Solar filament drier

How to keep filament dry while being too poor to afford electricity.

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The lion kingdom considered many ideas for drying filament involving peltier coolers which could be repurposed for atmospheric water generation.  The simplest solution has converged on a simple solar heated container.

The general idea is a transparent container just big enough to enclose the filament.  There would be 2 vents with air tight valves.  There would be a fan on the inside to circulate air & a fan outside a vent to force outside air in.  There would be a dewpoint sensor inside & outside.  The electronicals would be manes powered, but all the heat would come from the sun.

The inside fan would always be on.  The outside fan would turn on & the 2 vents would open when the outside dewpoint was lower than the inside dewpoint.  

This would entail ordering 3 humidity & temperature sensors.  1 extra would go to a readout on the lion kingdom's weather wall, in order to find an ideal time to use the filament.  

The mane problem is air tight valves big enough for a fan.  They must be air tight when the outside dewpoint is higher than the inside dewpoint.  The lion kingdom is keen on using its 2 Nidec blowers from 22 years ago.  They have small outlets which would reduce the valve size.  

The easiest solution might be an aquarium air pump

& aquarium check valves.

The valves could be closed by gravity when the pump is off, but they may only be water tight instead of air tight.

Valves closed by gravity & opened by air pressure would still be ideal.  Lions haven't had any luck with flaps of material.

Adafruit has an air pump.

& air valve.

Temperature & humidity sensor:

Airtight container:

This was the best match for a 1kg 60x200x200mm roll.  It stretches slightly to make it fit.

The tubing is the same 3mm ID silicon tube that the lion kingdom got for its humidifier air conditioner.  There's still the problem of making an airtight seal between the tubes & the filament container.  It might involve printing farsteners which can be stuffed with a lot of goo.

Of course, the cost has to be weighed against buying a new roll of filament every time it gets wet.

  • 3D printed butterfly valve

    lion mclionhead3 days ago 0 comments

    A solid week of banging on CAD models yielded a butterfly valve.

    This was the 1st to directly couple a PLA shaft to a servo shaft.  To start with, it uses friction.  It could resort to CA glue.  To achieve a static pressure on the valve, it relies on the servo supports applying a static spring pressure on the torque tube.  The servo powers off after 5 seconds to avoid wearing out the motor.  There's no sensor for valve position, so it could get stuck in 1 position.  

    The latest idea was a container with just 1 big valve.  The inside air should get hot during the day.  When the valve opens, the hot air leaves & the cold air enters.  At night when the container is colder than ambient, no air is replaced.  The valve is not as air tight as the former tubes.  

    The board got converted back to 5V, a MOSFET got taken out, a PWM driver got put in. 

  • Changing pumps

    lion mclionhead5 days ago 0 comments

    The old pump pulled down the humidity to the 20's.  The indoor swamp cooler didn't affect the humidity near the window.

    The decision was made to replace the pump, after a very noisy final TPU drying.  Lions have lived in a very noisy environment for 25 years, with confusers, atomizers & fans, but the inkjet printer pump was a uniquely difficult noise.

    After taking out the fuse connection & the stall LED, it became quite clear that the 3/4" ID tube was never going to have an airtight connection on top & it was never going to navigate the tight corners.  The angle connectors might have hope with narrower tube, but narrower tube requires a noisier pump.  

    The easiest fix with this design is going back to 1/4" tubing, using store bought barbed farsteners, & just enclosing the inkjet pump in something soundproof.  The inkjet pump turns out to fit 1/4" tubing better than 3mm tubing.

    Another idea is an air tight barn door on the side with no tubing or pump.  Position the circulation fan near the barn door.  When the inside dew point gets high enough, open the barn door & rely on the circulation fan to replace all the air.

  • New pump

    lion mclionhead05/12/2022 at 19:44 0 comments

    The blower they said could never be mounted on anything 25 years ago finally was fixed to a tube.  Through 2 ft of 3/4" ID tube, the airflow was greatly reduced but still useful.  It needs 12V to move any air through.  The tube could be doubled up.

    Only a tiny flake of the original 90's Gamma 28 label remanes.  

    Another key development besides mounting the blower was printing an elbow.  The only way to do it is to print an octagon sideways.  Each end of the octagon needs a separately printed adapter to attach to whatever it's attached to.  Holes were melted in the tube for farsteners.  It's tight enough to not need nuts.

    By now, it was clear that the new blower would make the dehydrator much bulkier & heavier.  A new surface mount board could fit directly on the blower & greatly shrink the window usage.  The wiring would have to go through a new orifice near the pump.  The pump doesn't have to be air tight.  Then there's the problem of balancing the container on the window.  

    The simpler solution is to keep the existing wiring in a container orifice, but the size requirement ended up making the lion kingdom go back to the inkjet pump.  To change to the blower pump would require moving the electronicals to a surface mount board on the blower.  Then, it would take less space than the inkjet pump.  The space constraints of having a job make it hard to use all of the lion kingdom's through hole parts.

