Twisted coil question

[Dconnor]

I have been playing with twisted coils lately. I understand ohms law, battery safety etc. if using dual coils you cut your resistance in half if wired in parallel. Is there a formula for twisted and how that will affect the resistance?

Example, I have been using a twisted 30 ga, wrapped on 5/64" drill bit, and comes to about .8 ohms.
Because it is really hot and I was bored I took a piece of the twisted 30ga, folded it in half and twisted that. Wrapped on the same drill bit and resistance is .63 ohms. I effectively added a whole other coil, and only reduced my resistance by about 25%. I am sure this has to do with the twisting, but thought some of you dual experts might have a better take. Pic below with cellucotton on AFC cyclone.

 

[twgbonehead]

At resistances that low, you can't consider the coil to be the only resistor in the path. The connection to your posts might be a contributor, as well as the switch, and the construction of your mod. And these resistances CAN change over time (sometimes abruptly!)

Also, the geometry is different; even though you're winding on the same size mandrel, the fact that your quadded-up wire is twice as thick means that the length of each strand of wire is longer than it would have been with the same doubled coil. Think about it; when you wind 2 pieces of wire together, the length of the "double-wrap" gets shorter, even though the length of each wire strand doesn't.

Do this a second time, and the effect is even more pronounced.

If you want to do multiple twists, do the following:
1. Twist a pair of wires together.
2. Measure the resistance of the twisted wire. Find the length that is twice the resistance you're looking for.
3. Double up that original length and re-twist. Find the length that is your target resistance.
4. WHATEVER the length of the double-twisted wire is, that's what you need for your coil.

You guys make it SO complicated, when it's actually really simple. Twist your wire, double twist it, wrap it around a strand of ribbon, braid it, dip it in hydrochloric acid and then baste it in a lye-vapor oven. I don't care.

But JUST before you wind your coil, measure out THE LENGTH OF WIRE THAT GIVES YOU THE RESISTANCE YOU WANT. Then use that length for the coil itself. Regardless of what you're using and how you wrap it this will give you what you're looking for!!!!!

 

[Raynman]

It would depend on how tight you twisted the wire before starting. Example if you used a foot of wire and it was twisted tight there would be more wire there and thus more resistance. A loose twisted would have less wire and less resistance. The number of coils doesn't matter as much as how much wire is actually on the coil. A foot of wire twisted tight might be 4 inches long the same foot not as tight might be 5 inches long. Hope I made sense.

 

[FACE MEAT]

Because it's wrapped around itself, each wire in a twisted coil travels farther to get from point A (positive post) to point B (negative post). Thus, the minor drop in resistance.

Although the reduction in resistance isn't drastic, you'll end up with a lot more surface area with which to vaporize liquid.

 

[Dconnor]

But JUST before you wind your coil, measure out THE LENGTH OF WIRE THAT GIVES YOU THE RESISTANCE YOU WANT. Then use that length for the coil itself. Regardless of what you're using and how you wrap it this will give you what you're looking for!!!!!

Got it on the geometry, that makes sense. Only problem with your measuring resistance before wrapping is I leave longer legs (particularly when mounting the coil side saddle) and trim off a good section of the wire. It is easier for me to duplicate the build if I log the wraps and what is used to wrap it on.

 

[Dconnor]

It would depend on how tight you twisted the wire before starting. Example if you used a foot of wire and it was twisted tight there would be more wire there and thus more resistance. A loose twisted would have less wire and less resistance. The number of coils doesn't matter as much as how much wire is actually on the coil. A foot of wire twisted tight might be 4 inches long the same foot not as tight might be 5 inches long. Hope I made sense.

Twisted till it broke on the drill. Makes sense though. Part of the reason I twisted a second time was that the first did not seem as tight as previous I had done. Combine that with the geometry mentioned above and it makes sense. Thanks all!

 

[Tony Spectacular]

Because it's wrapped around itself, each wire in a twisted coil travels farther to get from point A (positive post) to point B (negative post). Thus, the minor drop in resistance.

Although the reduction in resistance isn't drastic, you'll end up with a lot more surface area with which to vaporize liquid.

Mr. Meat: From your recently revised custom title, should I assume that you also want to be classified?