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Dominik 6280
(@dominik-6280)
Eminent Member
undervoltage MK3

Good morning all...

I have no knowledge of electricity and electronics, but the EinsiRambo card of my PRUSA mk3 only receives 22v from the power supply. It should receive in principle 24v ...

Could this be the cause of printer shutdown problems? (safety)? ... What could be the consequences of this undervoltage?

Thanks for your help...

Google Traduction...;-)

ACOZ-Belgium
PRUSA I3 MK3 - PRUSA Mini+

Posted : 12/12/2020 7:59 am
karl-herbert
(@karl-herbert)
Illustrious Member
RE: undervoltage MK3

I would disconnect the Einsy from the power supply and check the output voltage of the power supply. The voltage should be slightly above 24V.

Possibly the power supply is defective. In this case, I would , if there is still warranty, contact the prusachat.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen.

Posted : 12/12/2020 12:41 pm
Dominik 6280
(@dominik-6280)
Eminent Member
Topic starter answered:
RE: undervoltage MK3

Thank you for this quick response....
Here it is, it gives 22 volts ...

Ooops ... I don't know how to read a multimeter .... it's 24 volts ???Résultats Multimètre

This post was modified 2 years ago by Dominik 6280

ACOZ-Belgium
PRUSA I3 MK3 - PRUSA Mini+

Posted : 12/12/2020 1:17 pm
karl-herbert
(@karl-herbert)
Illustrious Member
RE: undervoltage MK3

@dominik-6280

I would say about 23.8V. That should actually be sufficient for the operation of the Einsy. Better would be e.g. 24.3V, because the voltage drops a bit (approx. 2%) when bed heater and nozzle are in full operation.

Would you describe the shutdown problem in more detail?

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen.

Posted : 12/12/2020 1:29 pm
Dominik 6280
(@dominik-6280)
Eminent Member
Topic starter answered:
RE: undervoltage MK3

During printing, the temperatures drop without an error message and continue to print cold until printing stops ...
I specify that I replaced the 2 thermistors and the fan of the nozzle. Sometimes I also get the message "THERMAL RUNAWAY". The Selftest goes well without any errors ...

ACOZ-Belgium
PRUSA I3 MK3 - PRUSA Mini+

Posted : 12/12/2020 2:00 pm
Patrick McNamara
(@patrick-mcnamara)
Estimable Member
RE: undervoltage MK3
Posted by: @karl-herbert

@dominik-6280

I would say about 23.8V. That should actually be sufficient for the operation of the Einsy. Better would be e.g. 24.3V, because the voltage drops a bit (approx. 2%) when bed heater and nozzle are in full operation.

Would you describe the shutdown problem in more detail?

Without seeing what the meter reads with the disconnected, to ensure it has been zero adjusted, all you can say is "it's about 24 volts". 

@dominik-6280:  The Mk3 has built in voltage sensing.  Enter the menu on the printer, go to the bottom and select support, scroll to the bottom and select voltages.  What does it say there?  Mine reports 24.1/24.0 (power/bed) when sitting idle and 23.9/23.7 when heating. 

I don't know, right off hand, if the Prusa firmware has a built in low voltage shutdown, but fundamentally the printer will work with significantly less that 24V.  The Einsy Rambo will run from 12V just fine.  The bed and nozzle heater aren't sensitive voltage other than the lower the voltage, the less heat they put out.  In theory, you could run the Mk3 off of 12V, you would just get half the heating capacity and wouldn't be able to print much.

Unless the firmware has a check, you could run off 23V with nothing more than a slight reduction in heating capacity, which would really only be noticeable with something like polycarbonate or some other high temperature compound.

Posted : 12/12/2020 3:11 pm
karl-herbert
(@karl-herbert)
Illustrious Member
RE: undervoltage MK3

@dominik-6280

Normally, the firmware should react to such temperature differences from 15 degrees after a time of 45 seconds and issue a thermal runaway. You have replaced the thermistors, but the error may be due to brittle cables or loose plug contacts. I would check this with the meter.
However, if everything fits - it may also help if you perform a factory reset and reflash the firmware.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen.

Posted : 12/12/2020 4:49 pm
Dominik 6280
(@dominik-6280)
Eminent Member
Topic starter answered:
RE: undervoltage MK3
Thanks to you two... in the support / voltage menu, I have 24.1v for both ... I launched a print that works ... but I know that the next one will crash ...

ACOZ-Belgium
PRUSA I3 MK3 - PRUSA Mini+

Posted : 13/12/2020 7:03 pm
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