eVic-VT mini?

[KenD]

Atroph and I have discussed (and even debated at one point) this topic at length in the RX200 thread we darn near hijacked (my apologies to all for that).

He's won me over and I feel I understand it now.

It's clear to me, based on the math of it, that the TCR of the circuit does "change" (so to speak) with a dual parallel config.

Forget the TCR of a material (which doesn't change), it's the combined circuit as a whole that matters.

As for Heat Flux, it lowers, not raises in a dual coil config.

If you look at the Steam Engine Coil Wrapping tool you can see this in action:

E.g. build: Ti, 28 gauge, Target Resistance .5 ohms (about 8 wraps for single, 16 wraps for dual) has a Heat Flux (how hot it gets) at 30 watts of 345.

Same build (same Target Resistance) in dual coil the Heat Flux drops to 86.

Because the mod doesn't know it's a dual coil, only knows the Target Resistance, it pushes the same wattage in both builds to do its TC thing.

That same wattage on the dual coil, viewed at a whole from the "fooled" mod, ends up reporting back less change in resistance (because the Heat Flux is lower).

Because it's reporting back less change in resistance, it's almost like a new material is present (the "circuit" becomes this new "material" so to speak).

Effectively, the TCR "changes" (from the mod's point of view) when hitting a dual coil at the same Target Resistance.

It's not the material that's changing, it's the parallel (rather than series) circuit.

I made a typo on the heat flux/capacity thing. Heat flux decreases and heat flux increases with both dual coils and lower gauge wire. Resistance increases as the coils heat up, more coil mass means that more power (watts) is needed to reach a certain temperature, meaning a tc mod will push more wattage to a dual coil of equal resistance but double the mass of a single coil. The effective tcr does not change. I don't now what the sc/dc setting does on mods that have it (any others than three xcube?) but it's been theorised that it simply increases the preheat.

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[Major911]

Just updated to firmware 3.0. I like the new screen layout. I notice that for the SS setting it now displays 316. I'm using 316L. Do I need to change anything or is it good to go with the default. I don't really understand all this TCR stuff


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[KenD]

Just updated to firmware 3.0. I like the new screen layout. I notice that for the SS setting it now displays 316. I'm using 316L. Do I need to change anything or is it good to go with the default. I don't really understand all this TCR stuff


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Ss316 and 316l have close enough tcr:s so the preprogrammed setting should be fine.

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[WickedWicks]

Here are some TCR values of various wires translated into VTC Mini speak:

Ni200: 0620
TitaniumGrade1: 0350 (According to the SX Mini Manual)
TitanimGrade1: 0366 (According to Steam-Engine.org)
SS304: 0105
SS316: 0092
SS317: 0088
SS430: 0138
NiFe30: 0320

That numbers do comply with official Joyetech ranges:

Nickel 600-700
NiFe 300-400
Titanium 300-400
SS (303, 304, 316, 317) 80-200

 

[seebo]

why are people ordering 316-317 wire, isn't 304 better? i was under the impression 317 is the worst wire to use for TC. from what i've read, the mod was calibrated using 304..

 

[Jalcide]

I made a typo on the heat flux/capacity thing. Heat flux decreases and heat flux increases with both dual coils and lower gauge wire. Resistance increases as the coils heat up, more coil mass means that more power (watts) is needed to reach a certain temperature, meaning a tc mod will push more wattage to a dual coil of equal resistance but double the mass of a single coil. The effective tcr does not change. I don't now what the sc/dc setting does on mods that have it (any others than three xcube?) but it's been theorised that it simply increases the preheat.

Sent from my M7_PLUS using Tapatalk

Yes, it will push more wattage at a dual coil in an attempt to reach what it thinks the temp should be, but based on a different Heat Flux value.

To do a sanity check, I just did this thought experiment on Steam Engine:

That little 28 gauge, .5 ohm single coil build at 30 watts is cranking out 345 for the Heat Flux.

To get that same Heat Flux in a dual config, it would take 120 watts.

