An Ore Smelter initially spawns at your base adjacent to your CPH. You need the Build Gun v2 to remove it. It smelts at a rate of ~16 ore/min* requiring 3.3 PPS and can hold 128 EU. Ore smelters can be modified by placing a Forced Induction Module on top which increase the smelting speed.
*Due to the time it takes to load ore into the smelter, the actual smelting time is slightly less than 16 ore/min.
If used below -30m you'll see this message when mousing over the smelter or inductor; "smelter starved of oxygen!". The smelter will operate at a drastically slower rate when deep enough underground.