resistance ranges

[mattrix]

Are TC resistance ranges rules or more like guidelines?

A mod will only achieve its maximum rated output over a range of resistances. I have some figures from a mod and it develops max Watt from 0.12 to 1.08 ohms.
It specifies a range of 0.1 to 1 ohms as its TC resistance range, almost the same as the max Watts range. Is this a coincidence?

Is the upper 1 ohm just arbitrarily chosen to match max power and it will provide TC at higher resistances or is it an enforced limit?

 

[APathos]

I would personally assume this is arbitrary unless there is some technical reason within the boards configuration. i.e. it applies max wattage for preheat until it hits the temperature (resistance change), but is programmed to need actual max wattage; just an example, but no reason it would ever be programmed this way.

Think you'd only know by actually trying it (or ask someone with the mod; or here), or post on the board/mod manufacture's forums; something like the evolv dna forums

 

[zoiDman]

Are TC resistance ranges rules or more like guidelines?

...

I think for Many TC Mods, the Resistance Range is a Programed value.

The reason, I believe, for the Top End of resistance has to do with the Ability of the board to Calculate coil temperature via Resistance Change.

In that as the Room Temperature Resistance becomes Higher and Higher, the Relative Error of the calculated Temperature becomes Greater and Greater. And I don't believe the Change in Relative Error is linear.

Could be all wrong on this. I'm not really a TC wonk. But that is what I believe is Going On.

 

[mattrix]

thanks folks,
@zoiDman I'm not sure I understand what your saying, but I would have thought the larger the resistance the larger the change (in resistance) and the easier for the mod to detect.

 

[Izan]

thanks folks,
@zoiDman I'm not sure I understand what your saying, but I would have thought the larger the resistance the larger the change (in resistance) and the easier for the mod to detect.

Why do you think that?
The % of change is greater at a lower resistance.

A timed race is accurate in seconds and milliseconds, If we time it with a calendar, we loose precision.
Consider, it is much easier to judge/notice/observe a 1mph increase in speed at 10mph, VS a 1mph increase at 100mph.
At 10mph, 1mph is 10%
At 100mph, 1mph is 1%.

HTH
Cheers
I

 

[mattrix]

@APathos I think I'd be hard pushed to find anyone who had made / uses high ohm TC coils. It just seemed too much of a coincidence that the specified range was so close to the max power range. Although the specified range is at room temperature where as the max power would be at operating temperatures. I'm not sure how to covert this range to room temp after reading Izans post.

@Izan I'm not sure I understand you either. You seem to suggest that the change in resistance is independent of the original value of the resistance. How do I calculate the change?

I always thought TCR was related to the percentage change in resistance.

 

[zoiDman]

thanks folks,
@zoiDman I'm not sure I understand what your saying, but I would have thought the larger the resistance the larger the change (in resistance) and the easier for the mod to detect.

I Large Resistance Change is what makes TC possible. That is why some Metal Alloys can't do TC. Because their Resistance Change from Room Temp to Vape temp Isn't great enough.

But does Voltage play a Role in this Also?

A Mod Doesn't output Watts. It output Volts. And there is a Maximum Voltage that a Mod can output. What is the Maximum Voltage your Mod can output?

If the Resistance of the Coil becomes to High, can the Mod reach a point where it Can't provide enough Voltage to maintain the Watts the users has set the Mod to?

 

[mattrix]

Large Resistance Change is what makes TC possible.

Thats why I thought a larger initial resistance would be better.
A 0.3 ohm coil might increase to 0.6 ohm,
whereas a 1.2 ohm would increase to 2.4 ohm.
Question is is there a maximum increase allowed?

Will the mod even fire a 1.2 ohm coil in TC mode?

As you pointed out, the mod is programmed and so can refuse to fire even if there is no technical reason not to.

 

[zoiDman]

Thats why I thought a larger initial resistance would be better.
A 0.3 ohm coil might increase to 0.6 ohm,
whereas a 1.2 ohm would increase to 2.4 ohm.
Question is is there a maximum increase allowed?

Will the mod even fire a 1.2 ohm coil in TC mode?

As you pointed out, the mod is programmed and so can refuse to fire even if there is no technical reason not to.

With some TC Mods, if the Room Temp Coil Ohms is greater than the Max TC Ohm Range, the mod will switch to VW Mode.

At 100% Efficiency, it would take 11.49 Volts to fire a 2.4 Ohms Coil if the Mod is set to 55 watts. Can a TC Mod output 11.49 Volts?

 

[mikepetro]

Are TC resistance ranges rules or more like guidelines?

A mod will only achieve its maximum rated output over a range of resistances. I have some figures from a mod and it develops max Watt from 0.12 to 1.08 ohms.
It specifies a range of 0.1 to 1 ohms as its TC resistance range, almost the same as the max Watts range. Is this a coincidence?

