Built two coils so far but both are 3.4 ohm or higher. I think I know the answer?

[toddrhodes]

I've rebuilt my rba twice now, once last night and once tonight. I'm using 32 AWG Kanthal and last night, I used a 1/16th drill bit with about 11 wraps and it came out to 3.4 ohms. Today while messing around on some other forums I learned about the machine screw method and found the smallest one I had in the house. On my calipers it checks in at about 3mm. So I used the same Kanthal with 6 wraps and, again, 3.5 ohms this time. I have some 2mm machine screws coming as I really like this method. It's fast and consistent and great for beginners IMO. So, because I am using such thin wire and the diameter is 3mm of my current rig, is that why my resistance is so high? I'd like to get down to the 1.7-2.0 ohm territory so I'm thinking if I up the gauge to 28 and lower the diameter, that's the answer, right? Here's my logic - thinner wire has more resistance, correct? That was my issue the first time. Thinking that 32 AWG Kanthal was actually lower resistance than 28, I put more wraps on the drill bit to avoid going too low. Tonight, I decreased the wraps but increased the diameter by a factor of 2 so, in the end, I get the same resistance just in a tighter package.

I just want to make sure I'm thinking about this the correct way. I haven't had any issues with either coil, I just have to drop the wattage down quite a bit so I don't get burnt hits. I think that has more to do with the juice I am using than anything (RY4 and a quasi RY4, to keep it simple).

Anyway, just wanted to run this by the experts, hoping I made sense!

TIA,
Todd

 

[State O' Flux]

So, because I am using such thin wire and the diameter is 3mm of my current rig, is that why my resistance is so high?

TIA,
Todd

Yep. If you want to build 2 & 3mm ID coils, you'll want to go with 26, 27, 28 ga Kanthal to get below 2.0Ω.
If you want to use 30 and 32 ga - you'll need a smaller ID... or, you'll need to twist two strands together to reduce resistance.

The chart below is for the ID of a coil, and has no relationship to wire gauge.

 

[toddrhodes]

Never thought about twisting it together, that's an interesting thought! From my days in car audio, I can use a drill to make a nice, easy to work with braided wire if it comes down to it. Wire is cheap though, I don't mind experimenting

 

[State O' Flux]

Never thought about twisting it together, that's an interesting thought! From my days in car audio, I can use a drill to make a nice, easy to work with braided wire if it comes down to it. Wire is cheap though, I don't mind experimenting

Yep again. A drill makes for a pretty, and snug twist. Basically, with a two wire twist, you end up with a resistance of about 1/2 that of a single wire gauge... give or take a bit. ;-)

Some believe, and I have no reason to think otherwise, that a 2 wire twist will have more surface area than an equivalent resistance single wire. I've done it... don't see much difference, but that's what makes theories so much fun.

 

[bosun]

Here are the resistances per inch for the various Kanthal gauges:

Kanthal A-1 Wire Specs: (Ohms Per Inch)

•28 AWG- 0.439 Ohms/in, 0.0508 Diameter (in.)

•30 AWG- 0.696 Ohms/in, 0.0100 Diameter (in.)

•32 AWG- 1.091 Ohms/in, 0.0080 Diameter (in.)

•33 AWG- 1.383 Ohms/in, 0.0071 Diameter (in.)

 

[Krizzell]

Yes twist the wires or use less wraps or build a micro coil. I use 32 ga but I don't get that high. You could try flat wire .5-.8 that would get you lower and covers more of the wick.