Designing circuitry for a squonk-box/MOD.

[Microzod]

Hello.

I am designing the circuit for my own squonk-box, I am designing the box it self in Fusion360(a free Autodesk software) and I am going to print it with a Wanhao Duplicator 6 3D-printer.

First I wanted to build a box with only 1 18650 battery(or if I could find another battery type to use 1 or more of) in order to build a as small a box as possible and I am still planning such a device but I have come to also plan a two 18650 device.

For the single 18650 device i want to achieve 80-100W max, and one of the most interesting parts of these designs is going to be the temperature control algorithm.

In ether of the revisions described above the device will be controlled by a Atmel XMEGA microcontroller(ATXmega128A1U, perhaps a smaller XMEGA but that is the one I have at home) and it does contain lots of fun stuff.

I have previously discussed this idea on another forum(edaboard.com) but I need to talk to people whom knows about vaping, much because I think that the design for a device like this is a unusual design and perhaps not optimum compared to most others DC-DC converters maybe due to the space constraints. So there a quite a few compromises that needs to be done and the purpose of it all is vaping and without that in mind the design can go in the wrong direction.

One idea that was raised on edaboard was to tailor my coil build to <=0,12Ω and then(this is for the single battery version) switch the current/voltage with a very minimalist circuit.
The minimum voltage of a Li-Ion battery being 3V(I hope) would then equal 3V/0,12Ω = 25A which is a common amperage for these kinds of batteries.

As for the two battery version, I had thought to implement a two-switch buck-boost converter much because such a design appears to be a lot of fun.

But I wonder, are the boost function ever needed?
I don't need a device which can output 200W, I usually use 60-70W but it would be nice to enable higher output power because I don't know where my vaping will lead in the future.
But while vaping with my Cuboid(sells as a 150W MOD but is upgraded to 200W with a software update)

I am somewhat confused right now as a effect of the massive online research I have been performing the last few days, and I am not done.

Oh and then I have a odd feature planned, I have many times been sitting in my sofa or bed vaping and then woken up only to find the MOD lying down in the sofa/bed with a big spot of juice that has been running out of the RDA/RDTA. This issue will be partly dealt with by a squonk box but in any case I plan to include a circuit that can be enabled through the menu on the OLED/LCD display that will(when activated) sound an alarm through a pezio transducer I think when and if the MOD is tilted more than some particular degree, I will have to experiment a little later on to determine the exact point that will trigger the alarm but that isn't important yet. The point is that such a feature will be included. I guess by means of a 3-axis accelerometer communicating with the mcu.

As for the temperature control, I was hoping that someone here knows more than I do but I am planning to include some calibration features that would needed to be performed for every particular atomizer to be used in order to be able to cancel out the atomizer resistance(I think I will connect a differential amplifier or instrumentation amplifier directly across the 510 connector n order to acquire a as accurate resistance measurement as possible(since I am pretty unimpressed by the Cuboids temperature control and resistance measurements).

But that is one of the great things with this kinds of hobby projects, I can use circuits and allow expensive components that would never be possible in a commercial product where the point is to make money.

What do you think about my start so far regarding my plans for a single battery version and the dual battery version?

Also, does anyone have any ideas for another battery configuration that could suffice?

I had hoped that I could find smaller batteries than 18650 and maybe parallel them in the bottom of the box in order to construct a thinner but longer than usual box.

Oh and I plan to use a BF 510 connector from Varitube.

Regards

 

[Alexander Mundy]

80 to 100W on a single 18650 is not advisable in my opinion. Pushing a single 18650 that hard will result in short run time, short battery life, and if you don't do your homework safety issues. I'm not saying it can't be done, just pointing out the drawbacks. First things first, check out Mooch's blog for real world testing of batteries. Mooch is a professional tester of lithium ion cells, is highly regarded, and lends his expertise to us freely. Mooch's blog | E-Cigarette Forum

 

[Microzod]

Well that I think is really good advice, and I found much interesting stuff to read from that link.

But is 25A really pushing a Sony VTC4(2100mah 28A/30A(from the link in Alexanders post))?

And I don't mind having to switch battery 1 or twice each day if that would mean a smaller box, I can never remember the name of those batteries that are roughly half the length of a 18650 and i little wider.
I have been thinking about using 3 of those in parallel and maybe even 3*2(3 parallel batteries in series with 3 more parallel, resulting in roughly the same height as 3 18650 next to each other but with the voltage of 2*3,7V and possibly capable of delivering quite a high current without over stressing the batteries. or två such smaller batteries in series paralleled with two more such stacks) each 3 pack stacked on top of the other(the idea is then to build a box that is pretty slim(width) and instead build a unusually long mod.
Since I am 3D-printing it and designing the circuit board(which will be produced in China) then maybe that could be a nice form factor for a box...

I think I should tell everyone reading this thread that I have quite severe ADD(Attention Deficit Disorder) which makes details hard to recall and I may at times loos my self in my thoughts. But it all works out in the end

 

[Microzod]

I have been thinking of printing my own squonk-bottle as well in order to be able to get a unique formm of the bottle to further minimize the size of the box.
I really doesn't need a super tiny box but I do not like those big things that looks like they contain 3 18650 batteries, they are just so darn large.

