a quick bit of advice regarding ni200 coils on any dna40 device. After I build the coil and making sure the screws holding the wire are super tight, I do a dry burn on the device set at 600. IF the coil gets red hot, the build is wrong. I mean, it will vape, but it will be temperamental. Twisted builds in my experience work better with the ni200 because the wire is so soft, but they are fussy. I would suggest people start with a standard spaced coil at 2.5+mm (this is what I did until I could build them with regular success). Yes the ni200 is harder to work with, but it just takes practice, just like kanthal. I have gotten limited success with twisted 30g ni200 contact coils, but I would say the success rate is 25%. Another way to test the build, is after vaping through a few ml's, take a look at the coil. If there are uneven black/dark coils in your build (say coils 2 and 3 out of the 8 wraps), then that build was not successful. At least this has been my experience
I refuse to do dry burns on nickel wire or even kanthal anymore for health/safety reasons. I am, at this point, only doing space coils around a 3mm screwdriver. To date, it has worked out well. Incredible vapor and taste with my juices. I have checked my coils after running several tanks in my lemo drop and all of the coils at this point have turned black; I credit this to the heavy vg/net's juices I am using.
You said that if the nickel coil gets red hot, with tc off, your build is wrong. Please explain. I am relatively new at building my own coils, so your expertise in this area would be appreciated.