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30watt heater with a 24watt dimmer?

Discussion in 'DIY' started by Ratchett, Jun 9, 2014.

  1. Ratchett

    Ratchett Delta 3D Studios Designer Accessory Maker

    Messages:
    1,269
    Hey all!

    My lathe turning friend geeked out when I showed him my Nano - he wanted to build his own log vape that day! So I've started to look into off-the-shelf parts (COTS) for my heat controller.

    The only thing I've found is a 12v inline PWM dimmer (for LED lights). However it is only 2 amps!

    I'm pretty sure I'm correct, but if I have a 30 or 40 watt ceramic heater, it will not burn out the PWM dimmer, correct?

    Moreover, if the dimmer is rated to 2 amps (24 watts) - how safe is it to run at max setting for extended periods of time? I'm concerned 24 watts is hardly enough power for building a log vape.
     
    215z likes this.
  2. vap999

    vap999 Well-Known Member

    Messages:
    208
    As I recall, various classic log vapes, including Eterras and Purple Days, used 8-12 watt resistors. Log vapes are inherently small and insulated. And because wood has its own operational temperature limits (dries out, crumbles), you can't put more than say 18 watts power within it (e.g., an 8 ohm resistor, at 12 volts, 1.5 amp). The same 8 ohms provides 25 watts at 14 volts. So, you might consider a heating element in this "sweet zone" readily covered by common variable voltage/power supplies. Otherwise, are you planning to use 120 volts for power. or high-power batteries for this log vape?

    Why wood? Why not 3D-printed vaporizers? What is the highest operating temperature plastic used with 3D printing? Can printing be done in PTFE/Teflon, PFA, silicone or nylon? How about printing with ceramics? Is that available yet?
     
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  3. Ratchett

    Ratchett Delta 3D Studios Designer Accessory Maker

    Messages:
    1,269
    Thanks for that, I wasn't aware of the operating wattages used in my competition.

    I will be using a 30watt ceramic heating cartridge. The other logs you've mentioned were using what I call "power resistors" - used to generate heat from power, these logs typically isolate the vapor path from the heating element. Like the nano, I will not be isolating the heating chamber from the vapor path.

    I have just ordered the parts. I'll be using the 2amp 12vdc PWM dimmer controller to control power output to the heater. I'll be using a transformer ("wall wart") to step down from 120vAC to 12vDC, connected to the inline PWM dimmer, which will be connected to the log which I'm building.

    One thing I've learned about 3D printing is that it's better to use the technology when it's advantageous to do it. Doing something for the sake of doing it doesn't always make sense. As the old saying goes - why re-invent the wheel?

    Currently the only material which is considered non-toxic and what I consider "vapor safe" is glazed ceramic. I *might* design a custom base for the log vape and have it 3D printed in ceramic, but otherwise, Wood is a cheaper, sustainable resource which has amazing thermal retention and durability for the price point. I don't see any reason to use anything but wood for the exterior of my vape.

    I believe my 30watt heating cartridge will be sufficient for my needs, and will not tax my dimmer (since it's maximum operating capacity is only 24watts @ 12vdc). Now my question is how reliable are these dimmer switches when running at maximum capacity (full throttle)?

    Also note, while I cannot print with silicone, I do create molds with plastic and cast parts using silicone molding (see the tapered plugs on my etsy store). But I haven't tried casting with any high-temperature silicon just yet. I'm currently using regular and aquarium grade (non-toxic) 100% silicone
     
    215z and OF like this.
  4. KeroZen

    KeroZen Chronic vapaholic

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    Location:
    On Air
    @Ratchett : you might also want to contact @Hippie Dickie and/or read his thead as I think he already sorted a lot of the problems you are likely to encounter (although his design has electronic temperature control, which I'd love to see in a log vape, but you are onto something simpler apparently..)
     
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  5. Ratchett

    Ratchett Delta 3D Studios Designer Accessory Maker

    Messages:
    1,269
    Thanks!

