Appropriate UPS power backup choice
Looking to buy UPS power backup supply that will suit my MK3 + CR10.
What Wattage and Volt-ampere UPS i should consider for 15ish minutes backup?
Can someone explain me Voltampere load in terms of consumption?
(since i print mostly PLA, with heatbed turned off after first layer my consumption of both printers at same time doesnt exceed 120ish Watts)
Despite my low average power consumption, i would still consider high peak consumption.
So I found 600W/1000VA suitable. but is it really necessary or i can opt 300-400W one.... hmm?
Re: Appropriate UPS power backup choice
VA*Power Factor=Watts.
Most UPSs assume a power factor of .7 for the purposes of rating capacity. The Prusa power supply has active power factor correction and so will have a power factor of 1. No idea about the CR-10.
As far as run time goes, an honestly specced UPS should run for around 15 minutes at half load. You need at least a 300W UPS for the Prusa. It will draw around 250W from the wall when heating. Assuming the CR-10 is similar, then you are looking at 600W or right about 1000VA for the UPS.
The average draw is much lower, but the problem is that when the hotend and bed are both heating, even for short periods that they are during printing, the draw could be in the 600W range and if the UPS is rated for less than the max drawn, it will likely go into overload protection.
BTW, if you want to take a reasonable guess at how long a UPS will run, find out what batteries it takes.
Total capacity=battery count x battery voltage x battery capacity. The most common mid range UPs battery is a 12V 7Ah battery. It has a capacity of 84watt-hours. So a UPS that has two of them has a total capacity of 168Wh. There is some inefficiency in the conversion from DC to AC -- lets assume 80% efficient. So available capacity is 134Wh. 15 minutes is one quarter of an hour so you could run a 538W load for about 15 minutes in that scenario. My guess is that the 600W UPS has a single 12V 7Ah battery in it, meaning you could run the same 538W load for 7 minutes, which would be about right.
Normal average load for the Prusa will depend on what material you are printing, but 100-150W would be in the ballpark. Again, assuming the CR-10 is marginally similar, then yes, if you want 15 minutes of run time, you probably do need a 600W UPS.