Well, we both know 120 watts would completely fry two little 28 gauge 8 wrap coils into oblivion.

So, without that specific HF being reached to match the single coil, and remembering it's the same base resistance being read for both builds, it can't be accurate (not the same effective TCR).

 

[Rockwell222]

Does anyone know if this new update fixes the resistance issues. My ohms dropped by .01 or .02 in TC. If someone that has this problem could help find out that would be great. My wife loves her VTC mini but we have to do tricks to make it work alright.

 

[Major911]

Atroph and I have discussed (and even debated at one point) this topic at length in the RX200 thread we darn near hijacked (my apologies to all for that).

He's won me over and I feel I understand it now.

It's clear to me, based on the math of it, that the TCR of the circuit does "change" (so to speak) with a dual parallel config.

Forget the TCR of a material (which doesn't change), it's the combined circuit as a whole that matters.

As for Heat Flux, it lowers, not raises in a dual coil config.

If you look at the Steam Engine Coil Wrapping tool you can see this in action:

E.g. build: Ti, 28 gauge, Target Resistance .5 ohms (about 8 wraps for single, 16 wraps for dual) has a Heat Flux (how hot it gets) at 30 watts of 345.

Same build (same Target Resistance) in dual coil the Heat Flux drops to 86, at the same 30w.

Because the mod doesn't know it's a dual coil, only knows the Target Resistance at a given snapshot in time, it's getting back resistance changes now driven by a lower Heat Flux than it would have for a single coil.

That same wattage (at a snaphot in time) on the dual coil, viewed as a whole from the "fooled" mod, ends up reporting back less change in resistance (because the Heat Flux is lower).

Because it's reporting back less change in resistance, it's almost like a new material is present (the "circuit" becomes this new "material" so to speak).

Effectively, the TCR "changes" (from the mod's point of view) when hitting a dual coil at the same Target Resistance.

It's not the material that's changing, it's the parallel (rather than series) circuit of the dual coil.

So if I understand you correctly. If I build a dual coil TC setup all the values are out the window and it won't vape accurately?


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[Jalcide]

So if I understand you correctly. If I build a dual coil TC setup all the values are out the window and it won't vape accurately?


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Correct, it won't vape accurately.

As for how far off it is, it depends on many factors.

I think the net effect can range from subtle -- and easily compensated for by changing temp and/or wattage -- to show-stopping.

For builds that are greatly affected by it, a custom TCR can come to the rescue (which we know have in the v3 update).

Some mods have a "dual coil" setting to address the problem, as well.

 

[Major911]

Well mine was show stopping. New build 316L 26g. Dual coils ohm at.27 Vapes great at 400 degrees for about 20 min. Then out of the blue nothing. Protecting right away no vapor. Bumped up to 500 no change. Found a custom TCR for 316L tried that. Same thing. Guess I'll try building a single.


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[MegaVap]

The new V3.00 update is looking great! It's so nice to be able to add my own TCRs. Great mod!

 

[Jalcide]

Well mine was show stopping. New build 316L 26g. Dual coils ohm at.27 Vapes great at 400 degrees for about 20 min. Then out of the blue nothing. Protecting right away no vapor. Bumped up to 500 no change. Found a custom TCR for 316L tried that. Same thing. Guess I'll try building a single.


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That sounds like two thing going on, perhaps.

The first is that you'll be getting an anemic vape with dual coils, for a given TCR, due to the reasons I've been discussing.

The second factor sounds like what happens when you have a high initial resistance reading and get too hot a vape.

It takes time for the chip's "refinement" feature to settle in.

My guess is the initial hot vape, is working in your favor and compensating for the dual build TCR issue. Then refinement kicks and crashes the party.

The way to test this is to fill the tank with liquid, suck some air through it and ensure it's cool. Then see if you don't get that anemic vape from the get-go. If you do, then that's probably it.

 

[mcclintock]

Yes, it will push more wattage at a dual coil in an attempt to reach what it thinks the temp should be, but based on a different Heat Flux value.

