Looks good! Thanks for the numbers. Don't pop a hernia moving that thing.
Threaded rod cell strapping and assembly
- Thread starter idontknowwhatimdoing
- Start date
If the plates are snug enough and the threaded rod is offset from the battery, there shouldn't be any contact.
Plastic case cells don't shrink when discharged. Plastic case cells can expand during charge cycle. That is why the flat sides are restrained with a panel. Could be 1/4 aluminum if careful of electrical contact. It could be plywood, no chance of short circuits. It could be ridged plastic, but not as desirable as plastic can deform in time. The rods are used to pull the plates against the sides of the cells. There is not a concern with torque if using ny-lock nuts. It is a matter of tightening the nut to pull the plates in firmly against the plastic cased cells so the cells do not expand. Just make them reasonably tight using a small wrench, not that 2 footer you keep for the 7/16 sockets. I have not read all, but I haven't seen a specification for torque on such restraints. There is some for soft pouch cells, a different animal.
Not that I know of and I believe some are taking this too seriously. From what I have read regarding cell compression I can not understand why EVE recommends the high amount of compression that they do. It is equal to 600 pounds of force. That is with 1C charge and discharge rates if I am understanding that part of the spec correctly.
My idea is to do whatever is necessary to keep the cells from expanding by arranging them snug between plywood, or metal. I believe plastic will bulge with the cells and not be able to handle the force.
Exactly and I see this as applying to aluminum cased cells and that should be all that is required. Using a low charge rate to fully charge the cells they should not expand and that's what I intend to do before mounting my cells between the plates.
My idea is to do whatever is necessary to keep the cells from expanding by arranging them snug between plywood, or metal. I believe plastic will bulge with the cells and not be able to handle the force.
Exactly and I see this as applying to aluminum cased cells and that should be all that is required. Using a low charge rate to fully charge the cells they should not expand and that's what I intend to do before mounting my cells between the plates.
Has anyone translated 300kgf to torque for a specific diameter rod like 1/4” and a specific thread (angle)?
My thought on how to approach this was to tighten to snug (or 300kgf if easy to measure in terms of torque) when near empty (~20% SOC) then charge to 100% (or whatever max you use), monitoring torque and backing off as needed.
If you can end up having close to 300kgf applied to cells at their maximum SOC, that’s probably as good as you can (easily) do.
My thought on how to approach this was to tighten to snug (or 300kgf if easy to measure in terms of torque) when near empty (~20% SOC) then charge to 100% (or whatever max you use), monitoring torque and backing off as needed.
If you can end up having close to 300kgf applied to cells at their maximum SOC, that’s probably as good as you can (easily) do.
1/4-20 dry, zinc plated rod/bolt, will produce about 75lbs of clamping force with 16.5 in-lbs of torque. This is pretty rough of course, lots of variables. It is quite easy to exceed that tightening with a 10" wrench for example. I posted a link earlier with a basic calculator for clamping load.
Given that the cells size, 600lb distributed across the cells surfaces is not even 10PSI. It may seem like a lot at first glance, but you can apply that much pressure with 2 fingers if you wanted to.
If you are using metal plates to clamp aluminum cased cells, you need some type of rubber or plastic layer. The cells are not perfectly square, with the edges being slightly proud when a compressive load is applied. So a 1/6" plastic or rubber sheet between the cell and clamping plate will provide some give and isolate the metal.
Given that the cells size, 600lb distributed across the cells surfaces is not even 10PSI. It may seem like a lot at first glance, but you can apply that much pressure with 2 fingers if you wanted to.
If you are using metal plates to clamp aluminum cased cells, you need some type of rubber or plastic layer. The cells are not perfectly square, with the edges being slightly proud when a compressive load is applied. So a 1/6" plastic or rubber sheet between the cell and clamping plate will provide some give and isolate the metal.
So you are assuming 300Kg applied to the full surface of the outermost cell (or 300Kg placed on the outside of the top cell if they were stacked vertically), correct?
17.36cm x 20.48cm = 355.5cm^2 of surface.
And 300Kg on 355.5cm^2 translates to 0.844 Kg/cm^2 or 12psi.
Am I understanding this correctly? I’ll admit that 12psi is less pressure than I was expecting, on the other hand, how to translate psi to inch-pounds on a torque wrench is unclear to me...
Yes.
@Luthj already answered that just before your post; he posted a link to a calculator on the previous page: https://www.engineersedge.com/calculators/torque_calc.htm
You can also do all the math by hand if you prefer of course
Yes.
@Luthj already answered that just before your post; he posted a link to a calculator on the previous page: https://www.engineersedge.com/calculators/torque_calc.htm
You can also do all the math by hand if you prefer of course
Thanks - no desire to perform all calculations by hand, but want to make sure I’m understanding correctly.
And one thing I’m lost on is how the math changes as the numbers of bolts increase.
Does every bolt need to apply 12psi of pressure (300Kg of force) or is that 300Kg of force divided by the number of bolts?
If every bolt applies 300Kg or 660 lbs of force, I come up with 33 inch-lbs of torque.
If using 4 bolts means each should only apply 75Kg of force rather than 300Kg, that would translate to a bit over 8 inch-lbs of torque (practically nothing).
I can understand stacking my battery vertically and putting a container full of 660 pints (82.5 gallons) of water on top of the stack and that seems like a lot of compression force (and too much trouble).
I’m having difficulty understanding how that 300Kg of force translates to the seemingly-small levels of torque we are talking about - seems like a lot less compression force...
It's the total force, for example if you have 6 bolts then each bolt needs to apply 50 kgf only.
You underestimate the clamping force a bolt can have, that's pretty common actually. Even a small bolt can have a few metric tons of clamping force at max torque.
OK, so your confirming that if using 6 bolts, each should apply 1/6th of the specified force, and if using 4 bolts, each should apply 1/4 or the required force.
4 bolts would need ~8 in-pounds of torque which isn’t much. The the torque wrench that I have reaches 600 ft--inches in minimum increments of 25 ft-inches, so looks like I’ll need to get a more sensitive torque wrench...
I suppose you’re right. Time to find a more sensitive torque wrench...
Which brings up a few other questions:
-Is overtorqueing by 50% or 100% a problem? We know 300Kga of force is needed to get the full 3500 cycles, but will going (modestly) above that cause damage / a problem?
-I was going to go with Aluminum ends both for strength as well as heat dissipation, but ABS plastic may be plenty strong enough (and much cheaper).
Don't get into the weeds here. I would go to 20 in-lbs and call it good. That's basically "snug" with a short wrench. The important thing is that you don't accidentally put 50in-lb+ by mistake.
Your not going to damage the cells with a few hundred extra pounds of clamping force. These cells are made with a nearly solid spiral wound laminate. It is quite strong in compression.
Does this forum support an ‘edit’ function? I see my typos but can find no way to fix them...
Good advice - thanks. And I assume you want to snug those cells to that level while they are 100% SOC, correct?
Now that I understand the torque is so modest, I may tighten when at low SOC and monitor how torque increases as the cells charge up to 100% (backing off as needed to maintain ~20in-lbs).
Thanks but I don’t see any edit option even immediately after replying - where does the ‘edit window’ appear?
I’m on my iPhone rather than a PC, so that might have something to do with it...
