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Some technical vaping hardware questions

Discussion in 'General Vaping Discussion' started by khoka, May 21, 2019.

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  1. khoka

    khoka Full Member

    May 21, 2019
    Hey all, I’m in the process of making a regulated box mod with a microcontroller and have a couple of technical questions:

    - How is a mod able to supply more current to an atomizer than it’s capable of drawing? In other words, why is the maximum wattage of the setup unaffected by the atomizers’s resistance? Is a constant current supply used?


    - More batteries in series equate to a higher voltage, which makes the atomizer draw more current (I = V/R). This rises the minimum resistance of the atomizer the vape can handle. Is a buck converter used to lower the voltage while stepping up current?


    - I’ve heard that some vapes are able to detect a dry wick, how is that done?


    - How do multi battery mods (8.4V+) charge off a 5V USB port?


    Thanks!
     
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  2. Izan

    Izan Vaping Master ECF Veteran

    Jul 1, 2012
    Mallorca, Spain
    Hi and welcome,
    Where are you located?
    What device and topper/tank are you using now?
    What other electronics projects have you undertaken?
    Which micro-controller have you selected?

    Cheers
    I
     
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  3. Eskie

    Eskie ECF Guru Verified Member ECF Veteran

    May 6, 2016
    NY
    Well, to tackle the several questions you have, I'll throw out a few explanations and we can move forward from there. The board on a regulated mod which allows for adjustment of the wattage delivered to the coil, is a DC-->DC converter. It can be a buck/boost or buck only circuit. As all power to the coil is delivered through this board, the resistance of the coil bears no relationship to the current draw on the other side, the battery. It's your wattage selection that determines the current draw, not the resistance.Of course the resistance and heat flux of the coil will influence the wattage you may select to use, but there is no direct electrical link between the battery and the coil , so Ohm's law does not come into play.

    As for dry hit protection, that's done a variety of ways, generally with a temp control type of setup on the board. As the coil heats, the resistance of the metal will change. Of course this requires a metal to have enough of a resistance change over the range of temperature that is detectable, usually defined by the TCR, Temperature Coefficient of Resistance, an inherent property of the metal. If the rise is "too fast" the power delivered would quickly be decreased, so a dry coil, which would not have any evaporative cooling would be throttled faster than under normal vaping conditions, hence "dry hit protection". That does mean the use of metals with a TCR that allows for detection, so SS is the most common these days, but Ti, and before that, Ni200 are most commonly required. Kanthal has an exceptionally low TCR, and therefore does not work in a temp control setting, but I know there are some claims out there about being able to accomplish this even with Kanthal and it beats me how they can do that.

    Finally, charging multiple batteries requires a battery management charging solution that allows for balanced charging, so all batteries are charged at the same time to maintain the same voltage across all in the set. Even in a single cell mod, the battery charging circuit still must offer under voltage/over voltage protection, and of course when in use for vaping an amp limit appropriate to the batteries and their properties you select to use.

    Hopefully that gives you a starting point in seeing how a mod with a regulated board functions. (disclaimer, any errors are either my own or that of an unintelligent autocorrect system)
     
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  4. Mordacai

    Mordacai Ultra Member ECF Veteran

    Jan 16, 2019
    UK
    Hello @khoka, I can at least answer the dry wick detection or temperature control question.

    As the temperature of the coil or coils increase so does their resistance. And when the wicking starts to dry out, it allows the coils to get hotter (it's to do with specific heat capacity).

    So the chipset monitors the resistance and keeps it as close to the set point, so more power is initially applied until target has been reached and then power is throttled keeping it at target.

    I hope that you find this useful.
     
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  5. Punk In Drublic

    Punk In Drublic Vaping Master ECF Veteran

    Aug 28, 2018
    Toronto, ON
    Great answer from @Eskie but to dive further into detail.

    There are 2 sides to a regulated circuit, the input (battery) side and output (coil) side. The battery side does not see the coil side, it only sees the power in which the regulated circuit is requesting.

    On the output (coil) side voltage is set based on the users coil resistance and prescribed power.

    V = √PxR

    Current is then calculated as

    I = V/R

    On the input (battery) side, current draw is based on the prescribed power and battery voltage.

