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Misunderstanding resistance
Steve698 Offline
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Post: #1
Misunderstanding resistance
As the title suggests there is something that isn't sinking in regarding coil resistance in my world. From what I can tell from the different builds I have tried, if I build a coil at .5 ohms and run it at 20w it ramps up at a reasonable rate and I get a decent vape, if I go higher on the W it gets hotter quicker until a point where it starts getting too hot or burning. If I do the same with a 1.5 ohm coil at 20w it takes forever to ramp up. So why is it said that higher ohm coils will save you burning through juice and battery time because that from my experience isn't the case as it takes 10 secs just ramp up the high ohm coil at 20w if it ramps at all. Surely the more wire in the coil the higher the resistance, the longer time to ramp up, the more power is needed to get it going. Please enlighten me as the opposite to what is said seems to be true from my experience.
09/11/17 10:37 PM
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MDC Offline
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Post: #2
RE: Misunderstanding resistance
(09/11/17 10:37 PM)Steve698 Wrote:  As the title suggests there is something that isn't sinking in regarding coil resistance in my world. From what I can tell from the different builds I have tried, if I build a coil at .5 ohms and run it at 20w it ramps up at a reasonable rate and I get a decent vape, if I go higher on the W it gets hotter quicker until a point where it starts getting too hot or burning. If I do the same with a 1.5 ohm coil at 20w it takes forever to ramp up. So why is it said that higher ohm coils will save you burning through juice and battery time because that from my experience isn't the case as it takes 10 secs just ramp up the high ohm coil at 20w if it ramps at all. Surely the more wire in the coil the higher the resistance, the longer time to ramp up, the more power is needed to get it going. Please enlighten me as the opposite to what is said seems to be true from my experience.

Wow, where do we start? Ramp up time depends on coil size, but that doesn't necessarily depend on resistance. A long coil might have high resistance due to it's length. Being long, ramp up time is high. A lower resistance coil made with thick wire might also have a long ramp up, as there is also more metal to heat up.

Super high power coils tend to be low resistance so the mod can drive them. A 2 ohm coil with a mod capable of 8v maximum output can only be driven to 32w, a 0.5 ohm coil to 128w.

The higher ohms using less juice is a fallacy with regulated mods, as the mod will simply use higher volts to drive the coil. Works with mech mods.

Basically, smaller coils and reduced air flow use less power and juice, and battery lasts longer, but vape volume is less. Big coils and open air flow produce vape volume but need more power and juice.

Though I don't need to use it, temperature control offers a quicker ramp up time with big coils by setting the watts cap high. The mod will pump maximum power through the coil until it heats up.

Back home after a fair few beers, so I won't go further than that for nowSmiling
09/11/17 11:10 PM
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Toby | iVapour Offline
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Post: #3
RE: Misunderstanding resistance
On a similar note I have wondered why you get something like a 1 ohm Atlantis coil that is rated 40-50w for direct lung inhale (most 1 ohm coils are rated at about 15w for MTL).

What would make its relatively high resistance to be designed to fire at a fairly high power, and what's the point in it?

It hasn't sold very well (at all) and I have wondered its supposed purpose...

10/11/17 03:28 PM
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MDC Offline
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RE: Misunderstanding resistance
(10/11/17 03:28 PM)Toby | iVapour Wrote:  On a similar note I have wondered why you get something like a 1 ohm Atlantis coil that is rated 40-50w for direct lung inhale (most 1 ohm coils are rated at about 15w for MTL).

What would make its relatively high resistance to be designed to fire at a fairly high power, and what's the point in it?

It hasn't sold very well (at all) and I have wondered its supposed purpose...

Presumably it's a relatively big but thin coil, likely in a vertical configuration. Nothing wrong with that in principle, but the mod has to be able to put out just over 7v to fully power it. Most regulated mods can handle that, but not all.

Higher resistance coils, all other things being equal, will be a tad more efficient than super-low resistance coils. Heat losses are proportional to the square of the current, and a low resistance coil will take more current from the mod's regulator output, at a lower voltage. So, the regulator and output wiring will run a touch warmer, wasting a bit of power. Some early TC mods running low resistance nickel coils were derated in TC mode, presumably for this reason. 75w in watts mode, 60w equivalent in TC mode for instance.
10/11/17 05:10 PM
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Ray_of_Light Offline
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Post: #5
RE: Misunderstanding resistance
If you use thinner wire to achieve 1.5 Ohm, so to keep the same coil mass of the 0.5 Ohm, you have the same ramp-up time.
Ramp-up time is related to the thermal inertia of the coil, not to its resistance.
26/11/17 05:01 PM
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MrGeneric Offline
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Post: #6
RE: Misunderstanding resistance
Hi, I found steam-engine a great way to understand coil resistance.

Default wire wizard page:
Kanthal A1 30gauge
Internal dia 2mm
Wraps 8
Resistance 1.934

Change gauge and wraps:
Kanthal A1 32gauge (Thinner, faster ramp up)
Internal dia 2mm
Wraps 5 (Shorter, faster ramp up)
Resistance 1.936

2nd coil same resistance, thinner and shorter=less material to heat, faster ramp up.
Fewer wraps of thinner wire (less surface area) in contact with cotton will vaporize less liquid.
That's how I understand it, (I think).
04/01/18 02:32 PM
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MDC Offline
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Post: #7
RE: Misunderstanding resistance
(04/01/18 02:32 PM)MrGeneric Wrote:  Hi, I found steam-engine a great way to understand coil resistance.

Default wire wizard page:
Kanthal A1 30gauge
Internal dia 2mm
Wraps 8
Resistance 1.934

Change gauge and wraps:
Kanthal A1 32gauge (Thinner, faster ramp up)
Internal dia 2mm
Wraps 5 (Shorter, faster ramp up)
Resistance 1.936

2nd coil same resistance, thinner and shorter=less material to heat, faster ramp up.
Fewer wraps of thinner wire (less surface area) in contact with cotton will vaporize less liquid.
That's how I understand it, (I think).

That's right. You will run the second coil at lower power than the first, for the same heat, but distributed over a smaller area.
04/01/18 02:39 PM
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