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 it'll often be simpler to use 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 on a dual coil RTA (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 featured in my first RTA video. Note that although we're using an Arbiter 2 for the demo 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 on our Arbiter 2. 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, 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
For this, 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 with the grub screws, perform a red heat burn & strum out any hotspots, ideally with ceramic tweezers but a small flat blade screwdriver will also suffice.
Also, (if space permits) I suggest spacing out the windings a little, just enough to see daylight between them, which 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 much larger juice well openings than their single-coil counterparts, as they're designed to accommodate cotton from two coils.
A common cause of flooding/leaking/gurgling is insufficient cotton in the juice well openings. Therefore, when setting up a dual deck in single coil mode, it's crucial to ensure there's sufficient cotton in them.
💡 There needs to be enough cotton & spread evenly in the well openings to prevent reservoir juice from bypassing it & entering the inner chamber. Only wick-resident juice is allowed in here
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.
To achieve this, once the cotton is threaded through (using a slight twisting action under tension to compress its diameter), we'll to cut it to slightly longer length than normal, and use the extra to bulk up the extra juice well space.
We'll want an even spread in the well openings, without gasps and with a gentle springiness against light pressure. So once threaded through the coil, spread the tails to eliminate any clumps but do not thin out by combing, as this may make it too sparse.
Feeding the tails into the juice well openings, ensure the cotton goes all the way through to the bottom of the build deck (contrary to what some utube vape channels suggest). Ensure that there are no visible gaps in the juice well openings (the cotton needs to forms a juice barrier between the outer reservoir and the inner chamber, but still allow equalisation of pressure (i.e. the back-flow of air bubbles) in the reservoir.
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 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
Priming
Priming
IME, the most common priming errors are trying to do it too quickly and/or over-saturating, both can lead to flooding, gurgling, juice ingestion, leaking and lack of vapour (even at high wattages). The only juice in the inner chamber should be soaked into the wick, non-wick juice in here is undesireable
There's no need to prime heavily, we don't want drips or flows over the wick, so just go slowly, allowing it to soak in fully before re-applying in a different place. Better to err on the side of too dry than too wet, and if your syringe is prone to unpredictable squirting of jets then consider a 5ml dripper bottle (see pic)
Dripper bottles cost pennies and can make priming much easier & less spillage. Generally made from LDPE and before you ask, no - personally I don't care about it being "plastic"
Filling
Filling
Squirting the juice in under pressure also seems to be a cause of flooding. I'm not exactly sure why, but it appears to be far better to fill slowly, again perhaps using a dripper bottle. Also, I suggest not filling right to the upper limit of the glass as this also seems to increase the risk of flooding. When completed, replace the cap without delay.
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