Grr. it looks like most of the protection ICs that I've seen that are available in small quantities and have over-current protection are at or below 0.3 cell voltage drop. My 2S pack drops about 1v at 10A at full duty cycle. I could probably blame 0.1~0.2v on my poly fuse, and that still leaves about ~0.4v drop per cell- about 0.04ohm internal resistance each cell. Way too close to max current on those protection ICs ;/ I could probably get it to work well at 0.4v drop per cell but those are available in full reels of a few thousand each. Maybe I could try get a handful of samples and find a lower quantity source, but to be honest, a 16A poly fuse and the smart high side switch (which actually protects closer to 20~30A at the 5~7V range, are sufficient overcurrent protection. In this case, I'll look for a simpler over-voltage + over-discharge protection at least and maybe stick in an integrated charger. I want to try get as many features added in each PCB run for R&D purposes.. @OF @hardboiledfrog @KeroZen anyone else any suggestions?
The auto-magic super rZToaster, or something like that..
- Thread starter rz
- Start date
-
- Tags
- diy induction heat vapcap
KeroZen
Chronic vapaholic
I found a couple interesting BMS for 2S a while ago that should be able to cope with your continuous current requirement, one from China and the other from the US. I ordered two samples of the Chinese one as the PCB was more compact but they've been sitting in my parts bin and I didn't test them yet.
Probably not what you are looking for as you are designing your whole circuit from scratch (where I wanted to just assemble ready-made parts more like a kit) but if you are interested I can try to find the links back.
I don't have much else to add at that point, excepted keep up the good work!
Probably not what you are looking for as you are designing your whole circuit from scratch (where I wanted to just assemble ready-made parts more like a kit) but if you are interested I can try to find the links back.
I don't have much else to add at that point, excepted keep up the good work!
@KeroZen yeah I didn't want to deal with BMS design yet, and ordered this 15A with balance. 2 months and it hasn't arrived yet so even if it worked and I designed around it I'd have to wait months for more and TBH I like this design phase even if its frustrating I'm learning a lot so will keep going. I also get to select the best components for the job as long as I get the design right. I find the chinese BMS's are designed pretty well though not always with the best components. Those ebay ones state ~11mOhm, though I've found some nice ~1mOhm transistors.. albeit the transistors I'd use would cost as much as the whole chinese BMS Now that I look at that 15A, I see it doesn't have overcurrent protection, though the 8A one does (at 16A) - this would probably work well enough for me cause 8A @ 8.4V is plenty. The only reason I bumped up capacitance to get 10A @ 8.4v is so that when the battery drops to ~6V there's still enough oomph to heat quick enough. I could probably dial it back at 8, deal with the slow heat at lower end of charge. that's still 0.3v drop @ 8Amps and I cant find small quantities of protection chips with a detection level above that (like 0.5v would be OK). I'm interested in the components your 2S BMSs use If you could get some part numbers of the ICs. Looks like a lot of them use SII chips..
Now that I look at that 15A, I see it doesn't have overcurrent protection, though the 8A one does (at 16A) - this would probably work well enough for me cause 8A @ 8.4V is plenty. The only reason I bumped up capacitance to get 10A @ 8.4v is so that when the battery drops to ~6V there's still enough oomph to heat quick enough. I could probably dial it back at 8, deal with the slow heat at lower end of charge. that's still 0.3v drop @ 8Amps and I cant find small quantities of protection chips with a detection level above that (like 0.5v would be OK). I'm interested in the components your 2S BMSs use If you could get some part numbers of the ICs. Looks like a lot of them use SII chips..AHHA! 
All the stated over-current ratings on those protection chips are voltages built up on the control transistors so the sum of their RDSon is what determines the actual current limits. So if overdischarge voltage is rated 0.3v, and RDSon(sum of charge and discharge control FETs) is about 10mOhm, overcurrent is set to 0.3/0.01=30A. Short circuit detection is usually 1.2V, so 1.2/0.01=120A. Perfect. I just have to select the right transistor pair with minimum RDSon to prevent inefficiency, but LARGE enough to provide good enough overcurrent protection. This makes so much more sense that relying on cell internal resistance in which case I calculated overcurrent at 7.5A and that was just not suitable for this application. I can now go back to original plan to use something like the s-8252 (which looks identical to the ricoh r5460 which mouser actually has stock of one with decent voltage levels! ) viva la staring at datasheets for long enough I think this is the new action item 
now time for some zzzz
All the stated over-current ratings on those protection chips are voltages built up on the control transistors so the sum of their RDSon is what determines the actual current limits. So if overdischarge voltage is rated 0.3v, and RDSon(sum of charge and discharge control FETs) is about 10mOhm, overcurrent is set to 0.3/0.01=30A. Short circuit detection is usually 1.2V, so 1.2/0.01=120A. Perfect. I just have to select the right transistor pair with minimum RDSon to prevent inefficiency, but LARGE enough to provide good enough overcurrent protection. This makes so much more sense that relying on cell internal resistance in which case I calculated overcurrent at 7.5A and that was just not suitable for this application. I can now go back to original plan to use something like the s-8252 (which looks identical to the ricoh r5460 which mouser actually has stock of one with decent voltage levels! ) viva la staring at datasheets for long enough I think this is the new action item now time for some zzzz
Last edited:
KeroZen
Chronic vapaholic
So I had a look using a magnifier on the Chinese BMS and it's using 6 of these FETs:
Alpha & Omega D514 >> http://store.alhekma4u.com/content/Transistors/FET/D514_AOD514.pdf
Which I found on aliexpress here >> https://www.aliexpress.com/store/product/10PCS-AOD514-D514-30V-46A/1904245_32661168413.html
Then there's a few passives, some kind of shunt resistance (just a trimmed piece of wire) and a single chip with 6 pins that I'm not able to identify (3ZK2 written on it but no luck on findchips) sorry!
Alpha & Omega D514 >> http://store.alhekma4u.com/content/Transistors/FET/D514_AOD514.pdf
Which I found on aliexpress here >> https://www.aliexpress.com/store/product/10PCS-AOD514-D514-30V-46A/1904245_32661168413.html
Then there's a few passives, some kind of shunt resistance (just a trimmed piece of wire) and a single chip with 6 pins that I'm not able to identify (3ZK2 written on it but no luck on findchips) sorry!
