901 atomizer disassembly

[mogur]

Okay, I should shut up now, but I can't stand it. With feedback from the temp sensor, a manual switch could preheat the coil until it reaches optimum temp, at which point a green led signals the user to draw, or an air valve opens up, and PWM (pulse width modulation) by the PIC would keep the coil at optimum temp, extinguish the green led for under temp, or light a red led for over temp. (For simplicity, probably a single, bicolor led.) It also might be possible to detect an oversaturated coil by sensing a low coil temperature after a normally sufficient time period has elasped, and/or the coil cannot sustain optimum temperature with full application of current, and therefore signal the user about the situation, so that sucking on undervaporized liquid could be avoided, as well as avoiding the burnt taste and fried coil elements for an overly dry atomizer. Ok, my sentences are running on, so I'll run off now.

 

[mogur]

Alas, the cold light of morning. Thermistors can't handle the temps, and I have no experience with thermocouples. If it was easy and cheap, the commercial products would already be using them. Based on temperature charts for the glowing color of nichrome, I figure that the coil heats to somewhere between 400 and 1000 degrees C, bumping the thermocouple type up from the common J and K types up to the more expensive R and S types. A brief glance at thermocouple circuits appears daunting with respect to the simplicity required in this situation.

If anyone has high temp measuring experience that knows of a simple and inexpensive circuit that might work here, I would greatly appreciate any input. Meanwhile, I will continue my quest, albeit at a somewhat reduced level of enthusiasm. Since accuracy is not required, I will look into using the amperage/voltage ratio to determine resistance change of the heating element itself. A suitable element material with sufficient TCR might therefore give a rough, but useable measure of temperature.

 

[kinabaloo]

Nice image, thanks for the details.

Will definately do an atomic analysis on this stuff later next week,
the magnetic properties fooled me into thinking it was a steel material.

Will be interested if any tin in this alloy; wrt tin found in deposit.

 

[kinabaloo]

Alas, the cold light of morning. Thermistors can't handle the temps, and I have no experience with thermocouples. If it was easy and cheap, the commercial products would already be using them. Based on temperature charts for the glowing color of nichrome, I figure that the coil heats to somewhere between 400 and 1000 degrees C, bumping the thermocouple type up from the common J and K types up to the more expensive R and S types. A brief glance at thermocouple circuits appears daunting with respect to the simplicity required in this situation.

If anyone has high temp measuring experience that knows of a simple and inexpensive circuit that might work here, I would greatly appreciate any input. Meanwhile, I will continue my quest, albeit at a somewhat reduced level of enthusiasm. Since accuracy is not required, I will look into using the amperage/voltage ratio to determine resistance change of the heating element itself. A suitable element material with sufficient TCR might therefore give a rough, but useable measure of temperature.

The resistance change is small but could be detected within the battery with a circuit based on a cmparator for example; no thermocouple required. But would need an override to perform burn-off.

A temperature limit of around 200C for normal operation. Might not sufficient to vaporise all the VG though, which might slowly build up on the coil. Hard to say without trying it. This might allow VG to be used at a lowish % (say 20%) to reduce VG decomposition significantly. And for this reason it is well worth investigating. Otherwise the advantage is prolonging atty life a little bit and reduce degradation of the deposit though that may entail faster buildup of deposit volume and a shorter atty life.

 

[kinabaloo]

What you are looking at is a simple steel heating element with ceramic insulator. The mesh material appears to be a copper nickel alloy, hence it breaking after a short time. The solution for this problem would be a 80/20 nickel-chromium alloy and I'd bet it would last for at least a year of daily use.

Keep in mind, no disrespect to suppliers, that failing units are their cash cow. If you buy a $10 atomizer and it lasts a year or more, there would be no more money in it for them.

No. The limiting factor is residue from the juice. No change is atty design that involves heating will change this.

 

[kinabaloo]

Yes thanks to mogur, Tom09 and Exogenesis we are learning a lot.

