way; and ensure that any one output can supply 10 amps for the bed heat (bed uses just over 6 amps nominal - so 7.5a is absolute minimum, 10 amps provides a margin).   A dual output 480w supply with 10 amps per output ... or a dual output 250w or 300w with parallel capability.

RE: Prusa i3 MK3 PSU shuts down

@tim-m30

I am testing the PSU by keeping the printer on without printing. Only once have the PSU shut down during printing, all the other times it has shut down when the printer was idle.

All the times, when the PSU has shut down, octoprint was connected to the printer. I am now keeping the printer on, not printing, with the octoprint USB cable attached but not connected.

When connected, octoprint regulary polls the temperature sensors on the bed and nozzle, so just now I am testing keeping the printer on but not connected.

So far it has not shut down within an hour.

Can the PSU be controlled from the Einsy board? E.g can the MCU schedule a power off command? I know there is a communication channel between the Einsy board and PSU for power loss detection, so that the printing can be halted and resumed.

I am thinking if the PSU shutdown is initiated by the firmware or though a gcode command from octoprint.

RE: Prusa i3 MK3 PSU shuts down

Depending on how you have things connected - USB vs direct - local environmental things can cause glitches that can do weird things.  Also, if your Rpi is a 0, I've heard there are com problems while printing.  But, in all my light reading, I haven't heard of printers shutting down randomly because of the Rpi - though I also haven't search for that.

ps: the printer does not have a remote shutdown capability.  It is a hard switch to power off.  So if you LCD is going dark, it probably isn't a firmware issue in that sense.  But the firmware could turn everything on all at once and possibly crowbar the power supply: but that's reaching.  I'd still vote for a short in the bed wiring; or an actual PS failure.

RE: Prusa i3 MK3 PSU shuts down

@tim-m30

I kept the printer on for 2h, idling, no active ocptoprint connection.

I have a laptop connected to the printer using USB, running octoprint, no rspi.

Ok, maybe its not the PSU shutting down, since you mention the hard switch. I will disconnect the PSU, check the wirings, and attach testpoints so that I can check the output voltage from the PSU when the printer has "shutdown".

If its providing 24V on both outputs, its the Einsy board that shuts down and the PSU is OK.

Also, I will try the reset button once, next time it has shut down. But I'am sure I tried the reset button the first time it happened.

Anyway, today I will try to run some short prints, that I need to get done,hopefully I will be able to diagnose the problem further if its the Einsy board or the PSU.

So to make it clear, the PSU to the right in my picture above cannot "shut down" on itself, e.g, if the power switch is on, the PSU is on.

If the power switch is on but the PSU does not deliver power, then the only explanation is a blown fuse or lack of grid power, but that is not the case here since no fuses has been blown/replaced, grid power is stable, the only thing I have noticed is that the LCD is black and the printer does not respond to octoprint. 

Next time it happends I will also check the power led on the Einsy board etc.

RE: Prusa i3 MK3 PSU shuts down

Based on one users wiring up the PSU incorrectly, if you have say a short in the heat bed, the PSU will crowbar. (which is better than blowing a fuse)

For all intents and purposes, it will be as if you powered it off.

If you are in there testing, I would disconnect one rail at a time (Einsy, heat bed) and see if you can determine which is the problem.

Chatting with support is always an option.

RE: Prusa i3 MK3 PSU shuts down

The stock power supply is single rail, so all wires must be removed.

RE: Prusa i3 MK3 PSU shuts down

As you can see in the diagram, the only OFF function is the switch.  The overload circuit will detect an over current situation and reduce the switching function until the overload goes away (at least in theory it should recover - but might require a power cycle - I have not personally tested how it works).  

It's also important to understand with a 240W PS the 15 amp fuse should never blow - 240W is 24V at 10A. The 5A fuses on the other hand, can open up ...

And while the black and silver supplies are different, I am guessing they are both single rail, no remote off capability, low cost LED power supplies. The latest is simply a bit higher quality because the silver supplies had some issues (internal buzzing/rattling being one).

RE: Prusa i3 MK3 PSU shuts down

At least on the black PSU, there are two +V lugs, and two -V lugs. 

One +- pair goes to the Einsy, the other +- pair powers the heatbed.

Step 30:

https://manual.prusa3d.com/Guide/7.+Heatbed++&+PSU+assembly+(Black+PSU)/1153

RE: Prusa i3 MK3 PSU shuts down

Same as the silver - two pairs of wires and internally there is only one single 24v rail.  A split rail supply wouldn't have enough juice (typically) to handle the bed heater as each rail would limit somewhere near 120w or 24v@5A (assuming a 240w supply).

The silver model has three sets of terminals for connection.  But is still a single output rail.

RE: Prusa i3 MK3 PSU shuts down

Here's what a 240w Meanwell supply looks like:

RE: Prusa i3 MK3 PSU shuts down

@tim-m30

Ok, good.

I have been running the printer the whole day, printing multiple items and not have had a single shutdown event at all. I am starting to suspect that it was the Einsy board shutting down when I had the black outs, but until it happens again I cannot say for sure what it was.

I still believe that there might be some issues with the printer, and if the PSU or anything related to the PSU is to suspect, I now know that I can replace the printer PSU with lab PSU with suitable power now that I know that internally there is only one power rail in the PSU.

Just to be sure, I verified the connectors for the heat bed and they did not show any sign of bad connection/overload.

Regarding the state of the old PSU, its quite noisy, especially during load. But that's common for many switched PSU's not optimized for low noise.

RE: Prusa i3 MK3 PSU shuts down

Just a follow up since my last post 2 weeks ago.

The printer was running without problems for about 2 weeks, last sunday it once shutdown again. First during bed/nozzle startup heating, then after being restarted and the print went through, it again shutdown while idle.

In the meanwhile, Prusa customer support responded, and just by referring to this thread Michaela at Prusa  shipped a new PSU which arrived last week. So when the printer failed again after 2 weeks I decided to stop printing until the PSU was replaced.

The new PSU has screw connectors for the leads, which is great since its then much easier to diagnose the power output while the system is running IF, knock on wood,  the problem would reappear.

Only drawback when swapping PSU's is that the attachment to the aluminum extrusions requires the M3 PSU holders to be in a different slot, so to fit the new PSU part of the frame has to be disassembled, a major teardown that I have postponed. Its now only attached to the frame.

I plan to try to print some holders that can be inserted without disassembling the frame, using M3 hexnuts inside. But at the moment, the PSU attachment is pretty rigid.

I also had a good reason to overhaul the printer for the first time in almost a year since it was built. The Y belt required tension since the selftest failed on loose belt/pulley.

Thanks Prusa research for a very quick response to my faulty PSU!

//Mattias Ernelli

RE: Prusa i3 MK3 PSU shuts down

Humm... did this sorted the problem ?

I was noticing the printer shutting down, was generally when idle e.g. after a print that would finish during the night, I would wake up to see the printer offline. A quick off/on on the power would turn the printer on again and would run with no problems.

But now, it has been doing it allot more frequently and today it stopped mid print for the first time.

Is this a known sign that the PSU requires replacing ?

RE: Prusa i3 MK3 PSU shuts down

Yes, with the new power supply I have never encountered the printer shutting down.

RE:

OK, which PSU did you got ? I haven't removed it yet but it seems the prusa shop dont sell them directly ... I am guessing its a mean well but need to confirm ... (EDIT: OK... actually searching by PSU it actually shows some products .. for some reasons earlier I could not find any)