Not too long ago we got a call from a guy named Tim (we will use the name Tim just in case his employer reads this). He called us in a panic. His company purchased a $19,900.00 3D printer from one of the major 3D printer manufacturers. He was told by his boss that he needed an uninterruptible power supply to protect and provide backup power for the printer. Tim did his research and found that the 3D printer’s specifications on the manufacturer’s website said that it consumed 7 amps at 120 volts. He multiplied 7 amps by 120 volts and got 840 watts. Tim then went out and bought a consumer 1500 KVA / 865 Watt uninterruptible power supply on sale for $199.99 online from a deal site because he had an uninterruptible power supply from the same manufacturer on his $499.00 computer and it worked fine.
The bargain UPS came in and Tim double checked his numbers before hooking it up. His calculations told him that the 3D printer would only use 840 watts and the bargain UPS said it had a maximum capacity of 865 watts. He plugged everything in and turned on the printer. From what we were told, the bargain uninterruptible power supply made a bunch of terrible sounding “clicking” noises and the almost $20k 3D printer made some “hard sounding jerking noises”, but wouldn’t come on completely. Tim was in deep (fill in your favorite four letter expletive here). Apparently they couldn’t get the printer ever to work correctly after that even when plugged directly into the facility’s power. Tim, employing standard CYA tactics, returned the printer to the manufacturer under the impression that it must have been damaged during shipping. To the best of our knowledge, he failed to mention his bargain UPS experiment to the manufacturer in fear of not having the replacement or repairs covered under warranty.
Everything worked as it should, so what was the problem? The bargain UPS intended for use with computers would have worked on a computer with up to an 865 watt load. The 3D printer’s average load after startup would be roughly around 840 watts according to documentation. There was nothing wrong with the socket that Tim used. The problem was the inrush current created by the 3D printer on startup which can be up to 16 times more than the “electrical requirements” listed on product literature available to end users depending on the model. This disconnect between readily available information on power usage and not so easily accessible inrush current usage comes to light in manufacturer site preparation guides. A simple example is on a production quality 3D printer where the site preparation guide (usually only available to distributors and existing customers) states that the unit consumes approximately 540 amps during startup, but only 34 amps on average. If you look online at the time of this writing, you can only find references to the 34 amp average load. Tim’s bargain UPS was simply not able to handle the inrush current. Tim spent about 1% of the cost of the 3D printer on power protection and he got what he paid for plus probably a few sleepless, stressful nights mulling over the unintended consequences of his actions.
We had experience with the particular 3D printer that Tim was using and sent a 6 KVA / 4,200 Watt uninterruptible power supply. It not only handled the inrush on the replacement 3D printer Tim received with no problem, but due to the extra batteries, provided approximately 20 times the backup time during a power outage of a single battery UPS. Tim later took advantage of the “generator mode” on our uninterruptible power supply and paired it with a backup generator on an automatic transfer switch to provide real-time, short-term, and long-term power conditioning, protection, and backup power for his employer’s manufacturing operations.