 

[mogur]

The resistance change is small but could be detected within the battery with a circuit based on a cmparator for example; no thermocouple required. But would need an override to perform burn-off.

A temperature limit of around 200C for normal operation. Might not sufficient to vaporise all the VG though, which might slowly build up on the coil. Hard to say without trying it. This might allow VG to be used at a lowish % (say 20%) to reduce VG decomposition significantly. And for this reason it is well worth investigating. Otherwise the advantage is prolonging atty life a little bit and reduce degradation of the deposit though that may entail faster buildup of deposit volume and a shorter atty life.

I've posted this chart somewhere else on this site, but it is pertinent here, so if the mods forgive me...

You'll notice that nichrome doesn't even glow much until about 650°C. You can test this yourself by holding a syringe needle with juice in it at the bottom of a flame from a bic lighter, which should be about 1000°C. (The top of the flame is around 1400°C.) Vapor will splutter out the end of the needle, but it will become apparent that 200 or 300°C would be insufficient to vaporize the majority of the fluid, in the short time period of inhalation.

The other thing this chart demonstrates is that for a given wire gauge of nichrome, temperature is solely dependent on the current flow through the wire. Voltage and resistance can vary all they want to (higher voltage/longer wire length, or lower voltage/shorter wire length), but the amperage uniquely determines temperature. For 38ga nichrome, this is approximately .6 to 1 amps, neatly fitting the experience we've had in measuring coil amperage. A minor caveat is that the chart applies to straight wire, coiled wire can decrease the current up to half of the values in the chart.

This fact can be used in two ways. First, a current shunt resistor input to the PIC A/D converter could represent temperature of the coil in a reliable way, and measured from within the battery unit as you just pointed out in your post. The second utilization would be for manually switched mods, where a simple constant current source circuit could be added to the switch circuit in place of micro control. This avoids over or under shoot of the coil temperature, and gains independence from the variable battery voltage.

 

[kinabaloo]

mogur - the problem with just using a current regulator is that it will slow the heat up consideably.

Atty coils run <200C in nomal operation when have juice on them (do not glow when wet).

 

[kinabaloo]

Here's an example circuit that should work to switch off power to atty coil when it gets hot. A voltage regulator would be needed.

The coil will heat up fast to the operating temperature but not higher; power is automatically disconnected and reapplied to maintain the optimum temperature. The 10nF capacitor and the heat capacity of the coil control the switching speed (the capacitor introduces a little hysteresis).

The values shown should about right. Adjust trimming potentiometer till the atty runs at optimum temperature.

Initially the coil will heat up when button pressed. The voltage across it is compared with the reference and soon as the voltage is greater, the mosefet is switched off (comparator output will go close to zero). If the atty cools and the resistance decreases, the voltage will decrease and the power applied again. In a 5 second power on this may occur 5-10 times, all autmatically controlled by this circuit.

One of the 10K resistors may need to be omitted (shorted) / replaced by a very low value such as 100ohm.

Edit: Actually, as the comparator is relative, the voltage drop of the battery under load should affect the circuit (much) so the voltage regulator can probably be omitted.

 

[mogur]

Most excellent circuit. The TCR of nichrome is very close to zero (.000085/C), and at 400C is equal to 1.03 (3%). That means the resistance change from 4 ohms cold to 400C is only .12 ohms. If I understand your circuit correctly, the comparator switches upon resistance change in the coil, and that might be perfect if your circuit is sensitive enough to be stable at that magnitude of resistance change.

As for the constant current method, I fail to see how it would slow up the heating of the coil. At turn on, the zero current condition would cause the circuit to apply full voltage to the coil. With a limited current circuit protecting the coil, applied voltage could be considerably increased, maybe as high as 12v, and would heat the coil much faster than 4.5v could. After optimum temperature (and therefore current) was reached, it would reduce the voltage to whatever was required to maintain the proper current (and therefore temperature). I don't see how that process would hinder the speed of heating or whether the coil was saturated or dry.

