Preheat oven to 300ºF. Line a baking tray with parchment paper. Using a sharp knife and steady hand or a mandolin, slice sweet potatoes thinly and uniformly. The thinner the slice, the crisper the chip.
Place slices in a bowl and drizzle with oil. Mix chili powder, paprika, chipotle and salt together in a small bowl. Sprinkle over sweet potatoes and toss to coat. Arrange slices in a single layer on baking tray and bake one tray at a time for about 40 minutes. If you have a convection oven, two trays can be baked at the same time. Oven temperatures vary from oven to oven, so check and adjust baking time. When chips look golden brown and have curled, remove the tray form the oven and let them rest for 10 minutes. Chips will crips up further as they rest.