    I'll read through his threads and see what I can learn. Indeed, for now, I'm looking to keep it simple while I play with the design. If things go well, maybe I'll look into some sort of control system to regulate the heat on the next iteration of the device
     
  6. OF

    OF Well-Known Member

    Messages:
    11,898
    Location:
    Left Coast
    I suggest you rethink this some. Traditional log vapes are 'open loop' devices. Their heaters put out a fixed level all the time and heat builds up to the point that losses (to the outside world) exactly equal the heat produced and the temperature stops building. They are adjusted, by trial and error, to stabilize (reach equilibrium) at the magic temperature. The heat is increased or decreased (but left constant) or the insulation and other factors controlling loss modified as needed to make that happen. It the 'thermal mass' is large relative to the heat needed to vape the stem the temperature stays stable though the hit(s).

    And then we have closed loop systems, like say Solo or Ascent. Here a 'too powerful' heater is used which it shut off completely (to let the unit 'coast') or throttled back as needed to keep temperature in check. Such systems heat faster (traditional log vapes can take a long time.....) and provide better control of temperature.

    And finally we have vapes like VG where the owner's skill at predicting how high it will go is part of the deal. Again, power is not uniform through the session. "Set and forget" only happens on the closed loop scheme. What I think you're looking at is a user adjustable version of the open loop scheme?

    The first order of business is, I think, to determine what range of powers you need to have in your design to span from say 350 to 425F? You're planning on using some existing 30 Watt heater? Fine and good. What resistance/voltage is it?

    That information will help decide if your control and load are matched well. You can't go by Watts, really, Ohm's law is in charge (again). Power is the product of voltage and current and resistance is what sets the relationship there.

    IMO a closed loop design (with a temperature sensor in the loop) has serious advantages here and should be considered. At the very least I suggest some 'number crunching' before ordering too much stuff. And in the end you'll have an adjustable temperature (of sorts) unit but once you set that it's no different from any other log vape (slow to heat, slow to respond to changes, not very efficient). Closed loop fixes a lot of that.

    The short answer is 'you'll never get more than a fraction of the 24 Watts (determined by the resistance) from that 30 Watt heater. Them's the rules.

    You know, this conversation is strangely familiar?

    OF
     
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  7. OF

    OF Well-Known Member

    Messages:
    11,898
    Location:
    Left Coast
    After some thought, perhaps 'running some numbers' might help get us on common ground? Just one 'for instance' to hopefully show how this good stuff works?

    Let's use that 30 Watt heater and drive it with a universal laptop supply like this one:
    http://www.amazon.com/Universal-Ada...404741449&sr=8-1&keywords=laptop power supply

    90 Watts, under $15 and has nine steps of output voltage from 15 to 24 Volts.

    So: 30 Watts divided by 24 Volts (maximum out for this supply) gives us 1.25 Amps as a target. 24 Volts divided by that 1.25 Amps means we'll need 19.2 Ohms, let's call it 20?

    At 24 Volts we'll have 24/20 or 1.2 Amps. !.2 Amps times 24 Volts is 28.l8 Watts produced (close enough for jazz?).

    At 15 Volts (lowest stitch output) you have 15 this time divided by the same 20 Ohms, for .75 Amps. 15 Volts times that .75 Amps gives us 11.3 Watts produced, a very wide and hopefully useful range to experiment with?

    So such a supply and a 20 Ohm heater will give you 11 to 29 Watts over 9 steps to play with.

    Just thinking out loud, but that's how electricity works in this case.

    OF
     
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  8. Ratchett

    Ratchett Delta 3D Studios Designer Accessory Maker

    Messages:
    1,269
    Heh, thanks for that. I'm really trying to stick with an open loop by your definitions and playing with the power supply to find the perfect zone, of course i'll be running thermal load tests with a thermistor to monitor temperature during testing (forced air tests, never direct draw, of course!)

    I'll probably use a VVPS to control the voltage to the heater. Right now I've opted to hold off for a bit and try to source a better heater core - I wasn't happy with my mounting options for the 30watt heater I already had.

    Lots of info to digest, and lots of logs to build. Fortunately my friend has a lot of dried silver maple wood to turn the prototypes. I'll keep you guys posted of what I build/find
     
    OF likes this.

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