TC beyond Ni200: Nickel Purity, Dicodes; Ti, SS, Resistherm NiFe30; Coefficient of Resistance

[TheBloke]

More good news - the ZiVipf NiFe30 wire is perfectly clean! Zero residue coming off onto a wet wipe.

 

[nic_fix]

thanks. well said. I agree 100%. people do not always understand. this can be dangerous even very dangerous like if you overheat ti. across the board it is a much better idea than tobacco.

 

[cigatron]

Titanium has risks if it's over heated, it's very important not to dry burn it, but should be very safe in the temperature control range.

So I've heard. It's true you shouldn't overheat Ti or it will develop Titanium Oxides/Dioxides which may be harmful to ones health. Dryburning at lower power levels is possible however if you're carefull not to let the coil get hotter than a faint red glow. I've been running the same Ti coil in my STmini for two months now. Its been dryburned, washed and rewicked dozens of times and is holding up quite well.

 

[TheBloke]

I've never had much luck dry burning Titanium. Like you I've tried to do it very gently, but I guess I always overdid it.

The key is the colour of the resulting wire. The OK colours are the default silver, yellow/gold, and then blue/purple. If it goes beyond blue/purple into a sort of greyish, powdery colour, then it's dead.

What colour is your wire after you make it glow softly? I had thought any glowing was a bad sign for Titanium but maybe I'm thinking of a much brighter glow.

 

[TheBloke]

I got the samples last week and tested and measured the new wire and figured out with my cotten test that the TCR should be around 50 ( 0,005) and that it must be Nifetherm 70 from Kanthal. I mailed my results to Zivipf and Thomas confirmed the Nifetherm 70. Because of the higher resistance, quite hight TCR and the very linear TCR I recommended Thomas the Nifetherm 52 in 3 sizes ( 0,28mm - 0,35mm - 0,40mm ) too. He wants to get them too. Kanthal offers these wires up to 1.8mm. If the Nifetherm sales ar good he will order different sizes too, I guess.

I just emailed Thomas to ask about this. Got the following, amazing response!

I have ordered yesterday NiFe52 in different diameters ( 0,25 0,28 0,32 0,35 0,40 )

and i will do a new order next week with bigger diameters of the NiFe30 wire​

Wonderful news! I can't wait to try all this.

Comparing the data sheet on NiFe52, to NiFe70, and using the TCR calc, I can see that:

• A 1.0Ω NiFe70 coil increases to 2.19Ω by 250°C - a TCR in this range of 0.0052 (matching Rudi's cotton test)
• A 1.0Ω NiFe52 coil increases to 1.93Ω by 250°C - a TCR in this range of 0.0040

So NiFe52, though lower than NiFe70, has an excellent TCR - higher than Titanium and Resistherm NiFe30.

Both 52 and 70 have a ceiling temp of 600°C (1110°F), matching Alloy 120 and Dicode's (Isabellenhütte's) Resistherm NiFe30.

I now wonder if there is any practical, noticeable difference between them. In other words, if we can get both Nifethal 70 and Nifethal 52 in 0.4mm, is there any reason to use one over the other? The higher TCR of NiFe70 suggests this is the best wire to use, other things being equal. But I wonder if there are other differences.

I am getting really excited to try all this new wire!

 

[TheBloke]

This also once again raises a question I have had many times: Why did Dicodes choose Isabellenhütte's NiFe30, when it has a lower TCR (0.0032) and is only available up to 0.28mm?? Based purely on these numbers, Resistherm seems like the worst of the NiFe30 wires they could use.

Was it a commercial decision - Isabellenhütte gave them a great deal? Or that they knew it was hard to get hold of and wanted to corner the market?

is there some other hidden benefit to Resistherm that we don't yet know?

Maybe I will try to email Dicodes and ask.

 

[joanquro]

Was it a commercial decision - Isabellenhütte gave them a great deal? Or that they knew it was hard to get hold of and wanted to corner the market?

Unfortunately, I think you're right in this point :-\, probably more the second.

