How do you know when you’ve pierced a terminal bottom on an EVE 280Ah cell?
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Sorry, not understanding.
You are saying that if there are more threads engaged that will make the total strength of the threads weaker (more likely to sheer versus strength of terminal bottom)???
I would have thought the opposite: when fewer threads engaged threads are more likely to sheer versus (fixed) strength of terminal bottom (especially since, by definition, fewer threads tapped likely means a thicker terminal bottom).
Taken to the limit, if there is only a single thread tapped, I’m pretty certain a torqued bolt would sheer off that thread before it punches through the (very thick) terminal bottom.
[EDIT: never mind, now I see how I misread, So you are saying a mm at the bottom is about as strong as a single (1mm) thread.
So less solid thickness below the last thread than total thickness of the threads could result in the terminal bottom getting pierced.
I would have thought that 1 mm of solid aluminum at the bottom would be stronger than 1 mm of thread, especially when you consider than stainless-rotating-on-aluminum contributes some cutting action that doesn’t happen at the bottom (at least not when considering piercing force of pressurized JB Weld).
But at least it’s a reference point - thanks.
Do we know the loyal length of the terminals in these EVE 280 Ah cells?]
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I am saying that without knowing how thick the terminal material is at the bottom of the hole, there is no way to determine the safe pressure.
If the bottom is thicker than 4 times the thread pitch, then its likely the threads will fail before the bottom does.
The threads won't fail unless you exceed the torque limit we have previously discussed.
If the bottom is thicker than 4 times the thread pitch, then its likely the threads will fail before the bottom does.
The threads won't fail unless you exceed the torque limit we have previously discussed.
I’m pretty sure that the torque needed to cause thread failure is directly proportional to how much thread in engaged.
I only had ~4 threads engaged and all but one handled 35 inch-lbs without issue.
if I had used double bus-bars and reduced the engaged threads to ~2-1/2, I’m pretty sure 35 inch-lbs would have stripped...
[PS: I edited my prior post after I understood how I had misread your earlier post, but our typing crossed in the ether...]
Meaning at less than 4 threads you may have difficulty handling 35 inch-lbs but the benefit of a 5th thread is marginal?
Has anyone seen a cross-section of these aluminum terminals? Do we know how thick they are?
Johan
Off-grid energy systems enthusiast.
Below are some approximate BLS 105Ah cell terminal dimensions derived from the same J5GURU Youtube channel.
Source: https://youtu.be/6d89tgUMEbI?t=280 (4:40min)
For M6 bolts, assuming a coarse thread, the pitch is 1mm, so a max of 5 3/4 turns would correspond to 5.75mm. It is tempting to apply theoretical analyses using e.g. a conservative 2mm aluminium bottom thickness being "sheared" out by the grub screws assuming zero thread friction due to epoxy "lubrication", infinite-strength-threads, but it is too darn complex to do on the back of an envelope. I want to see repeatable experimental results. Anyone?
For some more prismatic cell "teardowns": see here (not directly relevant for the problem at hand, but related).
If the thinner cells have a 7.6mm thick round aluminum terminal welded onto a 2mm thick aluminum (or copper) plate, you’re think the larger cells carrying more current would be at least that thick.Below are some approximate BLS 105Ah cell terminal dimensions derived from the same J5GURU Youtube channel.
Source: https://youtu.be/6d89tgUMEbI?t=280 (4:40min)
For M6 bolts, assuming a coarse thread, the pitch is 1mm, so a max of 5 3/4 turns would correspond to 5.75mm. It is tempting to apply theoretical analyses using e.g. a conservative 2mm aluminium bottom thickness being "sheared" out by the grub screws assuming zero thread friction due to epoxy "lubrication", infinite-strength-threads, but it is too darn complex to do on the back of an envelope. I want to see repeatable experimental results. Anyone?
For some more prismatic cell "teardowns": see here (not directly relevant for the problem at hand, but related).
View attachment 37094
I only went 1/8th turn beyond (what I thought was) bottom, but since I didn’t note when I stopped getting any oozing out of the top, hard for me to say whether I may have threaded close to 2 full turns after piercing the bottom (but I doubt it).
At this point, that cell is what it is, but the lessons for me are:
-use JB Weld for gluing terminals within the first hour (despite 4 hour set time). For me, this means only 1 battery / 2 terminals per batch.
-use enough JB Weld to get oozing out of the top (I use a matchstick-head sized dollop at the bottom of the terminal and another matchstick-head sized dollop on the cupped end of the grubscrew.
-thread grubscrew until resistance increases significantly, by which time you should start to see oozing out of the top thread within the next half-turn or so
-the final couple turns generally go very slowly - 1/8 turn every 1/2 minutes - but when in this phase, monitor torque required as well as continued oozing and if torque required reduces (it gets easier to turn) and there are no signs of further oozing, the terminal bottom may be in the process of giving out and it’s time to quit turning and call it a day.
codfish
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While JB is weld is a great product, how about penetrating threadlocker instead.
Finger tighten, and add a drop of this. I've never used it, but it sure sounds simpler.
www.permatex.com
Finger tighten, and add a drop of this. I've never used it, but it sure sounds simpler.
