@kirk said in How should we control the centrifugal pumps? TRIAC/thyristor etc? Need help from controls/electrical people:
It seems to work! At least enough for testing purposes. Here is a video: https://spectra.video/w/8xipM8aXnBkDXnu4kkRpqT
Here is the code for this test: https://codeberg.org/FBRC/RFB-test-cell/src/commit/d10834bc7dd67736e708c9a33832a5602ab3ca28/firmware/FlowrateRampTest.ino
@methylzero@mast.hpc.social said in How should we control the centrifugal pumps? TRIAC/thyristor etc? Need help from controls/electrical people:
Nice! Better than I expected honestly. At the low end of the speed range it sounds a bit unhappy. The thermal protection is only TP111 so it may not be fast enough to save the motor if it is stalled.
If this motor does work out, the manufacturer can make bigger ones and apparently you can choose the wet-side material. http://www.china-haiyi.com/product-48054-173640.html
Thank! I read some stuff that TRIACs can work for very small motors, and indeed this is only around 6 W, so I figured why not just try it. Yes, at the low end it made some funny sounds, nothing horrible, but this is not definitely not the optimal control strategy. It should hopefully allow us to do single-cell flow testing at close-to-appropriate flowrates, without having crazy fast flow or having to add a bunch of (chemically resistant) plumbing like a bypass/pump-around. For wet-side I think they have two standard options of PP and PVDF for the housing/impeller. Also, for some bigger pumps, they offer BLDC motors stock, apparently, which should be easier to slow down efficiently. Didn't know that TP111 designation either - sounds like it should auto-shut off if it gets too hot at steady state, but won't protect from a stall.
Also, just FYI, R.Flo, a Ukrainian all-iron RFB startup, posted a pic on LinkedIn with these pumps:
Which look to be the same version, but larger.
@methylzero@mast.hpc.social said in How should we control the centrifugal pumps? TRIAC/thyristor etc? Need help from controls/electrical people:
But one thing not good about these pumps is that they might not work great with really dense solutions, max. density is 1.1-1.3 depending on the model, which is .... not much.
Yeah I saw this and... we will cross that bridge if/when we get to it 
at this low of a price point I read the datasheets with a shaker of salt.
From CRC handbook for potassium iodide (just as a reference point for a salt we currently test with):
In real electrolytes we'll have other salts present at the same time, but even with a 1.3 SG max we may get to reasonable concentrations---as in, high enough to allow us to build out the rest of the system for a prototype. I figure over 1.3 SG the pump either fails faster or has otherwise reduced performance, but maybe we'll find out the hard way
@methylzero@mast.hpc.social @BillySmith @H4K1 @slash909uk@mastodon.me.uk
It seems to work! At least enough for testing purposes. Here is a video: https://spectra.video/w/8xipM8aXnBkDXnu4kkRpqT
Tested the pumps today, they work just fine switched on 110 V AC, will try the triac, if that doesn't work/it fries the motor, will disassemble and try to get a different motor on there.
Video of pumps running: https://spectra.video/w/9VddoPTvMvDCJ121B4fabf
Nice work, Daniel. I am thinking of plumbing solutions to the imbalance issue:
From A review of all-vanadium redox flow battery durability:
After studying the capacity fade for mixed acid electrolyte, UET [154] found that, during long‐term operation, the ratio of catholyte and anolyte concentration remained constant: 1.3:1. Based on this finding, they designed an overflow system with different volume (volume ratio: 1.3:1) anolyte and catholyte tanks, in which the volume ratio and total vanadium were kept constant. With the new design, the VRFB achieved long term capacity and efficiency stability. However, this design is only valid for the mixed acid electrolyte system. Recently, Wang et al [152] developed an electrolyte reflow method to solve the electrolyte imbalance issue for the sulfuric acidvanadium electrolyte system. Figure 10 shows the schematic of their method; without reflow, eventually all of the anolyte will move to the catholyte tank, while with reflow, the anolyte tank will always contain some electrolyte. Similar to the UET method, the volume ratio of catholyte to anolyte is a key parameter affecting the capacity stability and is highly dependent on the operating current density. Cycle life and total capacity were all improved with the reflow method.
There is also Capacity balancing for vanadium redox flow batteries through electrolyte overflow but it was retracted - they think they accidentally had a pinhole in their membrane for the test. But they did build a real overflow system:
I agree about loading up on sensors and then cutting them to the bare minimum as things mature---though some process sensors for chemicals can be pricey!
Are those food-safe pumps centrifugal? We need those to be power efficient---peristaltic won't do at scale.
Edit: saw your other comment, if these mag-drive centrifugal pumps are common in that industry that's great! Do you know what materials are commonly used and come into liquid contact? And what range of flowrates they can provide?
Stephen Hawes of Opulo has compiled some of their tools here:
The AutoBOM one seems to be based on those workflows above and looks pretty interesting
Probably too far involved but this sort of approach could be cool, if it was constrained to manufacturable shapes:
We introduce Fireshape, an open-source and automated shape optimization toolbox for the finite element software Firedrake. Fireshape is based on the moving mesh method and allows users with minimal shape optimization knowledge to tackle with ease challenging shape optimization problems constrained to partial differential equations (PDEs).
Linking to previous introductions:
