300KgF clamping fixtures and capacity loss?

[Short_Shot]

I mean. You didn't ask. You just stated that's what you'd use.

The issue is we can't answer that without knowing exactly what type of threaded rod you have, and even then there will be significant variation in the results that you won't be able to detect.

Hence: springs. Easy math. Easy to measure. Easy to test.

 

[Bleedingblue]

Depending on the thread pitch and materials you might be able to hit 165lb with single digit ftlbs of torque lol

Putting them to 165ft lbs will crush the cells.

You need to do some annoyingly complex math to figure out the exact value. That's why springs are far better for this.

Well the springs also need to be tightened up to a certain amount for compression of the springs. How did you know what force is being applied to the springs? Or you just snugged it enough to where they didn't move?

Of course spring tension is key, can't use any Ole spring as they are different

 

[Bleedingblue]

I mean. You didn't ask. You just stated that's what you'd use.

The issue is we can't answer that without knowing exactly what type of threaded rod you have, and even then there will be significant variation in the results that you won't be able to detect.

Hence: springs. Easy math. Easy to measure. Easy to test.

It's just a normal threaded rod 3/8 you get at lowes with standard threads.

 

[kpw]

Do NOT tighten to 165ft-lbs! That will FAR exceed the 12psi of pressure you want on the sides of the cells! I think you are confusing the TENSION required on the rods to get to 12psi with the TORQUE required to get there.

And yes, I'm using valve springs. They are cheap and easy to get.

what brand of valve springs did you use and for what head? got a link?

 

[OffGridICF]

Good plan. I had the same concern and it is the reason I built a set of custom 2/0 cables with welder’s cable and lugs.

I am considering the same approach. What amperage fuse are you using?

 

[Short_Shot]

Well the springs also need to be tightened up to a certain amount for compression of the springs. How did you know what force is being applied to the springs? Or you just snugged it enough to where they didn't move?

Of course spring tension is key, can't use any Ole spring as they are different

You can just measure how far you compress the springs and use the known spring rate to determine the load.

If you're really worried about proving it measuring the spring rate is much easier than trying to get a force sensor in place to check the torque load.

 

[Short_Shot]

I am considering the same approach. What amperage fuse are you using?

I used 2/0 wire for bus bars and a 150 amp class T fuse myself, if that helps.

 

[100 Proof]

what brand of valve springs did you use and for what head? got a link?

I used these. I measured their K values to be ~165#/inch. $3.29 each. Easy to get.

https://www.oreillyauto.com/detail/c/melling/melling-valve-spring/mel0/vs360?q=Melling+VS-360&pos=0

 

[Short_Shot]

In addition to valve springs, one can also buy tool and die or even just get generic springs for this, which usually outright give you that value in addition to dimensions.

Pricing varies wildly of course but it doesn't really matter what the rate actually is so long as it's high enough that some length of partial (not full) compression gives you the required force AND you have sufficient space for the length needed.


Of note, a longer spring will give you much more consistent force due to less variation from fully expanded to fully contracted cells but again takes more space up - and isn't that important anyways really.

 

[mikejoconnor]

You need to run it through a bolt pre-load calculator. I'm using 5/16th threaded rod, which means I want about 10 inch lbs across 4 bolts. https://www.engineersedge.com/calculators/torque_calc.htm

For the guys running springs, do your battery banks swell during the charge / discharge cycle? If so, about how much?

 

[100 Proof]

You need to run it through a bolt pre-load calculator. I'm using 5/16th threaded rod, which means I want about 10 inch lbs across 4 bolts. https://www.engineersedge.com/calculators/torque_calc.htm

For the guys running springs, do your battery banks swell during the charge / discharge cycle? If so, about how much?

Yes. About .5mm per cell.

 

[mikejoconnor]

ok, you've convinced me to go with springs. .5mm is insignificant enough to easily deal with, but sufficient enough that I could see it causing problems across 8 cells.

Thanks

 

[S Davis]

You need to run it through a bolt pre-load calculator. I'm using 5/16th threaded rod, which means I want about 10 inch lbs across 4 bolts. https://www.engineersedge.com/calculators/torque_calc.htm

For the guys running springs, do your battery banks swell during the charge / discharge cycle? If so, about how much?

My EVE 280n do as well, I haven’t measured. I mounted my whole battery assembly on vibration mounts so it can do what it wants. This also allows me to heat all the air space around the cells and keep the battery cell temperatures more even.

 

[curiouscarbon]

nice noctua fan. imagine it’s quiet and moves a decent amount of air

 

[S Davis]

nice noctua fan. imagine it’s quiet and moves a decent amount of air

Yes they do I was actually going to reduce the fan speed some, battery boxes are set to 45 degrees and the fans made a huge difference. The whole cell is heated instead of trying to put the pad on the bottom of the cells, in testing the silicone heat pads they just got too hot for me to be comfortable putting the cells in direct contact even spreading the heat with thin aluminum.

 

[Itohmamma]

I’ve got 4 rods so it is only 75KgF / 165 Lbs of force per thread…

The cells have no problem withstanding 660 lbs of force over that surface area.

So…What I am gathering is if I had 100 rods around them I would torque them each to 6.6 pounds…Somehow I’m escaping the physical logic of that force equation!

 

[Short_Shot]

So…What I am gathering is if I had 100 rods around them I would torque them each to 6.6 pounds…Somehow I’m escaping the physical logic of that force equation!

Noooo.

That's absolutely incorrect. Torque does not translate 1:1 to linear force. You would utterly crush the pack if you tried doing it that way.

 

[Dynoman]

Noooo.

That's absolutely incorrect. Torque does not translate 1:1 to linear force. You would utterly crush the pack if you tried doing it that way.

Short_Shot is right that would be way to much pressure.

I am using four 1/4 inch threaded rods on both of my 8S battery fixtures and the nuts were torqued to approximately 5 inch pounds using a torque wrench. My fixture is more or less just retaining the cells with very little pressure applied.
I am currently not using springs.