I didn’t want to take over the “New member introduction thread” with my questions, so I’ve started a new one.
At this point, I already have the 3D printed components. I should receive the remaining parts later this month.
One thing I was missing in the documentation was information about the material for the "polymer endplate". In the photo, “PETG 100%” was written on the endplate with a marker, so I used that material and infill.
I'm also interested in this topic. Polypropylene is not a trouble-free material. There are some other filaments classified as chemically resistant (https://help.prusa3d.com/filament-material-guide). Is PP the only suitable option?
I’ve finally completed the first tests of the battery.
@danielfp248, I used the parameters you suggested, but I had to enter one of the currents (either charge or discharge) with a negative sign. With each subsequent cycle, the efficiency improved (as shown below). Is this difference in capacity from cycle to cycle expected?
I expected the program to automatically adjust the pump RPMs, but it turned out I had to set them manually. I'm not sure if the values I chose were appropriate.
Now I understand why you mentioned that the connection combination didn’t make a difference 
However, I still have some doubts about the resulting voltage value—doesn’t it seem too low?
Before turning on the pumps, I zeroed Mystat. I’ve just realized that it should also be calibrated with a 1.000 kOhm resistor.
I used the tubing that came with the pumps. After completing five cycles, I emptied the electrolyte and rinsed the system several times with deionized water.
Now that I know the system works, I’ll look for proper electrolyte-resistant tubing and continue with further testing.
Here’s how the electrolyte’s color changed after just a few cycles:
It's been a while, but I’ve just configured a Raspberry Pi and got the mystat.py script working alongside Mystat and the Arduino. It looks like the chemistry is ready as well. Could I ask you for some instructions on how to proceed with the test using the mystat.py script? There are multiple options available, and I want to make sure everything is set up correctly
@sepi , thanks for the kind words. @danielfp248, @kirk It is really cool that you have done and made this project available! Building and testing it personally is an experience much more valuable than just reading an article.
I'll be honest — before the first test, I was a bit worried that a leak might suddenly appear.
I'm also glad, @danielfp248 , that you confirmed the accuracy of my results.
I'm looking forward to seeing your project develop!
Hi! I work at a technical university, in the mechanical engineering faculty. I'd like to build your prototype based on the documentation. Flow batteries are a new topic for me, but they could be very useful in my field, and this seems like a great way to get to know them better. I also saw your presentation on YouTube. I was about to ask about the peristaltic pump model, but I noticed you’ve just updated the documentation This forum looks really helpful in case I need any support or clarification. I’ll try to give some feedback if it’s useful to you.
@kirk Thank you! I'm starting to 3D print all the components.
The bottom of the endplates is perfectly flat. I sprayed the print area with Dimafix to make sure there would be no warping.
The most difficult material to print is PP due to adhesion and warping issues—I used a PP foil for that. What kind of surface did you use to print your PP components? I suspect the most common PP tape could cause leakage issues if a component is printed across the seam between two strips.
All the components are already ordered, including the MYSTAT. My department’s lab doesn’t have such a device.
Good to hear the packing tape hasn’t caused any leakage issues in your case. I ended up getting a PP adhesive foil that’s originally meant for covering book covers.
Hi! Thanks @kirk for that info. I still don't have all the components to start assembling the cell. I'll figure out how it will go and eventually reprint the jig.
Hi! I already have all the components. I had the brass plates CNC-cut, and I cut the 0.1 mm silicon gasket and grafoil with a knife (I 3D printed a template for that). I noticed that the documentation hasn't yet been updated to include the new Kamoer KPK200 pumps.
@kirk, could you send a photo showing how the tubing is connected (what length should the hoses be cut to?) and what the electrical connections are?
The documentation says to cut 4 separator sheets, but then only 3 are to be used. So is the 4th one not needed?
Also, I assume I don't need to worry about the graphite felt appearing white in your photos? It's not, for example, actually polypropylene felt mistakenly labeled as graphite felt? 
Thank you for the comprehensive answer — I think you've convinced me to go with PP 
While assembling the flow cell, I noticed that the manual doesn't mention anything about the Membrane Frame. I also have doubts whether the Membrane Frame model provided on the website isn't too thin (0.8 mm) to ensure a proper seal when using 4 membranes made from 230g/m² matte photo paper. Each membrane, according to my measurements, is 0.3 mm thick — which means the total thickness is 0.4 mm greater than the Membrane Frame's thickness. I also used 0.1 mm gaskets (as specified in the Bill of Materials), so such a large difference in thickness is unlikely to be compensated.
@kirk, do I need a thicker Membrane Frame or thicker inner gaskets?
Thank you @kirk . Yes, I had already understood it from your previous message.
I’ve finished the assembly and performed a leak test using demineralised water. The first attempt failed due to leaks in both reservoirs (see photo). After that, I made a small design change and increased the 3D printer’s flow rate for the infill. The new reservoirs seem fine now.
Did you encounter this problem too? How did you solve it?
The cell itself doesn’t leak. I used a torque of 3 Nm for now, but it already looks slightly distorted. Have you considered using more bolts?
I also wanted to ask: is silicone resistant to this type of chemistry? Since it’s used for gaskets, maybe silicone tubing could be used as well?
Regarding the Arduino program: it seems there are four defined pins — In1 (pin 9), In2 (pin 8), In3 (pin 7), and In4 (pin 6) — but they don't appear to serve any purpose.
As for the main Python program — should it work with no issues once the Arduino and MYSTAT are connected to the computer?
Another question before I start the test: I understand that I need to connect WE/SE to one electrode and CE/RE to the other. Does it matter which electrode is connected to which pair? Does the Mystat.py script differentiate between them?
Ok, thank you @danielfp248 ! I know I'm probably being a pain, but I just wanted to be absolutely sure:) So this part is already solved.
However, I have found out that mystat.py was not able to save results to a file.
On the Raspberry Pi that I am using right now, I was unable to install PyQt5 in a virtual environment following your readme.txt and requirements.txt file. The problem is known and I have not found a working solution for the venv setup. As a workaround, I was using the default version of Python and libraries. This was probably causing the file saving issue.
Happily, the script seems to be working on the Raspberry Pi's default system Python and libraries after changing the "choose_file" function to the following:
def choose_file(file_entry_field, questionstring):
"""Open a file dialog and write the path of the selected file to a given entry field."""
filedialog = QtWidgets.QFileDialog()
# Get the tuple (filename, filter) and take only the filename
filename, _ = filedialog.getSaveFileName(mainwidget, questionstring, "", "ASCII data (*.txt)",options=QtWidgets.QFileDialog.DontConfirmOverwrite)
file_entry_field.setText(filename)
I hope there will be no more incompatibility issues during battery testing
@sepi Sorry for the late reply. I'm glad the first attempt was successful and that I’ve learned how it works! I believe flow batteries are the future - at least for stationary systems. So, what’s next? Maybe I’ll try designing my own small battery…
