Flow Battery Research Collective

This is great sepi! A calibration wizard would be excellent, thanks for taking this on. I cloned your repo and was able to launch it on my PC, happy to help test in the future!

@sepi Without the four-wire control the pump speeds are definitely harder to manage, sorry to hear that, though the PWM regulator may help. Can you visually see how different the rotation speeds are? That should be rough proxy for volumetric flowrate. I am not surprised they won't spin below 11 V. @sepi said in My build (very slowly progressing): Is this 20-40ml/min measured with the cell in line or just the pump. Ideally best to measure with the cell inline, to be closer to the actual conditions. However, as the tubing wears, this can drift, just FYI. Not a huge deal but something to be aware of. @sepi said in My build (very slowly progressing): Is the figure obtained with water or electrolyte? Water for now, just as a proxy, minimize exposure to electrolyte. This is kind of a 1, maybe 2 significant digit measurement, no more (the volumetric flowrate). @sepi said in My build (very slowly progressing): What would you recommend doing against the excess flow? @sepi said in My build (very slowly progressing): the left passing up to 40% more water at the same voltage. At the same voltage, is the left pump spinning at (nearly) the same rate as the right? if they are spinning at the same rotational speed and the left is passing 40% more water, it sounds like there is some flow restriction in the right pump's flow loop. If they have identical flow loops (in terms of pressure drop), and are set at the same voltage, I would guess that they should rotate at similar speeds, but this may not be the case for the brushed motors (e.g. variance in motor properties). What is important for testing, is that both pumps are above a minimum flowrate to ensure good mass transfer, and that the pressure imbalance between the two sides isn't too great as to cause transfer of electrolyte from one side to another through the separator. If the flowrates aren't perfectly matched but those two previous conditions are met, it's not a big issue, although it's just better for repeatability for them to be the same.

The tubing is gone now, thanks for buying at my store

@doho that's a great idea, I'll give it a try!

Here is a video of assembling the large-format cell. https://spectra.video/w/m9RKg1QWrFdkkn9qUBFMTS FYI, you are meant two use two endplates per side (I used one here), I intentionally left the graphite felt out as this was for leak-testing, and the cell is missing washers on one side. The video illustrates the basic process of assembling our cell and how it is designed and seals. All the design files are available at https://codeberg.org/FBRC/RFB-large-format-cell. The setup is essentially there, waiting on chemicals and sorting out the power electronics set up and we should be able to run our first real charge/discharge tests with this large-format cell! The work to get to this point has been supported by the NGI0 Entrust Fund, a fund established by NLnet, to whom we are very grateful!

@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.

Charging to 6Ah/L at 30mA/cm2 and discharging at 5mA/cm2. At most we only get 2-3 Ah/L of available capacity, same as if we charged to 4Ah/L. [image: 1758211363268-f3e1b8fc-98a1-4c8b-b305-b4d4a5bedee6-image.png]

This test showed some deterioration on cycling: [image: 1758097795042-c586de1d-8d24-4884-bd7a-a00afb789080-image.png] I took out the catholyte and anolyte when charged (you can see the anolyte (left) and catholyte (right) in the pictures below). There isn't any hydroxide precipitation in either one. However there are some pieces of detached Fe metal on the anolyte, which I think are what causes the slight loss in capacity and increases in ohmic resistance as a function of time. [image: 1758097834649-5ee56443-1754-4f62-9a96-83d6194304ca-image-resized.png]

My pumps didn't have them, only the ones built into the pump. I saw that on some of your pictures, you have additional fittings between the different elements, I guess to make it easier to connect and disconnect the cell. In the end, it might make more sense to just shrink the barbs on the flowframe and/or tank a bit so the tubing comes off mor easily.

Congratulations, that's great to hear!

@danielfp248 huh, that makes a lot of sense.

@danielfp248 ah, that makes sense as a last resort measure but would it not be nice to not lose charge? Well it all depends on how easiy it is to counteract by setting a different flow for the different electrolytes.

@Vorg We will slowly get there but no, right now we don't have any kWh capacity battery. As I mentioned, it will be several years before we get there. The fun is to walk this path and make everything open source on the way.

@sepi Hi, if you do the selling of the tube, I would order 2 (two) meters.

@danielfp248 sorry, my question was not well formulated. I meant a potential between the electrolytes inside the cell independently the possibility of measuring them using an electrode. Or to formulate it differently, if you cut through the cell (lile you cut a sandwich) and plotted the electrical potential between the electrodes, how would it look like?

@czahl I am a huge fan of trying this, especially for the larger format where setups are likely to be more permanent. As kirk mentioned we have never actually tried it, so please let us know if you do!