Another possible advantage to a current limited circuit is that the coil wire diameter and/or length could be increased to enable either reduced heat up time or increased surface area of the coil. This would increase amperage, and of course only be viable for mods with larger power sources. The commercial units are probably tweaked pretty close to the optimum for the battery size allowed by their design.

A constant current circuit is almost identical to your design, except the comparator is a normal op amp and a current determining resistor is placed on the source side of the mosfet.

Oh yeah, there's tons of info on the net about nickel foam, now that Tom has steered us towards that material. It's used in a lot of different apps, but I think mainly as the positive electrode in NiMH & NiCd batteries.

 

[kinabaloo]

mogur - Very interesting info about the Nickel alloy foam - great research

The current to reach 200C will be a lot less than to reach 400C, so if the current is set to only enough to reach 200C it will take longer to reach it - because it takes time for the heat to build up due to the heat capacity of the wire. Ok, it's still pretty quick, but might be noticeable, say 1 second.

Yes, a constant current circuit could be made with an op amp (comparator) and mosfet that looks similar to my circuit. But that would be using the op amp in an analog way. My circuit is intially just on, then behaves like PCM once the oerational temperature is reached; the op-amp is hard-on or hard-off.

 

[mogur]

Yes, and that is the beauty of your circuit. I wasn't putting it down. And if it can discriminate the resistance change reliably, the circuit is bang on.

But to defend constant current supplies, I have to say that they would not restrict current in any way until the set temperature is reached. Why would it slow anything down? Both circuits would throw full voltage at the element until it reaches equilibrium. Why would it take longer due to the heat capacity of the heater element? Both circuits are obviously limited by that factor. Your circuit throws full battery voltage at it until it reaches temperature, then it cycles on and off to keep the temperature up. Mine would throw full voltage at it until it reaches temperature, also, then reduces voltage to keep the temperature up. The only difference is that your circuit monitors the small changes in resistance of the heater wire as it heats up. Mine only depends on a current determining resistor, located inside the battery compartment. Both need to be calibrated once.

 

[kinabaloo]

Yes, and that is the beauty of your circuit. I wasn't putting it down. And if it can discriminate the resistance change reliably, the circuit is bang on.

But to defend constant current supplies, I have to say that they would not restrict current in any way until the set temperature is reached. Why would it slow anything down? Both circuits would throw full voltage at the element until it reaches equilibrium. Why would it take longer due to the heat capacity of the heater element? Both circuits are obviously limited by that factor. Your circuit throws full battery voltage at it until it reaches temperature, then it cycles on and off to keep the temperature up. Mine would throw full voltage at it until it reaches temperature, also, then reduces voltage to keep the temperature up. The only difference is that your circuit monitors the small changes in resistance of the heater wire as it heats up. Mine only depends on a current determining resistor, located inside the battery compartment. Both need to be calibrated once.

The current you choose will be lower than normal so the coil will take longer to heat up. Or it will switch from full current to lower current somehow?

 

[mogur]

The current you choose will be lower than normal so the coil will take longer to heat up. Or it will switch from full current to lower current somehow?

Okay, you win this one, but I'll get you next time, grin.

 

[kinabaloo]

Okay, you win this one, but I'll get you next time, grin.

A constant voltage supply circuit for the atty is a good idea for simply maintaining atomiser performance for a certain period. But requires a higher voltage battery pack to start with so probably not worthwhile when traded with increased size in devices where smallness is desirable.



Luckily my temp. control circuit also behaves in such a way as to provide the feature of counteracting diminishing battery power. And I might not have explicitly realised that without this discussion

 

[Tom09]

Will be interested if any tin in this alloy; wrt tin found in deposit.