Permatex® Penetrating Grade Threadlocker GREEN
OEM specified. A low viscosity threadlocking liquid that wicks along the threads of preassembled fasteners to secure them in place. Since it is applied after assembly, preventive maintenance procedures are simplified. Ideal for fasteners ranging from #2 to 1/2" (2.2 to 12mm) in size. Localized...
www.permatex.com
My take on it:While JB is weld is a great product, how about penetrating threadlocker instead.
Finger tighten, and add a drop of this. I've never used it, but it sure sounds simpler.
Permatex® Penetrating Grade Threadlocker GREEN
OEM specified. A low viscosity threadlocking liquid that wicks along the threads of preassembled fasteners to secure them in place. Since it is applied after assembly, preventive maintenance procedures are simplified. Ideal for fasteners ranging from #2 to 1/2" (2.2 to 12mm) in size. Localized...
-thread locker will basically glue the threads in place and might prevent shear forces by limiting movement.
-JB weld may offer some additional structural strength by filling loose spaces between the thread interface
A bad analogy probably:
-thread locker is like spraying your foot with adhesive before you shove it in a boot. It dries and your foot and leg kind of sticks to the boot to prevent twisting and pull out
-JB weld is like putting some concrete in the bottom of the shoe and letting is squeeze up through your toes and around your ankle when you shove your foot in. Pretty solid once it sets. The danger is that you may not be able to get your foot all the way in because of the hydraulic effect
I think either will help prevent pull out, but JB weld is likely the stronger solution if you can make it work
codfish
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I agree in principle, but if a threadlocker is "permanent" and requires heating to 500F to release, then it seems like to must be doing a pretty good job of filling all those little spaces and bonding to each surface. I wonder what a dried drop of it feels like compared to JB Weld.
Seems like a bench top experiment would answer the question. piece of aluminum, drill and tap a few holes. Each one gets either JB Weld, red, green, blue threadlocker and a grub screw. wait till morning and evaluate.
That’s my guess as well.
I’m pretty confident JB Weld will recover my partially-stripped terminal more effectively than Loctite Red would have.
And I’m reasonably confident JB Weld will also do a superior job glueing grubscrews into my worn threads (not stripped, but upper 4 threads clearly worn from ~4 insertions/removals of stainless bolts, likely due to galling).
But from everything I’ve read about Loctite Red and experienced with JB Weld, if I ever find myself glueing grubscrews into pristine / unused aluminum threads, I believe Loctite Red should perform as well as JB Weld and sounds waaay easier to install, so I’d go that route in a heartbeat...
I have not personally messed with these threads/cells yet, but my prior experience with aluminum is that it can be prone to sloppy machining resulting is loose tolerance. Thread locker is good at preventing a bolt from turning in the hole, but most flavors are not good at filling gaps and providing additional structure where needed. When my cells arrive, I plan to assess the tolerance and make a call. My preference would be thread locker, but I'll consider an epoxy approach if things are really loose. My batteries are going in a van, so I don't want any questions on torque or reliabilty
That’s a good plan.
I didn’t have the wherewithal to check my thread depth and tightness of fit when my new EVE 280Ah cells came in (too excited
.I went straight to balancing and then capacity testing using the bundled busbars and bolts, only tightening by hand/finger, but I now know that means as much as 20 inch-lbs.
Each cell was only threaded and unthreaded 4 times through this process but the bottom line was that after I’d partially stripped a thread torquing to 35 inch-lbs and began planning to convert all terminals with grubscrews, the aluminum threads were all looser than I was comfortable with.
They could have arrived that way from the get-go or galling of stainless bolts in soft aluminum threads may have worn off some thread material and loosened them up after only 4 gentle threadings/unthreadings, but the bottom line is that after seeing how loose they were and discovering how effective JB Weld was, it was an easy decision to use JB Weld on all the loose threads.
I’m also shocked at how much JB Weld ends up being absorbed by the threads. I’m putting in two matchstick-head-sized dollops per thread, and once it starts oozing out, some of that is obviously not staying in the thread, but the total volume of the HB Weld I’m cleaning out around the threads at the top is less than 25% of the volume of what I added at the beginning.
Each ‘dollop’ is probably close to 2 drops worth, so about 4 drops going in and less than one drop coming out.
It’s a pretty painful process - I think it’s taking me about an hour for each cell, but it is very satisfying to see how well it comes out...
Frank in Thailand
making mistakes so you don't have to...
Personal experience, I've got too deep.
I could tell as there suddenly was no "stop"
I did not go all the way down!
What I did do (with all my threaded rods) is secure it with Locking agent (Loctite) with it, creating a new air tight seal.
If it was vacuum, it would have sucked in "contaminated air".
If it have stable pressure, then "nothing happened)
After 3 months of usage, I can not see or measure any difference between that cell and all the others
(32* 280Ah)
I hope this helps
I could tell as there suddenly was no "stop"
I did not go all the way down!
What I did do (with all my threaded rods) is secure it with Locking agent (Loctite) with it, creating a new air tight seal.
If it was vacuum, it would have sucked in "contaminated air".
If it have stable pressure, then "nothing happened)
After 3 months of usage, I can not see or measure any difference between that cell and all the others
(32* 280Ah)
I hope this helps
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