Power Supply failure  

Re: Power Supply failure

Fuses inside the PSU? Where are they?

Re: Power Supply failure

Every PSU contains some kind of fuse. Rarely they contain normal glass fuse on holder, mostly is soldered, either normal size or smaller one(sometimes in a shrink tube). If nothing else it has at least tiny PCB track which blows. You should check out.
If i look through the case of my Prusa PSU it has a fuse like on a picture (5Amps).

Re: Power Supply failure

Thanks. I did not knwo that was a fuse.

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Would it make sense to run the MK3 off of 220 mains voltage in the US? I already have a 220 outlet wired for the table saw...

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Based on the anecdotal evidence from this thread, it seems it would reduce the likelihood of power supply failure with the stock Prusa supply. It will halve the current requirements on the front end filter components as well as reducing the stress on the PFC/boost converter stage.

There certainly isn't any harm in doing so.

Re: Power Supply failure

Every PSU contains some kind of fuse. Rarely they contain normal glass fuse on holder, mostly is soldered, either normal size or smaller one(sometimes in a shrink tube). If nothing else it has at least tiny PCB track which blows. You should check out.
If i look through the case of my Prusa PSU it has a fuse like on a picture (5Amps).

I believe that is an Eaton Bussman 2.5Amp fuse https://www.newark.com/bussmann-by-eaton/ss-5-2-5a-ap/fuse-pcb-2-5a-250v-time-delay/dp/77K7912

Regards Joan

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Mine is FULLNESS ELECTRICAL CO, TSP T5A250V

Any time lag fuse with the same ratings, that physically fit, would work though. Note that the input fuse in the power supply is a 5 Amp fuse with the following ratings.

% of Ampere Rating Opening Time
150% 1 Hour ,Min
210% 2min,Max
275% 400ms Min,10s Max
400% 150ms Min,3s Max
1000% 20ms Min,150ms Max

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Mine is also T5A.

% of Ampere Rating Opening Time
150% 1 Hour ,Min
210% 2min,Max
275% 400ms Min,10s Max
400% 150ms Min,3s Max
1000% 20ms Min,150ms Max
this clearly shows why fuse can not prevent damage of ANY equipment. It can only prevent further damage (fire) once when equipment already fails. We used to say: "transistor is the best and fastest fuse". Sadly it (mostly) doesn't open circuit but goes into permanent conduction mode instead... 🙁

Re: Power Supply failure

I have also had a problem with my PSU. I have blown 2 PSU's in my MK3 since I received it in late November 2018(about 6 weeks). Both times I was printing TPE filament with extruder temp 240 and bed temp 90. Both times the PSU blew in less than 15 minutes of printing. I am in Canada. All of my other printing has been PLA with extruder temp 210-215 and bed temp 60-70 and I have had no problems. The dealer that I purchased it from replaced the first PSU with no questions asked, but now they say "there could be a problem with the wiring or another component" and require me to contact Prusa support directly.

After the first PSU blew, I purchased a Meanwell NES-350-24 as a spare, and have installed it now. It has printed several PLA jobs but I have not tried the higher temps with TPE yet.

Re: Power Supply failure

After the first PSU blew, I purchased a Meanwell NES-350-24 as a spare, and have installed it now. It has printed several PLA jobs but I have not tried the higher temps with TPE yet.

Go for it and have no fear. Your Meanwell PSU is inside a warranty.

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My PSU 230v blew on Thursday evening, hardly used the printer, however support at Prusa was excellent I should have anew PSU on Wednesday, think I might also look at alternative PSU,s are there any others out there as good as meanwell, as hard to find now and so many fakes on the market.

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I have a meanwell as a backup now.

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My PSU 230v blew on Thursday evening, hardly used the printer, however support at Prusa was excellent I should have anew PSU on Wednesday, think I might also look at alternative PSU,s are there any others out there as good as meanwell, as hard to find now and so many fakes on the market.

OK guys and thanks to Marek at Prusa for letting me teardown my PSU and this is the composant that has blown in my PSU, hope it helps to see what is going on, Prusa support are awesome, so electronics blow, but they where a 100% on the ball.

Re: Power Supply failure

Hmm. That is very interesting. Do you know what that part is and if they planning a change?

Re: Power Supply failure

Hmm. That is very interesting. Do you know what that part is and if they planning a change?

Its a 5 ohm Negative Temperature Coefficient Thermistor and is used to limit inrush current during initial power supply turn on. Prusa does not directly control the use of that particular part. The power supply is sourced from T-LED. While it is a Prusa specific supply, and it specifically marked for them, it is based on T-LEDs design and it is likely shared among several products that T-LED manufactures under their own branding, as well as for others.

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Thanks. You would think they would look for a replacement.

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Would be pretty hard to criticise the lads, it could have been a power surge, or anything, it is -6 celsius here at the moment so power fluctuations can happen............. 😉

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All these failures? That is a lot of power surges.

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All these failures? That is a lot of power surges.

They are not all the same and doesn't have the same root cause. But I think everybody would agree that more powerful PSU on MK3 would be beneficial for us 110V users.

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Understood. Might be good to do a lot of testing on 110v next time.