Fluxer Heaters, induction heaters for Dynavap

mr_cfromcali

Accessory Maker
Accessory Maker
just curious ... is the MOSFET getting hot, or is the ambient temp in the case from the heater coil making it hot?

The MOSFETs are getting hot because a LOT of power is running through them, generating a lot of heat, and that heat is concentrated directly underneath the MOSFETS. The design to this point did not consider this and didn’t provide any additional mechanism for spreading or dissipating that heat beyond the small footprint of the MOSFETs themselves. The new PCB addresses this and provides new copper surface areas near the MOSFETS for the heat from these chips to expand into and saturate. Should be a big improvement.

I always knew the chips got hot, but until this week I didn’t realize how hot or more importantly, how detrimental that was. It’s obvious to me now and I feel foolish for overlooking this, but blindspots are weird that way.

This has nothing to do with ambient temps or the proximity of the work coil.

Hope that helps.
 
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caliganja420

Well-Known Member
16mm coil owners, How have your experiences been to this point with your FD? I've been thinking the whole time I need the 14mm turbo charged Ferrari, but as I medicated last night it occurred to me that an even faster heatup time than my psm isn't for me. My psm heats hot to the click. I don't go past it or combust. I enjoy it thoroughly, but I could do with a more gentle heat source.
@mr_cfromcali might be a dumb question but is the battery life of the 16mm coil better than the other FD's?

Hey there, i have a 16mm coil FD. Before i sent it in to MrC, it was working really well. My heat was turned down so i would have to wait several seconds after the click for a nice full hit. I just got it back from repairs and it has been working very nicely. Now the heat is turned up and i can pull at the click, no more waiting. Battery life is unbelievable. 20+ bowls, unlike the lucid customs unit 3-5 bowls, LOL. The reason i sent it in is because every few days, i would just turn off. The unit would be on, and when i insert the tip to heat, the on light would shut off. I have not had any problems yet.
 

Hippie Dickie

The Herbal Cube
Manufacturer
The MOSFETs are getting hot

what is the RdsON (resistance) at your MOSFET gate voltage?

My MOSFET got blazing hot because i had the red LED tied to the Gate and that kept the gate voltage at about 2.5v - way too low to reach the 1.5 mOhm RdsON at a more proper 5v gate voltage ... i'm using the FDB8832 N-channel Fairchild PowerTrench MOSFET. A guy who designs high end audio equipment saw my thread and pointed this out to me about 8 years ago. i moved the LED to the ground end of the circuit and my MOSFET is at ambient now. i'm actually at 4.5v at the gate, and that is sufficiently high gate voltage to keep the RdsON quite low (<2 mOhm) and allow a bit more run time on the 2* 3.2v cells in series.

but for a bit more resiliency (i hope) i have moved my MOSFET to the other side of the pcb - to keep it out of the heater chamber.
 

mr_cfromcali

Accessory Maker
Accessory Maker
what is the RdsON (resistance) at your MOSFET gate voltage?

My MOSFET got blazing hot because i had the red LED tied to the Gate and that kept the gate voltage at about 2.5v - way too low to reach the 1.5 mOhm RdsON at a more proper 5v gate voltage ... i'm using the FDB8832 N-channel Fairchild PowerTrench MOSFET. A guy who designs high end audio equipment saw my thread and pointed this out to me about 8 years ago. i moved the LED to the ground end of the circuit and my MOSFET is at ambient now. i'm actually at 4.5v at the gate, and that is sufficiently high gate voltage to keep the RdsON quite low (<2 mOhm) and allow a bit more run time on the 2* 3.2v cells in series.

but for a bit more resiliency (i hope) i have moved my MOSFET to the other side of the pcb - to keep it out of the heater chamber.

Hi, and thanks for your post. I am using NVD5890NL MOSFETs; link to datasheet. They have an RdsON of
3.7 mOhms @ 10 V, 5.5 mOhms @ 4.5 V. My Gate voltages are consistently high - most recent oscilloscope graphs show that my heater MOSFET Gate voltage remains >7.5V throughout a heating cycle. I don't think low Gate voltage is responsible, but I will look at that measurement more closely next time I am setup to do so.
 

