Build Chamber Temp control with an external fan

Bambu Lab P1 Series User Mods
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I have a BENTO Box installed, (BentoBox V2.0 Activated Carbon Filter by thrutheframe - MakerWorld) but I have been working on an external HEPA/Activated Charcoal box for my P1S to further reduce particulate and VOC emissions. However, I am concerned about the extra back pressure that my external filter/charcoal will impose on the Chamber air flow and how it will affect the build chamber temperature.

I did a few test prints to see what the fan settings were as function of filament type, and (for layers 2 and above) when printing TPU the Part fan = 20%, Aux fan = 70% and the Chamber fan = 70%. But for PLA the Part fan = 0%, Aux fan = 70% and the Chamber fan = 60%.

I don’t know how Bambu decides on these Chamber Fan settings, but I assume that their settigs are making a crude attempt at controlling the temperature of the build chamber, and are accounting for the back pressure created by their internal activated charcoal filter.

In an attempt to compensate for the additional back pressure my filter system will impose, I am adding an external fan and using a 4-wire fan control module with a temperature sensor inside the build chamber to control the speed of an external fan attached to my filter. Without active heating, I won’t be able to get the temperature of the build chamber above that of the Build Plate, but I will be able to prevent the build chamber from getting too cool.

The P1S enclosure is fairly porus, so higher Chamber fan speeds means more external air is pulled into the build chamber, overriding the heating effect of the build plate. I am also assuming that with the additional back pressure imposed by my filter, the internal Chamber fan will basically be ineffective, and the chamber exhaust air flow will be determined by my external fan.

Any thoughts on this approach to the problem would be appreciated.

2

You might save yourself some work by using OrcaSlicer. Unlike Studio, the OrcaSlicer filament preset lets you easily modify exhaust fan speed.

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1 Like
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Try to measure the differential pressure instead of the temperature.

4

@mcmaven P1S using bed temperature and the material presets to determine the chamber fan behavior. It is a complicated process. instead of measuring the temperature, you can try to measure the pressure differential to achieve that. The basic idea behind any contamination control system which also applying to the enclosed 3D printer is to release the contamination in a controlled manner. Therefore, the 3D printer either creates a slightly positive pressure in the chamber to evenly release the low risk VOC through the gaps of the printer, or a negative pressure in the chamber to release the high risk VOC to user designated area via the chamber fan. If you plan to exhaust the VOC of any material which means you plan to always give the chamber a negative pressure, please go to Bambu Studio and enable active air filtration for the printer and the materials. The chamber fan only has about 45-50 CFM at 100% speed. The static pressure increases, the CFM dropps. same thing applies to the external fan. By measuring the differential pressure of the both fan, you can find the right external fan speed-the more static pressure, you need the higher fan speed. Keep the differential pressure within 0.2 water column.

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Maybe I could use an air flow meter similar to this one, with some LED/sensors to detect the level, to control the pressure differential.

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I guess my goals were ‘twofold’. I want a negative pressure to ensure that VOCs are captured, but I would also like to have passive temperature control in the build chamber.

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Chamber temps are used too. He needs to view the filament start gcode and also the m142 firmware line.

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I thought that only an X1C had a chamber temperature sensor.
Looking through the Start GCODE associated with a P1S I didn’t find any references to M142, but I did find several M106 references, where with
M106 Px Syyy, where x selected the fan; 1=extruder, 2=aux, and 3=chamber; and S=speed(0-255).

Looking at this article:

It says:

Code breakdown:
M142 P1 R35 S40
M142: Firmware node reference and activation
P1: Parts cooling fan (presence to activate to aid cooling hotend)
R35: Set Chamber Temp
S40: Speed of fan

However this command doesn’t mean anything to a P1S since it doens’t have a chamber temp sensor.
Does P1 mean something different for an M106 vs. a M142 command?
Why is the example referencing the “Parts cooling (extruder) fan” and not the chamber fan?
Also, defining S as the fan speed doesn’t make sense. Without an active heater, doesn’t the fan speed have to be dyamically varied to maintain a target temperture?
Is it really a minimum fan speed?

I’m so confused…

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Disregard my M142 reference. I don’t know why I thought you said “X1C”. However, to supplement, firmware references like the one I mentioned don’t make the most sense in syntax because they are referring to soemthing we can’t see on the other side (firmware code). Additionally, the code I reference is referencing the parts can because it’s supposed to be use in conjunction under those circumstances to prevent the “jamming”. However, most of the time, as the result of other code, it’s already on.

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I would consider deleting the m106 to experiment first, at your own risk, of course. But I will try to provide a breakdown of this code. I need to reference the terminology that Bambu most closely correlates with.

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Here is the thing that I’ve been working on:

Bento Large 05
Bento Large 05871×597 67.7 KB

The exhaust from the Chamber fan goes in the back, across the top, down through 4 HEPA filters, through a large Activated Charcoal filter, and finally out the back through a second fan. The fan used by Bambu can’t handle much of a pressure head. I’m concerned that my filter will introduce too much back pressure, basically blocking the Chamber fan’s efforts and raising the temperature inside the enclosure. The purpose of my fan is only to augment the Chamber fan, for the difference between what it expects for back pressure (e.g., pulling air through the internal activated charcoal filter), and the additional back pressure introduced pushing air through my filter.

