Trying to understand the basic rules of thumb

[BLUwazoo]

So, just went to a coil building class and built my first coil, with people watching me every step of the way. Looking at build #2 and just want to make sure that I understand the basic rules of thumb. Please correct me if I'm wrong on any of this, because I am SO green.

So, as I understand it:

1. The smaller the gauge # the bigger the wire. (i.e. 28 is bigger wire than 30)
2. The bigger the wire (the smaller the gauge), the lower the resistance per a given length of wire.
3. The bigger the size of the coil itself, the lower the resistance, because there is more wire. (Not totally sure on this one.)
4. If you are combining coils, you would divide by the number of coils to get the overall ohm rating. (i.e. Two coils at 1 ohm = .5 ohm.)
5. Once the coil is put together and you fire it and mash the wire together so the coils are all touching, this makes it a "micro coil."
6. Once you do this the ohm rating of the coil changes. (As I recall, it went up slightly, like about .2 ohm.)

So, for my second coil, I'm going to shoot for about 1.5 for a dual coil on my Igo-W. My eLeaf iStick won't fire below one ohm. That means I need to try to build two identical coils at 3 ohm each. I'm going to use the middle size pin that's in my new coil jig, which should be about the size of the mini-screwdriver that came with the Igo. Would you say that 10 to 12 wraps of 30 kanthal, will get me to 3 ohms? If not, what would you recommend changing?

Thank you in advance for you help!

 

[State O' Flux]

So, just went to a coil building class and built my first coil, with people watching me every step of the way. Looking at build #2 and just want to make sure that I understand the basic rules of thumb. Please correct me if I'm wrong on any of this, because I am SO green.

So, as I understand it:
The smaller the gauge # the bigger the wire. (i.e. 28 is bigger wire than 30) Yep.

The bigger the wire (the smaller the gauge), the lower the resistance per a given length of wire. Yep.

The bigger the size of the coil itself, the lower the resistance, because there is more wire. (Not totally sure on this one.)
Nope Length and thickness determine resistance... or lack of it. "Coil" diameter, number of wraps, shape and style have no bearing.

If you are combining coils, you would divide by the number of coils to get the overall ohm rating. (i.e. Two coils at 1 ohm = .5 ohm.)
Something like that. 2 coils in parallel = 1/2 the resistance of 1 coil. 3 coils = 1/3 of one, and so on.

Once the coil is put together and you fire it and mash the wire together so the coils are all touching, this makes it a "micro coil."
Nope. Technically. a "micro" is a coil of 1/16" (.062"/1.58mm) ID or less - compressed.

Once you do this the ohm rating of the coil changes. (As I recall, it went up slightly, like about .2 ohm.) No reason why it should... although resistance increases slightly as temperature does.

So, for my second coil, I'm going to shoot for about 1.5 for a dual coil on my Igo-W. My eLeaf iStick won't fire below one ohm. That means I need to try to build two identical coils at 3 ohm each. I'm going to use the middle size pin that's in my new coil jig, which should be about the size of the mini-screwdriver that came with the Igo. Would you say that 10 to 12 wraps of 30 kanthal, will get me to 3 ohms? If not, what would you recommend changing? Thank you in advance for you help!

Click on my first sigline hyperlink... that will help you model coils as desired. Remember... garbage in - garbage out. Might as well look at the second link too.

 

[BLUwazoo]

Wow, wow, wow! Thank you Dr.! Er, I mean State O' Flux. This is really awesome stuff!

 

[State O' Flux]

No worries.... you'll get there wazoo. If you don't have an electrical background, you're starting from square one, so even basic knowledge can take some time to learn and understand.

If you need help with the terms and information in Steam Engine, shoot me a PM.

Have fun.

 

[InMyImage]

+1 on steam-engine.org and make sure you know what size pin you are wrapping around because it does make a difference. if you are not sure, compare it to a drill bit, or use a drill bit. But keep in mind that if you compare to a drill bit, you pin will most likely be in mm's so it won't match up exactly to imperial bits unless you are not in the US or other sprinkling of countries that are primarily imperial.

Bill

 

[BLUwazoo]

Again, thank you!!! That calculator is very, very helpful. I've already been able to figure out that building a bigger diameter coil (2 mm.) will help me get to the point of having fewer wraps (12) and still get to where I want it to be. I'll use that a LOT!

 

[BLUwazoo]

I've ordered a micro screwdriver set that will be in this week that has them all marked by size. Unfortunately, the little coil jig I bought today doesn't tell you what they are. So, I'll have to wait until my screwdrivers come it (within a day or two) to tell what size the pins are in my jig. But this should definitely get me off to the races. Many thanks guys!

