Working on a new one

[Visus]

On voltages

I have had a heated , sorta argument, with people who think a 3 ohm 11/10 nano wrapped wick cannot beat or match a .4 slr ohm coil with vapor. 
I posted the heat chart and  at 2amps 32 gauge kanthal is almost 1600 degrees it takes almost 4 amps for #28 to do the same.
I have made both coils and there is not much difference except the 3 ohm is hotter..

They cannot believe the power of regulated mods versus their mechanical its funny..

Woot power and current is your vaping friend

Power it up Craig

Vape chart just for knowledge if you did not know how hot  when vaping, what it approaches when wick goes dry..

[CraigHB]

The thing is, there are a lot of variables involved with heating the wick of an atomizer.  First there's power which only represents the total heat generated.  Then the way in which the total heat is distributed has a significant effect.  Then there's the actual temperature of the wire.  My feeling is that it's more about wire temperature than power.  As as extreme example, you could use a 10 foot long heating wire and run 100 Watts through it and it would not get hot enough to make vapor.  So, just thinking in terms of power leaves out a lot of important considerations.

There's no real science in determining the best gauge, length, and power to apply in a heating coil.  It's rather subjective so I'd have to say it comes down to art more than science.  Certainly a number of characteristics can be sited in theory, but it really comes down to the feel of an atomizer's performance when the rubber hits the road.

[CraigHB]

I don't think I'm willing to give up that much efficiency to get those voltages below battery voltage so I'm going to have to give up on the idea of a high output buck-boost mod.

Looks like I spoke to soon.  I thought of yet another way to implement a buck-boost mod.  So, I guess I'm just determined to come up with something that works to my satisfaction here. 

I thought in terms of using two controllers.  It's a buck-boost converter that is literally a buck converter and a boost converter on one board.  I had to figure out a way to disable one controller or the other without actually using the chip's shutdown mode.  Shutting down a controller shuts down the whole circuit.  I have to fool the idle controller into keeping the current path fully open.  Pulling the feedback up for the boost controller or down for the buck controller does that.  It makes the controller think it's out of its regulation range so it goes idle without shutting down.  I tried this dual controller idea in the simulator and it works. 

Stuffing two controllers on my PCB is going to be quite a challenge.  Though it should resolve my previous efficiency issue and provide the 2.5 to 8V range I want out of a single cell.  Plus I can use two TI controllers and I love TI products, they make robust, really well designed parts.  That Linear stuff is crap, I'll never use them again.

[Visus]

I did a little researching into a chips for ya wondered if this company ever you crossed paths with.

http://www.intersil.com/content/intersil/en/products/power-management/switching-controllers.html?pi_ad_id=41434550032&gclid=CMzDsL7V7LwCFSXl7AodnwYAqw

They do not cover your voltage range but looks like they integrate a lot into the chips and can stack them. 

Costs are high was just wondering if they are legit chips..

[CraigHB]

I've looked at their stuff before.  I haven't used any of it so I can't say one way or the other on the quality myself.  I know they've been around a while and I've seen other products they make so I imagine quality should not be an issue with them.  Thanks for linking them for me.  I may revisit their product line-up to see if I missed something they offer.

Most of the converter controllers on the market are not designed for the relatively high outputs you see powering an atomizer.  They're really designed only to serve as power supplies for other electronics that don't see those kinds of power demands.  It seriously narrows the field when you start looking for stuff over 10 Watts.  The more requirements you have, the harder it is to find something that can do the job.

It seems I'm trying to do the impossible here.  Even when using two controllers, there's big problems I run into.  For example, I need a buck controller that is 100% duty cycle capable otherwise there's a dead spot where I can't regulate voltage output.  That hugely narrows the field for buck controllers.

Interestingly, the TPS43000 I'm using currently is 100% duty cycle capable and is a multi-topology controller (can be configured for either buck or boost).  The down side with that controller is it uses a P-channel high side switch instead of the better N-channel and it's voltage mode control.  That's actually not  a problem since I've already stabilized it, but I'd really like to have those N-channel high side switches if possible.  That's a really nice feature.  Also the package for the TPS43000 is pretty big, it's a TSSOP.  I need something in a 3x3 or 4x4 DFN.  It's not a problem when there's only one on the board, but to put two on the board, the larger package is a problem.