OK... I'm about to order parts for next round of R&D 
It's been a while, so I've attached some images below.
The board will currently measure 60x80mm. There's an extra 20mm of design on the bottom of the PCB with some extra things like the switche panels (2 different designs), and the IR sensor + LED array.( Ignore the large female sockets on the 3d image) - these will be cut off and assembled accordingly.
Major changes from previous prototype:
What's next? Order the stuff and try get a few fully working boards out of this batch. I'll have parts for about 5 boards all being well. I'd like to keep one or two (one to use and one to abuse), and would be glad to on-board some early bird beta-testers.
In the meantime, I've already ordered a hot-air rework station to help assembly, and have been drooling over the idea of building a reflow oven. Model predictive control looks really interesting and a reflow oven would be a great project to get into it with, though as it is my dev time is limited, so it looks like a kit is called for, something like this (@hardboiledfrog I see you made one, any input?). more $$!?!??! fuuuu...
My current design is not $$ optimized. The main culprit is the whole microcontroller which currently weighs in at ~13$. I'm now pondering integrating SAMD21 48Mhz ARM Cortex M0+ 32bit processor (~3$ with necessary components) (some info here) (@toofluff any experience with this chip?). Other little things, like I'm currently using a separate voltage regulator to control all peripherals. This is only an extra 1~2$, but can be solved with putting things to low power sleep properly. Will eventually get to that in software even though I already got pretty close.. and PCBs. I need to print 10's of them to really drive the cost down, and till my design matures and goes through extra testing, I'm not committing to building that many at a time.
I hadn't touched the software for a few months till yesterday. I wanted to do a quick optimization on insertion detection - slow the sample rate down to significantly reduce consumption while waiting. I should not mix tinkering and beer, bud, and anything to do with lithium ion batteries again. I ended up doing something odd with the timing and blew a transistor! Good thing I know a guy who could fix it, and I got to test out a different set of ultra-low on resistance + ultra low gate capacitance MOSFETS, which seem like a good candidate for the next build. All back in order again Otherwise, my two proto units have accumulated many hours of use. They're being switched on and off about 10 times a second in use, so the mechanism seems to work well when not f'd with. I did learn some valuable things from the miss-hap though. Like that I need to monitor the high side switch fault signal instead of turn it off and on again 10 times a second, which resets it And that poly fuses aren't as quick to respond - just like I expected actually, which is exactly why I want the battery protection circuit, since it can respond much faster than both the high side switch and the poly.. if only I can source the right ones.
Future goals? Well, I dunno.. It would be a huge step to do this all by the book, and even though it's actually working, I feel like there's still so much to improve+optimize, so I'll keep making incremental changes, and it only makes sense to make a few boards at a time. I'd love to have a few folks help with extensive tests
though I cannot cover all costs. With necessary tools and parts purchases, PCB manufacturing, etc, boards are costing me about a hundred bucks each to build up. I really don't want to make any extra $$ from this, at least yet, since I fear it would complicate things a lot ( @Hippie Dickie you know what I mean ) though I'd be glad to offset the costs a bit. In the meantime, I hope to have parts and PCBs in a few weeks from now + some building time. Then dev + change + do it again, building a handful of devices every few months along the way.
Ummm.. I think thats it for now.. or not.. but enough for now.
It's been a while, so I've attached some images below.
The board will currently measure 60x80mm. There's an extra 20mm of design on the bottom of the PCB with some extra things like the switche panels (2 different designs), and the IR sensor + LED array.( Ignore the large female sockets on the 3d image) - these will be cut off and assembled accordingly.
Major changes from previous prototype:
1. Layout change. I now placed the IH underneath the board, next to the batteries. This keeps the whole thing about 60mm wide (both the main coil and 18650 have 18mm diamater, + some margins).
On top of the board, all components are below 4.5mm tall, so all together, the thing should be about 27mm thick (minimum internal dimension of case). I'm still using a stock OLED panel which will be up front.
2. Added basic battery protection circuit based on S-8262 chip. I can't source a chip with the right thresholds for optimized protection. Right now, IH will draw about 10Amps though protection will only kick in at about 30Amps - a whopping 300% margin but better than nothing. There is also the High side switch which should cut out a short at about 20A, and the lower voltage circuitry all goes through a poly fuse. Good enough for now, and for further testing purposes. Ideally, I'd source a chip that would kick in at, say, 12Amps leaving a 20% margin, though I'd have to get a few hundred at least.. Not ready for that.
On top of the board, all components are below 4.5mm tall, so all together, the thing should be about 27mm thick (minimum internal dimension of case). I'm still using a stock OLED panel which will be up front.
2. Added basic battery protection circuit based on S-8262 chip. I can't source a chip with the right thresholds for optimized protection. Right now, IH will draw about 10Amps though protection will only kick in at about 30Amps - a whopping 300% margin but better than nothing. There is also the High side switch which should cut out a short at about 20A, and the lower voltage circuitry all goes through a poly fuse. Good enough for now, and for further testing purposes. Ideally, I'd source a chip that would kick in at, say, 12Amps leaving a 20% margin, though I'd have to get a few hundred at least.. Not ready for that.
3. USB charging! I really wanted this feature, and was looking for a more integrated solution than what I ended up with, but can't get stuck, so I just squished another boost circuit in there. It's designed to draw 1.5Amps from 5v usb for a 700mA charging current.
4. Switches and IR panel + a bunch of LEDs. A string of red + string of green will go under the glass tube. The brightness of these can be controlled to get red / green / yellow orange glow depending on status. On the board, the charger has one, and the input to the opto-isolator has one. I like the last one, as it's not connected to ANY digital logic - directly lit from the induction coil, a nice little indicator.
Those are the major changes. Another change, is that the microcontroller is mostly SMD pads now. I liked this cause it gave me more space to run wires between pins, but I re-organized the pins anyway since so wiring is much neater. I may move back to through holes to make development a bit easier and maybe offer this board without microcontroller for those inclined. I really wanted this feature, and was looking for a more integrated solution than what I ended up with, but can't get stuck, so I just squished another boost circuit in there. It's designed to draw 1.5Amps from 5v usb for a 700mA charging current.4. Switches and IR panel + a bunch of LEDs. A string of red + string of green will go under the glass tube. The brightness of these can be controlled to get red / green / yellow orange glow depending on status. On the board, the charger has one, and the input to the opto-isolator has one. I like the last one, as it's not connected to ANY digital logic - directly lit from the induction coil, a nice little indicator.
