Well the question remains about what is best practice for micro coils with NI200 to avoid or detect "hot spots" (either because some wraps share more heat with each other or because of shorts). I think it's time to build a new coil
Some more observations, not sure if they help anyone but anyways
I dismantled my previous 3.2id 11 wrap spaced 30AWG NI200 macro coil build. The wick was discolored and after washing it out under water it cleared up but there where very very small but visible char marks on the wick that did not wash away. So it was mostly gunk buildup but definite charing. I was vaping this coil at 450°F max but mostly 430°F so I assume as soon as you go above 400 or 410°F you do get some wick charing. I also set the temp limit to 600°F again to see if it glows at that temp and IT DOES NOT. So whatever happened with my previous strange experiment it must have been damaged wire or something. NI200 doesn't glow at 600°F. After this dry firing without glowing the wire was still very clean and reflective without discoloration, but if course I only vaped it for half a day.
Next I disabled temp protection and let this old coil dry fire. It started to glow as expected. Curiously the resistance quickly shoots up from 0.24 to around 1.2 ohm and above. I wish the DNA40 would display the resistance as well as the current temperature in temp control mode as well, but it might not be that practical. With my high magnification loupe I examined the cooled down coil and did not seem to have changed, still reflective but maybe a bit of a rougher surface. When I re enabled the temp control the resistance was stil 0.24 ohm so the glowing did not chance the coil significantly.
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Next I build a
20.5 wrap AWG30 NI200 single contact coil with ID 1.52mm. Just because this is what I usually build with kanthal, just thicker wire and about half the wraps. What's interesting is that steam-engine.org tells me it should have 16.22 wraps for 0.22 ohm but I have 20 and 1/2 wraps for that. Strange. This would indicate that the contacts between the wraps DO make the resistance slightly higher...
And WOW this coil is the shizzle compared to my previous macro coil! I immediately noticed that at 440°F it almost dumped 35 watts when limited with temp control! I vape at 35 watts (almost max) and let the temp control the vape. I dialed the temp back to 400°F and now I have a really thick, cool and flavorful vape. After that the initially thick vapor production went down, probably because the wick was supersaturated at the start.
I did notice a bit of darkness however at the center of the coil after firing. Probably the average temperature is right but higher in the center due to less liquid and lower at the ends. So probably I'll get a bit of wick charring in the center. This coil is just too long at 20 wraps. But definitely a step in the right direction.
At 410°F gives a bit more taste and is still cool. Dumps about 8 watts after reaching the temp limit.
At 420°F gives a vape that is neither cool nor warm. Now dumps about 10 watts.
At 430°F the vape is about how I like it, slightly warm. Now dumps about 12 watts.
The temperature of the vapor will probably vary a lot depending on the size of your chamber, cooling fins and most of all your drip tip. I use a longish ming vase shaped acrylic.
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Next I fiddled with the coil a bit and tried to pull it apart gently and spacing the coil slightly, by pulling at one end and raking it. Interestingly the resistance went up from 0.22 to 0.26 ohm which is closer to what steam-engine is telling me. This could indicate either that contact coils do reduce resistance due to "shorts" OR that I damaged the wire of the coil a bit at some place.
Without rewicking the coil now dumps about 20 watts at 430°F and has a warmer vape. Which indicates that the temp sensing is off now somehow... or the coil is damaged.
There was noticable discoloration in the middle of the coil before I fiddled with it, which indicates a wicking problem. So 20 wrap coils with ID 1.52mm aren't any good. For dual coils you'll have to increase your inner diameter to reach above 0.1 ohm with AWG30. Or go down to AWG32.
I think the coil was damaged or the temp sensing is just off for such a long thin coil, which isn't really that suprising because the wicking will just be bad in the middle. I think it's time to build a new coil lol
