Well, it’s a 300W (max) power supply on the Taz, IIRC.
The UPS has two numbers to watch for:
The first, typically the 1500 or 900 number, is given in Volt-Amps, a measure of total charge. That’s the total amount of BATTERY power the unit has, and it determines how long the UPS will run before it too dies. That is, the battery of a 1500VA unit might supply, say 12V at 125A total, and then the battery’s drained. Take it fast or take it slow, that’s all there is. The rating stamped on the batteries, typically 12V at 7A, is the 20-hour discharge rate for the batteries, meaning if you take 7A, it will hold up for 20 hrs +/- a few %. That’s the rate if you want the batteries to have optimally long life. No UPS that I’ve ever seen drains them at that slow rate. So, one of those batteries holds 1680 VA at the 20hr rate (12v x 7a x 20h). Discharge rates above the 20hr rate induce heat, which makes the battery give up its energy less efficiently, so their usable capacity will be significantly less, often derated by half. That’s why 1.5KVa units typically have at least two batteries, even though theoretically one battery has over 1600 VA.
The second number, the (inverter’s) power generating capacity, is more the number you’re asking for. This is the maximum number of watts that the connected loads can consume before the UPS-running-on-battery overheats. So for the Taz, you want a UPS rated typically at least 500W output to give yourself some margin, or in case you want to also run a laptop on the UPS. But, that margin is likely to never get used, because it represents a maximal power-drain situation that occurs over the whole of the power outage. Not likely. An at-temperature system draws surprisingly little power, if for no other reason than all the hot bits are already hot. During a fast-ramp warm up you might get close to the Taz power supply’s max, but that’s not likely. So, if you needed to use a 300W UPS (not to be confused with a 300VA unit), it would very likely work fine in every single instance it is ever called on.
When you connect things up to the UPS, be really strict about only powering essential things off that battery. When the power goes out, do you really need the lamp next to the printer on? Maybe use a flashlight? Nearly all UPS’s have plugs that have quality surge-suppression, but aren’t powered during an outage. Use 'em.
Another good way to make sure you’re getting the most out of that UPS are to test it periodically. Turn everything on that’s plugged into it, and then pull the plug. Yeah, there’s often a button, but pulling the plug on a running print job is a good cheap thrill. Newer UPS units have LCD screens that will say how many minutes it can keep going. Doing that and draining the battery down to about 25-30% will help prolong the battery life. Oh…battery life. The lead-acid batteries in the UPS will need to be replaced eventually, including proper recycling. Typically every 3-5 years. Warmer temps degrade them faster, it seems.
And finally, the fewer total number of machines that must be running to complete the job (in a power outage), the better. Printing from an SD card with a UPS is great. If you need a computer running it directly, consider a laptop with a battery and charger, instead of a desktop type machine. If your GCODE source files are stored on a network share, remember that if the power outage takes out that computer, printing will stop too. That’s why in my case I keep the network switch and other equipment running via UPS as well as just the printer.
Ack…one more. If you’re going to plug the UPS’s USB cable into a computer, remember that modern computers will shut down well before the battery is fully drained, regardless of any print job you might have running. So, go into the computer’s batter-power or UPS settings, and set it to not shut down the computer until that battery is almost completely dead. I think we’d all agree it’s better to have a dead battery and a good print than the other way around.
Hope that helps.