APC computer power backup works

I can now confirm a small APC power backup unit can keep printers going through at least a short power failure. A power pole went down a few Kms away from me and caused us to lose power for a few seconds and a lot of flickering and both my printers are still printing no problem.

These are old discontinued APC model BE500U, I have 3 of them with new or pretty new batteries and one of them is on the printers now. so they seem to be fast enough to switch over to not cause issues. it takes me 20 minutes at the most to get a generator up and running and I’m hoping it can power them for that long.


I assume that model is not a true sinewave? I used to buy APC, and every one of the has had some kind of board failure when even replacing the batteries did not work. I have one true sinewave Cyberpower and it’s been running longer than any APC i have owned. I am desperately waiting for their 1500VA true sinewave to come back into stock. Maybe I should forgo the wait and buy the modified sinwave, if it is working for you.

We had a 4 hour power failure a couple weeks back and ruined a 17 hour print with just minutes left to finish.:rage: By the time the power came on, the PRUSA wanted to continue, but the bed had already cooled down causing the print to release itself from the bed.

I was just thinking about a UPS system last night as I started another print during this storm. Fortunately all was well here in my corner of Dartmouth

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I haven’t had any trouble with these cheap ones, I just keep batteries in them. I might not rely on it if my printers had real crappy power supplies. the ones in there aren’t so bad… I don’t know about hours running off of them. they are kinda small.

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yeah so far so good. it just changed for rain. we got about 16" I’d say up the valley. JUst the one flicker that made the clock on the microwave reset and that was it

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If you still have your old APC UPS’s (the dead ones), check the motherboard for a very large power resistor (5 to 10W). In my experience, the resistor either bakes or, if you’re lucky, the repeated heating/cooling of that power resistor causes the solder at its leads to crack. I’ve repaired a few just by re-flowing the solder. A replacement resistor is about $5.00

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Glenn I’d love to know how long they run! If you ever have the opportunity…

I just started a print-in-place print of these hinges I’ve been seeing to try. I’ll let it go for a few minutes then pull the plug and see what happens. And it’ll tell me if it’s going to freeze too. I don’t think there’s enough clearance inside it for it to be scaled down as I have.

That’s a good tip @LEGOManiac I have one here that just squeals when I try turning it on

well. that was less than spectacular. it didn’t cause any problems for the printer but only went for 2 1/2 minutes. This APC unit last had a new battery in 2017 and was in use until last fall. so It might be a little better with a new unit but probably not by that much. I have some deep-cycle lead-acid batteries maybe I’ll hook one up and see if that works with it.

Heating the shop is a big deal so when I decided I was going to have more than one printer I made a sort of peninsula in the office with cabinets on a pedestal (inside a larger shop) that I installed a (camper) propane furnace under because it’s against an outside wall to vent. I can heat just the room with that in about 5 minutes and leave the rest of the shop at 10C or just above dew point to keep things from rusting. I also wanted the printers higher in the air, and this lifted the whole tabletop to about 48" I’d rather have the build plates closer to eye level.

So the little furnace runs off of 12v and I have a deep cycle there to runt hat for now and I wonder if I can use the APC unit to maintain that battery and provide backup for the printers? What makes a charger too small to charge a battery?

I have a converter unit coming to run the furnace from a supplier. so that will be 120v -->12v and provide 30 amp @ 12v for anything else. maybe LED lights?. It’ll be backed up with another 2 deep cycles I have.

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I checked R145 and R156. Both values and the solder look good to me. I think it goes deeper than this unfortunately.

The resister looks ok but IC11 sure looks like it has a hole in it

Check the diodes and (presumably) MOSFETs. Also, check the back side of the board very carefully for any cracked solder joints. Back in the day, I used to work on SAFT UPSs and their models tended to have a common failure path - always in the high current path - so I would immediately go checking every component along that path. R145 and R156 appear to be only 1 or 2 watts, whereas the SAFT units had 5 to 10 watt resistors and they got seriously hot. This could just be due to improvements in inverter efficiency.

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