Problems with my DIY flow battery

Full disclosure, I haven't made the best flow battery cell stack. If you have been reading my blog, I haven't even designed it myself. I have been replicating the cell stack from a Youtuber named CAYREX, every battery enthusiast should check his channel out. 

But I have been lazy, instead of reading books, research papers and patents on stack design and designing my own cell stack, I just took the STL files from Cayrex's Patreon page and got them 3d printed, but after months of battery testing and troubleshooting with someone else's stack. I'll be breaking down the difference between Industrial grade stacks and a DIY stack. The images I will show will be mainly of CAYREX's stack, but this is applicable for all DIY and lab scale stacks

Problem 1- Screws

This is a photo of flow battery cell stack from the internet -




Image 1-  Source 

This is a good stack but, its problem is that the screws are inside the stack housing. These will corrode very badly the moment the stack leaks and acid touches the SS screws, which is exactly what happened with my stack.
For months I was changing screws every 15 days because the screws themselves were corroding, moreover changing screws was a bigger headaches because they did not even have the strength left to get unscrewed. 
Lesson 1 - Put the screws away from the cell stack.

Problem 2 - Piping

This is the stack CAYREX designed -
Image 2
This stack is designed to accommodate pipe on to it, but here is another very big problem, if a large volume of liquid flows through the pipe, it puts back pressure and the liquid starts leaking before it reaches the stack. Not good, half the time I thought my bolts weren't tight enough but it was mostly this stack leaking externally.
The solution to this problem is called internal manifold and is solved in image 1, where the electrolyte pipes connect internally into the stack and travels internally into various cells. It has its own problems, but that's a post for later.

Problem 3- Compression

This is something CAYREX has solved for himself in his latest flow battery version, and this is something you'll know once you have a printed the stack and measure its dimensions. The thickness of the flow plate in image 2 is 5mm, the felt suggested by CAYREX should be 5 mm thick. But that's a bad idea, because the electrode we use, that is carbon felt, is 95 % empty, this means that there is only air in it, and air is a god awful conductor of electricity. So to accommodate for this, the felt has to be compressed by 20-25%, but if the frame and felt are both 5mm thick, then the felt cannot be compressed, that gives us very bad conductivity and efficiency. 
For months my stack used to charge for hours and discharge in minutes. I always thought I was doing something wrong, apparently geometry was against me.
Even CAYREX has redesigned his latest flow battery designs to account for compression.
Now since I have fought so many problems in the stack, and learnt the hard way, what doesn't work. If you are making your own battery my suggestion to you is don't copy the STL files, alter them to solve these problems and then try testing, it will be a bit slow but will save you months of headache and self doubt.
From now on, I will be doing the hard work and making my own cell stack. I'll be sure to post it once its completed and gives some tangible results.

None of this is AI generated, so feel free to fact check me and looking forward to your views and help. 

Mayank Jately

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