  • New TPU roll

    lion mclionhead05/10/2022 at 17:51 0 comments

    A full 1kg roll arrived wet from the factory, so it went into the dehydrator for 7 days.

    Most of those days were cloudy, but temperatures & humidity were higher than winter.  The dried filament still did a lot better on a part than the new filament.  It wasn't perfect, but it was good enough to not bother enhancing the drier.  

    Lions have found filament which isn't on a roll doesn't dry at all.  It seems to absorb water from being handled by lion paws.  

    The dehydrator has problems.  Blocking the inlet doesn't slow the pump down, so it's not very air tight anymore.  The pump is real noisy, now runs all day continuously, & turns on at night when the roll is fresh.  Waking up to the pump is brutal.  The pump has a duty cycle to limit the noise, but lions don't care if it wears out.  The best it can do is reach a constant equilibrium where the humidity is always lower on the inside than the outside & the filament is heated for part of the day.  

    There could be leaks where the tubes enter the container or the container itself could be keeling over.  That was the only container a lion could afford.  

    The plan is to replace the pump with a vintage Nidec blower.  Use the largest clear tube which is flexible.  Print right angle connectors & a connector to the blower.  Route all the wires through the air tubes.  The 1st step would be measuring how much air the blower can force through a tube of a certain diameter.

  • Fixing the air flow

    lion mclionhead03/09/2022 at 05:54 0 comments

    It shouldn't make any difference, but the lion kingdom finally realized cold air was being introduced from the top & sucked out of the bottom.  It was like pouring water into a pool while trying to suck air from the deep end.  The fan was supposed to mix the air, but maybe it wasn't effective enough.  Filament must have been mixing more air than the fan, thus making it partially work.  The original design had cold air being pumped into the bottom & drained from the top, but this was reversed when the lid popped off.

    The fixed routing has the air intake on the bottom, looping over the top, & then ingesting air from below the container next to the sensor.  This should keep cold air from exiting at night & warm air from exiting during the day.  The pump now sucks from the top with the outlet above the inlet. The inside sensor should rapidly detect a dewpoint rise when the pump runs.  

    Ideally, both air holes would be on top with the outlet & inlet below the container.  That wouldn't depend on a seal in the pump.

    It should be noted the adafruit pump is a surplus inkjet cleaning pump.  Dave briefly revealed one before throwing it away since he couldn't figure out what it was for.

    Whether or not the fan circulates the air, it's required to make the sensor accurate.  There's no other place for the sensor except in direct sunlight.

    Another test with no filament & fixed plumbing wasn't very encouraging.  The pump didn't stay on anymore, but we don't see interior dewpoint deviating from exterior dewpoint.  The journey began with water presumably coming out of the container itself, getting pumped out, but the nighttime dewpoint didn't fall any more after the pumping.  It's assumed water moves out of the air & condenses on the container at night.  

    The 2nd day, a dry cold front moved through, plummeting exterior dewpoint.  A lot of water got pumped out & the dewpoint dropped on the 2nd night.  On the 3rd & 4th days, interior dewpoint rose.  Obviously, absorption by the filament is a key reason why nighttime dewpoint falls.

    The sensor is colder than the inside air at night because the fan turns off to conserve electricity.  That might make the dewpoint appear lower.  It breaks away as soon as the fan turns off.

    It's believed contraction of the air at night causes outside air to get ingested.  Less air gets ingested when filament is in the container.  That would make valves a good idea, but valves would make the lid pop off during the day.  The valve would have to open when inside temperature was higher than outside temperature.

    It already gains a lot of isolation by having an air tight pump & an intake tube long enough to absorb a lot of expansion.  It's never going to be a very efficient process if it is to be affordable.

  • Empty container week 1

    lion mclionhead03/06/2022 at 06:32 0 comments

    So moved it to floating point, reduced the logging from 5 seconds to 30 seconds & tested with no filament.

    Nothing should have been adding water to the air, yet now the pump ran all day, every day except when it was cloudy.  The most obvious difference is the nighttime dewpoint stayed a lot higher.  So the filament was absorbing water at night.  It's a bit confounding why the daytime dewpoint kept going up if there was no filament releasing water.  The most likely reason is leakage & improved floating point accuracy causing the pump to run more.  

    Water must leak in at night, then get pumped out during the day.  With filament, the water leaks in at night, gets absorbed by the filament, then gets released during the day with just enough native water from the filament to eventually dry it out.  The excess water given off by the filament may be enough to overcome the inefficiencies.  Without filament, we just see the inefficiencies.  Would have hoped for more efficient water extraction, so these sensors & air ducts could be applied to atmospheric water generation.