Jill NYC

Portable Hoarder
16mm coil owners, How have your experiences been to this point with your FD? I've been thinking the whole time I need the 14mm turbo charged Ferrari, but as I medicated last night it oc
I use my 16mm FD several times a week and it has treated me very well. I have similar experience as @Rollingstoned (except never had to send in).
 

mario

Well-Known Member
I have had my 14mm coil FD since the first batch of them went out before the mosfet issues. Mine is running strong and perfectly since then. I have a small bit of cardboard between the heater and the battery compartment and that has been fine since that was mentioned on here.

I am not sure why mine has been running smoothly even with all the heat issues and such. It hasn’t faltered even once yet. Anyways, just wanted to put it out there for anyone on the fence. The heater is amazing and when it works right, it is worth every damn penny. I see other posts on reddit with other heaters and at the end of the day I would trade my FD for anything.
 

mr_cfromcali

Accessory Maker
Accessory Maker
Hate to be that guy but any updates on repairs and stuff?

Hi,

I am trying to make sure the heaters work as expected. Please see this post for the most recent news: http://fuckcombustion.com/threads/f...eaters-for-dynavap.33573/page-43#post-1382695

The newly revised PCBs that I need to make repairs are finally shipping today, from China.

They will get here Friday or Monday.

I will test them as soon as they get here, and as soon as I'm confident they work as expected and resolve the underlying problems they are supposed to fix, I will use them.

I will post here w/more news when I have it.

Thanks for your patience.
 

mr_cfromcali

Accessory Maker
Accessory Maker
It's time for a triple popcorn Fluxer update - an update so wordy I needed to split it into two parts.

:popcorn::popcorn::popcorn:

In the next two posts, the Flux Deluxe's MOSFET saga takes a few extra twists and turns - and my write up is extra wordy, too - but I finally (!) determine a true root cause of my MOSFET issues and reach some conclusions about the path forward. It was a full weekend, so pack yourself a fresh bowl and settle in for a long-ish update. :leaf:


Part I: New PCBs vs. Old Issues


As I mentioned last week, I redesigned the FD's PCB to add some copper heat sinks near the MOSFETs, on both sides of the PCB. I wanted to evaluate a few potential changes, so there are several different versions of these new PCBs coming. The differences between them are very minor, however, and their heating circuits are identical, so any of them should be capable heaters, and all include the latest fixes, etc.

The first two versions of the new PCBs came on Friday, and that evening I built up a few of the new boards for evaluation. The results were very revealing, and forced me to reconsider some previous decisions.

Or as I put it at the time: Fuck! :bang: Which is par for the course around here... :rolleyes:

Surprise PCB revelation #1: The new thermal dissipation/heat sink areas I added to the circuit boards work very well. They transfer heat even better than I anticipated they would.

Surprise PCB revelation #2: They did NOT, however, solve the issue of the MOSFETs killing themselves. If anything, the new heat sinks made things even worse! The new PCBs were extremely efficient MOSFET killing machines. Which, y'know, was not part of the game plan. What fresh hell was this?

:popcorn:

Not wanting to accept these results at first - and being a stubborn person - I spent the next several, very frustrating hours confirming all of the stuff I just mentioned: the new PCBs were performing exactly as I expected them to as far as their heat transfer capabilities - they transferred a lot of heat to the new copper surfaces I added. But that add'l heat transfer didn't mitigate MOSFET failures, and if anything it exacerbated them! WTF was going on?! The observed voltages remained good throughout these failures, BTW. So if it wasn't voltage and it wasn't heat, then what element was I actually fighting here? What was my true enemy? It had to be something pretty obvious, as the new PCB was killing the NVD5890L MOSFETS at an alarming rate.

Thinking hat time. :sherlock:

I looked at my clues: The new heat transfer areas of the PCB were getting hot to the touch - which I took to mean they were working as I expected them to work - but the MOSFETs and the areas around them became extremely hot, very rapidly. And the MOSFETs were dying, too, also very rapidly. Each test was taking 10+ minutes to setup and less than 3 seconds to execute, which was also getting old. I needed to figure out what was going on ASAP, before I ran out of MOSFETs and/or patience.

When I considered all of the above evidence, it looked like the MOSFETs themselves couldn't dissipate power quickly enough. The new PCBs allowed the MOSFETs to offload a considerable amount of heat (meaning they could run harder, as they has less thermal resistance), and now they were now running so efficiently they practically sizzled - and then died. Hmmm - this wasn't a problem of shedding some "extra" heat. This was looking like a straight-up miscalculation. Just how much power was being pulled through these MOSFETs by the 14mm coil? :hmm:

I danced all around this question while I was evaluating the voltage spike situation, but for some reason I didn't ask this specific question, and I should have. In retrospect it was an obvious blind spot. :uhoh:

I took some fresh measurements and then re-calculated the heater's actual power output with the 14mm coil. I then compared those measurements to the datasheet (specs) for the MOSFETs I have been using.