I hope I'm wrong.

Enviado desde mi A0001 mediante Tapatalk

 

[TheBloke]

OK, here's one useful difference between NiFe52 and NiFe70 - the resistance of 52 is higher, very usefully higher.

From the datasheets:

• NiFe70: 0.20Ω per mm^2/m
• NiFe52: 0.37Ω per mm^2/m

Putting that into numbers for useful gauges from the American Wire Gauge chart.

• 29G is 0.064 mm^2
• 28G is 0.081 mm^2
• 26G is 0.129 mm^2
• 24G is 0.205 mm^2

Therefore:

• NiFe70
  • 28G: 0.20 / 0.081 = 2.47Ω/m
    • An 8 wrap x 3mm ID coil is approx 100mm = 0.247Ω
  • 26G: 0.20 / 0.129 = 1.55Ω/m
    • An 8 wrap x 3mm ID coil is approx 100mm = 0.155Ω
  • 24G: 0.20 / 0.205 = 0.98Ω/m
    • An 8 wrap x 3mm ID coil is approx 100mm = 0.098Ω
• NiFe52:
  • 28G: 0.37 / 0.081 = 4.57Ω/m
    • An 8 wraps, 3mm ID coil is approx 100mm = 0.457Ω
  • 26G: 0.37 / 0.129 = 2.87Ω/m
    • An 8 wraps, 3mm ID coil is approx 100mm = 0.287Ω
  • 24G: 0.37 / 0.205 = 1.80Ω/m
    • An 8 wraps, 3mm ID coil is approx 100mm = 0.180Ω

That is very interesting.

26G is currently my usual gauge, but I do 24G coils in a couple of atomizers. With NiFe70, 24G @ < 0.1Ω is definitely out as far as I'm concerned. I have several mods with a 0.1Ω lower limit, and I don't want to be forced to add wraps, and especially not do the build/check resistance/damn it's too low/adjust/check.. dance that I remember with loathing from my Ni200 days.

I don't even want to be building to 0.155Ω as a matter of course either, if I can avoid it.

For one thing, it's less accurate overall: the lower the coil resistance, the higher the error from static resistance in the atomizer. 0.01Ω of Static Resistance in an atomizer causes a 20°C temperature inaccuracy for a 0.12Ω coil, compared to only 2.5°C of inaccuracy for a 0.50Ω coil. (FYI the coil wire/TCR is irrelevant to the level of inaccuracy from SR; the same numbers apply for Ni200, Titanium, etc.)

Therefore I like to build to higher resistances when I can. Not to mention the reduced power/battery requirements. And low resistance can rule out dual coil and more exotic builds with thicker and twisted wires. Exactly as we see with Ni200.

NiFe52 on the other hand has a reasonable resistance range. A little lower than Titanium, but higher than Resistherm NiFe30. I have a couple of 24G Titanium builds right now, and they come out to 0.28Ω, compared to 0.18Ω for NiFe52 @ 24G. It's under 0.20Ω but it's doable. And my standard coils of 26G @ 0.287Ω is fine.

We talked earlier about Dicodes and their Resistherm decision. Let's add a resistance comparison to that, comparing against the 29G that Dicodes supply Resistherm in:

• NiFe70 @ 29G: 0.20 / 0.064 = 3.13Ω/m
• NiFe52 @ 29G: 0.37 / 0.064 = 5.78Ω/m

Dicodes' Resistherm @ 29G is 5.5Ω/m. So it beats NiFe70, but loses to NiFe52 (only just.)

So the question is, is NiFe52 just as good for vaping as NiFe70 / Alloy 120 / Resistherm NiFe30? It's definitely different - all the other wires we've looked at are 30% Ni, this is 52%.

So if we're giving Dicodes the benefit of the doubt, maybe NiFe52 is not as good for some reason.

