KB3D EDRY Dry Box (3D-90CA) Humidity Reading is inaccurate
After testing with my concrete RH meter I noticed the reading is inaccurate by around 10% higher than the set RH level. I even went as far as measuring the dew point in a glass of water to verify the RH accuracy of my meter, and it is spot on.
I read on this forum about someone else experiencing a similar reading issue and wanted to verify it myself. Since it is pretty consistent with what they saw I wonder if their humidity sensor is too close to the dessicant. Makes me think the Eureka/Statpro boxes are better designed since they seem to purely be time-based and they place a separate meter right on the door.
It's unfortunate because I can't get the box to go below 10% RH after several hours. And I specifically bought this box to print nylon from and store filament in. I'm not saying it won't work, and that over the course of a few days or weeks that it won't finally achieve its reading. It will take further monitoring, but given how far off the reading is, it doesn't exactly inspire confidence.
Anyone else have this dry box and a RH meter to contribute to testing this theory out?
RE: KB3D EDRY Dry Box (3D-90CA) Humidity Reading is inaccurate
I wonder if their humidity sensor is too close to the dessicant.
You could test that hypothesis by running the dryer without desiccant loaded.
Temperature gradients are another likely cause. If the built-in hygrometer sits in a very warm region and you placed your additional meter in a colder spot, the same air will have a higher relative humidity where it is cooler. In which case the real question would be at which temperature the filament sits -- if it mostly sees the warm air, the reading of the built-in hygrometer would be correct.
To test the "temperature gradient" hypothesis, you could try to place your extra hygrometer right next to the built-in one and check whether that results in better agreement of their readings.
I am not familiar with the KB3D EDRY. Does it have fans built in? If not, could you add one to force a more homogeneous air distribution?
RE: KB3D EDRY Dry Box (3D-90CA) Humidity Reading is inaccurate
After testing with my concrete RH meter I noticed the reading is inaccurate by around 10% higher than the set RH level. I even went as far as measuring the dew point in a glass of water to verify the RH accuracy of my meter, and it is spot on.
I read on this forum about someone else experiencing a similar reading issue and wanted to verify it myself. Since it is pretty consistent with what they saw I wonder if their humidity sensor is too close to the dessicant. Makes me think the Eureka/Statpro boxes are better designed since they seem to purely be time-based and they place a separate meter right on the door.
It's unfortunate because I can't get the box to go below 10% RH after several hours. And I specifically bought this box to print nylon from and store filament in. I'm not saying it won't work, and that over the course of a few days or weeks that it won't finally achieve its reading. It will take further monitoring, but given how far off the reading is, it doesn't exactly inspire confidence.
Anyone else have this dry box and a RH meter to contribute to testing this theory out?
Most of the cheap hydrometers (the kind that usually come with dry boxes) bottom out at 10%. As a general rule for nylon whether or not it's been in a dry box I still dry it before a print.
RE: KB3D EDRY Dry Box (3D-90CA) Humidity Reading is inaccurate
Most of the cheap hydrometers (the kind that usually come with dry boxes) bottom out at 10%. As a general rule for nylon whether or not it's been in a dry box I still dry it before a print.
I looked up the KB3D EDRY and it is somewhat advanced -- uses a cool plate inside the chamber to condense humidity, rather than heating the air. They claim that they can get to below 1% -- but of course that would be inaccurate if their RH readings are 10% below reality.
But I am still wondering about gradients (temperature and RH) inside the chamber. Forced convection is not mentioned in the product description. If there is no internal fan, that would look like a plausible upgrade.
RE: KB3D EDRY Dry Box (3D-90CA) Humidity Reading is inaccurate
Yeah that was the whole point of getting this thing, use it to store dry filament and print from so it's never exposed to ambient humidity. It claims to go down to 1% RH but it's not accurately reading the chamber RH. I personally couldn't find much info on the sensor location but it is overall a pretty simple machine and the Display panel appears to be far too simple to contain the RH sensor. The only other location is in the Dehumidifier unit itself, which would make sense why it reads so low. Problem is this box takes real time measurements so in theory as the air circulates (it does have a fan) it will slowly reach equilibrium with the set RH level. But it ran for 8 hours today in a 47% ambient RH room and the lowest it got was 10.6% RH in the chamber when set to 1% humidity. The unit was actively running all day. Granted it also isn't 100% sealed. It has 4x ptfe hose entry points that are small but not plugged. So maybe that was enough to let enough air in?
RE: KB3D EDRY Dry Box (3D-90CA) Humidity Reading is inaccurate
I wonder if their humidity sensor is too close to the dessicant.
You could test that hypothesis by running the dryer without desiccant loaded.
Temperature gradients are another likely cause. If the built-in hygrometer sits in a very warm region and you placed your additional meter in a colder spot, the same air will have a higher relative humidity where it is cooler. In which case the real question would be at which temperature the filament sits -- if it mostly sees the warm air, the reading of the built-in hygrometer would be correct.
To test the "temperature gradient" hypothesis, you could try to place your extra hygrometer right next to the built-in one and check whether that results in better agreement of their readings.
I am not familiar with the KB3D EDRY. Does it have fans built in? If not, could you add one to force a more homogeneous air distribution?
It does have a fan. I did set my hygrometer on top of the dehumidifier unit, it was still off 7-10%
RE: KB3D EDRY Dry Box (3D-90CA) Humidity Reading is inaccurate
Upon closer inspection, KB3D's 1% RH claim does not seem plausible.
- The cold plate in the EDRY unit can't operate below 0°C -- you want the water to drip off it, it's not a freeze-dryer. So for a best-case analysis, let's assume it cools down to exactly 0°C.
- Then, in my understanding, it can dry air down to a point where its dew point is 0°C. If the air were dryer than that, condensation would no longer occur at the cold plate, i.e. no more drying action.
- Air with a dew point of 0°C (i.e. 100% RH at 0°C) will have a RH of 26% at room temperature. Assuming that there is no active heating in the box, that's what we should be looking at. To get to 1% RH, you would have to heat the air to 86°C -- too hot for most filaments.
If the above is correct, even the 10.6% you observed would be optimistic. (Should be achievable at 35°C -- all under the probably optimistic assumption that the cooler goes down to 0°C.) Am I overlooking something? Is there strong active heating in the chamber too?