:sherlock:

:uhoh:

:ugh:

:doh:

I observed that the 14mm coil is capable of pulling quite a bit of power (i.e., current) through this circuit: ~9.6A, which is consistent with its performance.

The spec for power dissipation is given in Watts, and Wattage is calculated by multiplying Current X Voltage.

The heater's voltage is nominally 12VDC, but a fresh set of batteries is actually a few mV higher than that. 12.6V is probably the highest state of charge these batteries are likely to exhibit, so I used that value for these calculations. It's the power level one might encounter with a fresh set of Sony VTC5-D (high current discharge) batteries.

Using that figure, the math says that a 14mm Flux Deluxe is capable of pulling about 121W of power through the heater MOSFETs in about an instant. Which is a lot.

NB: This is a reminder that 18650 batteries pack a lot of amps, so treat your batteries with respect, and inspect your heaters regularly for potential issues! Silicone wires nick easily. If you notice anything that needs attention, please drop me a line. I am happy to work w/you to fix potential safety issues.

:popcorn:

To this point, I have been using the NVD5890N as my heater MOSFET. This is the spec sheet for the NVD5890N, and I've circled its Power Dissipation limit in red:

NVD5890-N-data-sheet.png


The NVD5890N MOSFET is rated to dissipate a maximum of 107 Watts.

As I just showed, a Flux Deluxe w/a 14mm coil is capable of pulling about 121 Watts.

:\

I am over the power dissipation limit of these MOSFETs by >10%. That's obviously not a good place to be, but nonetheless, I am grateful to discover this, as it's an answer that explains just about everything! No device performs well at its limits, and when you exceed a device's limits by >10% - and especially when that limit is something critical like the fucking power dissipation limit of the MOSFETs!!! :doh: - you are going to to see some bad things occur.

This is exactly the sort of smoking gun I was looking for and hoping I would eventually find. I am thrilled I finally found it! Hindsight is 20/20, and this sure seems obvious now, but I somehow kept missing it until I had cleared away all of these other issues that I mistook it for.

So this is it, folks. This is the root cause of the Flux Deluxe's MOSFET issues: I am drawing more power through my MOSFETs than they can dissipate. THAT's what's been killing them. :rip:

:shit:


I am not proud of this oversight, but I am SO happy that I finally (!!!!!), positively identified it. This is the answer I was looking for, and it was right in front of me the whole time. D'Oh! :doh:

Thankfully, this is an easy problem to address: there are many other MOSFETs out there in the world, and some of those have power dissipation capacities that can easily handle the power demands of a 120W device. And you can even search for them by their desired specifications. :brow:

I have been using the NVD5890N MOSFET since @stardustsailor recommended it back in October, and it is a great chip for an IH; it's been one of the secrets of the Flux Deluxe's quick performance. I was so impressed with the NVD5890N's performance that I have been taking it for granted that this chip could handle whatever I threw at it, as it was a beast! :haw: Unfortunately, even in Beast Mode, it tops out at a max of 107W, and I am regularly exceeding that. No wonder it's dying! The wonder is that it is working as well as it is for so many of you! :shrug:

Continued in Part 2: A New Chip in the House
 
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mr_cfromcali

Accessory Maker
Accessory Maker
Part 2: A new Chip in the House


Now, prior to switching to the NVD5890N, I was using a different chip in my IH builds: the LR7843.

This is an excerpt from the LR7843's datasheet. I have circled its power dissipation spec in red:

IR7843-datasheet.png


"Maximum Power Dissipation: 140W"

:cheers:


Why, hello old friend! Long time, no see. :brow:

Since I have previously used these LR7843 chips to build induction heaters, I still had a few on hand.

I put together a different 14mm coil build with a new PCB and a pair of these LR7843 chips.

If you've been following this project for a while, you will be familiar with the oscilloscope graphs and the voltage waveforms I have shown previously.

The NVD5890N ran itself very hard, and the voltage waveform reflected that, with voltage spikes that topped 70V or more when unsuppressed. :uhh: It took a whip and a chair (and the proper TVS diodes) to tame those chips.

