MICRO COILS - Selecting the right gauge wire to hit your target resistance

[super_X_drifter]

When building micro coils, It's important to select the correct wire to hit your target resistance (ohms) when you build a coil

I like to use 10 or 11 wraps to get my resistance. These days I have a preference of 1.3 to 1.5 ohms.

This handy chart can take the guesswork out of it for you. Here I rolled up 10 wrap micro coils around the .055" mandrel on the darkzero coil jig using 27, 28, 29 & 30 gauge Kanthal A1. The chart will indicate that 29 gauge is the correct wire for me to use to get the resistance I want in my coil.

27 ga:

28 ga:

29 ga:

30 ga:

I made the following notes during this exercise, noting that it's the first time I've ever used 4 different gauges back to back:

27 ga - the screws tend to loosen up if the coil is even subtly moved.

29 ga - perfect balance between ease of wrapping and wire thickness. Screws stay nice and tight.

30 ga - feels extremely thin. The most difficult to wrap a micro coil with. Deforms easily.

 

[super_X_drifter]

Micro coil fact sheet:

 

[State O' Flux]

Fine job Super... and a bump - so that your efforts to share practical knowledge doesn't slide off into the twilight zone too soon - from lack of participation.

PM for you as well.

 

[Papa_Lazarou]

Nice info to know. Thanks for doing the experiment and sharing with us folk

 

[State O' Flux]

Nice info to know.

Yes... but will you award him "winner of the internet" - or too soon to tell? ;-)

 

[propofokgov]

Good Work Super! I'd be curious to know how long the Kanthal ended up being stretched out after it was measured, mostly just out of curiosity

 

[super_X_drifter]

Good Work Super! I'd be curious to know how long the Kanthal ended up being stretched out after it was measured, mostly just out of curiosity

Thank you

I threw away those coils. I've never measured the length but may try in the future.

 

[super_X_drifter]

Here's another set of resistances taken from micro coils wrapped around a 1.5mm mandrel

 

[oplholik]

Good Work Super! I'd be curious to know how long the Kanthal ended up being stretched out after it was measured, mostly just out of curiosity

Excellent idea for those small coils that you can't see to count wraps.

 

[oplholik]

My 30g, 7 wrap coils measure .068" long consistently. I measured with a digital caliper at the top of the coil opposite of the tails.
Now when I wrap, I can just check that instead of squinting, and straining the ole eyes.

Thanks propo.

 

[propofokgov]

My 30g, 7 wrap coils measure .068" long consistently. I measured with a digital caliper at the top of the coil opposite of the tails.
Now when I wrap, I can just check that instead of squinting, and straining the ole eyes.

Thanks propo.

No problem oplholik, glad I could help! I was also thinking it would be good to know the full unwrapped length of wire from contact point to contact point to get a sense of how much wire was being used. I know the distance of the leads can play a part in the resistance measurements of the coils and to have a standard lead length might help with consistency.

 

[scscheib]

Great info. I have a question, how do I get the ohms up to around 2.1-2.5? I am using 30 gauge and 2mm silica (newb,lol). I will eventually get to cotton but I've only wrapped a couple so far and I am at 1.2-1.3 ohms with 4-5 coils. Do I simply just need to increase the amount of my coils? That doesn't seem right since your wrapping 10-12 and still getting that low ohm. Obviously the size of the coil has much to do with it also?

 

[State O' Flux]

Great info. I have a question, how do I get the ohms up to around 2.1-2.5? I am using 30 gauge and 2mm silica (newb,lol). I will eventually get to cotton but I've only wrapped a couple so far and I am at 1.2-1.3 ohms with 4-5 coils. Do I simply just need to increase the amount of my coils? That doesn't seem right since your wrapping 10-12 and still getting that low ohm. Obviously the size of the coil has much to do with it also?

Previously called "vape calc"... now called "Steam Engine".

 

[scscheib]

Previously called "vape calc"... now called "Steam Engine".

Excellent, thank you!

 

[jball49]

Interesting info, when you say mandrel, is it the typical wire looping type that is graduated to different diameters all the way up? If so, wondering how you decided to use that instead of what I have read so many say they use such as drill bits, etc?

 

[State O' Flux]

Interesting info, when you say mandrel, is it the typical wire looping type that is graduated to different diameters all the way up? If so, wondering how you decided to use that instead of what I have read so many say they use such as drill bits, etc?

Many of us, with machining and metals manufacturing backgrounds, use the term mandrel, as it better describes what the tool is purposed for, and IMO... it tends to imply a degree of freedom in your choices.

A drill bit can be a mandrel... as can a toothpick, paper clip or needle. So, when I say "use a 1.5mm mandrel" - it means for you to use anything that will suffice as a mandrel with which to wrap a wire coil of a specific size, and yet... not specifically a drill bit.

 

[jball49]

Many of us, with machining and metals manufacturing backgrounds, use the term mandrel, as it better describes what the tool is purposed for, and IMO... it tends to imply a degree of freedom in your choices.

A drill bit can be a mandrel... as can a toothpick, paper clip or needle. So, when I say "use a 1.5mm mandrel" - it means for you to use anything that will suffice as a mandrel with which to wrap a wire coil of a specific size, and yet... not specifically a drill bit.

Thank you for clarifying that for me, I appreciate it!

 

[State O' Flux]

Thank you for clarifying that for me, I appreciate it!

No problemo. Can't move forward without a bit of clarity. ;-)

 

[etherealink]

Great info. I have a question, how do I get the ohms up to around 2.1-2.5? I am using 30 gauge and 2mm silica (newb,lol). I will eventually get to cotton but I've only wrapped a couple so far and I am at 1.2-1.3 ohms with 4-5 coils. Do I simply just need to increase the amount of my coils? That doesn't seem right since your wrapping 10-12 and still getting that low ohm. Obviously the size of the coil has much to do with it also?

To get to 2.3 ohms around a 2mm mandrel (silica in this case) you would need 3.2 inches of wire (plus the legs/leads) and it would be a micro-style coil in this case, where the wraps are touching.

The difference is most micro coils are around 1.5mm mandrels and are wrapped tight around the mandrel with the wraps touching each other.

The easiest way to explain the relationship of resistance and wire gauge is that the thinner the wire, the higher the resistance. And when you wrap wire around a smaller mandrel you can use more wraps and still use the same amount of wire, meaning the resistance is the same. When you wrap coils with spaced out wraps you will end up with less wraps and still have the same resistance.

If you have a smart phone, check out Vaper's Toolbox, so far it has been fairly accurate.

 

[jball49]

To get to 2.3 ohms around a 2mm mandrel (silica in this case) you would need 3.2 inches of wire (plus the legs/leads) and it would be a micro-style coil in this case, where the wraps are touching.

The difference is most micro coils are around 1.5mm mandrels and are wrapped tight around the mandrel with the wraps touching each other.

The easiest way to explain the relationship of resistance and wire gauge is that the thinner the wire, the higher the resistance. And when you wrap wire around a smaller mandrel you can use more wraps and still use the same amount of wire, meaning the resistance is the same. When you wrap coils with spaced out wraps you will end up with less wraps and still have the same resistance.

If you have a smart phone, check out Vaper's Toolbox, so far it has been fairly accurate.

Apparently if you have a Droid smart phone, already went through this and isn't available for iPhone as far as I could find. Drats, lol.