RDA Wicking issues with high-power (40+ watt) builds

[jersey_emt]

My usual builds run in the 25-35 watt range, but with my new MVP 3.0 Pro I've been trying out builds at 40+ watts. Unfortunately I am running into some difficulty with wicking. Even with large diameter 3 mm coils, which allow large pieces of cotton to be used to wick juice more quickly, I am getting burnt taste with draws longer than 2.5 seconds or so. I've tried various amounts of cotton, everything from quite loose to quite tight and everything in between with no success.

Any tips on getting juice to wick fast enough for 5+ second draws at ~50 watts?

 

[Hitcat44]

What RDA are you using?
I have found the Key to be not "tight" through the Coil but "taut". Then just long enough to barely lap into the Juice Well on length. Then I taper-cut the ends (like a dagger-point) as Fluid tends to like to travel and increases flow from small to large areas within any Conduit.
I coil on a 3/32" Bit with 26 ga and have never had an issue with dry hitting even on the occasion I hit it like a starving man on a Buffet. Unless I have run out of Juice of course. I prefer RDAs with a 5-6mm deep Well so can hit it fairly hard several times before needing a re-load.

 

[jersey_emt]

My equipment is listed in my signature, but I have been using only the Holmes V2, Freakshow, and TOBH v2.5 for these build attempts. Like I mentioned in my initial post, I have tried just about every amount of cotton, from being able to feed through with essentially zero resistance, to extremely tight (where you have to tightly twist the opposite side of the wick you are pulling on in order for it to even get through the coil, and everything in between. In the past, I've always used enough cotton to offer a bit of resistance when pulling it through the coil.

I also always use just enough cotton to touch the deck, since I very often change flavors (having massively long wicks or cotton "clouds" makes it impractical to switch flavors frequently).

I will try cutting the edges to taper them down like you suggested. Does that really have such a significant effect on wicking speed? I can understand that it might help a new (dry) wick get moist faster, but once saturated, won't it limit the amount of juice it is able to wick? Because my cotton is going to have to wick quite a bit faster than what it does now if it will work for 5+ second draws at 50 watts.

 

[Hitcat44]

In short without going into Dissertation and Fluid Dynamics,,,, Yes. Yes it does make a noticeable difference.

 

[sonicbomb]

In short without going into Dissertation and Fluid Dynamics,,,, Yes. Yes it foes make a noticeable difference.

You had me at conduit...

 

[Cacique]

What ohms are you using and what were you doing before? I would suggest going on Steam Engine and punching in your old build, then play with the amount of wraps you need to do to get a similar heat flux at the desired watts. Are you making a coil higher in ohms, or is the only change the diameter?

 

[Asquad]

sounds like you getting hot spots in the coil. punch your build into steam engine and check your leg loss. it should be under 10%. and make sure your heat flux is not too hot. ive found anything over 750 gives me hot spots and the same issue.

 

[jdawg111]

I have that problem sometimes too. This will sound stupid but it works... Fire it with out drawing on it, instead blow on it shortly as if you were clearing an old flavor. After you blow on it for a second or too drip some fluid on both sides of your coil. Also if you don't mind juice on your fingers you can twist the cotton around in the coil and if you see any dry spots soak em down. It's not hot spots or any of that. You just aren't saturated with juice in the cotton enclosed by the coil. Happens to me every rewick

 

[jersey_emt]

I tried the wicking suggestion from Hitcat44 and it did improve things, thanks! Up to 45 - 50 watts with single coils now works fine, and I don't get any burnt taste except for draws longer than 8 seconds or so. But 55 - 60 watts is still giving me issues with single coils. Now with dual coil builds there are no issues at all, because at 60 watts each coil is only getting 30 watts of power.

Is it just not possible to have a single coil build that will handle 5+ second draws at 60 watts? I've tried using lower gauge wire with more wraps to keep the heat flux down, but I just can't seem to do it. The best I have been able to do was with a 24 gauge single coil build with 11 wraps around a 2.3 mm rod, which works out to 0.81 ohms and a heat flux of 331 mW/mm^2, which starts to burn right around the 5-second mark, even with a fully saturated wick.

Any other suggestions? Or should I just stick with dual coils for my 50 - 60 watt builds? I prefer the simplicity of single coils, but if dual coils are the only way for me to do this it's not a huge deal, because 90% of the time I vape well under 40 watts, and my single-coil builds work just fine there. It just would be nice to have a single-coil build that could handle 60 watts for 7-8 second draws.

Thanks in advance for any assistance.