Following your documentation – feedback & questions
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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:
@gus Awesome news! Congratulations on your first successful test. Your results are really nice. The potentials are normal, when you charge to high SOC the potential will likely be around ~50mV higher at start of discharge. The resistance of your cell is actually quite low, so you did a really good job building everything
What you observed is normal, when charging to very low SOC values (5-10%), the lack of full Zn stripping creates a metal film that continuously builds and increases the coulomb and energy efficiency of the device per cycle. Basically you have Zn that is not discharged that is more conductive and easier to plate onto and then strip from. If you continue you would see it stabilize somewhere around 80-85% CE and 70-75% EE. The color change you observe in the electrolytes is normal. The catholyte is normally red (gets black as you get more I3-) while the anolyte is normally transparent or slightly yellow due to the presence of I3- that leaks from the catholyte through the membrane (as the membrane is not selective).
Ideally on a fully discharged cell both electrolytes should go back to fully transparent, but since we have oxygen reacting with some iodide, this never happens.
About the pump speeds, I generally charge/discharge at around 30-35% of the total pump speed. When you cycle for a long time you will also notice fluid transfer from the anolyte to the catholyte. To avoid this, you can run the catholyte pump slower and the anolyte pump faster (see here https://www.sciencedirect.com/science/article/abs/pii/S138589472100098X). A ratio of 1:7 (catholyte:anolyte speed) was found in this paper to work best for this. I have never run it so fast, in my experience running the catholyte at 45% and the anolyte at 30% is usually enough of a difference to prevent most of the migration.
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It is incredibly exciting to see you guys reproducing the kit! We are really excited about completely independent third parties being able to just build and run this thing.
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@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! -
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Hello everyone! It’s been a while
I’ve returned to testing the flow cell and even built a second one to check repeatability. I’m wondering what could cause such a large difference in performance between them. The second cell showed only 0.85 V during discharge (compared to 1.15 V for the first one).There was also a warning during the discharge of the first (better) cell:
“The command b'RANGE 2' resulted in an unexpected response. The expected response was ‘OK’; the actual response was ‘WAIT’.”
After closing this warning and restarting the charge/discharge cycles, the system no longer stopped charging the cell at 10 mAh as before. I manually stopped the cycle at 22 mAh.
The cell was left in the workshop, and I was remotely connected from home to the Raspberry Pi controlling the pumps and Mystat. The next day, when I returned to the workshop, both tubes from the pumps had detached from the cell, and the electrolyte had spilled on the table.
Do you have any idea what might have happened?I also wanted to ask whether you’ve tried different gasket materials—such as FKM (Viton) rubber or expanded PTFE (ePTFE)?
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@gus afaik, the firmware from kirks repo with the python mystat application is not actually the latest one (it's missing the extended range). Check the updated page on the mystat docs: https://fbrc.codeberg.page/rfb-dev-kit/pstat.html which links to thw correct version. I'm not 100% sure if that is the issue you are encountering but it might be.
Concerning the detached tubing, I could imagine the felt getting clogged somehow leading to an ovepressure making the tubes pop off. I'm having some issues with gas being pulled into one container, leading to pressure buildup in the container. I have no clue yet where this comes from.
Good luck with your further investigations! You might want to rzun your future experiments in a transparent PP box in the future. I will for sure once I'm ready for actual electrolyte.
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Hello everyone! It’s been a while
I’ve returned to testing the flow cell and even built a second one to check repeatability. I’m wondering what could cause such a large difference in performance between them. The second cell showed only 0.85 V during discharge (compared to 1.15 V for the first one).There was also a warning during the discharge of the first (better) cell:
“The command b'RANGE 2' resulted in an unexpected response. The expected response was ‘OK’; the actual response was ‘WAIT’.”
After closing this warning and restarting the charge/discharge cycles, the system no longer stopped charging the cell at 10 mAh as before. I manually stopped the cycle at 22 mAh.
The cell was left in the workshop, and I was remotely connected from home to the Raspberry Pi controlling the pumps and Mystat. The next day, when I returned to the workshop, both tubes from the pumps had detached from the cell, and the electrolyte had spilled on the table.
Do you have any idea what might have happened?I also wanted to ask whether you’ve tried different gasket materials—such as FKM (Viton) rubber or expanded PTFE (ePTFE)?
@gus said in Following your documentation – feedback & questions:
I’ve returned to testing the flow cell and even built a second one to check repeatability. I’m wondering what could cause such a large difference in performance between them.
Hey, welcome back! As sepi said, please upload the correct firmware to the MYSTAT as an outdated version was previously present in the repo, also be sure to recalibrate your MYSTAT before cycling again, this is likely the source IMO. It wouldn't be bad to add some sort of calibration reminder/routine into the MYSTAT software...
@sepi said in Following your documentation – feedback & questions:
Good luck with your further investigations! You might want to rzun your future experiments in a transparent PP box in the future. I will for sure once I'm ready for actual electrolyte.
Definitely a good idea!
@gus said in Following your documentation – feedback & questions:
The next day, when I returned to the workshop, both tubes from the pumps had detached from the cell, and the electrolyte had spilled on the table.
Do you have any idea what might have happened?Ah shoot, sorry to hear this. I suspect if the MYSTAT was out of calibration it may have caused issues with the cycling. An issue with the iodide-containing chemistries is possible clogging of the felts with iodine if something goes wrong; normally the triethylene glycol should prevent this by forming a soluble complex, but it's possible your system got outside the normal operating range. I'd try again fresh (in a PP box/spill tray/secondary containment), with a calibrated MYSTAT running the latest firmware. Tagging @danielfp248 in case he has any suggestions.
