Best Coil Resistance for a Sony VCT4 in a SMPL Mech Mod?

Woodsman · May 26, 2015

Okay, so I'm going to experiment with a mech mod now (I've been all about DNA40/Ni200 but want to try a mech mod so I ordered a SMPL clone).
So...I'll be vaping with a HOBO RDA, single coil, 28 gauge Kanthal.
When I build my coil, what Ohms reading should I shoot for?

State O' Flux · May 26, 2015

You need to learn a bit about Ohm's law. With a mech, you use wire appropriate for the build... at the Ohm's law parity value established by the net resistance and the battery fully charged voltage of 4.2V.

With a 28 gauge single coil of 1.1Ω, you'll draw 16 watts, for a warm heat flux of 258 mW/mm² +/-. Drop down to 1.0Ω even, and you have 18 watts and a very warm HF of 320 mW/mm² +/-. Go up to 1.2Ω at 15 watts and you have a slightly cooler HF of 222 mW/mm² +/-.

pulsevape · May 26, 2015

that's a matter of personal taste...you'll have to decide that for yourself...just make sure you know the limitations of your battery.

Woodsman · May 27, 2015

State O' Flux said:
You need to learn a bit about Ohm's law. With a mech, you use wire appropriate for the build... at the Ohm's law parity value established by the net resistance and the battery fully charged voltage of 4.2V.

With a 28 gauge single coil of 1.1Ω, you'll draw 16 watts, for a warm heat flux of 258 mW/mm² +/-. Drop down to 1.0Ω even, and you have 18 watts and a very warm HF of 320 mW/mm² +/-. Go up to 1.2Ω at 15 watts and you have a slightly cooler HF of 222 mW/mm² +/-.

Okay, let me rephrase the question. If YOU were building a coil for a VCT4 in a mech mod, what ohms would you choose?

Woodsman · May 27, 2015

Okay, I went for the Vapeshadow youtube tutorial. He builds a dual coil with 28 gauge Kanthal.
Seven wraps on a 1/8" drill bit, final ohm reading 0.8.
He did comment that he prefers a 0.3 to 0.4 build, for a warmer vape.
NOTE: Lightningvapes lists the resistance per foot according to wire gauge. That's helpful information, I suppose.
Oh. by the way...
Stateoflux...that is helpful info, thank you. The Steam Engine guide/calculator, etc.
I always appreciate ANY information that others take the time to share with me.

ConcreteBob · May 30, 2015

With 28ga Kanthal, there's not a lot of builds you'll be able to do that will be risky on a genuine VTC4. But regardless, you should know how to calculate your amperage draw. I highly recommend getting Steam Engine. But if you want clouds, try twisted the wire and running 8 wraps on a 2.5mm id with dual coils. Still well within the safe range, warm vape, and excellent cloud and flavor production.

Mike H. · May 30, 2015

A sony vtc4 of course is 30 amps...you want some head room so you dont go over this..so you can go as low of an ohm as you want untill it equals 30 amps being drawn but i would consider 20 maybe 25 amps a safe zone.

Thicker wire will require more power in general to heat up so its not just about ohms...a 24g .5 coil will want more power to heat up than a 28g .5 ohm...Less battery life in general.

ConcreteBob · May 30, 2015

It does take higher wattage to produce heat in thicker wire. And higher wattage will require more energy from the battery, so it will certainly decrease battery life. And yes, the safe rating for a VTC4 continuous drain is 30a. The continuous drain is what you need to use for safety ratings. The pulse power has a higher rating, but pulse power times vary from 1 second to 6 seconds, depending on the manufacturer. So, it is not a dependable or safe way to calculate battery safety ranges.

ConcreteBob · May 30, 2015

Here's a setup for you. Pulling 25a, which is within the safe range for a VTC4, and assuming 3.7v, you can safely go to .15 ohm. A .15 ohm build with 28ga Kanthal is basically straight wires. Well, not quite, but you'll be safe with most anything you build. But regardless, you need to know how to calculate this.

Woodsman · May 30, 2015

ConcreteBob said:
Here's a setup for you. Pulling 25a, which is within the safe range for a VTC4, and assuming 3.7v, you can safely go to .15 ohm. A .15 ohm build with 28ga Kanthal is basically straight wires. Well, not quite, but you'll be safe with most anything you build. But regardless, you need to know how to calculate this.

I plan to stick with 0.8 in the beginning. But yes, I do need to study up on how to calculate this. I have the recommendations of State O' Flux to guide me. Just need to put my nose to the grindstone and get to learning!!
Steam Engine - The Vapist's Calculator
Steam Engine Advanced Users Guide
Surface Area & Heat Flux - In Practice
The Basic Mech & RDA Info Guide

Woodsman · May 30, 2015

Thanks everyone for the info. This is my go-to source so I don't vent a battery.

Woodsman · May 30, 2015

Woodsman said:
Thanks everyone for the info. This is my go-to source so I don't vent a battery.

That Steam Engine calculator is great!! I was afraid it would be rocket science, but the rocket scientists have already done the hard part.
Seems that building a dual coil deck with 28g Kanthal=half the resistance of a single coil deck (same diameter, same # of wraps). So, if I build a dual coil deck, 5 wraps on a 3mm screwdriver, I should end up with a total resistance of 0.55 for the deck (1.1 per coil/2). That's how I understand what I read, but I'm not done studying...just beginning. Need to learn this. Need to set aside intrusive thoughts that want to say it's not important. This is important! If I am a Vaper, I want to be a real Vaper, not a Vaper Lite!!

Best Coil Resistance for a Sony VCT4 in a SMPL Mech Mod?

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