 

[InMyImage]

Oh, and don't worry about the "leg length" setting. I've fiddled with it and it doesn't have a significant impact on the resistance whether you set it at 1 or 10.

 

[InMyImage]

if you knw what brand it is, google it and you may find a listing that states what size pins it comes with and can figure it out by just comparing them to each other.
One of them will most likely be 2mm's so if you have a ruler with mm's that will give you an easy base too. You may have time to call the shop before it closes too...

 

[State O' Flux]

I've ordered a micro screwdriver set that will be in this week that has them all marked by size. Unfortunately, the little coil jig I bought today doesn't tell you what they are. So, I'll have to wait until my screwdrivers come it (within a day or two) to tell what size the pins are in my jig. But this should definitely get me off to the races. Many thanks guys!

Drop a few bucks on a cheap digital caliper... one that reads in mm and decimal inch. Comes in handy for converting.

Also, if you click on the x/y" box under "inner diameter of coil" in the upper right, and click on any fractional size, it will show it's equivalent in metric... if you're in "metric units" (upper left). If you're in "imperial units"... the decimal inch equivalent will be displayed.

 

[BLUwazoo]

Great suggestions guys! I did Google it (Tobeco brand). Turns out it's in inches. I figured all of this stuff was made overseas, so would be in metric sizes. And the screwdriver set is in metric sizes, so I should have a repeatable "coil jig" size for either way.

Thanks again for the fast and helpful advice!

 

[BLUwazoo]

I notice that there is no mention of the phenomenon identified on #5 & 6. Does the resistance, in fact, change when you heat the coil and then mash them together so that the coils all touch? Or was my ohm meter just reading it wrong? Does it go up or down?

 

[InMyImage]

Yes, squishing can have an impact on your ohms. The actual impact will depend on how tightly you have wrapped them to begin with.

One tip that will help you get them tighter to begin with is to run a lighter or torch down the wire heating it to red hot as you move along it's length. This anneals the wire and makes it more malleable dramatically decreasing springback.

The biggest thing I've learned is not stress the small stuff. You'll get them tighter and tighter as you get more experience.

Focus your frustration potential on getting the legs through the tiny holes without screwing them up first LOL

 

[BLUwazoo]

"Yes, squishing can have an impact on your ohms. The actual impact will depend on how tightly you have wrapped them to begin with."
Thank you for the confirmation! I was afraid my ohm meter was going wonky, but the guy at the coil building class said that this can happen.

"Focus your frustration potential on getting the legs through the tiny holes without screwing them up first LOL"
Ha ha! Yes, I totally get that. The reason my first build, of a single coil on an Igo-W, which can handle double coils, was that I couldn't figure out how to get the leg of one coil from getting stuck in the second coil, and I was afraid of a short!

 

[InMyImage]

Yeah, I have not built many myself yet and I'm still deciding which method I prefer, locking down the center post first or the outside posts first. I'm planning to go inside out next build.

I screwed up last time because I didn't have the post hole screwed down all the way and my ohms were reading at the single coil level. After I figured it out, I accidentally overdid it and broke the wire when trying to screw it down and had to start over on one of my coils.

 

[State O' Flux]

Not trying to be a dick here... just wanting to clarify misconceptions.

Yes, squishing can have an impact on your ohms. The actual impact will depend on how tightly you have wrapped them to begin with.

Although a common misconception, this is not true. Allow me to explain.

When heated, Kanthal wire (iron-chromium-aluminum) generates an aluminum oxide insulative coating on it's outside surface that protects the individual coil wraps (with a compressed coil) from shorting, one to another. This is called alumina (Al2O3).

This is most clearly noticed when you test fire a new compressed coil... the coil initially shorts and heats unevenly. The more you fire it (and shape it to final perfection) however, the more evenly it will heat - from the hot center out to the cooler ends.
This is the alumina layer developing and insulating the coils surface. Although the coils are "touching", the electrically conductive component of the coils are insulated by the alumina coating.

The self-generating, protective oxide layer is both thermally conductive and electrically resistive. Pretty convenient for us, and several billion other handy applications for heating coils.

Consider as well... for a given length and thickness of wire, the resistance does not change whether it's a 7 wrap conventional coil or a 7 wrap compressed coil.
Again... resistance for a given length does not change any appreciable amount.

One tip that will help you get them tighter to begin with is to run a lighter or torch down the wire heating it to red hot as you move along it's length. This anneals the wire and makes it more malleable dramatically decreasing springback.