To do a sanity check, I just did this thought experiment on Steam Engine:

That little 28 gauge, .5 ohm single coil build at 30 watts is cranking out 345 for the Heat Flux.

To get that same Heat Flux in a dual config, it would take 120 watts.

Well, we both know 120 watts would completely fry two little 28 gauge 8 wrap coils into oblivion.

So, without that specific HF being reached to match the single coil, and remembering it's the same base resistance being read for both builds, it can't be accurate (not the same effective TCR).

I think you left the same total resistance and didn't notice that became two 16 wrap coils. If it shows the same heat flux, the wire is no more likely to fry (which would only happen when dry burning on any usable setup anyway).

 

[Carnage9270]

Anyone figured out a tcr value for sweet spot wire? Dug this puppy back out for some tcr lovin, but the TI profile is pretty anemic.

 

[KenD]

Yes, it will push more wattage at a dual coil in an attempt to reach what it thinks the temp should be, but based on a different Heat Flux value.

To do a sanity check, I just did this thought experiment on Steam Engine:

That little 28 gauge, .5 ohm single coil build at 30 watts is cranking out 345 for the Heat Flux.

To get that same Heat Flux in a dual config, it would take 120 watts.

Well, we both know 120 watts would completely fry two little 28 gauge 8 wrap coils into oblivion.

So, without that specific HF being reached to match the single coil, and remembering it's the same base resistance being read for both builds, it can't be accurate (not the same effective TCR).

I'm in no way an expert on this, but I think your calculation is off. Seems that the SE coil calculator gives results per coil, not for all the coils combined (I base this on all the other measurements being per coil, but @Dampmaskin would have to confirm that). This means that in order to achieve the same heat flux of 345 mW/mm2 as a single coil you need 60w, not 120w.

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[Jalcide]

I think you left the same total resistance and didn't notice that became two 16 wrap coils. If it shows the same heat flux, the wire is no more likely to fry (which would only happen when dry burning on any usable setup anyway).

...I think your calculation is off.

You're right. :headsmack:

So, 120 watts for two 16 wrap may not pop.

We can't add the Heat Flux value of the two wires together though. It's what happens in each wire, and then the two get averaged.

 

[Spirometry]

Yes, it will push more wattage at a dual coil in an attempt to reach what it thinks the temp should be, but based on a different Heat Flux value.

To do a sanity check, I just did this thought experiment on Steam Engine:

That little 28 gauge, .5 ohm single coil build at 30 watts is cranking out 345 for the Heat Flux.

To get that same Heat Flux in a dual config, it would take 120 watts.

Well, we both know 120 watts would completely fry two little 28 gauge 8 wrap coils into oblivion.

So, without that specific HF being reached to match the single coil, and remembering it's the same base resistance being read for both builds, it can't be accurate (not the same effective TCR).

Take both 0.5 builds, throw them in the oven 450° they will still have the same resistance (0.888Ω)

The reason the dual coil has 4 times less heatflux and needs 4 times the power is because it has 4 times the mass (we usually build duals @ half the resistance having twice the mass and needing twice the power) . It has nothing to do with the TCR. Want a little proof, go back to steam-engine and do those 0.5 coils with kanthal. The resistance won't change with heat, so you can't blame it on tcr. Steam engine will also tell you the mass.

 

[ImThatGuy]

Confused...you lost me at "Hello"...

On that note, I shall continue vaping my kanthals...

 

[Anthony Newcomer]

I just upgraded my VTC Mini to firmware version 3.0 it changes the display format again to only power, volt, ohms, amps and battery life icon. I use it with the RBA coil for the Kanger Subtank Plus Black at 30watts running a .6ohm coil with the RBA deck. Wide open airflow on the subtank with many different juice ratios and I must say that It is one of the best Tanks I have used. The VTC Mini is a great TC Box mod whether you operate it in wattage mode or Temp control although I have yet to use the TC functionality I am very happy with the VW mode whether im using a tank or RDA. Here is a picture of the new display output for the firmware V3.0

 

[ariffza]

Is it me or the new layout is not as nice looking as FW2.0?