Measuring low and sub ohm?

[Avalynn]

Hi there, new to this forum and I'm glad I found it!

I have been mainly reading a lot and decided that it's time I start contributing to the forum, after all it's where I learned a lot about vaping in the past couple months.

My roommate and I decided to get two rebuild-able atomizers and I am enjoying winding my own coils. We got a Aqua and SQuape clones, being used in a Nemesis clones.

A question I have is how are people measuring their coil resistances?
Do you use the two, four, or two with current measurement method? or perhaps something more elaborate?

I've read a couple times though the sub-ohm forums and here people people measuring with a multimeter. A couple ways of measuring resistances are using the 2-wire method, Kelvin (4 wire method) and the 2-wire with constant current.

I've tried this and my coils are about 0.95 ohms according to my fluke multimeter, while taking a Kelvin (4-wire) resistance measurement gets me a 0.8865 Ohm from a HP multimeter. This is a slight difference of about 0.0635 ohms while it may not seems like much, I wonder how much it would affect a a coil of 0.2 ohms using the 2 wire measurement method.

I have read around the sub-ohm forum and I figure measuring your coil resistance is important on a mechanical mod to ensure a known current output so your battery can handle it. I will one day get into sub-ohm vaping of 0.5 but for now I am enjoying what I have.

Edit: Yay my pictures work, and don't forget to REL your meter is you do a two wire measurement! If there is not REL function then measure the resistance drop across the leads and minus that from the measurement. I did that in the above process and still got the 0.0635 difference between 2 and 4 wire measurements.

If you're interesting in a bit more on how 4-wire measurements works then take a look at this:
http://edn.com/design/test-and-measurement/4411117/Two-wire-vs--four-wire-resistance-measurements
and a quick video on it:
https://www.youtube.com/watch?v=0vMvCVyOp9g

 

[radio5]

Have you considered buying a few precision resistors to use as known references, to check your meter(s) with? Maybe a 1/2 ohm and a 1 ohm or something like that. 1% is probably fine, but you can get higher accuracy for more money.
Not sure it's worth sweating such small differences though, since you're measuring it cold anyway.

 

[Hypatia]

I use my hubby's Fluke in addition to a "black box" ohm meter from the vape shop. The Fluke reads higher, but if you touch to two leads together first and see what that reading is (likely ~0.1-0.2 or so), subtract that from the reading you're getting. Also, any meter will have a certain level of error (every measurement tool in the world will, as well).

That's why sub-ohming must be approached with the level of uncertainty factored in (i.e. 0.2 ohm coils are VERY strongly ill advised). Good luck, 0.95 vs. 0.90 readings are essentially the same number (within the confidence interval). Well within the range of safe vaping ohmage. Cheers.

 

[*deleon517*]

i keep it simple i use a standard multimeter, measure its internal resistance first and subtract that from the atties resistance, number is always consistent with my vamo, zmax, and black box. I have tested on a wide range of builds from quad .4ohm to single coil 2.8ish ohm's.

 

[moondragon]

Nice equipment, Avalynn!

I initially used a Cen-Tech multimeter which I originally purchased for monitoring battery voltage. It only has 2 wires. Now I use a "cartomizer and atomizer ohm meter" box. According to product documentation, the box does have an accuracy of +- 0.2%, but I also am not building sub-ohm coils. I like to stay around 1.8 ohms.

 

[Avalynn]

Have you considered buying a few precision resistors to use as known references, to check your meter(s) with? Maybe a 1/2 ohm and a 1 ohm or something like that. 1% is probably fine, but you can get higher accuracy for more money.
Not sure it's worth sweating such small differences though, since you're measuring it cold anyway.

Yup, I have some pretty precise resistors 0.1% and constant current devices for references. I am curious of the resistance under load and how much the heating of the wire changes the resistance. I know for very precise zener diodes a heater is packaged with it to create a reference without having temperature affect it.

I agree that every meter in the world will have a certain level of error but that's why we have specific references to calibrate against and hope those references are also accurate lol! I just wanted to demonstrate the difference between 2 and 4 wire ohm measurement and that leads can skew results, nothing life changing but something to think about.

Thanks moondragon, I have some 1980's test equipment tech but they all work very well surprisingly and are within spec to boot!

I don't think I will ever go down to .2 ohms and 0.06 ohm difference can seem like a very small margin but at a very low resistance it difference of over 3 amps, which is a lot in my opinion. So always play it safe