What's next? Order the stuff and try get a few fully working boards out of this batch. I'll have parts for about 5 boards all being well. I'd like to keep one or two (one to use and one to abuse), and would be glad to on-board some early bird beta-testers.
In the meantime, I've already ordered a hot-air rework station to help assembly, and have been drooling over the idea of building a reflow oven. Model predictive control looks really interesting and a reflow oven would be a great project to get into it with, though as it is my dev time is limited, so it looks like a kit is called for, something like this (@hardboiledfrog I see you made one, any input?). more $$!?!??! fuuuu...
My current design is not $$ optimized. The main culprit is the whole microcontroller which currently weighs in at ~13$. I'm now pondering integrating SAMD21 48Mhz ARM Cortex M0+ 32bit processor (~3$ with necessary components) (some info here) (@toofluff any experience with this chip?). Other little things, like I'm currently using a separate voltage regulator to control all peripherals. This is only an extra 1~2$, but can be solved with putting things to low power sleep properly. Will eventually get to that in software even though I already got pretty close.. and PCBs. I need to print 10's of them to really drive the cost down, and till my design matures and goes through extra testing, I'm not committing to building that many at a time.
I hadn't touched the software for a few months till yesterday. I wanted to do a quick optimization on insertion detection - slow the sample rate down to significantly reduce consumption while waiting. I should not mix tinkering and beer, bud, and anything to do with lithium ion batteries again. I ended up doing something odd with the timing and blew a transistor! Good thing I know a guy who could fix it, and I got to test out a different set of ultra-low on resistance + ultra low gate capacitance MOSFETS, which seem like a good candidate for the next build. All back in order again
Otherwise, my two proto units have accumulated many hours of use. They're being switched on and off about 10 times a second in use, so the mechanism seems to work well when not f'd with. I did learn some valuable things from the miss-hap though. Like that I need to monitor the high side switch fault signal instead of turn it off and on again 10 times a second, which resets it And that poly fuses aren't as quick to respond - just like I expected actually, which is exactly why I want the battery protection circuit, since it can respond much faster than both the high side switch and the poly.. if only I can source the right ones.Future goals? Well, I dunno.. It would be a huge step to do this all by the book, and even though it's actually working, I feel like there's still so much to improve+optimize, so I'll keep making incremental changes, and it only makes sense to make a few boards at a time. I'd love to have a few folks help with extensive tests
though I cannot cover all costs. With necessary tools and parts purchases, PCB manufacturing, etc, boards are costing me about a hundred bucks each to build up. I really don't want to make any extra $$ from this, at least yet, since I fear it would complicate things a lot ( @Hippie Dickie you know what I mean ) though I'd be glad to offset the costs a bit. In the meantime, I hope to have parts and PCBs in a few weeks from now + some building time. Then dev + change + do it again, building a handful of devices every few months along the way.Ummm.. I think thats it for now.. or not.. but enough for now.
Last edited:
I haven't finished putting it together yet, but V0.2 is working at l(e)ast !
Battery protection circuit seems to be working, as in, when inserting batteries it's disconnected untilI I 'wake' it up with a charging voltage. I haven't yet simulated fault conditions, drained a battery enough in there to get low voltage cutoff, nor tested overvoltage yet, so, still in progress..
On board voltage boost works to drive the mosfet gates
It had some hiccups with an external power supply set to lower end of the expected voltage range (~5.5V) though I hope it'll work bettwe with batteries, Otherwise I'll need to tweak it a little like add some input / output capacitance, maybe lower the output voltage from the current 18.5V to ~12v which should be enough since I've found some good MOSFETS for the IH with both low Rds and gate capacitance, so they open up pretty quickly, stay cool, and don't really need their gates driven so hard.The OLED breakout that I designed needs some tweaking, so I'm still using the fallback prebuilt module option for now. Hopefully it'll work in V0.3 cause the module adds a bit of unnecessary bulk.
I'm using (2x)18awg for the 6 work coil windings, and with the 4x0.33uF capacitance this thing was pushing about 15A! I've limited it to 70% max duty cycle for now for ~10A, though I really don't need so much power. Will either go back to 4x0.22 or 3x0.33 which will still be plenty.
The work coil is a bit too close to the battery, and the board itself gets a bit hot in use which warms the batteries up. When the design settles a bit, I'll use 2Oz coppper on the PCBs. For now, I'll add some external wire to connect between the coil and caps yo reduce board heating up a little. Reducing capacitance will also reduce current and keep things a bit cooler. Eventually, I hope the enclosure will have some heatsinking built in to keep it all cool (thinking some wood + aluminum/copper heatsink panel)
That huge bulging external microcontroller will eventually be soldered flat, though I'll be experimenting with integrating an MCU directly on the PCB.
I still have to populate the onboard charging circuitry - a second boost charger (designed for 5v@1.5Amax -> 9V@0.75A) will connect to a simple linear 2S lithium charger. Should work with any 5v@2A USB charger.
So, I feel like 10 step forward 2 steps back. Happy with my progress, but still got what to do
@KeroZen Driving Two Mosfets. This IH design (royer oscillator/modified mazzilli flyback diver) is self resonant, each side turns the other off, so it's more like an analog circuit than digital driving. I read about some failed attempts of integrating gate drivers. It may be possible but I just haven't got much experience with gate drivers, so maybe it's my ignorance not yours 
I'll try look into them again, and if you have some experience with them, would love to discuss while I clue myself up a bit more.
MOSFET threshold voltage is just a threshold, and it takes time for the gate to open properly which is usually at a higher voltage. I'm currently using mossies with Vth=~4v. If it were switching at very low frequencies, it may be fine, but at ~24Khz, even driving at 8~9V, they got VERY hot. 6~7V was usually catastrophic. Driving them harder opened them up much faster and significantly reduced switching loss. Finding mossies with low gate capacitance helps open them up much quicker and was more influencial than a slightly lower threshold. Just like batteries, seems there aren't (m)any free lunches here either.. there's always this trading between physical size, Rds (~max current), lower Vgs, gate capacitance (~switching losses) etc..
Anyway, the biggest reason is that I just happened to have a cheap voltage booster module on hand, and experimented with it. It worked perfectly and I could lower the source voltage to about 4~5 volts before oscillation stopped (but mossies stayed much cooler throughout) which is perfect for 2S.
