What size UPS for an M2?

[zemlin]

I just lost a print 16 hours in due to a thunderstorm - and it's a paid job on a tight schedule. I can't afford to have it happen again and there are more storms in the forecast.

What size UPS do I need to get for an M2. I don't feel I need significant run time, just enough to get through a few seconds of a power glitch.

Thanks.

[ednisley]

What size UPS do I need to get for an M2.

Something around 500 W should do the trick; the platform heater soaks up a bit over 200 W. The extruder heater is 40-ish W, all the motors might add up to 100 W, and the electronics round the total upward to the next multiple of 100 W. Add more if you have a PC + display feeding G-Code to the printer.

Remember that the "big number" touted in UPS ratings is the reactive power (volt·amp = VA) and the "little number" is the real power (watt = W). Buy based on the total real power and it'll be all good.

You'll get no more than 10 to 20 minutes of runtime from a UPS, no matter what its power rating may be, because they're really designed to let you properly shut down a desktop PC after a blackout. The batteries simply aren't big enough for an extended outage.

As the batteries age, the run time will decrease, so test the thing maybe once a year: plug the UPS into a power strip, turn on the platform heater, shut off the power strip, and time how long the M2 runs. If you don't test it occasionally, eventually the UPS will instantly shut down when the lights go off, giving you your first heads-up about defunct batteries.

I have an ancient Belkin 1200 VA / 670 W UPS on the M2, but this one (now powering my desktop PC) should suffice:
https://www.amazon.com/gp/product/B00429N192

[zemlin]

Thanks, Ed.

[zemlin]

Got this model at Costco for $100
https://www.bhphotovideo.com/c/product/ ... r_lcd.html
Thanks again.

Turns out power was not the root cause of the failure, but I'm still glad to have the backup as I have had prints stop during a storm.

[insta]

I run an 1875VA UPS for 6x M2s -- it won't hold all printers running at once, I just have 6 plugged into it. I added extra batteries to it, and should be able to get around an hour of runtime off a single M2 with the platform heater at full tilt.

[ednisley]

should be able to get around an hour of runtime

Have you actually tested it to make sure?

AFAICT, it'll destroy itself long before then, because the power transistors lack enough heatsink capacity for more than a few tens of minutes.

If it resembles the UPS circuits I've seen, the transistors mount on milled aluminum blocks, not finned extrusions, with no external ventilation and just enough heat capacity for the worst-case operating conditions:
https://softsolder.com/2011/07/22/mge-e ... rangement/



The design principle consists of having the batteries go flat before the semiconductors overheat. Adding more battery capacity (more or bigger batteries) means the transistors will be the first to fail.

I'd really like to be proven wrong, though!

[insta]

It's actually forced cooling with heatsinks instead of heatsoaks. It has provisions on the internal PCB to add external batteries as well

And, no, I haven't tested it yet. I don't have all my M2s in the rack, they are rotating through the robot hospital after my move.

[ednisley]

forced cooling with heatsinks instead of heatsoaks.

Ah! Not the consumer-grade gear found underfoot around here.

Objection withdrawn: you're doin' it right!