    I = P/V

    As battery voltage depletes with use, current draw increases in order to meet the prescribed power. The devices efficiency also comes into play in determining current draw on the input side.

    An example: A user installs a 0.3 ohm coil and sets the power to 50 watts with a single cell device that has an efficiency of 90%

    Coil side

    V = 3.8 volts
    I = 12.6 amps

    Battery side at nominal 3.7 battery voltage

    I = 50watts/3.7v/0.9 = 15 amps

    At 3.2 volts, the usual cut toff of many devices that would be 17.4 amps

    As for maximum wattage and resistance. The specifications for many of these devices are more marketing than actual fact. There are both voltage and current limitations to these devices which depending on design will dictate what the maximum wattage it is able to achieve with a specific resistance, despite what is claimed on the box. Using the above calculation of V = √PxR, we can see that a “claimed” 200 watt device with a 8.4 max voltage is unable to operate at it’s maximum power for any coil resistance above 0.35 ohms. And if the same device had a 30 amp limitation then it will be unable to operate at it’s maximum power with any resistance under 0.23 ohms. This example is of course a best case scenario for even their voltage and current limitation specs may not be entirely accurate.
     
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  6. charlie1465

    charlie1465 Vaping Master ECF Veteran

    Welcome to the friendly bunch :)

    Nothing to add here you have already had excellent answers by @Eskie and @Punk In Drublic
     
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  7. khoka

    khoka Full Member

    May 21, 2019
    Alright, thanks everyone. So the regulator between the battery and coil side is just basically a constant current supply, right? Also, isn’t the output power of a buck/boost always the same as the input? So wouldn’t wattage control be impossible because voltage is stepped down as current goes up, resulting in the same wattage?
     
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  8. Izan

    Izan Vaping Master ECF Veteran

    Jul 1, 2012
    Mallorca, Spain
    Are you confident you are qualified to undertake a task of this magnitude?


    Cheers
    I
     
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  9. khoka

    khoka Full Member

    May 21, 2019
    I’m from Warsaw, Poland.

    Smok novo, formerly smok pen 22

    Arduino projects, as in mosfets, relays, motors

    I’ve chosen an atmega 328 breakout board
     
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  10. Punk In Drublic

    Punk In Drublic Vaping Master ECF Veteran

    Aug 28, 2018
    Toronto, ON
    If I understand your questions correctly.

    In simplest terms. You request 50 watts from your device. The regulated circuit will request 50 watts + efficiency from the batteries. At 90 % efficiency that can be an additional 5 watts. The regulated circuit will apply that 50 watts in terms of voltage/current depending on your coils resistance.
     
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  11. Rossum

    Rossum Surly Curmudgeon Verified Member ECF Veteran

    Supporting member
    Dec 14, 2013
    NE FL
    No. The most straightforward approach to a regulated mod is to output constant (but adjustable) voltage.

    However, in order to protect the circuit against shorts on the output, you should monitor the current being drawn. So when the user presses the fire button, you start out firing at some very low voltage for a moment an check the amount if current being drawn. This allows you to calculate the resistance of the coil (actually it's the series resistance of everything on the output of your board, so wiring + atty + coil). From there, it's not a great leap calculate and let the the user select watts instead of volts.

    Now to really do wattage mode right, you need to keep monitoring the current drawn at all times while firing. This allows you to change your output voltage dynamically to compensate for changes in resistance with temperature. Some coil materials like Kanthal and nichrome don't have much resistance change with temperature, but others like stainless steel, titanium, and nickel do.

    Temperature control (and dry hit protection) takes it one step further. If you know exactly what coil material is being used, you can use that material's TCR (temperature coefficient of resistance) to deduce the coil's temperature based on how much its resistance has changed from cold. But there are a number of reasons why doing this really well is more complicated than it first appears. It took the company that pioneered it (Evolv Vapor) several years and several generations of devices to refine it to the point that it worked consistently well.

    Now that's the output. But a proper regulated device also pays attention to what's going on at the battery input. At an absolute minimum, you should monitor the input voltage constantly. This allows you to determine that battery's state of charge based on its at-rest/no-load voltage, and also how much its voltage sags under load. Too much sag under load is bad; it indicates you're stressing the battery too much. This could be due to the user having installed a battery that's not suitable for the power level he's vaping at, or it could be due to a battery that's just plain worn out due to age and cycles. In either case, it's would probably be best not to to keep firing...
     