[CraigHB]

So I've been looking at another buck-boost design for some time now.  I mentioned before I was going to try a new topology that I've never seen used before.  It allows me to use a standard boost controller to build a non-inverting buck-boost converter.  It does that by making use of a virtual ground at battery positive.  Buck controllers are sometimes used to build an inverting boost converter.  This is sort of the same thing, but using a boost controller to build a non-inverting buck-boost converter.

I finally got a hold of the PSpice software I need to run the specific controller model TI provides for the TPS43061 which is the controller I plan to use.  Simulation of the circuit has shown it works.  I can build a design running off a single cell for 40 Watts with a 2-8V range and maximal output current of 15A.  I need to go through some fine tuning on the sim then I guess I'll be off to a circuit board design.  Hopefully I'll have better luck with this than the last, but I have a lot more faith in TI to provide solid working parts.  I'm going to use TI power MOSFETs as well.

I mentioned before I had efficiency concerns with this topology, but I think I've managed to get power loss within reason by using MOSFETs with very low R_DS(on) and by dropping inductance to get a lower DCR on the inductor.  Effeciency is not fantastic, but according to the sim, it does around 93% at moderate loads which is tolerable.  It gets as low as 85% when pulling 15A maximal. 

One interesting note is a little bird from TI told me they're going to be releasing a 4 switch buck-boost converter controller by the end of the year.  This is the best topology for a buck-boost converter, highly efficient.  A 4 switch buck-boost converter could probably make 90% at maximal output currents.

The Linear controller I used that failed miserably was a 4 switch topology, but the failure was Linear's fault for releasing a controller that fails to meet advertised specs.  I'll for sure be doing controller board with the one from TI when it comes out.  I'm sure it won't have the same problem of being total crap like the Linear part.  TI makes really good stuff, the best.

[Breaktru]

Good to hear that Craig. I'm sure this one will work out better. Maybe a bit of hair pulling but I know you'll manage another fantastic result as your powerblok was/is.

[CraigHB]

Thanks Dave,

BTW, I did a rework on my boost only design.  It's good for 10A and 40W now.  I'm doing the assembly on the first of the new batch of boards in between work on a new design.  I'll post some pics when I get it assembled.  I've never actually posted pics of my controller boards here, (mods yes, boards no), but with the myriad of high output controller boards out there now, I'm not concerned about disclosing the details.

[iusedtoanalog]

Great to hear you still have your EE spirit. Craig I feel like this path makes the most sense with components that are available.  My hat is off to you sir. Keep fighting the good fight. 

[Visus]

Wow I understand how your getting virtual ground by watching eevblog on opamps and how to switch around ground and always being -1v less to whats coming at the input on the output and somehow ground goes virtual where it is impossible to be ground but it is.  lol

So a  buck feeding the 3061 and the 3061 powering the buck and in return being fed the min ~4.5v. of a lipo 3.7v cell..   Mindboggling

Good build wishes to ya hope these parts are the sauce. To bad cant look over shoulder and ask a slurry of em...

[CraigHB]

Great to hear you still have your EE spirit.

Yeah, I do.  Sometimes I lose it when things don't work out, but it usually comes back at some point.

Wow I understand how your getting virtual ground by watching eevblog on opamps and how to switch around ground and always being -1v less to whats coming at the input on the output and somehow ground goes virtual where it is impossible to be ground but it is.

Virtual grounds are just strange and they do present problems.  I have an issue to work out, but I figure it will come out in the wash.  It makes PCB ground negative with respect to the ground on the atomizer connector.

[Breaktru]

Thanks Dave,

BTW, I did a rework on my boost only design.  It's good for 10A and 40W now.

Wow Craig, that's mighty impressive for a boost design 

[CraigHB]

It's pretty good I suppose.  Boosters are more tricky to get big currents out of like you can with a buck converter.  You're sort of going uphill with a booster, but it's not just that.  In control system speak, there's an extra right half plane pole in the transfer function due to an extra term in the duty cycle expression.  That extra pole makes feedback harder to compensate since it digs into phase margin a good amount.  At very high duty cycles it can be impossible to stabilize a booster.  That sounds out there, but it's just the mathematical way of saying a boost converter is harder to tune for high outputs than a buck converter.  Buck-boost has the same problem when boosting so it's limited in the same way.

I'm also limited by PCB space.  I sure could use a a bigger inductor for more inductance and less DCR.  I need a smaller display to get more room on top for bigger parts or more parts, but I'm dead set on using the FSTN type.  That's the only type that is readable in direct sunlight.  The display I'm using is the smallest one of its type I can find.  I'm always on the lookout for something smaller, but I really like the particular display I'm using.  It uses a pin header instead of an unruly FPC ribbon cable like most do.