I hope we'll be able to find out very soon when Thomas@Zivipf's gets his NiFe52

 

[druckle]

I think it might be interesting to compare the linearity of the resistance curves for the various wires in the NiFe family. Changes in the NI-Fe content will have a big effect on the Curie temperature and I would expect the resistance curves to be highly nonlinear and quite different for various NI/Fe ratios. That's not going to matter for something like a DNA 200 where the whole curve can be entered into the device but it could make other devices pretty wonky with respect to temperature accuracy.

Duane

 

[cigatron]

I've never had much luck dry burning Titanium. Like you I've tried to do it very gently, but I guess I always overdid it.

The key is the colour of the resulting wire. The OK colours are the default silver, yellow/gold, and then blue/purple. If it goes beyond blue/purple into a sort of greyish, powdery colour, then it's dead.

What colour is your wire after you make it glow softly? I had thought any glowing was a bad sign for Titanium but maybe I'm thinking of a much brighter glow.

It looks like this after 21 dryburns and 7 rewickings; that is 3 short dryburns with water rinses before each rewicking.

I only pulse Ti untill I see ANY portion if the coil turn red. That's usually the outside turns of the coil on first pulse. I then rinse and repeat untill the coil appears to want to fire inside out. Might be important to note that I blow on the coil immediately after each pulse to quickly cool it off and to encourage the gunk to smoulder off. After the third pulse I rinse while brushing the white oxides off the coil.

Not sure what you mean by "then it's dead" if overheated. I have overheated my Ti coils to the point that they were covered with white/grey oxides and they all cleaned up as shown in the pic. After two months of daily use and 15 rewickings (about 45 dryburn pulses) they still have the same color but with more pitting. The only negative thing I have noticed with using Ti for extended periods is that the res increases after multiple dryburns. My three Ti builds started at .20 ohms and now all three are at .22 ohms. I'm assuming that the loss of base metal to the creation of oxides is what's causing this but I believe the loss is happening during the dryburning sessions; not while vaping. At any rate they still vape great.

Should I stop using coils that look like my pic?

 

[TheBloke]

I think it might be interesting to compare the linearity of the resistance curves for the various wires in the NiFe family. Changes in the NI-Fe content will have a big effect on the Curie temperature and I would expect the resistance curves to be highly nonlinear and quite different for various NI/Fe ratios. That's not going to matter for something like a DNA 200 where the whole curve can be entered into the device but it could make other devices pretty wonky with respect to temperature accuracy.

Duane

Yes excellent point. And you might have touched upon another justification for Dicodes using Resistherm. The Resistherm NiFe30 data sheet (from Isabellenhütte, not Dicodes) makes a point of showing the TCR graph from 0°C - 300°C, which is for all intents and purposes linear:

I haven't done any graphing yet (kinda hoping @vapealone might do it for us? ) but looking at the plain numbers on the NiFe70 and NiFe52 data sheets, I see for example:

NiFe52 @ 200°C = 1.73 = 0.73 gain from 0
NiFe52 @ 400°C = 2.49 = 1.49 gain from 0; 0.76 gain from 200 (vs 0.73 for first 200°C)

That looks pretty linear to me, and looking at the 100, and 300 figures seems to suggest a similar pattern. There's a 0.33 increase from 0-100, a 0.40 increase from 100-200, and another 0.40 from 200-300. That looks pretty nice.

However:

NiFe70 @ 200°C = 1.91 = 0.91 gain from 0
NiFe70 @ 400°C = 3.03 = 2.03 gain from 0; 1.12 gain from 200 (vs 0.91 from first 200°C)

Is a little less so; the resistance increase is increasing at the higher temperatures in the case of 70.

To be sure, I have a feeling that a curve such as 70 seems to be showing from 0-400 is not going to be hugely noticeable even on a flat-TCR mod. Especially as we really only care about 0-250°C or so, and can work out the TCR for that range specifically.

But it does, at first glance, seem another benefit to NiFe52.

If @vapealone is not available I will have a go myself at putting them into a copy of his sheet, but maybe he'll pop up tonight and do it for us (I think he probably already has Kanthal's NiFe30 on there, but I think not NiFe52?)

