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DaddyFixIt
(@daddyfixit)
Active Member
UPSU for Prusa

I'm trying to workout the specs details for an Uninterrupted Power Supply Unit for my Prusa i3 MK3.  I plan to use a stack of 18650 batteries with a BMS.  I'm looking to have it get charged with the original PSU, but the printer powered with he UPS unit.  What I need to know is the Amperage requirements on the output of the Prusa PSU.  Has anyone worked this sort of thing worked out yet?  Are there any DIY UPSes designed for the Prusa yet?  I plan to use this to power the unit, and lighting system to have the system run without AC power for about an hour.  Any help would be appreciated.

Posted : 20/12/2019 5:58 pm
rmm200
(@rmm200)
Noble Member
RE: UPSU for Prusa

The Prusa PSU is 240 watts, and is considered marginally adequate. I.E. don't add lights or Pi to it.

That gives you 10 amps at 24 Volts. I would not plan on much lower than that.

Posted : 20/12/2019 6:13 pm
DaddyFixIt
(@daddyfixit)
Active Member
Topic starter answered:
RE: UPSU for Prusa

Sounds like my UPSU will have an additional improvement side effect.  I've currently got a PiZeroW on it which works perfectly, but I'll just have to make the UPSU to have a higher wattage so to accommodate add-on Pi or Lights.  Thanks for the info.

Posted : 20/12/2019 6:30 pm
rickr
(@rickr)
Active Member
RE: UPSU for Prusa

I'd be very careful with what your planning on doing from a safety perspective you can't simultaneously charge the battery and run the printer full tilt as I doubt the power supply is rated to handle that if you modify the firmware and manage the battery charge so it only happens when the printer is idle and trickle charges otherwise it would work to share the PSU. Also I believe you will have to ironically turn off the power loss recovery routine as that is tied to the power good signal from the PSU I'm pretty sure so even if you lift the DC bus using a battery bank you will probably have the printer pause anyways as it will detect the loss of AC input and enter the power loss recovery mode.

Posted : 21/12/2019 12:20 am
Nikolai
(@nikolai)
Noble Member
RE: UPSU for Prusa

I wouldn't recommend to fiddle with LiPo/LiIon batteries in the DIY area. They are highly inflammable and can explode under certain conditions. Especially because the printer can draw a lot of power in short amount of time. That can heat up the batteries very fast. So you would need monitoring and controlling system for each cell in order to handle it save. Same applies to the charging process.

Please consider buying something which is approved and tested for operation. You can get 500W UPS for around $100. Your life and people in your house are more important then couple saved dollars.

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Posted : 21/12/2019 12:38 am
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