Installing a Single Coil on a Dual Coil RTA
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Intro
Intro
Many dual coil RTAs can be set up for either one or two coils. However, if only one coil is needed then using a purpose-designed single coil RTA, which will sidestep the common newbie problem of failing to allow for extra cotton in the larger juice well openings (described below).
However, here we'll install a single coil in a dual-coil RTA & make it function like our single-coil Destiny RTA as in my first RTA video. Note that although we're using an Arbiter 2 here, the procedure is effectively identical for the Dead Rabbit V3 and many other dual coil RTAs
If needed, re-watch my RTA video before proceeding, plus I'll also assume you've checked and prepared your RTA as shown here
Coil Choice
Coil Choice
In my Destiny video, I used a single coil of 6 turn 26x2+36 clapton, inner Ø3mm, & we could theoretically use the same here. However, since the Arbiter has a smaller inter-terminal gap, we'll use it's four-terminal deck to install a coil with offset legs of 5.5 turns (offset coil legs depart from the circumference half a turn before a complete turn).
WireBuddy shows a max of 6 turns, so 5.5 will be no problem. Also, it's suggesting a max Wattage of 23 for 6 turns, and 19W for 5, so for 5.5 turns we'll be good for up to around 20-21ish Watts max without risking pushing the coil into overload.
We'll use Ni80 or Kanthal A1 wire, which'll eliminate any concerns about whether our mod has the Stainless Steel Firmware Bug (described here - scroll down to "Stainless Steel Firmware Bug")
Consult wirebuddy for coil particulars
Coil Winding
Coil Winding
I wound the coil around the 3mm part of a stepped diameter coil rod (see this page for details). This, like many other coil winding tools, produces a slightly oversized inner Ø (by ~0.2mm), but for our purposes this can be ignored.
To cut the correct coil leg length, use a coily measuring tool (see this page for description), or micrometer (the manufacturers recommend 5mm for both Arbiter Solo & Dead Rabbit V3). However, be prepared to trim further to visually obtain the correct height. In short, ensure there's sufficient space beneath the coil for airflow, but don't mount so high as to risk contact with the main body when assembled.
Left & centre: trimming the coil legs to the manufacturer's specs with a "coily" tool or micrometer (5mm for Arbiter 2 and Dead Rabbit V3 RTA). These aren't essential and it can be done by sight with care.
Right: coil ready for installation, 5.5 turns with offset legs. Coil shown is anticlockwise, but for the Arbiter and DR V3, it can be either in single coil mode
Fitting The Coil
Fitting The Coil
As we have 4 terminals available, we'll mount the coil as shown, central along/across the deck and horizontally level.
After securing the terminal grub screws, perform a red heat burn & strum out any hotspots, ideally with ceramic tweezers but a small flat blade screwdriver will also suffice.
If space permits, I suggest spacing out the windings a little, just enough to see daylight between them. This will reduce the risk of introducing inter-winding electrical contacts during the coil threading
How a 3mm i/d coil should look on the Arbiter 2. (use a similar height for the Dead Rabbit V3). Offset coil legs simplify fitting on this deck, use any two terminals that cross the peek insulator strip
Left: Initial red-heat dry burn showing significant hotpots.
Mid: Heating evenly from inside to out following strumming and a gentle separation of the windings.
Right: Cooled with windings separated just enough to see daylight between windings. So now ready for wicking.
Ceramic tweezers cost pennies & make coil tasks much easier. Order a few pairs if you don't have any.
Wicking
Wicking
Dual-coil decks normally have significantly larger juice well openings than their single-coil counterparts, as they're designed to accommodate cotton from two coils.
When fitting a single coil in a dual coil deck, a (very) common newbie mistake is using insufficient cotton in the well openings, and/or not having it evenly spread out. The well openings form a barrier between the juice reservoir (visible through the glass) and the inner chamber where the only juice should be that which is soaked into the wick. Any drops or pools of juice in the inner chamber causes "flooding" - i.e. such as gurgling, leaking & poor vapour production.
So in short, we need to ensure that there's enough cotton in the juice well openings, & evenly spread to prevent flooding, but not packed so tightly that the backflow of pressure-equalising air bubbles (to the reservoir) is prevented, which can lead to juice flow problems.
The Arbiter 2 juice well openings (left) are significantly larger than the Destiny's (right) because they're designed to take cotton from two wicks, not one. So ensure sufficient cotton in them or expect gurgling/leaks.
We'll thread the cotton through the coil (using a slight twisting action under tension to compress its diameter), and cut the wick tails to a somewhat longer length than normal (see pic), using the extra to bulk up the additional space in the juice well openings.
Thinning of the wick tails almost certainly won't be needed, just inspect and separate any clumps that might have been stuck by the cutting process.
Feed the tails into the juice well openings. We'll want an even spread of cotton, without gaps & with a gentle springiness against light pressure. So spread the tails to eliminate any clumps, but don't thin out by combing, as this may make it too sparse.
Pics below show how a good coil might appear when newly wicked with dry cotton (i.e. before priming).
Cutting cotton a bit longer for single coil in a dual coil RTA, the extra helps fill the larger juice well openings. Actual extra length depends on your cotton thickness plus juice variance in juice well opening size.
Plentiful cotton under slight compression within the coil, showing upward "shoulders" as it emerges
Ensure even spread of cotton without gaps in the juice well openings.
Ensure cotton comes through from above, right down to the lower base as shown
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