[Claviger]

Craig - Your EE knowledge is impressive Far beyond mine for sure.

Just thinking the other day, since I cannot find a control that exists to do exactly what I want. Couldn't it be possible to have a boost circuit that takes Vin range of 3 - 4.2 volts and boosts it to 12v, non adjustable. The boost would then feed a buck circuit the 12v, which in turn can control from 3.5 v - 10 v? Excuse me if this is what you mentioned a couple of posts ago.

Just thinking it might be easier if you could have a constant boost output to alleviate tuning issues and crossover points between buck/boost.  I found a couple of boost controllers capable of doing this at up 20 amps, surface mount stuff, well beyond my fabrication skills   A dual sided PCB could allow you to keep the overall size of the part quite small I would think.

TI has a buck controller I found that will take something like 6-36 volt input and allows you to regulate from 3-24 volts or so, can't recall exactly but the buck portion is definitely available already. 

I also found a boost controller on digikey that would work for this purpose, again way too small for my fat fingers to work with.

Seeing your incredible fabrication skills, I would think you could do this without much of a challenge, then add something like the low voltage detector you linked to mamu in the other thread for battery cut off.  Throw in a couple of fuses and an 1s6s lcd and digital pot and you'd have 20 amp capable from 3-10 volts @ up to 20 amps with full safety and adjust ability.

Just an idea, please don't shoot a layman for brainstorming

[CraigHB]

Hehe, I wont' shoot at you for brainstorming (funny comment).

Anyway, what you're thinking is the approach PWM mods from China use.  First they boost the voltage, then they PWM it down to the desired output.

Generally, using two regulators in series is something to avoid.  The reason is the losses from each regulator multiply.  So, if you were to use a regulator with 90% efficiency in series with another regulator with 90% efficiency, you would end up with 81% efficiency, which is pretty dismal. 

Anything under 90% is something to avoid.  As it is, I'm not too pleased about the 85% at maximal outputs I'm getting with my current design.  Though the boost only design I did before does pretty good with efficiency hovering around 90% at maximal outputs.

BTW, when you see someone claim their design is getting like 95% efficiency they're full of it.  My boost design can do 98% under optimal conditions, but when you load the crap out of stuff, efficiency takes a hit.  Nobody gets around that.

You didn't quote any part numbers there, but I think you're talking about controllers, yeah?  That's the base part you start with that determines everything else in a converter design.  I've been scouring listings for the next best controller literally for years now.  I'm using the best and latest stuff that I can find from the usual suspects. 

For anyone looking to build their own converter's there's a lot of FM involved in converter design and I can tell you it can be strange sometimes.  Sometimes it's more art than science.  It's certainly possible for a hobbyist to design and build a converter, but be prepared for some mystery and frustration.

In terms of modules, I don't pay as much attention to those since I build my own converters, but if there's a boost module capable of 20 Amps out there, I'd sure like to see it and I'm sure a lot of people would want to get a hold of it.

[Claviger]

I know I ran across one recently but couldn't use it. The 10 thumbs I have don't agree with very fine soldering work!

Let the search commence.

Found what stuck in my brain as a high amp booster. A bit big, obsolete according to TI, too low of an ouput voltage, probably very expensive, and not sure it would work.  Great help, I know:-)  Maybe it gives you an idea.

http://www.digikey.com/product-detail/en/PT7746N/PT7746N-ND/323476

[BigHoffy]

I was wondering, and this is probably caveman stupid lol. but can you use like an arduino or some other controller to switch from buck to boost and not have both running at the same time. this may be what your already doin without the arduino I have no clue. I just thought it might help with efficiency if not. even possibly sensing the batteries output and if you are selecting under that voltage it goes into buck mode, and if your selecting higher it chooses to boost it. also if your right in the sweet spot which is likely never then just letting it flow? I have no clue what kind of chip you got going of much on the matter at all but I have played with arduino a bit. its open source robotics stuff and could make a nice programmable controller, but definitely will not handle the high end output. maybe the lower end but at the same time im not sure how clean the signal would be. I do know it uses PWM, which might give that weird rattle like the older vamo's. pulse vaping lol. also arduino is open source so there is a lot of code already written for it, you might be able to find code that does exactly what your looking for. anything that goes to market that uses arduino they have to supply source code for. I didn't even know it at the time when I built my uav quadcopter but she is powered on arduino, so I can swap between a few different flight controller programs. anyway now I'm way off topic. just thought it could get your creative juices flowing again. even all the brushless ESC's are arduino I have purchased which again I did not know at the time. Might be able to run a Arduino for buck and ESC for boost with some firmware modding and extra circuitry wizardry who knows. get yourself a 40a 14.8v mod that will pop your coil faster than you can say titty twister, or turn a 1k lumen flashlight head into the bat signal. for a split second.