 

[TheBloke]

However I do think we can probably say that none of the alloys we're looking at will be highly non-linear. I think/hope we'll be talking about small deviations at most, at least in the vaping range of up to 300°C max (and 250°C in most cases.)

 

[TheBloke]

Not sure what you mean by "then it's dead" if overheated. I have overheated my Ti coils to the point that they were covered with white/grey oxides and they all cleaned up as shown in the pic. After two months of daily use and 15 rewickings (about 45 dryburn pulses) they still have the same color but with more pitting. The only negative thing I have noticed with using Ti for extended periods is that the res increases after multiple dryburns. My three Ti builds started at .20 ohms and now all three are at .22 ohms. I'm assuming that the loss of base metal to the creation of oxides is what's causing this but I believe the loss is happening during the dryburning sessions; not while vaping. At any rate they still vape great.

Should I stop using coils that look like my pic?

What I thought I understood was that when the white/grey powdery stuff appeared, the coil should no longer be used. I just throw them away at that point. But you may well be right - after all, if the oxide disappears with cleaning, presumably it's not there any more to cause trouble! I would be slightly worried about increasing resistance though - any degradation of the metal surface sounds slightly troubling to me. But only in principle, not because I know of specific risks.

@druckle is the expert, let's see what he thinks.

What I will say though is that Titanium is cheap, coiling is easy, and personally if I had the slightest doubt I would just throw away and start again. It's often quicker and easier to make a new coil than it is to wash an existing one. And I'm someone who isn't particularly talented at coiling. Does depend on the atomizer of course.

One exception I make is that I do sometimes wash coils in my ultrasonic bath - but that's easy too, in fact easier than re-coiling because I just remove the wick and put the whole atomizer base, with coil still attached, in the bath and run it. When I take it out I just re-tighten the screws and I'm good to go. And they've not been dry burnt, so it's just washing juice off as an alternative to re-coiling. I have not seen the resistance changed by the bath (though I've haven't so far washed a single coil more than once.)

 

[druckle]

What I thought I understood was that when the white/grey powdery stuff appeared, the coil should no longer be used. I just throw them away at that point. But you may well be right - after all, if the oxide disappears with cleaning, presumably it's not there any more to cause trouble! I would be slightly worried about increasing resistance though - any degradation of the metal surface sounds slightly troubling to me. But only in principle, not because I know of specific risks.

@druckle is the expert, let's see what he thinks.

What I will say though is that Titanium is cheap, coiling is easy, and personally if I had the slightest doubt I would just throw away and start again. It's often quicker and easier to make a new coil than it is to wash an existing one. And I'm someone who isn't particularly talented at coiling. Does depend on the atomizer of course.

One exception I make is that I do sometimes wash coils in my ultrasonic bath - but that's easy too, in fact easier than re-coiling because I just remove the wick and put the whole atomizer base, with coil still attached, in the bath and run it. When I take it out I just re-tighten the screws and I'm good to go. And they've not been dry burnt, so it's just washing juice off as an alternative to re-coiling. I have not seen the resistance changed by the bath (though I've haven't so far washed a single coil more than once.)

If the Ti wire is cleaned thoroughly to remove any loose oxide I don't see a problem with using the coil for a long time. The roughness of the surface is going to make it more difficult to clean off the oxide but I don't think that's going to be a deal breaker. The diameter of the wire is definitely going to decrease a little as oxide forms but the increase in resistance isn't going to be a big deal either.

I guess the bottom line is that there's really no problem with what Cigatron is doing. As long as he's sure the wire doesn't have loose oxide he's good to go, over and over again.

I agree though that the Ti wire is cheap and it's no big deal to make a new coil. It might even be faster than a thorough cleaning sometimes.

Duane

 

[druckle]

However I do think we can probably say that none of the alloys we're looking at will be highly non-linear. I think/hope we'll be talking about small deviations at most, at least in the vaping range of up to 300°C max (and 250°C in most cases.)

