Temperature dependant resistance

[fused2explode]

As a high voltage engineer, I know what impedance is (equivalent to resistance in an A/C circuit) but not really resistance. In its basic form the same rules apply. Basically the law says that the higher the temp, the higher the resistance. We are using circuits that are trying to increase temp by using resistance wire. Now my question is are you measuring your ohms / current when under heavy load? Because by this theory your resistance should increase the longer you're firing your build. Has anybody done the proper testing while firing for > 5 seconds? I don't believe we are drawing as much current as we think the longer we hold down the fire button. Any thoughts from people in the know? I've seen builds that by the regular formulas used by most on this forum and under batteries rated for lower limits should go into thermal runaway under stress do not... I believe it has to do with the temp. Any thoughts?

 

[State O' Flux]

(Sandvik) Kanthal has provided relative resistivity per temperature specification in this datasheet... up to a maximum temperature of 1400°F.

 

[fused2explode]

(Sandvik) Kanthal has provided relative resistivity per temperature specification in this datasheet... up to a maximum temperature of 1400°F.

Thanks for the info. In real situations these numbers can become construed by a lot of variables. Has anyone actually tested the resistance change on an actual build? I see people use these ohm meters that are rated at +/- .1 or .2 ohms which makes sub ohm builds inaccurate

 

[State O' Flux]

Has anyone actually tested the resistance change on an actual build?
I don't think so... but I'm sure someone has tested the rise in resistance to temperature in an unrelated area. Unlikely however that you could draw any direct comparisons. Equipment is an issue... not so much accuracy as there are plenty of knowledgeable folks who own good kit, including decent pyrometers... but few with equipment capable of the speed and recording capabilities necessary to produce a graph.
I see people use these ohm meters that are rated at +/- .1 or .2 ohms which makes sub ohm builds inaccurate

To look at it from the perspective of one who's been around for awhile... I'm just thankful when I encounter someone new to sub-ohm who actually has any kind of meter at all.

If you spend time reading the threads, particularly in the rebuildable atomizers sub-forum (and recently introduced sub-ohm forum), the number of people who are fishing for a "good build"... because neither do they own any meter of any kind, nor do they have the first clue of Ohm's law math... is frightening.

I use to gently (and on occasion not so gently) chastise people who didn't have some sort of ohm meter, preferably both a good quality ohm/build box and DMM... but now, having spent entire days chastising OP after OP, I'll say something about the safety aspects of verifying resistance... and walk away.