PWM temp.-control for atty heater coil : pics and vid

[kinabaloo]

Am currently investigating temperature control of the atty heater coil, to save battery power, avoid over heating/burning.

One way is to monitor the temperature. And one way to do that is my monitoring the resistance of the nichrome element (no change needed in the atomiser).

Another way is to output a 'profile' of current, approximating how real-time temp control would behave - initial high current then reduced to just enough to keep the coil vaping.

Either way, the choice for current supply is between variable current and pulsed current (pulse width modulation) - varying the on/off cycle times (proportion of on-time); this can save power wasted by the analog version.

Heat capacity of the coil will smooth out the temperature. Though this heating and coolong happens rather quickly (less than half a second). So a frequency of at least 20Hz is required; could be much higher, say 200Hz.

In the video I have slowed the circuit right down (~1Hz) so that the effect on the coil can be seen; I have the coil out of the atty and plugged into my breadboard.

Video: http://www.kinabaloo.com/pwm.AVI

Notice the slight lag in time between power on (as seen by LED) and coil reaching red-hot. When the coil is not dry the juice keeps the temp down. This can be seen when I apply a drop of VG.

I worked out the current required to get a nice vape without the coil reaching red-hot temp.s when dry but this takes over 5 seconds to heatup the coil when it is not dry. Hence the need for temperature control.

 

[jaybird]

great idea, how small could this be made? have you tested this in a mod?

 

[kinabaloo]

great idea, how small could this be made? have you tested this in a mod?

Early days, but this will not take long.

It will translate to a mod without problems

 

[kinabaloo]

Was taking some more pics of the heater coil in my experimental setup when I suddenly noticed something odd - the coil had become clean!

Have detailed this, with pics, in this thread: http://www.e-cigarette-forum.com/fo...ean-method-pics-new-discovery.html#post373044

 

[kinabaloo]

Following the previous vid, this next one shows the coil temp being adjusted by turning a small potentiometer that changes the pulse width ('duty cycle'). By hand in this case, but it will be controlled by temp. monitoring or 'timed profile approximation' later.

This time you see the LED and coil brightness vary but do not see the individual current pulses this time as the frequency has been stepped up to about 200Hz.

The vid is not perfect because those little pots don't fit in the breadboard properly so I am trying to hold it down/in while adjusting it and also holding the camera and monitoring the picture!

http://www.kinabaloo.com/pwm2.AVI

 

[mogur]

Way to go. Now you're making me push ahead on the microchip design mod. I'm playing with the coil temps now, but very nice job you did on making the coils. Using fiberglass wick?

 

[kinabaloo]

Way to go. Now you're making me push ahead on the microchip design mod. I'm playing with the coil temps now, but very nice job you did on making the coils. Using fiberglass wick?

Didn't make them mogur - it's just a plain old 901, extracted and cleaned by heating up.

How is your wafer fabrication going? What are you going to put on it?

I have an idea for an atty mod that you might be interested in - that does not rely on air intake pulling droplets from the mesh. But maybe this is for later, as making attys is not an easy at home task (for more than one).

 

[kinabaloo]

ps: full current from a 3.7 li-ion to a 901 coil reaches yellow hot. The temp just below faint glowing that does vape, though slowly, is 2/3 of the full current.

The simplest possible method for temp control occured to me today - place a light sensitive device near coil
Better still an IR sensitive one.

But I am going to be monitoring resistance changes in the nichrome.

Full current initially then reduced as resistance increases (4% from room temp to full heat).

ps: that big air-core coil in one of the photos has nothing to do with vaping; it's for an RF project.
Not my secret new atty project. Definetely not!

 

[mogur]

ps: full current from a 3.7 li-ion to a 901 coil reaches yellow hot. The temp just below faint glowing that does vape, though slowly, is 2/3 of the full current.

The simplest possible method for temp control occured to me today - place a light sensitive device near coil
Better still an IR sensitive one.

But I am going to be monitoring resistance changes in the nichrome.

Full current initially then reduced as resistance increases (4% from room temp to full heat).

ps: that big air-core coil in one of the photos has nothing to do with vaping; it's for an RF project.
Not my secret new atty project. Definetely not!

Grin, the light sensistive trick is one I've been mulling over in my mind, too. They make some pretty small LDOs, and they're the easiest interface I've ever had to deal with. My last project was a humidity, temp, light, and CO2 controller for greenhouses and grow rooms.

As for the resistance monitor, you might want to look at a resistance wire thread I'm planning to post tomorrow. It covers most heater alloys and elemental metals. Nichrome has such a tiny TCR, there may be a more suitable wire for feedback.

Working on a pcb for modders, as well as trying to get the cigar back up and running. So, guess I'll get back to it.

 

[kinabaloo]

Grin, the light sensistive trick is one I've been mulling over in my mind, too. They make some pretty small LDOs, and they're the easiest interface I've ever had to deal with. My last project was a humidity, temp, light, and CO2 controller for greenhouses and grow rooms.

As for the resistance monitor, you might want to look at a resistance wire thread I'm planning to post tomorrow. It covers most heater alloys and elemental metals. Nichrome has such a tiny TCR, there may be a more suitable wire for feedback.

Working on a pcb for modders, as well as trying to get the cigar back up and running. So, guess I'll get back to it.

I will be using the heater coil itself as the monitor - sensing its change of resistance.

I have been thinking about providing touch switch modules, possibly combined with ready adjusted 901 sockets and perhaps also LED/resistor combos - just add battery and on/off switch; just has power-in wires, an LED on some wires and the ready-to-go atty connector. But not sure if want to be a supplier as such.

A little later, a temp. controlled module too; perhaps part of the total module.

 

[kinabaloo]

A funny thing have thought about on and off : a wind turbine driven e-cig. No battery required - so carbon neutral - or whatever

The wind in question being the draw/puff. Small internal generator. Might not be an easy draw though ... LOL

Hmmmm - maybe better I stick to using a motor powered by the battery to assist the draw

People may laugh ... but I am going to make it ...

... one day ...

maintaining air flow is one way to protect against over-heating, after all.


ps: the only problem with the light transducer is that it requires a specialized atty; this is the beauty of the atty's nichrome coil AS the sensor. Will work with any atty. Small TCS no problem - electronics can work with a percent or two without difficulty. And I have planned a means of self-calibration so it doesn't matter if the atty ages or is changed. Or battery fades, etc.

 

[ichaya]

A funny thing have thought about on and off : a wind turbine driven e-cig. No battery required - so carbon neutral - or whatever

The wind in question being the draw/puff. Small internal generator. Might not be an easy draw though ... LOL

Hmmmm - maybe better I stick to using a motor powered by the battery to assist the draw

People may laugh ... but I am going to make it ...

... one day ...

maintaining air flow is one way to protect against over-heating, after all.


ps: the only problem with the light transducer is that it requires a specialized atty; this is the beauty of the atty's nichrome coil AS the sensor. Will work with any atty. Small TCS no problem - electronics can work with a percent or two without difficulty. And I have planned a means of self-calibration so it doesn't matter if the atty ages or is changed. Or battery fades, etc.

OK the fact that you guys are very knowledgable is great.

But your conversations are so far above my knowlege of electronics that I can't even tell if you are joking.

And that is a bit frightening.

I'm still trying to figure out that comparative circuit!!!