Since I'm monitoring the frequency and bit-banging the PWM in ~1ms increments, I can make sure the unit is always oscillating (@24Khz, it switches about 48 times every ms) . As soon as the count drops too much, I shut down the gate drivers and high side switch (if it hasn't already turned itself off with it's own overcurrent protection. I couldnt find response time specs in the DS for the high side overcurrent protection). Also monitoring the battery current draw with a threshold, along with the BMS stuff. I'm trying to throw as many failsafes possible into this thing cause I've seen what a shorted battery can do..
Thanks! Possibly. I've even thought of open sourcing the whole design but it's just not mature enough yet and I don't want anyone trying to build something that could short circuit on them. I'm not so sure about a DIY PCB since most of the components are SMD and I've moved away a bit from the modularity(/ bring your own microcontroller) in favor of compactness. I'm a lot more likely to open source the software though (mostly because my programming (relatively) sucks and I'm sure many people can do a better job). I may do two designs though, one without batteries. I currently see this thing as an accessory to a wonderful vape that welcomes accessories, and I'd like to extend that. Providing pre-soldered board without a case is definitely an option. As for the case, there are some interesting options bubbling along though design is still up for changes (parts need to shift a bit for thermal reasons, buttons and display can move around, etc) so nothing solidified yet. Once things are settled, I'd love to see what the rest of you can do with it I certainly can't keep this in a padded cardboard box forever.
I'll try look into them again, and if you have some experience with them, would love to discuss while I clue myself up a bit more.MOSFET threshold voltage is just a threshold, and it takes time for the gate to open properly which is usually at a higher voltage. I'm currently using mossies with Vth=~4v. If it were switching at very low frequencies, it may be fine, but at ~24Khz, even driving at 8~9V, they got VERY hot. 6~7V was usually catastrophic. Driving them harder opened them up much faster and significantly reduced switching loss. Finding mossies with low gate capacitance helps open them up much quicker and was more influencial than a slightly lower threshold. Just like batteries, seems there aren't (m)any free lunches here either.. there's always this trading between physical size, Rds (~max current), lower Vgs, gate capacitance (~switching losses) etc..
Anyway, the biggest reason is that I just happened to have a cheap voltage booster module on hand, and experimented with it. It worked perfectly and I could lower the source voltage to about 4~5 volts before oscillation stopped (but mossies stayed much cooler throughout) which is perfect for 2S.
Since I'm monitoring the frequency and bit-banging the PWM in ~1ms increments, I can make sure the unit is always oscillating (@24Khz, it switches about 48 times every ms) . As soon as the count drops too much, I shut down the gate drivers and high side switch (if it hasn't already turned itself off with it's own overcurrent protection. I couldnt find response time specs in the DS for the high side overcurrent protection). Also monitoring the battery current draw with a threshold, along with the BMS stuff. I'm trying to throw as many failsafes possible into this thing cause I've seen what a shorted battery can do..
Thanks!
Possibly. I've even thought of open sourcing the whole design but it's just not mature enough yet and I don't want anyone trying to build something that could short circuit on them. I'm not so sure about a DIY PCB since most of the components are SMD and I've moved away a bit from the modularity(/ bring your own microcontroller) in favor of compactness. I'm a lot more likely to open source the software though (mostly because my programming (relatively) sucks and I'm sure many people can do a better job). I may do two designs though, one without batteries. I currently see this thing as an accessory to a wonderful vape that welcomes accessories, and I'd like to extend that. Providing pre-soldered board without a case is definitely an option. As for the case, there are some interesting options bubbling along though design is still up for changes (parts need to shift a bit for thermal reasons, buttons and display can move around, etc) so nothing solidified yet. Once things are settled, I'd love to see what the rest of you can do with it I certainly can't keep this in a padded cardboard box forever.
Last edited:
KeroZen
Chronic vapaholic
Ah right, of course it's not as simple. Then maybe a driver won't work indeed. That's unfortunate because they help precisely to open hard and fast, minimizing the losses.
I don't recall if you did already, but would it be possible to tell us the FET part numbers you are currently using?
I've probably mentioned one somewhere but I've tried a few. The ones in my latest build are FDD9410. I haven't extensively tested them yet though they ran cool enough in initial testing. I haven't even scoped out their gates yet. I first fired them up last night, and rushed to set my PWM to 70% as it wanted to pull 15A. Then I played with the LEDs a bit before forcing myself to zzz
I've also used 30V transistors. As their max voltage goes down some parameters do improve though 30V was too close to the recommended 4X supply voltage for my comfort (in practive it's max 8.4V - about a 1V drop along the way x 3.14 = about +/-25V, but I feel better with 40V)
I've already tested about 5~6 out of the 7~8 different kinds I have (every order I've added ~10x one or two different ones. One didn't work though i think there were other issues with that build. Some ran noticably warmer than other. Now that I have a hot-air station it'll be much easier to switch and test, though the FDD9410 seem good enough for now. If I spend too much time A/Bing everything, I wouldn't have gotten so far..
I've also got a little box filled with fried transistors. Mostly from earlier builds. Fortunately since the frequency counting and current monitoring I haven't fried anything
I got to play a bit more
I spoke too soon about killing transistors. I wanted to do a quick mod and remove one of the tank capacitors (3x0.33 is enough). I also wanted to add some external wire to assist the current between the coil and capacitors. I also wanted to drink beer. and had been testing my heater. and. dunno.
Well. I do.. I hooked those two simple wires up wrong. Killed a transistor 
. Easy to find and fix at least. Not a typical problem, which I had hoped the BMS would have prevented, though nothing else went up in smoke at least 
In the end, I modified the coil a bit too, and removed a cap. The lower current doesn't heat the board up as much so seems good. I'll eventually use thicker copper on the PCB anyway, so will definitely be enough - and I've got some layout changes on my mind which will improve things even more.
I did however end up with a good testing session. I was previously limiting current with a maximum duty cycle for my PWM, so I could take 15A down to 10A average (max) by just being on for ~2/3 of the time. However, this increases the voltage drop on the batteries which results in the undervoltage protection kicking in earlier. The modified coil and reduced capacitors run at about 12A @100% Duty instead of 15(full battery, even less at lower voltage) now so gives an extra bit of battery life before undervoltage kicks in WHILE IN USE. - a battery low indicator will be flashing on screen by then anyway, so you've been warned. Removing that cap also frees up some space so I can try cram most/all the heat-producing circuitry away from the batteries. For instance, I'm thinking of moving the while IH bit (caps, coil, transistors, and a few resistors/dioded) all on a daughterboard that would be mounted perpendicular on the edge of the board, easy to attach a side panel heatsink This little module may be more relevant for providing as a DIY kit.