Although this might be considered an arguable point, a few facts. All genuine Sandvik (via Temco) Kanthal A1 wire is pre-annealed. I find that no torching is required even with wire as thick as 22 gauge. Use of proper tools to apply consistent tension to the wire produces a tight coil requiring very little to no added dry fire / tweezer compression.

I'd be happy to discuss these points further... if you like.

 

[BLUwazoo]

Not trying to be a dick here... just wanting to clarify misconceptions. I'd be happy to discuss these points further... if you like.

No, I don't think you're being a dick. I appreciate the information! Like I said, I'm a complete novice. But, the question is, when I built a coil, it measured one way. Then, when I heated it and compressed it so that all the coils touched, it seemed to change the resistance. I believe (but can't remember for sure) that it went up by about .2 ohm. Was this a fluke of my ohm meter, or a real effect?

 

[State O' Flux]

No, I don't think you're being a dick. I appreciate the information! Like I said, I'm a complete novice. But, the question is, when I built a coil, it measured one way. Then, when I heated it and compressed it so that all the coils touched, it seemed to change the resistance. I believe (but can't remember for sure) that it went up by about .2 ohm. Was this a fluke of my ohm meter, or a real effect?

As you weren't conducting a controlled test for such a phenomena, it is highly likely to be an anomaly for which you have not taken one of several possible alternate, and more plausible, causes into account.
I can think of several reasons which might cause an increase (or decrease) in resistance.
The first (and probably the most common) might be where a post screw loosens slightly, after a new build has been heat cycled a few times in a dry fire. Always check you screws before putting an atty into service and again several times during it's useful life.

A coil, during the course of it's lifespan can both lose and gain resistance... often with the result of appearing to have not changed at all, or increasing/decreasing in only milliohm values. As the wire degrades, resistance may increase due to a loss of cross-sectional area and/or thermal fatigue.
A compressed coil can decrease in resistance, again as the wire degrades and it's insulative alumina layer is consumed - exposing it's electrically conductive core - with the resultant possibility of random shorting from wrap to wrap, much as it did when brand new, before the alumina layer fully developed.

In my own experience, as one who rarely uses a coil for more than 4-5 weeks... when I conduct a final resistance test (a practice I no longer keep, due to boring consistency), using either a USA Ohm Meter, Fluke 88 with "Tech-Thing Half-Ohm" milliohm adapter or Extech 4-wire milliohm meter... I've never seen a substantive change from the original desired value.

 

[InMyImage]

No problem with detailed responses to explain and educate, I'm prone to them myself

That being said, in my admittedly little experience, I've also seen a change in resistance readings pre and post "squishing" similar to what @BLUwazoo is seeing and that does not appear to be a screw tension issue when I have doublechecked them out of habit.

As for the annealing, the wire may be pre-annealed, but I'd have to say that there is enough work hardening during the coiling process to cause a re-annealing to make a difference in how easy it is to work with the wire. Again this is an experiencential observation. There is a definite observable difference in firing the wire prior to building the coil and it is something that I see commonly done by people demonstrating how to build coils, so there definitely appears to be a benefit to doing it, at least with the Kanthal A1 that I'm getting from Lightning Vapes in both 32g and 28g.

 

[BLUwazoo]

You know, the more I think about it, the more I think the ohm meter in my eLeaf is just unreliable. I seem to recall it "drifting" by .1 or .2 ohms even on regular Kangertech coils. I just got another iStick today. Will test them to see if they measure the same. I also think State's first suggestion is a likely culprit. At the coil building class, one person's readings were going up and down a little bit. It turned out that the coil wasn't screwed in tightly enough.

 

[Zamazam]

You know, the more I think about it, the more I think the ohm meter in my eLeaf is just unreliable. I seem to recall it "drifting" by .1 or .2 ohms even on regular Kangertech coils. I just got another iStick today. Will test them to see if they measure the same. I also think State's first suggestion is a likely culprit. At the coil building class, one person's readings were going up and down a little bit. It turned out that the coil wasn't screwed in tightly enough.

The iSticks tend to be a bit hot, or firing above the listed wattage/voltage.

 

[BLUwazoo]

Thanks Zamazam. That might be because it's configured to read in "pulse mode" rather than RMS. In other words, the power is provided in a square wave, rather than a sine wave. However, there's more to it than that. I truly think my silver iStick reads ohms in an unreliable manner. Like I said, I've seen it swing a tiny bit even when using a factory 1.8 Kangertech coil. That shouldn't happen. Haven't seen that happen yet with my new blue one, but then, I've also used the 510/ego thread adapter (which my first one didn't come with) to connect the atomizer head. I have a feeling that the non-adjustable pin might contribute something to the erratic readings.