Posted this in the wrong thread. Reposting this here where it belongs:
Got results from my research to report.
I found a stackup of McMaster Carr spring washers that will do what I think is needed.
My criteria is to limit force at 100% SOC to 15 PSI. I have read that these cells expand between 0.7mm to 0.8mm from 0% to 100% SOC. I am working with 4 cell stacks in each compression frame. This totals up to 3.5mm of travel so that became my goal.
I am using 5/16" x 18 hardware and 18 TPI = 0.058 "/turn:
0.058 "/turn x 25.4 mm/" x 2.5 turns = 3.683 mm of travel.
I ordered and tested a number of different spring washers from McMaster Carr, and one the worked for me is this one.
McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.
www.mcmaster.com
What I found is that a stack of 12 of these disc springs in series <><><><><><> resulted in a force of 100 kg when compressed with 2.5 turns of the nut. This is starting with the nut finger tight (close to 0 kg). I then turned the nut 2.5 turns and my load cell read ~ 100 kg (+/-5 kg).
I am going to declare victory and that is how I am going to build my compression cells. I am going to keep working to see if I can refine these results, but I think I am close enough to move to building compression cells. When I finish my compression cells I will test a set of 4 cells in compression with the load cell on one of the threaded rods and measure the peak force at 100% SOC. I will determine what the correct preload is then.
Here is a pic of my test setup.
View attachment 33863
And I finally found a use for that old welding coupon. Makes a nice base plate for a load cell.
F.Y.I. Avoid stainless steel hardware like the plague. I started testing with a stainless steel bolt and flange nut and after a half dozen cycles the nut galled on the bolt so bad I had to cut if off my fixture. I am really glad I have a band saw.
View attachment 33865
P.S. Forget using a torque wrench to set compression. I tried that with my load cell and saw tremendous non-repeatability (+/-50%) when trying to use a torque wrench to set pressure. Springs are very repeatable. I am getting +/-5% variation from one test cycle to the next.
Using the torque wrench with lubrication on the threads might be more consistent, but don't forget these cells are going to expand as you charge them. Even if you just run the nuts in finger tight at 0% SOC, I predict you will be applying way too much compression at 100% SOC unless you have springs to provide compliance.