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  12. MyMagicMist

    MyMagicMist Ultra Member ECF Veteran

    Mar 28, 2014
    WV, USA
    Good reason to like Kanthal.

    *sighs, nods, uses a mechanical & keeps it simple*

    Not everyone can or should, I know. If you start though and realize you've a knack of "feeling" out how you're vaping, as well as backing that up with a few good calculations, might as well.
     
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  13. Rossum

    Rossum Surly Curmudgeon Verified Member ECF Veteran

    Supporting member
    Dec 14, 2013
    NE FL
    Indeed. Back in the dark ages before microprocessors were available to monitor and compensate for temperature-dependent changes in real time, heating elements with very low TCR were highly sought after, but weren't always available for some applications. Try using straight molybdenum or silicon carbide heating elements in really high temperature applications (such as an industrial furnace where Kanthal or nichrome would literally melt) and you'll see as much as an 8:1 change in resistance between a hot element and a cold one. BTDT back in the early 1990s, and built some of the first microprocessor based controls for those beasts. These didn't control tens or hundreds of watts either, they controlled tens or hundreds of kilowatts. I remember rearing Evolv's Variable Wattage patent about five years ago and thinking, "That's cute, but should have been rejected as blatantly obvious 'cause we were doing essentially the same thing 20+ years ago."
     
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  14. DaveP

    DaveP PV Master & Musician ECF Veteran

    Supporting member
    May 22, 2010
    Central GA
    The MAX power of a mod is limited by its ability to synthesize voltage across a given resistance.

    Voltage is the key variable in most variable mods. The logic varies the voltage to maintain the power output. Power is calculated using E^2/R. If the resistance is too high, then the mod may not be able to adjust the voltage to the coil to create a given power output. At that point the user must change the coil resistance to put the equation back into a usable range or move to a multiple battery mod. A single battery mod is limited to somewhere in the 60 watt range. To go higher you need a dual or triple battery mod.

    A temperature controlled mod can sense a dry wick because the voltage peaks quickly since there's no liquid to act as a heat sink. A dry coil quickly changes resistance to an out of range number, telling the mod that the wick is dry, so it shuts down before the wick burns. A voltage controlled mod just burns the wick in two.

    Balanced charging is available in some multi-battery mods, but the best are the Evolv DNA mods. In all case, it's best to use a dedicated multi-bay charger for removable cells.
     
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  15. MyMagicMist

    MyMagicMist Ultra Member ECF Veteran

    Mar 28, 2014
    WV, USA
    Not sure if one of those industrial furnaces would match up to what I saw one day on a trip with my grandfather, Ernest (Ernie) Badgley. He took me over to "the yard" up in "steel town" along the Ohio River. The guy at the gate was nice enough. Knew he picked up the phone and called out to my uncle Thomas as soon as we pulled on through. Big Ernie showed me 'the crucible" where he poured sweat, blood, tears into molten steel. "See that Buck, they stopped letting us do it because we did it best."

    He said it liked to get twice as hot as the sun on some days. They had to keep two walls open, one out to the river, one out to the bank. He missed going to work, missed "mother". So we headed out and got just a bit down the road and the police officer pulled us over. "Buck, get my teamster card from the dash box," Ernie told me and I did. He give it to the officer and said "Son, that says I worked with your grandfather, your father and knew them as good men. Now, you be a good man too and we'll settle this by letting me go home."

    The poor officer was so red faced. "Sir, I need you to sit in my car a minute. Your son will be here to take you home."

    That night Ernie poured his milk all over the counter and put the container in the cabinet where he got the cup from. Of course, I cleaned it up before my dad saw it .. he knew though. Took six to eight orderlies to wrestle big old bear Ernie back into bed. He was coming home to see Mother., that night in October.

    Yeah, I figure most anything melts in industrial furnaces, crucibles, ... dreams, hopes, lives. Excuse me, think I figured out that insomnia.
     
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  16. basilia
    This message by basilia has been removed from public view. Deleted by a moderator, May 24, 2019, Reason: Spam.
    May 24, 2019
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