Is the upper 1 ohm just arbitrarily chosen to match max power and it will provide TC at higher resistances or is it an enforced limit?

No, it is not arbitrary, it is a design function.

See these charts from Evolv for example showing resistance to power relationship design of DNA250 board.

Resistance along the bottom, wattage along the side:

 

[mikepetro]

Same chart, but on the 75w model

 

[GeorgeS]

Why do you think that?
The % of change is greater at a lower resistance.

Umm... this is not exactly correct.

In TC mode larger base resistances change more than lower base resistances.

The chip limits can be: Current (low resistance), Voltage (high resistance) and how many bits the ADC/uCPU in the chipset can resolve.

 

[Izan]

Umm... this is not exactly correct.

In TC mode larger base resistances change more than lower base resistances.
.

Are we both talking about % of change?

A .25Ω coil (base resistance) increased 100% is .5Ω, 200% would be .75Ω and 300% hits 1Ω.
A 1.5Ω coil (base resistance) increased 100% is 3Ω. (Max on most TC devices)
I.5 ohm increase is greater than a .75ohm increase, but the percent of change is less. 100% Vs 300%

HTH
I

 

[VapNMirrors]

These power curves are a function of the board: it's max voltage and current dictate the power at each resistance.

 

[GeorgeS]

Are we both talking about % of change?

A .25Ω coil (base resistance) increased 100% is .5Ω, 200% would be .75Ω and 300% hits 1Ω.
A 1.5Ω coil (base resistance) increased 100% is 3Ω. (Max on most TC devices)
I.5 ohm increase is greater than a .75ohm increase, but the percent of change is less. 100% Vs 300%

HTH
I

Using TI-01 as an example, no matter WHAT the base resistance at room temperature, at 392F the resistance will be: base_resistance*1.66318.

So given a:
0.1 ohm coil at room temperature it will be 0.166318 ohms at 392F.
1.0 ohm coil at room temperature it will be 1.66318 ohms at 392F.

Keep in mind that TI01 has a decent (366) TCR. To reach %200 the coil would have to be a whooping 572F!! (%300 change would be over 800F)

A larger base resistance gives more granularity in the vaping range. 0.66318 ohms is 10x larger (more accurate) change than 0.066318 ohms.

 

[mattrix]

With some TC Mods, if the Room Temp Coil Ohms is greater than the Max TC Ohm Range, the mod will switch to VW Mode.

Good point, that explains the limit.

At 100% Efficiency, it would take 11.49 Volts to fire a 2.4 Ohms Coil if the Mod is set to 55 watts. Can a TC Mod output 11.49 Volts?

What does any mod do when you ask for more than it can do, -the best it can.

More important, Is that what 55 watts means?

Once you reach operating temperature, R=2.4 ohm, maintain 55 watts at the output. Then the temperature controller would need to be pulsing the output on/off.

 

[zoiDman]

Using TI-01 as an example, no matter WHAT the base resistance at room temperature, at 392F the resistance will be: base_resistance*1.66318.

So given a:
0.1 ohm coil at room temperature it will be 0.166318 ohms at 392F.
1.0 ohm coil at room temperature it will be 1.66318 ohms at 392F.

Keep in mind that TI01 has a decent (366) TCR. To reach %200 the coil would have to be a whooping 572F!! (%300 change would be over 800F)

A larger base resistance gives more granularity in the vaping range. 0.66318 ohms is 10x larger (more accurate) change than 0.066318 ohms.

So to circle this back to matrix's original question...

Is the 1.0 Ohm Limit for on TC being set so that the Mod can still maintain the Maximum Wattage the Mod can be set to without Exceeding the Max Voltage the Mod is capable of outputting?

 

[zoiDman]

Good point, that explains the limit.

What does any mod do when you ask for more than it can do, -the best it can.

More important, Is that what 55 watts means?

...

Not sure I understand what you are Asking?

 

[GeorgeS]

So to circle this back to matrix's original question...

Is the 1.0 Ohm Limit for on TC being set so that the Mod can still maintain the Maximum Wattage the Mod can be set to without Exceeding the Max Voltage the Mod is capable of outputting?

In most cases I don't believe so.

Otherwise the Wattage mode would have the same resistance limitation as TC mode does.

I have two theories: the output path in the mod between TC and VW mode is different or it is a limitation of computational resolution in the chip.

 

[zoiDman]

...

I have two theories: the output path in the mod between TC and VW mode is different or it is a limitation of computational resolution in the chip.

The Second one is what I always thought was going on. From what I have Read and from others have said.

But I'll be the 1st to say that I'm not an Expert on TC