 

[Microzod]

Would you still think it is too much to demand 70W from a single 18650?

 

[Microzod]

Although I have a wide electronics interest I haven't worked with batteries like this before, I may have read much about Li-Ion batteries in theory and used them for low-power applications but I haven't implemented them into a design like this so I am somewhat lost at this part.

 

[Microzod]

Wow, I'm used to the posts being put into on single post when 1 person posts after his/hers own post instead of making multiple posts.

Anyway I looked and found out what those batteries I thought of is named and that idea is scratched, looks like it is ether 1 or 2 18650 that is what I have to go for.

I think I will choose to go for a 2 18650 design first and then after that maybe make a 1 18650 design if I feel like it is any point in that.

 

[Alexander Mundy]

I use a filament from Makergeeks that used to be called EN40 but got renamed to Makerflex to print bottles. Shore hardness of 40 so it's rubber band soft. It is FDA food safe, but of course isn't technically after printed since the printer would have to be certified. The original I use was called "natural" and at 1mm wall thickness it isn't clear but I can see the liquid level inside. Here is one I printed for the Dripbox mod.

 

[Microzod]

That is really great news that makes me very happy, because I have been planning to print my own bottles while I always thought that it will probably not be that great and I will probably end up with buying some bottle.

In what format has this plastic been delivered in when you have used it?
Also when you write "It is FDA food safe, but of course isn't technically after printed since the printer would have to be certified" it sound pretty clear, but just to be thorough, do you know if it is possible that a plastic like that wouldn't in practice be safe after printing?
I at least imagine that something in a plastic could change by the heating process, although such things are probably very hard to know if you aren't an expert in plastic development or something.

Regarding the circuit for my squonk-box, I have thought about ohm's law from a purely theoretical point of view and now that I do the calculations I do understand why the boost function could be needed. Or it depends, I am considering using 2 18650 batteries in parallel and accept that I can only use sub-ohm coils.
The highest resistance I am using is 0.5Ω and in those situation I have 26W as a maximum limit so that's no problem.

And by using them in parallel I would enable much lower resistances to be used which I want to be able to do.

I have never used as low a resistance as what I am about to mention and I don't know what kind of wattage's one would need at those resistances but only to put some number on things, would it be safe to use two 18650 rated for 25A in parallel connected to a coil build that added up to 0,05Ω supplied with a power of 100W which would result in a current of 44.72(not taking into account the resistance of the atomizer and wiring)?
And if not, could anyone put an number on the maximum current safely drawn from 25A batteries(of course it is nothing more than an estimation that you never would be responsible for but I'd like to get an idea of safe current draw, I haven't seen anything telling me such things but I might have missed it).

 

[Microzod]

Okey so I have come to realize that a lot of my approach of this has been dead wrong and faulty, the thing is that in all my earlier designs and projects the main point have been data converters and they have been done in a fashion where I have been able to do simple estimates while putting the system together and then observe the results.

And my thinking has been the same in this case with the result that in between of everything I have been reading about batteries and other parts of the system my thoughts about this has been about what I would like my device to be able to do or how it should be capable of being used.

But that is not how this sort of design can be made and I need to determine and establish fixed parameters such as the lowest resistance possible, at least an estimate of the resistance between the sense wires connecting to the 510 connector and the actual coils, and maximum power levels for the specific resistances of the possible coils and so on.

I will pull out my LCR-meter to measure a Fat Daddy 510 BF connector connected to a few of my atomizers to find out how large the resistance is without the coils, then I can start designing the current measurement circuit.

I have hoped that I would be able to design a system that would allow as a minimum 0,05Ω builds, but with the device I have today I can't use less than 0,1Ω.

Does anyone have experience vaping with 0,05Ω builds?

Is there anyone that thinks that there are a correlation between a particular power setting for a 0,21Ω dual coil build and the power setting of a 0,05Ω build to result in an comparable vape that I could estimate to get an idea about what power levels I would need to be satisfied while using a 0,05Ω build?

Because I am currently vaping with a Troll V2 25mm with a 0,21Ω(dual coils each made out of 8,5 turns with a single 24AWG SS316L wire), and I have a build in my Troll V2 22mm that is 0,12Ω(dual coils each made out of one 24AWG Kanthal A1 wire + one 24AWG SS316L wire wound in a simple parallel wire fashion with 4,5 turns equaling 9 turns in total).

And with the 0,21Ω build I need 70W while I need 75W with the 0,12Ω build(which is the maximum that my Cuboid will allow which from what I have been told in this thread is not a good idea as it draws 24.3A from two series 18650 batteries) but those two builds at the respecting wattage of 70W and 75 W is comparable to each other, would it be stupid to think that the relation between those two builds and there wattage would be a acceptable premise for extrapolating the wattage needed for a 0,05Ω build?

Where do I get 0,05Ω from? It is just a sort of randomly chosen minimum, I definitely want to build a device that can handle <0,1Ω and 0,05Ω sounds like a value that would allow me to build whatever I'd like.