I built up the charging circuit. It works Kind of. I designed it for an input range of 4.5-5.5V for USB charging, with an output of 0.75A. The boost circuit doesn't seem able to start up the charger properly when charging voltage input is 5V, it worked at 5.3V though. The charging circuit thermally throttles itself down to about 450mA anyway and still creates some heat. In it's current location on the board, it was the charging circuit that warmed up the batteries while charging (which would take 3~4 hours to charge at 0.75A, ~7Hrs at 0.45A). I already added some copper on the PCB to keep the temp down (it's a linear charger after all), but it would need to be moved away from the batteries to prevent warming them up. Or I need to use a switching charger instead which are usually all step down, so I'd need to switch voltage up for it to be switched down again. DOH. I'll need to continue my search for a more suitable solution as this solution was rushed to fit it into this R&D round anyway and wasn't necessarily the best choice. In the meantime, I dropped charging current to 250mA - keeps the charging circuit cooler. It'll take ~10 hours for a full charge in the meanwhile, or just overnight top-ups every now and then (for now). This lower charge current also means 5v@500mA input, so I can safely charge it from any USB2.0+ spec port
I also learnt the the BMS chip I have likes to be permanently connected to a pack, as in, after changing batteries, it needs to be jump started (bypassed momentarily) for it to stay awake itself. This would be inconvenient for an end-user to do. May be solved with a different BMS circuit or some other method I'll look into it but I'm glad this is working for now.
A bunch of other things along the way, and many things learnt. I'll incorporate as much as I can into the next revision which I feel is closing in on something
Meanwhile... back to (actual day job) work..
I spoke too soon about killing transistors. I wanted to do a quick mod and remove one of the tank capacitors (3x0.33 is enough). I also wanted to add some external wire to assist the current between the coil and capacitors. I also wanted to drink beer. and had been testing my heater. and. dunno.
Well. I do.. I hooked those two simple wires up wrong. Killed a transistor . Easy to find and fix at least. Not a typical problem, which I had hoped the BMS would have prevented, though nothing else went up in smoke at least In the end, I modified the coil a bit too, and removed a cap. The lower current doesn't heat the board up as much so seems good. I'll eventually use thicker copper on the PCB anyway, so will definitely be enough - and I've got some layout changes on my mind which will improve things even more.
I did however end up with a good testing session. I was previously limiting current with a maximum duty cycle for my PWM, so I could take 15A down to 10A average (max) by just being on for ~2/3 of the time. However, this increases the voltage drop on the batteries which results in the undervoltage protection kicking in earlier. The modified coil and reduced capacitors run at about 12A @100% Duty instead of 15(full battery, even less at lower voltage) now so gives an extra bit of battery life before undervoltage kicks in WHILE IN USE. - a battery low indicator will be flashing on screen by then anyway, so you've been warned. Removing that cap also frees up some space so I can try cram most/all the heat-producing circuitry away from the batteries. For instance, I'm thinking of moving the while IH bit (caps, coil, transistors, and a few resistors/dioded) all on a daughterboard that would be mounted perpendicular on the edge of the board, easy to attach a side panel heatsink
This little module may be more relevant for providing as a DIY kit.I built up the charging circuit. It works
Kind of. I designed it for an input range of 4.5-5.5V for USB charging, with an output of 0.75A. The boost circuit doesn't seem able to start up the charger properly when charging voltage input is 5V, it worked at 5.3V though. The charging circuit thermally throttles itself down to about 450mA anyway and still creates some heat. In it's current location on the board, it was the charging circuit that warmed up the batteries while charging (which would take 3~4 hours to charge at 0.75A, ~7Hrs at 0.45A). I already added some copper on the PCB to keep the temp down (it's a linear charger after all), but it would need to be moved away from the batteries to prevent warming them up. Or I need to use a switching charger instead which are usually all step down, so I'd need to switch voltage up for it to be switched down again. DOH. I'll need to continue my search for a more suitable solution as this solution was rushed to fit it into this R&D round anyway and wasn't necessarily the best choice. In the meantime, I dropped charging current to 250mA - keeps the charging circuit cooler. It'll take ~10 hours for a full charge in the meanwhile, or just overnight top-ups every now and then (for now). This lower charge current also means 5v@500mA input, so I can safely charge it from any USB2.0+ spec port I also learnt the the BMS chip I have likes to be permanently connected to a pack, as in, after changing batteries, it needs to be jump started (bypassed momentarily) for it to stay awake itself. This would be inconvenient for an end-user to do. May be solved with a different BMS circuit or some other method I'll look into it but I'm glad this is working for now.
A bunch of other things along the way, and many things learnt. I'll incorporate as much as I can into the next revision which I feel is closing in on something
Meanwhile... back to (actual day job) work..
Last edited:
kentuckyshark
New Member
Hey rz, love the work you have done on this! You have inspired me, however I am not nearly as electrically inclined as you are so I am taking a more KISS approach using as many off the shelf parts as possible.
I did not notice that you had resolved an issue with the FOV on the temp sensor and now I am in the same boat you were before you replaced that. I saw you mentioned using a 35 degree FOV, however I was wondering if you could offer any more insight before I go ordering another sensor. I saw the mlx90614 is available in 12, 10 and 5 FOV also, is there any particular reason you chose 35?
Thanks in advance!
I did not notice that you had resolved an issue with the FOV on the temp sensor and now I am in the same boat you were before you replaced that. I saw you mentioned using a 35 degree FOV, however I was wondering if you could offer any more insight before I go ordering another sensor. I saw the mlx90614 is available in 12, 10 and 5 FOV also, is there any particular reason you chose 35?
Thanks in advance!
@kentuckyshark that's great! If you're already encountering those kind of problems you're pretty far on
The main problems I had with the wide FOV was that if the Vapcap cap wasn't sitting flush against the casing of the IR sensor, there was a whole lot of stray IR peeking through the gap. The stay IR depended on the temperature of the IH coil which would change during the session. Additionally there are other issues with the heat gradient introduced onto the IR sensor, magnified by the direct contact of the cap. By using a smaller ID glass tube, I managed to keep the VC straight and the cap flush which resolved the stray IR issue and was actually usable but still not ideal.