I was also going to attach my filter to the body of the printer. I have a TPU gasket between the body of my filter and the exhaust vent attached to the back of the printer. I’m worried that if my filter sat on the table next to the printer the joint between the vent and my filter will get a lot of flexing. And it would be worse if anti-vibration feet were used.

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@mcmaven Take a deep breath—you’re overthinking this. I’m sorry if my explanation caused any confusion. My HVAC engineer friend used a Differential Pressure Manometer to measure the P1S chamber pressure and the pressure difference between the chamber and the outside. Since both the P1S and X1C aren’t sealed, and WITHOUT ANY EXTERNAL FAN OR FORCE, the pressure difference is consistently around -0.001 to 0.001 inHg in all fan setting combinations. Essentially, this can be considered no difference at all.

People on the forum keep discussing AUX fan and chamber fan speed settings causing air backflow. Honestly, you can ignore those discussions. The AUX fan has a max airflow of about 50 CFM, while the chamber fan can move around 100 CFM at max speed. Even with the AUX fan running at full speed and the chamber fan off, the pressure difference remains at 0.001 inHg, which is negligible.

According to the HVAC engineer, unless you’re using a fan capable of moving air at 250 CFM or more, there’s no need to worry anything about temperature drop.

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Your system has 4 HEPA filters and a large Activated Charcoal filter, which collectively create significant static pressure. This increased resistance impacts both fans, as they have to work harder to push air through the filters. Essentially, your second fan is just assisting the chamber fan in handling the workload rather than making a substantial difference in performance, especially if its maximum airflow rating is below 250 CFM.

15

Got a chance talk to my friend again and showed him your design. Quote of his words:

The design has a lot of 90-degree bends, which can cause higher static pressure and restrict airflow.

Take a look at the picture I attached for reference. Just a quick suggestion from him—after the first bend at the chamber fan exhaust, try designing the rest of the system in a more straight, in-line setup to keep the airflow smoother and more efficient. If you must stick to this design for some reason, then the good side is you totally don’t have to worry about the chamber temp drop at all. The bad side is you may experience chamber fan fail at some point if the second fan is not strong enough.

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92b7c203a60e904df396c80cf41e47b1412c98d3871×597 95 KB

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Hi Darth,

Thanks for taking so much time with this.

Originally my design was passive, but I was worried about the static pressure that I was introducing, so I added a fan to act as an assist.

According to a friend, I can get a better head with a blower fan than a radial fan. But I found the selection of 80mm 4-wire blowers fairly limited, so I thought that I’d try a radial fan first. However, I designed the fan mount so it could be easily swapped out if I needed to change the fan type.

Without having to worry about chamber temp drop any more (and thanks for sorting out that point!), all I need is enough air flow to generate a negative pressure in the build chamber, so the air flow velocity should be fairly minimal. I was thinking that as long as the cross-sectional area of the various paths is equal to or greater than that of the fan diameter, then the paths wouldn’t be contributing too much to the back pressure. Even so, I was hoping that my extra fan could make up the difference.

The BentoBox (BentoBox V2.0 Activated Carbon Filter by thrutheframe - MakerWorld) that I already have installed, has 3 stacked components held together with magnets; HEPA, Charcoal, and Fans. The center component holds an activated charcoal “cartridge”. His design splits the cartridge into 3 chambers separated by perforated, printed dividers. He suggests partially filling the chambers so the charcoal pellets are loosely packed and minimize impeding the air flow.

I have a similar design, but my cartridge is much larger, divided into 5 sections, and I have stainless steel screens between them. Key to both designs I believe is that the air flows vertically through the chambers with the charcoal spread loosely on each level. So I need to at some point convert the lateral air flow from the Chamber Fan into a vertical stream. And the orientation of the HEPA filters don’t matter.

Here is a picture of my cartridge design. There is a TPU gasket between the HEPA and Charcoal cartdiges, and I haven’t cut the screen yet… I went with the stainless steel screen because printing dividers would take a long time, and the screen is much more porous.

image
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I’d be interested in your opinion on the ‘chambers’ approach. Can I just pack the cartridge full of charcoal?
A;so, going back to the cross-section argument, I’m concerned that the gaps between packed charcoal pellets could cause a lot of back pressure.

And based on your suggestions, I will work on a redesign that will minimize the corners.

Regards, Steve

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Blower fans can typically handle higher static pressure, but as I mentioned earlier, the P1S and X1C aren’t sealed, so static pressure isn’t a significant factor here. What you need is a strong enough EC fan (not a standard DC fan) that can self-adjust and deliver around 100–150 CFM. So your P1S chamber can always under negative pressure. Many high-end HVAC systems use EC fans because they can adapt their airflow to compensate for higher static pressure. For your filtration design, you might want to take a look at the IQ Air GCX MultiGas as a reference:

18

So a brushless radial fan should do the job?

Thanks for the pointer to IQ Air. That’s pretty fancy stuff. We got some HEPA/Charcoal air purifiers in the house, because of the forest fire smoke that we get in the summer. But generally they go all year round.

I really want to thank you for all the help. I have a couple of other projects that I need to finish first, but now I’m really looking foward to get this one done.

Steve