Oh yes, the source of tin is a very important point! If the mesh material would become confirmed to be Ni, it could more likely be excluded to provide a possible source of tin. State of the art in nickel foam production appears to be the chemical vapor deposition route (lower tech facilities might still be in production, though). This makes use of a chemical transport process that is also known from nickel refinery (Mond process). Therefore, the mesh can be expected to be of very high purity (INCO Foam commercial brand claims 99.9% Ni, for instance).
I took some time to read up the various posts on solder corrosion. I couldn’t find if there has been a definitive answer on the actual solder composition. Maybe Exogenesis could perhaps remind to dedicate an additional analyses on a solder blob to address the discomforting problem of metal mobilization. Not that I would really worry about tin (not hazardous), but reserve concerns about what unknowns do occur in the tin-bearing alloy that could become dissolved with it.

 

[kinabaloo]

Oh yes, the source of tin is a very important point! If the mesh material would become confirmed to be Ni, it could more likely be excluded to provide a possible source of tin. State of the art in nickel foam production appears to be the chemical vapor deposition route (lower tech facilities might still be in production, though). This makes use of a chemical transport process that is also known from nickel refinery (Mond process). Therefore, the mesh can be expected to be of very high purity (INCO Foam commercial brand claims 99.9% Ni, for instance).
I took some time to read up the various posts on solder corrosion. I couldn’t find if there has been a definitive answer on the actual solder composition. Maybe Exogenesis could perhaps remind to dedicate an additional analyses on a solder blob to address the discomforting problem of metal mobilization. Not that I would really worry about tin (not hazardous), but reserve concerns about what unknowns do occur in the tin-bearing alloy that could become dissolved with it.

Tin has no role in our biochemistry (and metal form would probably be unmetabolizable anyway; it might work as an oxidising catalyst. And as we are talking about possible particles in nano size, some of whch might become inhaled into the lung where they might stay for a considerable time, it is of some concern I think. Tin is a common contact allergen.

The juice is greater contact with the metal foam. But at the point of contact the solder joint alloy will get pretty hot; either could be the source (it is unlikely to have originated in the juice). Common 'lead-free' solder: 96% Tin 4% Silver.

 

[exogenesis]

Didn't see your last post Tom09

I'll add the solder blobs to the analysis list, also will compare
some silver solder, ordinary solder & lead-free solder.

 

[kinabaloo]

Didn't see your last post Tom09

I'll add the solder blobs to the analysis list, also will compare
some silver solder, ordinary solder & lead-free solder.

That will tell us which solder is used; my money is on lead-free r.t. silver.

The main interest ten is whether the metal foam contains any tin. Some say the mayerial is steel but I think it will be nickel, possibly alloyed with tin.

Of course, both might be the source.

Some time ago smeone mentioned the phenomena of spontaneous growths of fine threads from metals and it might be these, having broken free, that is the mechabism for the tin getting into the deposit. An alternative I think is some electrolysis (or at least electochemical action). Or simply the juice chemically acting on the allot of either the solder of foam (in the case of the solder, possibly via the flux).

Look forward to the results Exo ...

 

[exogenesis]

Fairly sure the solder will have no lead in it, certainly tin tho.

Also bear in mind that the XPS analysis of carbon-gunk that showed high tin levels
was 'surface only' analysis.
Meaning that it's possible the tin is only at the surface, rather than in the bulk.

I'd guess that it is probably uniform-ish through the mass though,
at some point I'll etch into a carbon mass to see the formulation changes with depth.

And for perspective : tin was 'only' 2.3% of the total gunk mass of about 20 mg,
(the total mass was only about 1000th of the mass of e-liquid 'vaped')

So that equals 0.5mg tin, & each of the 2 solder blobs must be around 4 mg,
so roughly 10% of the solder blob's tin mass ends up in a really gunked coil.
(20+ ml vaped, without cleaning).

-actually now I work it out, it still sounds quite a high proportion of the tin available.

But I'm thinking that you lose more of the solder than that to burn-clean cycles.
(judging from close examination of a multiply-heated test-coil)