I never had any issues with my filament rolls until got this P1S combo…
Now I rarely empty a roll as I often use different colours or filaments.
Storing them in sealed bags and containers works but it is becoming a hassle.
And with the humidity sky high during winter moisture can be a problem as well.
Below is my general ideas and how I am planning to go from small protoype to full sized fridge.
As it is VERY long I placed it into a spoiler.
Read at your own risk if interested
I had the idea for a fridge solution for quite a while now, just no free fridge to try and modify.
With that finally out of the way I started to order some of the hardware I don’t have, can’t print or am too lazy to program myself…
As it is just a proof concept thing I decided to document the idea(s), basic concept and all here so I keep adding pics and such along the way.
If nothing else it would give me an easy way to look back but I hope some people, especially in very humid areas, might find enough info and inspiration from it to try similar.
So what’s the deal here?
Stage one is a bar fridge to hold whatever amount of roll I fit in.
Probably just as a dryer with no tubes for the filament or such.
MY version will have quite a few customs thrown it but once that all works as planned I will do it again.
Why again you wonder?
Because then I only have to include BOM to use a Sunlu or other cheap dryer as the brains.
Means you could then just get a cheap filament dryer, add some parts and let it control a big and well insulated chamber with a door
What’s the working concepts?
For starters heat paired with circulation as for any filament dryer.
The a fan forced heater paired with a large diameter silica gel container.
Optional the cold trap:
As most won’t mod the actual fridge part a suitable metal flask filled with ice will provide the required condensation of the humid air.
To be drained out of the fridge through a drip line or emptied manually - up to you.
My bar fridge will have the evaporator plate removed and replaced with a cold finger - a copper tuber that fills with refrigerant.
Same thing just automated and why more convenient.
Proof of concept of course meaning going large shortly after - pending the free display fridge.
For that a tiny heater and one fan won’t do.
But some well place abuse will do just fine
Here me out as it will be a few month before I tackle the big one:
A (preferably display) fridge has no issues without the evaporator and condenser.
But we have two problems, one we already have with the bar fridge.
Some filament have to be dried at well over 50 degrees Celsius.
And most fridges are just not designed to have it hot inside so most plastics have to come out or at least checked for suitability.
And then there is actual heating and drying power required.
For just storage and drying new rolls before use something small will do fine…
But if want PLA, PETG, Nylon, TPU and what not in there…
Correct! We need two independent heating systems.
One for general and storage needs the other to dry those higher temp filaments.
Thankfully we can do the same thing twice here.
Meaning we just add a chamber inside the fridge to dry filament while the rest is just to KEEP it dry.
If insulated a bit the heat inside there should not be an issue as we can use it to keep the fridge warm for the other rolls.
Ok, but what if you are in one those countries were humidity levels of 80 or more percent are common for many weeks or even months of the year?
Unless you won’t to mod actual cooling parts of the fridge there might be way that only requires any well insulated box.
Dedicated DE-humidfiers for rooms in your home are available in all sizes, down to tiny for the use in your wardrobe.
They are literally just the most wasteful version of a heat pump possible.
They take in ambient air, run it through the condenser followed by going right through the evaporator.
The hot air condenses, drips off and your bedroom allows you to sleep in no time at all.
Simply include one of those machines into your box or right next to it so you only need to route the intake back into your dryer box.
As the air coming out will always be warmer than the air going in the will kick out once the intake air gets too hot.
This of course only works up to a certain ambient temp…
In order to make this work even in hot and humid climates:
Take a small sized de-humidifier and take it apart…
Strip down what you can in order to separate the evaporator coils from the condenser coils.
All you need if enough angle or distance so you can add a custom housing around the evaporator part.
The rest can be mangled back together so that the original fan works just for the condenser coils.
There will be temp sensors…
Usually just one for the evaporator to make sure it won’t freeze over - leave that one one but insulate it a bit to the outside.
If there is a second than this one is usually there to check the outgoing air temp.
Simply route this one into the INCOMING airstream for the condenser.
With that sorted you only need to use a fan to force the air inside your box through the evaporator.
DON’T go overboard here as even a small one can remove a litre or more per day…
And that working in normal conditions and not for a tiny box…
Stay tuned to see how the prototype turns out to get the right ideas and to avoid the mistakes I might make along the way
If you are in a hurry and keen to DIY just ask …
A dehumidifier is just an air conditioner with the evaporator (cold part) and the condenser (hot part) back-to-back. Condensation occurs on the evaporator cold coils as it picks up heat from the condenser in front of it.