The LR7843 seems to take a more relaxed approach to life, probably because I am still 20W below its power dissipation limit. Check out this incredibly ho-hum waveform at the conclusion of an LR7843-powered heating cycle (yellow line show Gate voltage, purple shows Source voltage):

SDS00174.png


Max voltage : 13.2V! There was NO inductive voltage spike. :o

Hubba hubba! :love:

I re-ran this test again. In fact, I re-ran it multiple times over the following 30 minutes, and at different times since, just to be absolutely certain I wasn't misreading the results. I even re-tested a NVG5890N-powered heater in the middle of things, just to be sure the scope was set correctly. The results remained consistent, and have continued to remain consistent since then. The LR7843 performs very well in this role.

:tup:

Also - and this was the true shocker for me - the above results were generated without any sort of TVS diode installed! The only additional circuit protection present is the switch's "debounce" components. :o:o:o:o:o

The PCB remained relatively cool, too, and didn't heat up as it did with the previous chip. The areas of the PCB that were legitimately too hot to touch with the NVG5890N were merely "warm" with the LR7843.

:popcorn:

Since the NVG5890N's heat dissipation tops out at 107W, the path forward for this device is going to involve using a different MOSFET. The LR7843 looks VERY ready to step (back) into that role.


Other observations with these new LR7843 MOSFETs:

When paired w/the 14mm coil, the LR7843 doesn't heat as aggressively as the same coil does with the NVG5890N. The heating time with the new MOSFET takes 1-2 seconds longer, and the penetration of the magnetic flux is slightly less powerful than it was with the NVG5890N. I think these are pretty acceptable tradeoffs for much (!) greater reliability, but I want to report it as it is a difference I have observed.

The LR7843 chip looks like it's able to perform its IH duties with a lot less stress, and (hopefully!) less drama for me and you.

The install is a straightforward MOSFET replacement and doesn't appear to require any add'l circuitry, which will mean a much quicker turnaround time for repairs.

I have some more LR7843 MOSFETs coming today or tomorrow, as I only had a few left on hand. I currently have two test beds going with LR7843 chips in them. I will make a few more once the add'l chips arrive. So far, though, the two test beds I've made have been performing very, very well. More testing is needed of course, but so far, so good.

:popcorn::popcorn::popcorn:


So what does this mean in the bigger picture, and how will this affect you as a Fluxer Heaters customer or owner?

It means good things!! These are comparatively easy parts to swap in, for example - the new MOSFET is the same footprint as the previous MOSFET, so that's a straight-up replacement. The full repair looks like it will entail replacing all four MOSFETs and installing a different debounce capacitor, which is also very straightforward. This is a much better outlook than having to replace the PCB, which is where things were headed as recently as last week.

The time and effort I put into voltage spike suppression has been beneficial to the project, too, even if the new chips don't necessarily need the protection circuitry the NVD5890N's did. I learned a lot by doing all of the research, and that knowledge gives me a lot of confidence that I am interpreting these results correctly. :tup:

Finally, I want to emphasize that these new chips run much, much cooler than the previous chips. It's like night and day. I interpret that to be the real confirmation that a new chip like the LR7843 (or another similarly spec'd chip with a better power dissipation capacity) is the way forward for this device.


Next steps:

1. I am currently confirming that the LR7843 is a stable solution, even as I evaluate a few other chips with similar specs that also look promising. This is underway right now, and I'll test them harder just as soon as more of them arrive, lol. I can already see that the LR7843s are MUCH more stable than the chips they are replacing - they look good. If they continue to hold up, I expect to start using them to make repairs ASAP.

2. Fix and test the heaters customers have sent in for repair. This is the first task as soon as I finish my evaluations.

3. Start cranking out new heaters again, show off some new features I've been developing, and finally move this project forward again! :rockon:

Where things stand at the moment:
  1. I finally understand the original issue, and know with certainty what was killing the NVG5890N MOSFETs.
  2. I know how to resolve the issue's root cause.
  3. I am currently testing a potential solution.
  4. The testing so far is looking very good!

I'll be able to test this solution more aggressively once more LR7843 chips show up, which will be today or tomorrow.

Here's to knowledge, even if you have to fight for it! :science:

That's all for now. Thanks for your support!

Cheers,
:leaf:
 
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Fat Freddy

FUCK CANCER TOO !
It's time for a triple popcorn Fluxer update - an update so wordy I needed to split it into two parts.