Currently I've got 10deg IR sensor though I don't think there's much of a difference between this and the 35deg sensor for this purpose. I've cut a 'mini cd' like shape - a disc with a hole, out of a silicone baking sheet, this reduced the gradient on the sensor. The glass isn't in direct contact with the IR sensor either as I've got some silicone between them too. Still, there are a bunch of issues with the IR sensor so I wouldn't call it VERY precise nor accurate, just like the cap tip temperature isn't really a true representation of chamber temperature (there's a lot going on), but it's close enough to work well for the cause specially when you get a feeling for how it all works.
As for my progress. Family, work, life, etc, I had to slow down a little with this project or go completely
. Just a little though..
I've got the SAMD21G18A microcontroller working with all current features. I flashed it with Arduino zero bootloader and had to switch out a bunch of libraries. It's a but slower than the Teensy 3.2 though so had to optimize a few of my routines. When support matures I'll probably use a SAMD51 series which will be significantly faster and close enough to easily upgrade.
I've moved my battery protection to high a side chip, S8253A, and am designing an MP2639A based charging circuit instead of the boost+linear charger. (@KeroZen )the MP2639A does actually balance in the end.I've still got to finalize current BOM hopefully in time for a shipping opportunity. Then do board layout for the changes which includes moving the main IH bits to a small daughter board to keep heat away from the batteries and easier to cool down. So, progress.. just a little slower pace than my otherwise obsessive self would be at..
The main problems I had with the wide FOV was that if the Vapcap cap wasn't sitting flush against the casing of the IR sensor, there was a whole lot of stray IR peeking through the gap. The stay IR depended on the temperature of the IH coil which would change during the session. Additionally there are other issues with the heat gradient introduced onto the IR sensor, magnified by the direct contact of the cap. By using a smaller ID glass tube, I managed to keep the VC straight and the cap flush which resolved the stray IR issue and was actually usable but still not ideal.
Currently I've got 10deg IR sensor though I don't think there's much of a difference between this and the 35deg sensor for this purpose. I've cut a 'mini cd' like shape - a disc with a hole, out of a silicone baking sheet, this reduced the gradient on the sensor. The glass isn't in direct contact with the IR sensor either as I've got some silicone between them too. Still, there are a bunch of issues with the IR sensor so I wouldn't call it VERY precise nor accurate, just like the cap tip temperature isn't really a true representation of chamber temperature (there's a lot going on), but it's close enough to work well for the cause specially when you get a feeling for how it all works.
As for my progress. Family, work, life, etc, I had to slow down a little with this project or go completely
. Just a little though..I've got the SAMD21G18A microcontroller working with all current features
. I flashed it with Arduino zero bootloader and had to switch out a bunch of libraries. It's a but slower than the Teensy 3.2 though so had to optimize a few of my routines. When support matures I'll probably use a SAMD51 series which will be significantly faster and close enough to easily upgrade. I've moved my battery protection to high a side chip, S8253A, and am designing an MP2639A based charging circuit instead of the boost+linear charger. (@KeroZen )the MP2639A does actually balance in the end
.I've still got to finalize current BOM hopefully in time for a shipping opportunity. Then do board layout for the changes which includes moving the main IH bits to a small daughter board to keep heat away from the batteries and easier to cool down. So, progress.. just a little slower pace than my otherwise obsessive self would be at..
KeroZen
Chronic vapaholic
Hey mate, sorry for the answer delay. I wanted to suggest you a few alternative FETs that I sourced for a project of mine. They seem to be better for the job than the one you selected, especially because they are "logic level", meaning they are more or less fully switched on at 5V (of course the higher the better)
The first is from Texas Instruments and has the best FOM I found, with a value between 82.5 and 129 (using min and max values for Rds(on) and Qg) Its Vgs(th) is only 1.8V (typ) Rds(on) is great but not the best, but it's a good compromise vs gate charge and switching speed: http://www.ti.com/lit/ds/symlink/csd18502kcs.pdf
Then there is this second one also from TI which has a better Rds(on) but worse on the other aspects, and a higher FOM in the end. If you spend more time open than switching it's a nice alternative and good to keep in your parts bin anyway: http://www.ti.com/lit/ds/symlink/csd18510kcs.pdf
Finally if you want a good compromise in between, there's this one from Toshiba, only 30A though and sightly slower but excellent nonetheless: https://www.digikey.com/product-det...torage/TK3R1E04PLS1X/TK3R1E04PLS1X-ND/6570928
I know you are using SMT packages but I think there are equivalents on their catalogs matching the footprint you used. For my usage TO-220 was the best as they are able to dissipate more heat and can be mounted directly on heat sinks etc.
Last edited:
@KeroZen looks like good chips indeed though I'm not sure ideal for fast switching IH at logic level.
I've played with some logic level MOSFETs for IH and lost plenty of them down at 5~7 volts probably due to slower switching and lockup. I think low gate capacitance and large gate resistor voltage is crucial for fast switching without a gate driver. When a 2S pack is down to the last few puffs at around 6V, under a ~10A draw the MOSFET is only seeing around 5V which doesn't charge the gates fast enough and will likely lead to lockup. For a faster switch, I boosted the gate voltage up (currently to about 15V). Since gate voltage is boosted now anyway, I think the exact threshold voltage is less influential to thermal performance than having a lower gate capacitance. Most of these good MOSFETS would probably work pretty well with the boosted voltage specially with decent thermal design they can be kept cool enough for the brief use.
I've found the biggest thermal contributor for the IH is the coil itself. A lot of that heat goes through the glass tube and eventually warms up the IR sensor which I've set as the limiting factor. The board by the coil gets hot also due to the higher currents between the coil and caps, so I'll be beefing up that copper. I've used some silicone to insulate the IR sensor from the glass tube which helps keep the sensor cool. When I use it by myself the IR sensor gets to about 60deg (c). With someone else dipping it sometimes hits the software limited 75deg which slows us down. If I can draw heat away from the coil with a heat sink or something, it should handle an orgy pretty well..
As for progress. I've solved a standby power consumption issue I had with the SAMD21 chip. It currently sleeps at about 190uA which I'm happy with.
