Dual coil question....

[Equilibrium]

With dual coils, what causes one coil to heat up faster than the other one??

 

[Despraci]

Could be a couple different reasons;
Post connection on one is loose ore tighter then the other, or better connection
Slight ohm difference in coils
Spacing in the wraps

 

[steved5600]

What Despraci said or the coils are spaced differently. Make sure they both heat from the center and have no hot spots or a coil is touching something. Dry fire it without a wick and press the coils together so there is little gap between the loops. check to see if the wrap counts are the same.

 

[Equilibrium]

Thanks! Yeah, they both fire from the inside out and all the coils are tight against each other but one fires about a second and a half before the other one. I think the legs on the one that fires first are just a tad longer. I mean just barely longer.

On dual coils, how can you test the resistance of each individual coil? I know what the resistance of each coil should be (1.9 ohm)and I know what the final resistance is of both coils (.9) and all that jives, so I think they are both the same as far as resistance goes.

 

[DaveP]

Thanks! Yeah, they both fire from the inside out and all the coils are tight against each other but one fires about a second and a half before the other one. I think the legs on the one that fires first are just a tad longer. I mean just barely longer.

On dual coils, how can you test the resistance of each individual coil? I know what the resistance of each coil should be (1.9 ohm)and I know what the final resistance is of both coils (.9) and all that jives, so I think they are both the same as far as resistance goes.

The only way to check is to measure them separately with a volt-ohm meter. While they are installed, all you can do is measure the parallel value of the combination. If one is a little higher and the other lower, that could contribute to faster and slower glow times.

FWIW, the single coil I'm now vaping on my Kayfun is 1.5 ohms. When I dry burn it from a cold start one side glows first and the the glow spreads across the coil. After that, It glows from the center out each time until I let it get cold again. It seems to have a hot loop on one end, but inspection with an eye loupe reveals that it's nicely spaced from all the other coils.

I'd change it, but it produces great vapor and really good flavor. I just change the cotton wick and continue on.

 

[Equilibrium]

Thanks!
Combined resistance meters out to what it's supposed to... 2 coils @ 1.9 = .95. My meter is saying .9, so I'm confident in the resistance of each coil. I think it's the spacing from the posts that's got me off. Unfortunately, I've already cut the excess wire off so I can't really adjust. Gonna have to rebuild I guess. Damn it!

 

[Baditude]

You can probably put a drill bit or precision screwdriver into the coils while still attached to the posts, and manipulate the slower-burning coil left or right a little bit, which should change the resistance a little bit. May work if you don't want to rebuild another coil.

 

[Cullin Kin]

I don't think the problem is that complex. Two things: 1) Are your leg lengths the same between each coil and their respective posts? 2) What gauge kanthal are you using and are your post holes big enough to accommodate without overlapping or laying over one another?

With these, pretty much all possible problems have been listed so it has to be one of them. Unless there is a problem with your RDA, which I doubt.

 

[Equilibrium]

I'm using 28g wire and the RDA is a Helios. The center post has two holes, one for each wire, so no overlap.
I'm gonna try and adjust again as Baditude suggested. Thanks y'all!

 

[Added]

Not sure if you got it fixed or not. Sometimes this happens to me even when evenly spaced and same wraps etc. Take the tip of your tweezers or what ever you're using and gently strum the outside wraps on your coils. Not sure why but that works for me when I can't figure out what else is going on.

 

[AttyPops]

Meters use very low current to measure resistance (they are cautious...don't want to fry components).

Anyway...slight shorts may not show up with a meter, but will under high-amp use. That's why "strumming" the coils can help. I also think that heating a coil can very slightly change the shape and make or break a short. All theory of course.

My best guess, and

 

[DaveP]

For what it's worth, I was at Harbor Freight yesterday and picked up a jeweler's eye loupe for $4.99. By combining the two lenses you can get 3.3x, 5x, and 16.5x magnifications. It's a good hands free device for inspecting the things we have talked about in this thread. You never know when you have adjacent coils lightly touching. They clip on to the side frames of eyeglasses with a plastic coated metal clip. If you don't wear glasses, buy a cheap pair of reading glasses and pop out the lenses and use the frames (or buy a 1x pair).

http://www.harborfreight.com/165x-jewelers-clip-on-eye-loupe-94364.html

I know we squeeze coils together after dry burning, but there's tiny spaces between as they relax. If one or two of those are touching it greatly changes the overall resistance. That can happen when the wick is inserted if you use cotton, rayon, or other materials that are insertable.

I also bought the 6pc set of tweezers. One has a thumb slide lock for holding things up for inspection. Another is spring loaded. Another $4.99 tool set that's worth much more for vapers. You can see tiny machine marks on the ends where a line worker took the time to smooth the edges and ensure complete and even closure of the tips.

http://www.harborfreight.com/6-piece-fine-point-tweezer-set-93598.html