:popcorn::popcorn::popcorn:

In the next two posts, the Flux Deluxe's MOSFET saga takes a few extra twists and turns - and my write up is extra wordy, too - but I finally (!) determine a true root cause of my MOSFET issues and reach some conclusions about the path forward. It was a full weekend, so pack yourself a fresh bowl and settle in for a long-ish update. :leaf:

Or? Orrrrrrrrrrrr??????

Maybe you could just wake us all up when your movie is finally ready to be watched?

:zzz::zzz::zzz::zzz::zzz::zzz::zzz:

.
 
Fat Freddy,

Jill NYC

Portable Hoarder
I am amazed by your perseverance. I would have rolled up in a ball about three re-tests ago!
You are genuinely inspiring me to keep pushing as I muddle my way through a period of transition.
Thanks @mr_cfromcali for sharing your journey even though I only understand about 35% of the technical stuff.
 

MothChewMoth

Gamer Extraordinaire
No likes given! Hope I took that the wrong way. I took it as rude. Most of us love the updates.
It came off as that way to me as well, and I couldn't disagree more.

As a pending customer who is really excited about obtaining one (and a tech nerd), reading in detail about his trials and tribulations is really satisfying. To me, it shows how passionate @mr_cfromcali is about this project, and that he cares to include us all in his iterations.

Seriously, thanks for typing out these novels. I just kicked back with my new wenge Milaana stem from Ed and savored every word.
 

Gray Area

Well-Known Member
I too like the updates and I've already got a working unit :nod:

Anyway, just to dumb the conversation down a bit (and the real reason I came to post)...

My FD#14 is still chugging along very nicely, performing consistently since I got it from the first batch. It is a 16mm coil though, which could account for that.

Anyway the little glass disc has come detached from the plastic button cover (which is still in place).
So looking online for a high temp silicone sealant/glue, and there's all sorts of shit. From instant gaskets, to oven door repair stuff etc.
@mr_cfromcali I was wondering what you used or would suggest for a repair?? Don't fancy using something that's going to stink or give off gamma radiation or whatever each time I use it ;)

Pleased to see you make progress, must have been really frustrating.
 

mr_cfromcali

Accessory Maker
Accessory Maker
Anyway the little glass disc has come detached from the plastic button cover (which is still in place)
So looking online for a high temp silicone sealant/glue, and there's all sorts of shit. From instant gaskets, to oven door repair stuff etc.
@mr_cfromcali I was wondering what you used or would suggest for a repair?? Don't fancy using something that's going to stink or give off gamma radiation or whatever each time I use it ;)

Sorry your Pyrex button fell off, @Gray Area. Here are some suggestions:

This stuff is food safe, with decent adhesion: https://www.amazon.com/dp/B01LRLELK...&pd_rd_r=e0a86163-868e-11e9-89d0-b7902472ba38

They also make a 450°F version, but it isn't as strong.

This stuff has superior adhesion, IMO, but is not specifically called out as food safe: https://www.amazon.com/gp/product/B001G47AD4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

BTW, you only need a small amount of the adhesive to reattach the button - the size of a match head, or half a grain of rice. Too much will interfere with the operation of the switch, so use the minimum amount if possible. Also, the new adhesive will stick better if you can remove the residue of the old stuff and rough up the surface a bit, though you will need to remove the chassis (PCB + battery holder) from the case, and will probably need to carefully bend the coil away from the switch to access its surface.

The coil is just copper wire and can be bent and re-bent. it is forgiving and flexible, but for best results try not to bend it any more than necessary.

Hope this helps! Thanks for the kind words, too - very happy to hear your heater is still working so well for you! :tup:
 

mario

Well-Known Member
I love these updates. They keep reinforcing why I hopped on the project as early as I did. My 14mm coil continues to impress and works just fine.

When everything settles and there isn't an enormous amount of work already ahead, I'll probably send mine in for the upgrades and such, but it's working fine now so I don't want to throw mine in there and cause someone else to wait if they don't have to.

Amazing updates as always, thank you for taking such good care of us and keeping us all using your work in a safe responsible way. There are many companies out there that wouldn't care even 10% of how much you do. :)
 

bluegray

Well-Known Member
Thanks for all the info! I'm building my own, and this thread has proved invaluable.

One thing I still don't understand though. Is the whole SS tip heated up by the induction coil, or just the cap?
And if it's the cap, is it the whole cap? Or only the disc that clicks? I've had a few sessions where the AVB is noticeably darker at the tip, so it would seem it's hottest at that end.
 
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