I started trying to build coils just a few months ago. I now have 4 different ohm measurement devices, and they vary widely. I have:
A pretty good multi-meter. It won’t “settle”. Once well attached to a naked coil with mini alligator clips, the display will rotate through a range of about 0.5 ohms. Even the base reading (no coil, leads attached to each other) floats around about 0.3 ohms.
A SmokTech meter. Small black box device. I screw on a head with naked coil until it first gives a read out. Then, if I tighten it a little (1/4 turn) the read out changes. Tighten some more and more ohm change. Often a 0.5 ohm range.
A “new” CoilMaster Ohm meter. Just like the SmokTech, but not as bad. The range between first-reading and fully tightened is about 0.3 ohms. The first-reading value on the CoilMaster is 0.3 ohms different than the SmokTech.
A KangerTech “Kbox Mini” mod. Put a coil in there and the readout is soild, no fluctuation. But, if I tweak the coil just a little (raise it, lower it, straighten it). The readout changes, again up to 0.5 ohms. If I take the coil out (before triming the legs) and put it in a different head (Kanger vs. Aspire vs. VandyVape), the Kbox Mini gives me different readings, varying up to 0.4 ohms. These heads look identical (same leg length).
After I wick and juice the coil, and vape a few hits, the ohms drop 0.3 to 0.5 ohms. My last build was a soild 2.9 before use. After vaping a few minutes it now reads a solid 2.4.
This is all on Kanthal 28, 30, and 32 gage, single strand wire at targets of 1.8 to 2.2 ohms based on the SteamEngine calculator. My measured ohms always come out higher than the SteamEngine calcs, but I guess that’s the difference between theory and practice? So, am I doing something wrong, or is that just the way it is?
Most ohm meters are not accurate, that’s why I only use a DNA device to measure ohms.
I mainly use mech mods with 0.08 - 0.1 ohm builds, so for me an accurate ohm reading is important, but for regulated mods at the ohm levels you mentioned, accuracy is less important, as least as far as safety goes.
Coils that are hot will often read differently to coils that are cold.
The impedance will drop as you tighten an atomiser into a mod or meter because you’re increasing the surface area of the connection, improving the conductivity of the circuit.
And a ‘wet’ coil is a better (or more efficient) conductor than a dry one.
The box you are using is probably to blame, i noticed the same thing, i have a fluke as multimeter (not cheap stuff) and the closest reading from it are whit my dna board, plus as stated above a wet and hot coil will varies a bit.
So i dont think your doing anything wrong, as long as you get your joy from your bulid and can replicate it!
That .3 ohms is the internal resistance of the meter circuit itself. That needs to be subtracted from the coil’s resistance reading.
My multi meter reads .3 ohms when I hold the leads together. (give it a few seconds to settle down)
Connecting the leads to the center pin & base of my Kayfun (the closest coil I had available) reads 1.9 ohms on the multi meter. Subtracting the .3 ohms of the meter’s internal resistance I get 1.6 ohms.
Reading the Kayfun’s resistance on the evic mini mod shows 1.58 ohms.
The multi meter is pretty accurate if you take into account the internal resistance of the meter circuit itself.
For the purpose of vaping I’m satisfied with the accuracy of something like the 521 Tab. It will read well within the “ball park” measurement I need for building. The only multimeter I have is a very old Fluke and meters of that day were not designed for low resistances. I guess you could buy a milliohm meter but they are pricey. Entry level is between $300 and $500. I honestly don’t think the additional accuracy would be of any great value for vaping however. As much as anything I look for changes. I build a coil and it measures .3Ω. I screw the vapor chamber on and now it reads .1Ω. I’ve got a problem Houston. On a mod, I look for “ball park” and stable, taking into consideration TCR fluctuations.
Yeah, for S&G’s I got out the 521 Tab and checked the same Kayfun. 1.54 ohms on the Tab. Three different measurements, on three different meters. Well within my accuracy needs. I just use what my mod says for reference. What the mod / battery ‘sees’ is what’s important.Especially true with TC and when using mechs.
Edit: I don’t do TC, but from what little I understand about it, the mod uses coil resistance to calculate the power, and ultimately, the temp. I think.
Building on a mech requires more accuracy and care, for sure. But on my regulateds, I’ve come to a pretty happy place with a combination of the theoretical estimates at Steam Engine and my own experience, and in most cases it works fine.
You get the estimate from Steam Engine and then build it out. Put it on the regulated mod you will use it on and let the mod’s readings be your guide. After a while as you build more, you will get a fundamental understanding of your builds and how they will come out. Nowadays I know that X metal, X gauge, X inner diameter, and X wraps will net me X Ohms, and it will work out. Of course this pertains to regulated devices. Mechs require more attention to detail.
TC uses the TCR of the chosen metal. TCR is the temperature coefficient of resistance; in other words, a predictable value based on how much the metal’s resistance changes along the temperature range. Since that measurement is predictable and known for each metal, the mod can fairly accurately measure the temperature of the build. In a nutshell that is how TC works.
