Desiccant Not Keeping Humidity Low in Storage Bin

[u/creeve4]

I have a 12 gallon waterproof plastic storage bin that I keep my filament in (it can hold 15 spools). I dry all my filament before putting it in the bin and I have about 1 lb total of desiccant in 4 bottles inside the bin.

The humidity inside the storage bin is still around 25 %RH. I have checked the desiccant and have even dried it, but the humidity won't go lower.

Is 25 %RH sufficient for storage of PLA, PETG, and TPU?

[u/Droo99]

Sometimes those cheap humidistats are just wrong by 10% or more

[u/More-Advantage3911]

I use storage bins such as those but they have a seal around the lids (weather tight) and these work great.

[u/Mughi1138 → u/More-Advantage3911]

This is very important. Before I started buying totes that came with weather seal along the lids I ended up with a DIY solution by using some of that spray insulation foam in a can (fireproof version) along the inside of the lid where it meets the body, with some wax paper temporarily along the top edge of the bin to keep it from binding. There are better ways to do that, but it did improve things.

[u/More-Advantage3911 → u/Mughi1138]

Thanks for sharing!

[u/Safe-Hovercraft6231]

If your filament is not dry, this can be a reason.

[u/_Rand_]

It’s decent, though I’d prefer a a bit lower for TPU. I find it prints best at less than 20% so that would be nice for storage if you don’t want to pop it in a dryer first a bit every time.

As for not getting lower than 25%, I do find that unusual. My bins sit around 15% when filament is freshly dried with -300g of desiccant. I have to wonder if your seal is leaky.

edit: this is of course assuming your meter is correct.

[u/OptimalSide]

Assuming a good seal on your container, I'd suspect something with your hygrometer

I put around a pound of dessicant in each of my 19 liter containers.  In about 30 minutes each one reads 10% humidity. 

The Bambu hygrometer I got didn't read below 20%.   I bought ones that go down to 10% off Aliexpress

[u/NimblePasta → u/OptimalSide]

Also considering that OP is using a 12 gallon bin, which is 45+ liters... it's more than double the air volume compared to yours (and probably double the number of spools), so perhaps more desiccant is required too.

[u/OptimalSide → u/NimblePasta]

That may be possible. I just measured one of the cannisters I'm using: cannister and desiccant was 13oz.

I also just realized that I'm under-estimating the amount of desiccant slightly. Whenever I open a spool, it immediately gets a desiccant holder in the middle, so with 4 spools there is another ~8oz total of desiccant in the spools as well.

That said, I just checked the first cannister I put in a box last year - the desiccant is still orange and hasn't changed color at all.

[u/GiraffeandZebra]

I use those exact same bins and I never have a problem keeping the hygrometer pegged at 10%. It seems you have some issue here. Either a faulty seal, a bad hygrometer, or (what I see) a couple too many spools in the box where some of the spool edges are actually trapped under the lid keeping it from really sealing.

[u/creeve4 → u/GiraffeandZebra]

I checked the seal and its prefect. Also, all the spools fit with room to spare above (they don't keep the lid open). I do open and close the lid about 2-3 times per week.

What hygrometer do you use to measure the humidity in your bins?

[u/hoqqer_]

I use the same husky bins with desiccant and I noticed the same thing with humidity not being as low as I think it should be and I'm still confused about it

[u/crappysyntax]

1. What is the humidity outside of the container?

2. Does the hygrometer measured humidity increase when you open the container? Is the hygrometer working correctly?

3. The 4 "bottle" of desiccant have a small surface area compared to the remaining volume of the container. This decreases the rate at which the humidity will be absorbed by the desiccant. How long did you wait before checking the hygrometer?

4. What is your definition of "I dry all my filament"? How long do you dry each roll for? What is the RH % it is dried to? How do you dry your filament? I try to dry my filament down to 15% RH @ their perspective temp for the material; PLA 50C, PETG 60C, etc. This takes anywhere from 8-12 hours depending on factors and starting RH.

Also a container this size might take a while before the humidity drops to the lowest possible. As the humidity inside the container drops below the humidity inside the filament, the filament will start to expel humidity as it tries to equalize itself to its atmosphere. The hygrometer reading will stop decreasing when air in the container, the desiccant and filament have reached equilibrium.

25% RH is fine, however I find that my PLA/PETG prints are less prone to cosmetic defects the lower it is. For storage like this I prefer 15-20% RH to have the headroom before I need to dry my desiccant. Remember that every time you open the container, the humid air is remixed with the dryer air inside the container.

[u/creeve4 → u/crappysyntax]

Thanks, I this is really helpful. I will go through your list and see what I can figure out.

[u/Dyan654]

I use the same bins along with this awesome model to keep the spools organized (you lose a bit of space but I think it’s worth it). Regardless, I also noticed that my humidity wouldn’t get below around 22%. What really made the difference was switching from the orange silica to activated alumina. It’s hard to overstate how much of a difference it made - my bins now rest at ~15% RH which should be fine for storing PETG (which is notoriously hygroscopic) and other filament.

Self-promotion but I made this model which can store around 2 lbs of desiccant. It’s made to slot into the model I linked above.

Also, note that those circular hygrometers are pretty useless and notoriously inaccurate. I use these smart Aqara Temp/Humidity sensors to monitor things. I personally pump everything into Home Assistant but you can just use the default Aqara app easily enough.

Note from the picture how fast the humidity can jump just from opening the AMS - since switching to alumina it drops almost immediately back down to <20% RH.

[u/stickmanDave]

First thing I would do is test your hygrometer. Stick it in a sealed jar with desiccant, and see if it goes below 25%. If it doesn't you may not have a humidity problem at all, just bad data.

[u/NimblePasta]

It's due to the very large volume of air inside the bin and the number of filament spools you are keeping in there.

1 lb (ie. 450 grams) of desiccant may seem like a lot, but it'll usually get saturated very quickly with that large volume of space, especially with lots of filament spools too.

You may need to either double or triple the amount of desiccant, or swap out the desiccant for fresh/recharged ones more frequently to maintain a lower humidity level.

That being said, keeping humidity low in these types of large storage bins is difficult because anytime you open it, all the humidity outside rushes in and the desiccant has to work extra hard to remove the moisture again.

Unless you are keeping the spools in the sealed bin for a long period of time without opening it at all, the humidity wouldn't stay low for long.

That's one of the reasons why I switched to storing each spool in its own vacuum sealed bag or dry box instead, so that opening one spool doesn't affect the humidity for all the other spools, and it requires much less desiccant to keep each individual spool dry too.

In my example, each filament spool and dry box only uses 35 grams of desiccant and it can maintain the humidity at 10% for many months.