I would guess that for that for the alloys we've discussed so far there won't be a lot of nonlinearity in the lower temperature ranges but I think it would be good to know for sure before using the wire in a device that doesn't allow resistance to be considered over the useful temperature range. I would imagine that there will be data available in the literature for a lot of alloys in the NI-Fe family since they are commonly used for heating elements etc.

Duane

 

[cigatron]

If the Ti wire is cleaned thoroughly to remove any loose oxide I don't see a problem with using the coil for a long time. The roughness of the surface is going to make it more difficult to clean off the oxide but I don't think that's going to be a deal breaker. The diameter of the wire is definitely going to decrease a little as oxide forms but the increase in resistance isn't going to be a big deal either.

I guess the bottom line is that there's really no problem with what Cigatron is doing. As long as he's sure the wire doesn't have loose oxide he's good to go, over and over again.

I agree though that the Ti wire is cheap and it's no big deal to make a new coil. It might even be faster than a thorough cleaning sometimes.

Duane

Thanks for the quick reply, much appreciated. Good to be reassured I'm not doing anything stupid.

The whole dryburn and brushing process takes me less than 2 minutes. Yes, I've timed it....I'm weird like that. Lol. I can wind a new coil in under a minute with my DIY winder but it takes me about 2 additional minutes to mount the coil with good symmetry. Sometimes longer if things go awry. So for me it's slightly faster and much less fussy to dryburn and wash. But I get your point...if the coil surface looks questionable I will recoil. Thanks, @druckle

 

[funkyrudi]

vapealone has both wires ( 70 + 52 ) in his datasheet

TC beyond Ni200: Nickel Purity, Dicodes; Ti, SS, Resistherm NiFe30; Coefficient of Resistance | Page 38 | E-Cigarette Forum

While the Nife70s TCR is increasing with the temperature, the NiFe52s TCR is decreasing, but is more linear over our temperature range. IMHO there is no reason why the NiFe52 should not work as good as all the others.

Thanks @TheBloke, Thomas asked me which gauges he should order, but he didn`t tell me what he actually ordered.

 

[funkyrudi]

I would guess that for that for the alloys we've discussed so far there won't be a lot of nonlinearity in the lower temperature ranges but I think it would be good to know for sure before using the wire in a device that doesn't allow resistance to be considered over the useful temperature range. I would imagine that there will be data available in the literature for a lot of alloys in the NI-Fe family since they are commonly used for heating elements etc.

Duane

http://www.kanthal.com/Global/Downl...ting wire and strip/S-KA026-B-ENG-2012-01.pdf
You`ll find NiFe70 on page 72+73 and NiFe52 on page 74+75. They don`t write the TCR but the TFR above the list

 

[TheBloke]

vapealone has both wires ( 70 + 52 ) in his datasheet

TC beyond Ni200: Nickel Purity, Dicodes; Ti, SS, Resistherm NiFe30; Coefficient of Resistance | Page 38 | E-Cigarette Forum

While the Nife70s TCR is increasing with the temperature, the NiFe52s TCR is decreasing, but is more linear over our temperature range. IMHO there is no reason why the NiFe52 should not work as good as all the others.

Thanks @TheBloke, Thomas asked me which gauges he should order, but he didn`t tell me what he actually ordered.

Awesome, thanks for the link. And yeah both 70 and 52 look fine, but 52 definitely better

And wow, I forgot just how excellent this spreadsheet is. Superb work, @vapealone ! It really has everything.

 

[TheBloke]

Here's the TFR graph of the two NiFethal alloys alongside Resistherm and Titanium (vapealone's graph, just with the other wires removed):

I'm happy to say that all of those are linear enough to be very accurate with a single-TCR mod.

So NiFethal 25 is looking like a winner at the moment! The lower TCR than 70 won't matter - it's still higher than Titanium and Resistherm - and it is in anyway slightly more linear. The higher resistance is going to be really helpful, and in fact will also help overall accuracy in real life vaping situations.

Great work @funkyrudi getting Thomas to stock this wire! I can't wait to try it.