I've decided to stick with my currently tried and tested low side battery protection for now though I'm still in the middle of board design changes for the updated charging module. I've slowed development down a little to stay sane with a bunch of other things keeping me busy lately, but I'll get back into it soon enough..
I've played with some logic level MOSFETs for IH and lost plenty of them down at 5~7 volts probably due to slower switching and lockup. I think low gate capacitance and large gate resistor voltage is crucial for fast switching without a gate driver. When a 2S pack is down to the last few puffs at around 6V, under a ~10A draw the MOSFET is only seeing around 5V which doesn't charge the gates fast enough and will likely lead to lockup. For a faster switch, I boosted the gate voltage up (currently to about 15V). Since gate voltage is boosted now anyway, I think the exact threshold voltage is less influential to thermal performance than having a lower gate capacitance. Most of these good MOSFETS would probably work pretty well with the boosted voltage specially with decent thermal design they can be kept cool enough for the brief use.
I've found the biggest thermal contributor for the IH is the coil itself. A lot of that heat goes through the glass tube and eventually warms up the IR sensor which I've set as the limiting factor. The board by the coil gets hot also due to the higher currents between the coil and caps, so I'll be beefing up that copper. I've used some silicone to insulate the IR sensor from the glass tube which helps keep the sensor cool. When I use it by myself the IR sensor gets to about 60deg (c). With someone else dipping it sometimes hits the software limited 75deg which slows us down. If I can draw heat away from the coil with a heat sink or something, it should handle an orgy pretty well..
As for progress. I've solved a standby power consumption issue I had with the SAMD21 chip. It currently sleeps at about 190uA which I'm happy with.
I've decided to stick with my currently tried and tested low side battery protection for now though I'm still in the middle of board design changes for the updated charging module. I've slowed development down a little to stay sane with a bunch of other things keeping me busy lately, but I'll get back into it soon enough..
So that feeling after moving all the furniture around, then coming up with a (possibly) better way, so moving it around again. Some things we just don't see until we get a chance to sit in the wrong place. So I'm moving it all around again, but I'll eventually find a good arrangement
I'm still working with two series 18650 batteries. The rest of the bulky stuff take up a little less than the volume of a 18650 battery (glass tube in coil, sensors, capacitors, chokes..).
My initial modularization efforts were just to put the IH parts (coil + cap + transistors, chokes, little bits) on a separate part, and mount it long edgewise perpendicular, like three batteries side by side. I made good progress but eh.
recent efforts have been towards modularizing out the 'smart' bits, having the microcontroller and oled display + buttons on a separate board. The IH bits could be arranged more squarely, just above the two batteries, so the finale shape would be like 2 x18650 batteries side by side, with added 50% length. The whole smartboard would have muuuuch more space like this, and it would make it easier for other DIYers to do their own whole contoller section, and have the power, upgraded charging, and IH block all taken care of in one. I'm feeling better with this layout, and I've made good progress with this redesign.. though there are still some challenges, and a bit of 'wiring up' which is still waiting for a few more design decisions which I'm spending way too much time thinking about in a somewhat leisurely manner. family first and work just behind + doc said take it easy, so..
Annnd... Now I've got some other ideas (which I may even choose not to do), to separate it differently. Keep the batteries, protection and charging as one board without any brains or IH stuff. This can work as a generic power base for all sorts of projects, including some other experimentation I'd like to get around to (@RastaBuddhaTao). The IH+smartboard could all be on one other module, or even broken up further.. dunno. Part of me is pushing myself towards obsessive engineering, because I think that's kind of a getaway for me, but I need to balance it with satisfaction of actually getting something done I've still got lot's to learn about keeping it simple( ie, master @Pipes), So I will make concessions, and still many changes. Must. Not. Spend. More. time... Thinking. About. Low. Profile. Board.To.board. connectors...just..solder..the..damn..thing.
I love the community here though. Still so much to learn from many of you, and I've had some good conversation with some
. specially the fact that some of you will buy multiple versions of the same damn thing!! (<looking at my little dynavap collection 
>) and with room for us all, big or small, I'm glad we all share ideas in a constructive way. So.. Still here.. Still lots to do.. Thank you for your patience and 
vapor for the masses .../
? 
I'm still working with two series 18650 batteries. The rest of the bulky stuff take up a little less than the volume of a 18650 battery (glass tube in coil, sensors, capacitors, chokes..).
My initial modularization efforts were just to put the IH parts (coil + cap + transistors, chokes, little bits) on a separate part, and mount it long edgewise perpendicular, like three batteries side by side. I made good progress but eh.
recent efforts have been towards modularizing out the 'smart' bits, having the microcontroller and oled display + buttons on a separate board. The IH bits could be arranged more squarely, just above the two batteries, so the finale shape would be like 2 x18650 batteries side by side, with added 50% length. The whole smartboard would have muuuuch more space like this, and it would make it easier for other DIYers to do their own whole contoller section, and have the power, upgraded charging, and IH block all taken care of in one. I'm feeling better with this layout, and I've made good progress with this redesign.. though there are still some challenges, and a bit of 'wiring up' which is still waiting for a few more design decisions which I'm spending way too much time thinking about in a somewhat leisurely manner. family first
and work just behind + doc said take it easy, so..Annnd... Now I've got some other ideas (which I may even choose not to do), to separate it differently. Keep the batteries, protection and charging as one board without any brains or IH stuff. This can work as a generic power base for all sorts of projects, including some other experimentation I'd like to get around to (@RastaBuddhaTao
). The IH+smartboard could all be on one other module, or even broken up further.. dunno. Part of me is pushing myself towards obsessive engineering, because I think that's kind of a getaway for me, but I need to balance it with satisfaction of actually getting something done I've still got lot's to learn about keeping it simple( ie, master @Pipes), So I will make concessions, and still many changes. Must. Not. Spend. More. time... Thinking. About. Low. Profile. Board.To.board. connectors...just..solder..the..damn..thing.I love the community here though. Still so much to learn from many of you, and I've had some good conversation with some
. specially the fact that some of you will buy multiple versions of the same damn thing!! (<looking at my little dynavap collection >) and with room for us all, big or small, I'm glad we all share ideas in a constructive way. So.. Still here.. Still lots to do.. Thank you for your patience and vapor for the masses .../?
