The engineers dilemma.

[Lance_Wallen]

I has it.

I'm working on a new mod design. I approached this project the same way I approach all my networking projects (I'm an IT architect by trade, amateur machinist/artist/mechanical engineer for fun).

I created my requirements and a budget, I sourced my components and I started to do the balancing act on the requirements cause we all know requirements are liquid and you always have some give and take.

My requirements:
Durable and long lasting.
Vapes for a full day on a charge (for my useage, which equates to 1400mAh min)
has an integrated battery with micro USB charging.
Variable voltage/wattage.
Small easy form factor.

Budget wise, it was easy, I just odnt' go buy 20 dollar switches or build the thing out of gold.

So I picked up some anti vandal switches in stainless steel, nice durable pots with a long lifespan, decided after much kvetching to go with 2 IMR 18350s in parallel because of their good mAh, C rating, and the ability to stack em parallel to get a power pack ~36x36x18mm. I picked the dna board and it's charging board because of the price and functionality, the size is nice too.

I started playing in autodesk inventor, moved things around, minimized material and found a form factor that puts everything in the most effecient and useable configuration possible with just enough material in the case to give it structural integrity but not so much that it adds weight or too much void space increasing the size of the mod.... And I'm unhappy.

Hence the engineers dilemma... I have to start sacrificing on one requirement to meet expectations on another and balance that. Right now with the anti vandal switch and pot I chose (for durability) those two components are taking up almost the same amount of realestate as my batteries... that's unacceptable. batteries should be the only thing you make large space sacrifices for because mAh can only come with added volume when working within the constraints of battery chemistry we have to work within.

So I can downgrade my switches, I don't 'have' to use a rated switch. I can get a PCB mount baby switch like the one in the provari and just make my own button for it, that's easy enough... but the life cycle on those switches isn't that great, they're no where near as durable as a monster anti vandal mechanical switch. Same goes for the pot, I can downsize my pot pretty easily, they make some downright tiny 1k-10k pots. The one I'm using is around 18x5mm for the actual pot with a 15mm shaft, made out of aluminum with a slotted knurled tip.. As far as pots go, it's a pretty little bugger. But again... between the pot and the switch I'm using half my mod space for electromechanical components. Downgrade those and I sacrifice durability, don't downgrade them and my VW mod with an integrated battery charger ends up being the same size as a reo grand and it's not even a feeder. To me that's unacceptable, but building this thing only to have the switch or pot crap out on me in 3 months is also not acceptable.

I dunno that I'm looking for a solution, I'm just posting my thoughts hoping I'm not the only person having to deal with the geekiest sophies choice ever

 

[Scottua25]

I'm fighting the same battle. Have 2 18350's, a pot, a switch, and a DNA in a solidworks assembly and just looking at that am not sure about a workable case design. The thing won't quite have the form factor I'm looking for and I don't even have an atty connector in there yet. But, then I want to be able to swap batteries if needed. Good luck to you, though, if I come up with anything I'll post if you'd like but at this point it's almost not worth it to me to keep going. I'm the type that likes to see the finished product on the screen before I start spending.

 

[DaveP]

I'd scrap the dual battery idea. Reverse charging is a likely possibility if someone puts a freshly charged battery in along with one that's lower in voltage. Li-ion or IMR, they will still try to equalize each other and that will result in a fast charge that creates sudden heat and failure. Li-ion will vent and explode. IMR will heat up and die, hopefully with no venting.

Your circuit should use a reliable low voltage switch to insert a low to turn on the circuit, not complete a high current circuit. That lets you cut costs significantly.

Variable voltage/wattage demands an ASIC controller that performs those functions. To vary either, you need a diagnostic mode that lets you change parameters. That requires a display to show current settings and allow the user to navigate through the choices.

Someone here can suggest an ASIC that will do that, but most of the ones in use are probably proprietary chips designed for a specific mod. Some of the experimenter forums where people use blank chips that accept a firmware download are around if you can find them. If you can program it, you can create most anything these days. Driving a MOSFET will be needed to handle the current. The trick is building it small enough to fit in a case with the batteries and still be hand held comfortably.

Good luck.

 

[Lance_Wallen]

I'm not worried about the switched batteries. I'm not planning on changing batteries. It's got an onboard charger so they'll be 'permanent'. I'll be able to change them but I'm soldering them together into a pack.

As for the VV, I've got that covered with the DNA board. I know I can use a tiny switch, it's basically a logic function. The switching is actually handled on the DNA board, I just need a NO 'thing' to trigger it. I really 'can' go with a smaller switch and pot. I just like the durability of the parts I picked out. I'll be staring at my cad file for a while then probably spec out some smaller switches, redo my arrangement and see if I can get a form factor I like better. I just wish I could get a LIPO single cell, 10c+ battery with 1600ish mAh that was in a 30x30x20 form factor. Since I can't I'm stacking my 18350s for a 36x36x18.

 

[DaveP]

The AW 18650 IMR has a 10C rating.

You might want to take a look at this mod. It has everything you want and more, with discussions from the developer on how things were done and how they work. He reveals the micro-controller number and it also has a built-in USB charger port.

High WATTS/AMPS - Boost MCU Mod w/ Nokia Display - Page 2

 

[Lance_Wallen]

thats good stuff. It's not quite what I'm after though. 1. it's lower mAh than what I've got built, mine is similar in volume, that one has a screen which I don't really want on mine (aesthetic choice). Overall, it's very nice. Jus tnot what I'm tryin to make... thanks for the link though

My goal is to build a model that I can run on my CNC for a simple build out of a variety of materials so I can make a wooden one, a metal one, delrin, whatever. I basically want a darwin without the screen and in a better form factor. Hence the DNA board, integrated battery, usb charging, 510 connection.

I just need to bite it, get a smaller switch and pot and redo my model. if I shrink the pot and switch I can probably stack the electromechanicals on one side above the batteries and recess the atty connector to shrink the overall mod size and protect a carto/tank/atomizer when the mod gets inevitably dropped.

 

[DaveP]

The world is slowly changing to variable voltage since chips are coming out that support it. It's the way to go for those who change coil resistances and like to tweak the voltage for particular juices.

BTW, I'm a CCNA (recent Netacad grad) and a retired Xerox Field Service Engineer. I spent lots of my early years experimenting with logic circuits, controllers, and after hours projects just to learn micro-circuits and analog devices. I was the guy in the 70's who went to Radio Shack and bought one of every new logic chip that arrived. I breadboarded them and built ring counters, decade counters, digital clocks, and control circuits. I fell away when home computers got popular. After that, I was modding my computers and learning to program .

I'm still interested in how they work, but I'm satisfied these days to buy off the shelf working devices. I upgrade my desktop every few years as it becomes obsolete. Right now, I'm shopping for last years hot CPU cheap, a good budget motherboard, and budget gaming video card for an upgrade. I usually buy what I can get for $300 or so and use those parts. I've never been into paying top price for cutting edge that will be half price later.