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Running MK3+ on battery  

Active Member
Running MK3+ on battery

A search didn't turn anything up on this, so I thought I'd throw it out there.

I'm an amateur radio operator and I run my 100W transceiver with a LiFePO4 battery.  The radio needs 13.8V DC and draws close to 20A peak.  I got a battery from Bioenno, with a 4A charger, and it's a great solution at much lower cost than a big beefy power supply.  When I'm listening, the radio draws a couple of amps, so the battery charges.  As a side benefit, I get half an hour or 45 minutes of operation if power is lost, but I didn't do it for that reason.

I was thinking of using a UPS to avoid losing prints, but I realized that I'd just be adding two inefficiencies: the UPS DC->AC, then the MK3 power supply.  Instead, I can just use the same sort of setup for the MK3.  Has anyone run the printer on battery?  I assume it will be no problem, since the load is relatively smooth.

Posted : 15/08/2023 12:34 am
Veteran Member Moderator
RE: Running MK3+ on battery

UPS is a self managing system typically the UPS is on, all of the time, and the load is only on, when required.
Batteries for the Prusa would mean that you need to disconnect the prusa power supply, connect the battery charger to the battery, and then connect the battery to the printer,  (the battery charger would probably need to be larger than your present battery charger, to ensure that the batteries recharge faster than the printer depletes the battery, if you are using this setup as an alternative to a UPS, you may need a charger with say twice the peak power of the printer, in order to restore the battery after a power outage, whilst still running the printer.)
after printing you would need to remember to disconnect the printer from the battery, to prevent running the battery flat. and later disconnect the charger from the batteries,
your prusa would not be able to work from mains until you reconnect the prusa power supply. 
connecting both the prusa power supply and the battery to the printer at the same time may have 'interesting results'...   turning on the Prusa Mains power supply, whilst connected to the lithium battery, is not an approved charging method. Lithium batteries are a bit fussy about charging... and may object with flames... 
Prusa Mk3, Mk4 and XL are 24 volt systems, so you would need two batteries and probably a battery management system, to maintain a balanced battery system
with the Mk3 power supply you are switching something in the region of one, or two amps AC depending upon the input voltage, on battery you may be switching up to ten amps DC, if you switch off whilst heating... (the current load at idle will be much lower but what ever switching system you use, must be rated for more than ten amps constant supply to prevent power loss and over heating of the switching circuit )

If you handle all of that, you should be able to run your printer off lithium batteries

73's Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Posted : 15/08/2023 7:51 am
Illustrious Member
RE: Running MK3+ on battery

The MK3 PSU converts mains to 24v.  So you would need a 24V battery, and then you would have to bypass the switching power supply.  You would also have to bypass the power panic function.

UPS is probably simpler but be very careful if you get one, the afore mentioned power panic can still detect mains loss with many of them so only certain types are suitable for a MK3.  There are several posts already on running a MK3 with UPS units.  Use a google search with the site: filter as the forum search leaves a lot to be desired (it sucks).

Posted : 15/08/2023 7:53 am
Active Member
Topic starter answered:
RE: Running MK3+ on battery

I agree with your points, and I would run the Prusa on battery only, and just use the power supply for something else.

Bioenno Power (not an ad for them, but their battery has been great for me) has a 24V 20 Ah battery with integrated PCM and a 4A charger.  As long as mains is on, the 4A output by the charger will be adequate for PLA, although perhaps not for higher heat.  For PLA, the battery will always be fully charged, and if mains quits, I could run almost 7 hours on the battery.

Thanks and 73s


Posted : 15/08/2023 7:15 pm
Active Member
Topic starter answered:
RE: Running MK3+ on battery

Thanks for the point about the power panic: I'll have to look into that.  The battery I'm looking at is 24V 20 Ah.

Thanks also for the tip on search.

Posted : 15/08/2023 7:17 pm
Active Member
RE: Running MK3+ on battery

Just going to add:
In my country we have scheduled power shedding. And staying in a rural area, failure can happen any time. So I invested in an inverter.
Before the inverter, Power panic has always been an iffy thing for me. I had a lot of failures. One case when power is restored it is not stable and go off again within a few seconds. My MK3 lost the last saved position before I can do anything.
With the inverter which is not a pure sine wave, the power panic always triggered (Power panic sense the AC input on a Prusa, and not the 24 DC output like other makes).
Since I disconnected the power panic, just running through the inverter, I had no print failures. Been running for 6 months now with daily power failures.

Having batteries running an inverter is slightly less efficient, but you get the job done.

Posted : 21/08/2023 5:42 pm