Last edited:
szai
Well-Known Member
So that feeling after moving all the furniture around, then coming up with a (possibly) better way, so moving it around again. Some things we just don't see until we get a chance to sit in the wrong place. So I'm moving it all around again, but I'll eventually find a good arrangement
I'm still working with two series 18650 batteries. The rest of the bulky stuff take up a little less than the volume of a 18650 battery (glass tube in coil, sensors, capacitors, chokes..).
My initial modularization efforts were just to put the IH parts (coil + cap + transistors, chokes, little bits) on a separate part, and mount it long edgewise perpendicular, like three batteries side by side. I made good progress but eh.
recent efforts have been towards modularizing out the 'smart' bits, having the microcontroller and oled display + buttons on a separate board. The IH bits could be arranged more squarely, just above the two batteries, so the finale shape would be like 2 x18650 batteries side by side, with added 50% length. The whole smartboard would have muuuuch more space like this, and it would make it easier for other DIYers to do their own whole contoller section, and have the power, upgraded charging, and IH block all taken care of in one. I'm feeling better with this layout, and I've made good progress with this redesign.. though there are still some challenges, and a bit of 'wiring up' which is still waiting for a few more design decisions which I'm spending way too much time thinking about in a somewhat leisurely manner. family first
Annnd... Now I've got some other ideas (which I may even choose not to do), to separate it differently. Keep the batteries, protection and charging as one board without any brains or IH stuff. This can work as a generic power base for all sorts of projects, including some other experimentation I'd like to get around to (@RastaBuddhaTao
I love the community here though. Still so much to learn from many of you, and I've had some good conversation with some
Have you considered having the induction cool oriented horizontally and out of the side vs the top? It'll kind of be like holding a fat pipe. A fat pipe into which you will place a Vaporizer.
@szai I have considered it, it makes some things a bit easier like not having a weird perpendicular mounting mechanism for the sensor and LED string. It doesnt fair too well with thickness though. The sensor is about 1cm tall, and the coil is just under 2cm long, with a little space between them ( I need to avoid heating the sensor itself ), which adds up to about 3cm above the PCB that the IR sensor sits on. I could shave off a little by reducing coil size, but still.. would be pretty thick in the end.
Current design's thickness is 4mm max component height (on the outer side of the PCB) + 1.6mm pcb + 18mm battery diameter (minus the point that the prototype's microcontroller is mounted externally on a large detachable connector, a generic OLED module is on a 27mm short edge PCB, etc..).
But my recent efforts are to thermally isolate the batteries as much as possible. I don't want the hot stuff on the same PCB the batteries are mounted to. One solution is to stack PCBs, and this gives me a lot more real estate. Placing the IH module on top of the batteries (length wise), rather than beside them, reduced the footprint a bit, so I've been more comfortable with the little extra thickness from the extra stack.. and in this orientation, it may even make sense to mount the coil 'standing up' kind of thing. Will definitely play around with it in my head a bit more now. This is kind of where I'm stuck right now. I'm very happy with my first few prototypes and I've learnt a lot from them, now with quiet a few different ideas of how to place things, and a lot of thinking about things in cause it's a lot of work to progress with the design and change again and again.. so my layout is a bit of a mess now, and I'm just moving things around... will only start cleaning it all up and finalizing when I'm comfortable with a direction..
Otherwise, there are three biggish changes between my previous design and next:
1. change boost + linear charge circuit to a much better switching charging design.. so I hope this works
2. change the microcontroller out for an onboard one. I was previously using an external MCU, then wired up a little ATSAMD21 chip on an experimental PCB I printed, which works, now I have to design that chip straight in.
3. fix the oled interface. I designed an oled breakout as an experiment but it didnt work so I'm still using a prebuild module. I've already made some fixes and hope round two will work out better... but it may not.. I may not even need an oled. I could just use some LEDs to create a meter... but that's not what this is just yet.. maybe Was even thinking of a capacitive slider, alongside an LED meter.. but I'm not at that level of elegance yet. For now it's still a geeked out piece of tech with an over-informative OLED. artistic refinements to come in future iterations I hope.
Current design's thickness is 4mm max component height (on the outer side of the PCB) + 1.6mm pcb + 18mm battery diameter (minus the point that the prototype's microcontroller is mounted externally on a large detachable connector, a generic OLED module is on a 27mm short edge PCB, etc..).
But my recent efforts are to thermally isolate the batteries as much as possible. I don't want the hot stuff on the same PCB the batteries are mounted to. One solution is to stack PCBs, and this gives me a lot more real estate. Placing the IH module on top of the batteries (length wise), rather than beside them, reduced the footprint a bit, so I've been more comfortable with the little extra thickness from the extra stack.. and in this orientation, it may even make sense to mount the coil 'standing up' kind of thing. Will definitely play around with it in my head a bit more now. This is kind of where I'm stuck right now. I'm very happy with my first few prototypes and I've learnt a lot from them, now with quiet a few different ideas of how to place things, and a lot of thinking about things in cause it's a lot of work to progress with the design and change again and again.. so my layout is a bit of a mess now, and I'm just moving things around... will only start cleaning it all up and finalizing when I'm comfortable with a direction..
Otherwise, there are three biggish changes between my previous design and next:
1. change boost + linear charge circuit to a much better switching charging design.. so I hope this works
2. change the microcontroller out for an onboard one. I was previously using an external MCU, then wired up a little ATSAMD21 chip on an experimental PCB I printed, which works, now I have to design that chip straight in.
3. fix the oled interface. I designed an oled breakout as an experiment but it didnt work so I'm still using a prebuild module. I've already made some fixes and hope round two will work out better... but it may not.. I may not even need an oled. I could just use some LEDs to create a meter... but that's not what this is just yet.. maybe
Was even thinking of a capacitive slider, alongside an LED meter.. but I'm not at that level of elegance yet. For now it's still a geeked out piece of tech with an over-informative OLED. artistic refinements to come in future iterations I hope.
Hogni
Honi soit qui mal y pense
@polykoma , welcome! Nice to see new guys from Berlin here!
@rz What are you currently working on, still an VC IH or are you meanwhile working on an IH vape?
BTW there will soon come a new IH Vape from Dr. Dabber
@rz What are you currently working on, still an VC IH or are you meanwhile working on an IH vape?
BTW there will soon come a new IH Vape from Dr. Dabber