(static) Mod resistance compensation

Discussion in 'Suggestions' started by tcvaper, May 17, 2017.

  1. tcvaper

    tcvaper New Member

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    This would be useful to increase the accuracy of temperature control. It is something you can find in the Escribe software that is used with DNA devices.
    It allows the user to enter the value of the total resistance measured by the mod (i.e. by looking at live resistance) when the 510 is shorted (i.e. using a dripper with a big-fat short between the posts).
    This is roughly the sum of all cabling/connections/510 resistance, which is "static" resistance that doesn't change with temperature and hence should be "subtracted" by the algorithm that performs analysis of live resistance to determine at what temperature the coil currently is.
    Of course, there are much more details, but I think you get the idea and I don't think this should be terribly difficult to do. I'm already doing something that has the same effect by playing with the SHUNT % value, but I have always to tweak it if I change atomizer because the static resistance of the mod is fixed and so the % of it with regards to the resistance of the coil will vary with the coil, so if you implement a dedicated field that the user can fill with the value measured for the mod resistance, everything will be done only once.
    Oh, while I was saying it I just thought that you might just simply implement it by translating the mod resistance entered by the user into a proper value for the SHUNT% every time a new atomizer base resistance is acquired... Just an idea...
     
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  2. spado

    spado Member

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    I think that the last sentence is not what you were trying to describe above.
    It is actually simpler, it would just involve summing the "resistance compensation" setting to the reading value, it should not become a multiplication like in the case of the SHUNT% ...
    As to if this feature is actually needed depends on how variable the internal resistance of different mods is, but it could still be useful to compensate in user built devices (like 3D printed BF mods using Joyetech electronics).
    This feature would definitively be easy to implement and would take this CFW another step even closer to DNA level of features!
     
  3. tcvaper

    tcvaper New Member

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    Yes, of course it is much simpler if you just subtract the static resistance from Rbase in the "dR = Rbase * (TCR * dT)" calculation, I was just offering an alternative that doesn't even require to touch any of the already implemented algorithms. Sometimes one just feels safer if he can add functionalities by simply "adding-on-top-of-what-you-already-have", even if it's a bit more complicated, just because he doesn't have to touch more sensitive parts of the software...
    That said, from my limited experience I can tell you that just among joyetech/eleaf product, the difference in mod resistance is not irrelevant. I have measured, with that copper-510-tool that ensures a quite stiff hard short, the following mod resistances:

    1) Evic primo mini: 0,007 ohms
    2) Evic vtc-mini (1st gen, no clock): 0,012
    3) Eleaf istick 75: 0,016
    4) Egrip II: 0,022
    5) Vaporflask lite: 0,009

    Of course these are just my particular instances of those mods, I don't claim for these to be statistically relevant, but nonetheless I can confirm that the same coil (SS316L, of course a higher TCR would be much more tolerant) requires tens of degrees of correction across those different mods to vape the same.
    Being able to configure the static resistance of each of them would probably stop requiring to always tinker (and think) about correcting the temperature...
     
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  4. spado

    spado Member

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    Very interesting data, thank you for providing it!
    By the looks of it, and the implications you already mentioned, it seems that adding the feature would benefit not only the cases of user built mods, but also the different models that come out of the factory, unifying the experience even further.
    I can't argue more about the technical stuff, cause I wouldn't know enough... I guess my intuitive thinking was not taking into consideration the complexity of the already involved algos.
    If @maelstrom2001 decides to implement this I assume he'll know what'd be easier or best, whichever fits the code's needs.
     
  5. Zviratko

    Zviratko New Member

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    You should take into account also the non-resistant path in the atomizer and the coil itself. Does your coil glow absolutely evenly when firing? I bet it doesn't.
    While this feature sounds useful, in practice it's easier to just ignore that "200C" is supposed to represent a temperature, and just look at it as an arbitrary number saying how hot it is. "200C" will not be the same with different mods/attys/coils and builds, no mattery how hard you try, and the same effect can be achieved by setting it +-10C or offsetting the base resistance.
     
  6. tcvaper

    tcvaper New Member

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    That's true: mod resistance is only one of the two components of static (i.e. not-varying-with-temperature) resistance, the second component being in the atomizer, but I've settled down on only using TC-friendly atomizers with very short and good electrical connections, where I've found their contribution to static resistance is much less than the contribution coming from the mods, so that I'm usually happy with just compensating for the latter.

    That's also true, but hey, if you can have an easy setting on your mods that can slightly reduce the inaccuracy (and if you don't care you just leave it at zero and just play a bit more with setting the temperature as you suggest), why not?
    Yes the feature doesn't change drastically the performance of the mod, but also it should be an easy one to implement and it might give you back just a little more convenience in use, so why not consider it?
     
  7. DLC86

    DLC86 New Member

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    Hi everybody, I confirm what @tcvaper has found out, mod internal resistance varies quite a bit, even among identical boxes it seems.
    My measurements are:

    1) evic vtc mini: 0,007
    2) another vtc mini: 0,011
    3) istick pico: 0,009
    4) evic primo mini: 0,005

    Anyway by reading your discussion another idea came to my mind to expand further tcvaper's suggestion:
    Add an atomizer resistance setting in every profile too.
    This way we could firstly measure and set mod's internal resistance with a copper shunter on the 510 connector.
    After that attach the atomizer, measure its internal resistance by shunting its deck and save it in its own profile.

    I think all this would eliminate most inaccuracies and lead to the most precise achievable TC
     
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  8. Hypnofrog

    Hypnofrog New Member

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    That would be a great Feature, so i have to calibrate my mods one time, but after calibration i can use same configuration and same W/Temperture Setting on all of them.
     
  9. ReikoKitsune

    ReikoKitsune Developer
    NFE Team

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    This possibility is already on the way :cool:
     
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