[CraigHB]

http://www.digikey.com/product-detail/en/PT7746N/PT7746N-ND/323476

"The PT7746 only operates in combination with a PT7770 series regulator and is not a stand-alone product.  Please refer to the PT7771,  PT7772, or PT7777 series..."

Not really something you could use in an e-cig mod.  The part itself is rather monsterous in size and it's not a stand-alone product.  I'm sure the companion part is just as ridiculously large. 

Our limitations in power output mainly come from our size constraints and portability requirements.  If it weren't for that, you could simply plug into the wall limited only by the 1500 Watts available from the outlet.  When you're limited to a board that can fit in a hand-held box or a 22mm tube running off a battery, that really narrows the ability to provide power output.

[CraigHB]

I was wondering, and this is probably caveman stupid lol. but can you use like an arduino or some other controller to switch from buck to boost and not have both running at the same time. this may be what your already doin without the arduino I have no clue. I just thought it might help with efficiency if not. even possibly sensing the batteries output and if you are selecting under that voltage it goes into buck mode, and if your selecting higher it chooses to boost it. also if your right in the sweet spot which is likely never then just letting it flow? I have no clue what kind of chip you got going of much on the matter at all but I have played with arduino a bit. its open source robotics stuff and could make a nice programmable controller, but definitely will not handle the high end output. maybe the lower end but at the same time im not sure how clean the signal would be. I do know it uses PWM, which might give that weird rattle like the older vamo's. pulse vaping lol. also arduino is open source so there is a lot of code already written for it, you might be able to find code that does exactly what your looking for. anything that goes to market that uses arduino they have to supply source code for. I didn't even know it at the time when I built my uav quadcopter but she is powered on arduino, so I can swap between a few different flight controller programs. anyway now I'm way off topic. just thought it could get your creative juices flowing again. even all the brushless ESC's are arduino I have purchased which again I did not know at the time. Might be able to run a Arduino for buck and ESC for boost with some firmware modding and extra circuitry wizardry who knows. get yourself a 40a 14.8v mod that will pop your coil faster than you can say titty twister, or turn a 1k lumen flashlight head into the bat signal. for a split second.

Not to be nitpicky (but I am), it would help me a lot in reading your posts if you could separate your thoughts in paragraphs.  It's rather intimidating to see a bit block of text like that.  I would rather like to read your posts.

</nitpicking>

You make some good points so I would not say you're being too elementary here.

I had actually thought in terms of using two controllers.  Put one on standby while the other is engaged.  The MCU would be able to sense when each is required and switch them over seamlessly.  However, I run into a space issue with that.  Not only is there the additional controller, but also some additional parts to handle switching them in and out.  I just don't have room for something like that on my PCB.

The above is actually the 4 switch buck-boost topology I mentioned before, but utilized with two controllers.  Ideally, you want to use one controller to handle both sets of switches.   It just saves a ton of space and extra components that way.  The problem is that the 4 switch topology is something new in terms of product designs.  There's a number of controllers available for low outputs, but not for high outputs.  There's only one high output controller I know of right now.  I already tried it and it was a fail.  TI is supposed to be releasing a high output 4 switch controller this year.

Obviously YiHi got it worked out with the SX350, however, there are a lot of ICs that are domestic to China we don't see here in the states.  Evidently a high output buck-boost controller is one of them.

In terms of MCUs, right now I'm using Microchip 16 bit parts (PIC24F), but Arduino is nice in that it's open source and USB based.  However, Microchip does a pretty good job with their tools.  They're all free except for the programmer/debugger which is not terribly expensive.  I like their stuff a lot and I'll stick with it.  The Arduino stuff does have some nice advantages, but the Microchip stuff does too.  You really can't knock either one.

There are simply tons and tons of MCU products out there.  They are one of the most plentiful products in terms of integrated circuits.  There's a wide array of options for any one of a big number of MCU platforms so its' hard to say there's one that's best all around.  They all have their merits.  Some have more merits than others.