The gas refrigerant in the system is compressed by a pump and changes to a liquid in the condenser. The liquid then passes through a restriction or control valve where the liquid changes back into gas in the evaporator generating the cold which condenses the moisture out of air forced through it. It’s the cold that condenses the moisture out of the air, not the hot side.
I think I have to clear some thought up here
Yes, it is sort of a big project but not the first environmental control system I whacked together.
The compressor being abused with a cold trap instead of the evaporator coil actually works rather well.
Especially inside a HEATED compartment.
That’s the second stage though and will be added once the first stage works within expected parameters.
You can dry the filament whichever PASSIVE way you like but won’t get below 30% of humidity left in the filament.
Forced air does help a little bit here but there won’t be any airflow between the layers of neatly wound roll of filament.
THAT is where the heating comes in - hot air takes on more moisture than cold air, at least in terms of this moisture NOT condensing in the air.
With the air inside the fridge circulating through both the heating element and the silica gel it is only a matter of not getting the silica gel too hot.
The moisture in the air will stay in the air if it cools down a bit.
Means the colder air in the fridge goes through the beads and after that through the heating element.
I have done many times on various scales and it does work well if there is enough air going through the gel.
Problem is that in this assisted passive way the result highly depends on the temps you can crank up and control.
For example heating the entire fridge to over 70 degrees to dry some Nylon or TPU is no problem but making the silica gel take on moisture at those temp will be a problem.
That is were the ACTIVE part comes for stage two.
Even with just 10% of humidity in the air a cold trap will still cause condensation, still removes moisture from the air.
If this water is drained out it no longer is able to affect things inside the fridge.
I will start with just ice as getting the evaporator plate and tubes out requires to take out the refrigerant first.
As I have no trade quality equipment at hand it means I have to first build a suitable system to get this part done.
(No I really don’t like venting vintage refrigerants of the worst kind into the atmosphere, I prefer to re-use it)
The physics behind are quite simple as well.
You can even get the idea from a good weather forecast.
The DEW POINT is the temperature at which moisture in the atmosphere condenses.
For example, if it gets cold over night and you car windows cool down BELOW the dew point you will find your cars dripping wet in the morning - or iced up if temps kept dropping below 0 after the moisture condensed.
In a closed system the dew point is defined Only by the thermal capacity of the cooling part.
As long as it is able to get between 2 and 10 degrees the moisture will condense if the air inside the system is at least 15 degrees.
The bigger the temp difference and humidity levels the more condensation will happen.
I built a freezer dryer for a friend a few years using a chest freezer, fan and heating lamp - despite this approach it was and still is able to dry food almost as quickly as a similar sized commercial freezer dryer - just that the real one costs a few thousands more LOL
Biggest hurdle at this size is to ensure the temp won’t get much higher than what is set for the filament.
I will probably revert to some tiny PIC controller or Arduino in order to get readings from 3 or 4 temp sensors for the storage area plus and additional two for the drying compartment in the big one.
So what’s the deal with the de-humidifier then ?
These things, even the small ones have plenty of capacity for the job.
And if don’t won’t to deal with refrigerants and making custom coils it is the next best thing.
Sure you could just just a discarded water cooler and this way get the cold trap for free - but I have not seen any around here for free in ages, they seem to be out of fashion in Australia.
The easiest way to abuse them for a larger sized storage box goes like this:
Have a fan and little heater in the box so that you can maintain a temp over 40 to 50 degrees Celsius if need be.
A mains powered 100W heater is more than plenty.
Like those used in cold climates as an anti frost device in tiny toilets or pantries.
You abuse a cheap dual channel digital fridge controller.
They provide an output to turn something on if the temp goes too high and if the temp gets too low.
All you do is to set the temp difference, e.g. for 45 inside the box you could go with 47 for the upper cut off and 20 for the lower.
The heater is turned on with the fan until the temp gets to 47, then it shuts off and the de-humidifier starts.
Below 20 it shuts off and the heating cycle starts again.
With the tiny heater it takes a while to warm up - in which time the cold side of the de-humidifier still stays cold (About 5 minutes but still).
If the box or fridge is too small a little timer is required to allow for maintained top temp for longer - at least twice as long as it takes to those inner layers on the rolls to temp.
I hope I made it bit clearer now.
Once the build starts things will be way more obvious in the pics.
As said, if want specific questions answered please ask - I won’t bite and take some criticism if not too abusive.
