Most of them use a food dehydrator Graham - but I found this on the internet for you:
You can easily accomplish this with an ordinary oven. Slice bananas that are just ripe a little thicker than you want the chip to be. After slicing you have the option of coating with a little oil to boost the flavor, coconut oil works best. arrange your chips on a wire cake cooling rack. Nest this rack inside a sheet pan or on top of a cookie baking pan. Bake in the oven at the lowest possible setting, this will vary depending on your oven but should be somewhere between 175-200F degrees. The amount of time it will take will vary depending on what the temperature so pay attention the first time you do it , check every hour. it shouldnt take more 6-8 hours, but check each hour and when they are to your liking you will know the correct time for future reference. obviously the thinner the chip the faster it will dry too. and make alot, as many sheets as you can fit in your oven since its a time consuming process you don't want to be baking for eight hours every other day. Freeze your chips to preserve them even longer.