  • PETG week 3

    lion mclionhead02/15/2022 at 23:49 0 comments

    A few more weeks didn't show any more drying of PETG, even with a dry cold front pushing up pumping activity.  Suspect the grey color doesn't absorb as much heat as TPU & it's slower to absorb or release water. The equilibrium might be a point where the pump still turns on every day rather than a point where the pump never turns on.  There could be a newly formed leak.

    All the filament has been dried during the driest winter in Calif* history.  In past winters, there would be many cloudy days or even rainy days where the pump wouldn't turn on & leakage might cause the filament to reabsorb water.  How well it works in a normal winter or whether it gets dry enough in normal humidity is still unknown.  1 scenario has the dehydrator permanently storing filament during normal weather.  Another scenario has the filament transferred to ziploc bags after the 1st dry cold front.

    There was an attempt to make a desiccant pack out of some calcium chloride to save money.  The leading idea was a paper towel & some scotch.  It's definitely not as durable as the $7 Bezos item.

    TBH, the lion kingdom has serious doubts if those $7 packs really work.  How does the fabric really change color?  Does the fabric color accurately reflect the water content?  Does the air really get through the fabric?  How durable are they really?  They certainly have the packaging & marketing to appear intended for a certain use.  If calcium chloride works, the drytote should be dunked in some water to test it.

  • Drying PETG

    lion mclionhead02/07/2022 at 23:38 0 comments

    The lion kingdom suspects the AHT20's with fixed point magnus equations aren't very accurate.  The multi millionaire neighbors with back yards show 8C dewpoint & 21C temperature.  Dewpoint might still depend on elevation & lions did experience a lot more rust on the bottom floor.

    Serial port glitches continue to start when outside temperature is 30C.  It's going to need an external crystal.  Together with the desire for floating point, it points to a new board.

    A few days drying PETG weren't as decisive as TPU.  Maybe the pump ran less over time because less water was being taken out over time, but the outside dewpoint was also getting higher.  PETG would absorb less heat because it's not black.  The dry weather during the TPU didn't happen with PETG.

  • Long term storage

    lion mclionhead02/06/2022 at 00:25 0 comments

    There are 2.5 gallon ziplocs suitable for filament.  Not sure what else they're suitable for.  If only China shipped filament in reusable bags instead of their disposable bags.  Just stuff the dessicant in the hole.  As soon as the next roll was put in the dehydrator, the pump went back on & the dew point went up.  

    The dry filament once again printed without voids & it didn't cost a fortune in heating.

    It was no longer straight.

    Enough water leaked in by day 8 to briefly turn on the pump, but as soon as the container was opened, it went back on full time.  It was good evidence of the advantage of actively controlled ventilation over a passive system.  There should be a control study without filament to see how much measurement error is turning on the pump.

    The only permanent indication that the filament is dry is the pump not turning on for a whole day.  It should be integrated in the apartment router to show a status page.  

  • Day 7

    lion mclionhead02/05/2022 at 01:18 0 comments

    On the 7th day, not enough water came out of the filament to turn on the pump & the nighttime dewpoint matched the night before.  All the water was taken out of the filament that this method could take out & very little new water seemed to leak in.

    Of course, the on point was within the error bounds, but it was close enough to consider the reaction done.   If the inside dew point rounded high, there would not have been enough difference in dew point to cause any significant removal of water. It was decided not to upgrade microcontrollers to get a more precise dew point.  

    Also the outside dewpoint went back to normal.  It might have finished sooner if an offshore flow didn't create 2 exceptionally dry days.  The normal humidity will probably leak in & cause the pump to turn back on over time.

    The next step is to wait for peak heating to draw out all the water again & transfer the PLA to another enclosure with desiccant.  The dehydrator's next task is drying PETG.  Because of the damaging effects of UV, there's no other choice but to store dry filament in bulky containers containing desiccant.  The lion kingdom couldn't find any airtight bags smaller than giant tupperware.  The dehydrator needs to be moved away from the window, sealed by valves, & filled with desiccant to store filament.

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crun wrote 12 hours ago point

A very simple passive valve is a tube of polythene (i.e a plastic bag) or nylon fabric, with it's axis horizontal, and a vertical flange plane at one end. When you turn the fan on, it straightens out and air flows. When you turn the fan off it folds over and closes.

This works better arranged as a long flat tube than a round one. Fortuitously this is kind of how ziplok plastic bags already come.

These can be better than a flap valve, where it is quite hard to get a very light flap to seal when closed.

Quite a good way to collect solar heat is to suck your inlet air through a black fabric (that the sun heats). You don't need a cover glass, because the thin layer of heated air on the outside is being sucked in, instead of being lost when you have a solid black surface. It could also be a dust filter.

I would think that only very low flow rate would be needed, so perhaps just having a solar panel inside the box directly connected to a small fan would do the whole job

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