Compress or not, flexible busbar or not

[justgary]

That might be your entire point but maybe (bare with me here) you were overlooking how much more force was involved to compress 8 cells instead of 4 because of your view point. Did you read post #237. Am I wrong?

I have told you you are wrong all day now. You are wrong.

We are not expressing opinions, we are quoting physics.

 

[Cheap 4-life]

Did you read post #237 how is the way I see it regarding pushing the car incorrect.
I’ll try to explain it several different ways..
If you put 16 equally strong people behind one another and all try to push a car the car would move a lot easier than if one person was trying to push it.. thats ofcourse If the first fellas arms could hold up.. that’s because there’s more force with 16 people than one. It is simple physics.
Or you could look at it like 2 walls moving in trying to crush 16 people back to back. 8 one way pushing on one wall and 8 the other way. Those 16 people would put a lot more force on the walls in an attempt to stop the wall from crushing them than one person (cell) would.. that extra force of each additional person creates more force. Not 16 times more force because they are back to back not aside of each other pushing but still 1 person/cell is less force than 16 people/cells which creates more pressure

 

[justgary]

I’m ok with your opinions, I’m not ignoring or arguing, simply typing my point which you do not agree with

Because you are wrong. Accept it.

Getting aggravated because we have a difference in opinion.

We don't have a difference of opinion. We all agree that you can compress, not compress, use springs, use foam, whatever.

What is frustrating is that we keep trying to teach you how the physics works and you won't accept it and move on. Telling us that we can leave the thread since we don't agree with you only will cause someone else to read your explanations and get it wrong also. I don't want to have to explain it to someone else later on, so I am sticking with this until you get it.

 

[justgary]

you were overlooking how much more force was involved to compress 8 cells instead of 4 because of your view point.

I didn't overlook anything. I clamped one four cell pack, then I clamped four eight cell packs after that. The clamping force was always the same. My viewpoint coincides with physics.

 

[noenegdod]

So let’s use your hydraulic ram. If that ram pressed with just enough force to keep one cell flat at 100% SOC. Would that ram be able to keep 8 cells at 100% SOC just as flat as it did the one cell using only that same exact amount of force?

Yes

I’m not saying ending up at the same psi. I’m saying the same amount of force. because that’s what’s applied to the rigid walls.

Forget PSI that was something that someone on here converted from the 300kg of force that was in the eve doc. Yes, the same amount of force is required to keep a stack of 8 compressed as it would to keep a single cell compressed. BUT. If you took all 8 cells and laid them all flat, not in a stack but narrow side to narrow side and had huge plates acting on the big side of all the cells, that would require 8x as much force.

I’d think it would take more force same as more force would be applied to the rigid walls to create the same psi in the 8cell vs 1 cell pack

No.

 

[Cheap 4-life]

Or how I like to look at it. If I’m pushing on a car trying to move it (like I’m one cell trying to expand) and my equally strong buddy (second cell trying to expand) pushes on my back, we will create more force/mass therefore more easily moving the car. Now if that car was against a concrete wall (like cells against fixed rigid end plates) then my buddy and I would simply be exerting our force against the concrete wall, which is more force than I could put on the concrete wall if I was the only pusher.. which would create a higher psi at the concrete wall..
Point is 2 cells (2 people) apply more force to the end plate (concrete wall) than one cell (one person would), which creates more pressure throughout the rig or throughout the push/SOC.
Since my buddy is pushing on my back it’s not double the force as it would be if he was pushing aside of me but it’s still more force with two of us like it would be with 1 cell against another cell, which makes more force than just one cell.
I might not have went to college but I have pushed a lot of cars..

Explain how this is wrong. Or do people defy the laws of physics

 

[noenegdod]

My understanding is having one hydraulic ram behind another will indeed create more force.

No this is wrong. if you put all the cylinders in a row pushing on each other, they can push further distance but the force they can push with is the same.

In a diy battery pack the pressure is held/applied by the endplates that could be fixed with a rigid rig. So the more cells the more force applied to the endplate therefore more pressure through the cells. Which is why a higher pressure is experienced by each cell as the cell gets a higher SOC in a compressed/fixed/rigid inclosure..
Or how I like to look at it. If I’m pushing on a car trying to move it (like I’m one cell trying to expand) and my equally strong buddy (second cell trying to expand) pushes on my back, we will create more force/mass therefore more easily moving the car. Now if that car was against a concrete wall (like cells against fixed rigid end plates) then my buddy and I would simply be exerting our force against the concrete wall, which is more force than I could put on the concrete wall if I was the only pusher.. which would create a higher psi at the concrete wall..
Point is 2 cells (2 people) apply more force to the end plate (concrete wall) than one cell (one person would), which creates more pressure throughout the rig or throughout the push/SOC.
Since my buddy is pushing on my back it’s not double the force as it would be if he was pushing aside of me but it’s still more force with two of us like it would be with 1 cell against another cell, which makes more force than just one cell.
I might not have went to college but I have pushed a lot of cars..

Again, no. what happens if if your buddy is twice as strong as you? He would simply crush you and you become useless. However if your buddy was beside you and not pushing on your back, then the force you apply would be additive. He pushes twice as hard as you push as hard as you so you get a total of 3 yous pushing. Does this make sense? You have to get your head around this. This is right and how it works. Read it as many times as it takes.

 

[noenegdod]

I’m ok with your opinions, I’m not ignoring or arguing, simply typing my point which you do not agree with which again is fine, we all can’t agree and even agree less on this highly debatable subject.. but since your implying that I’m doing something wrong, then heres what your doing wrong. Getting aggravated because we have a difference in opinion. You are making implications about the data sheet that imo do not make sense but go along with your opinion that a fixed/rigid fixture is fine.

This is not my opinion, I have never said that. That is what the EVE document that was posted on here said. Im just trying to help you understand something that is escaping you.

 

[Cheap 4-life]

Again, no. what happens if if your buddy is twice as strong as you? He would simply crush you and you become useless. However if your buddy was beside you and not pushing on your back, then the force you apply would be additive. He pushes twice as hard as you push as hard as you so you get a total of 3 yous pushing. Does this make sense? You have to get your head around this. This is right and how it works. Read it as many times as it take

I said he was equally strong similar to how each battery cell would apply the same force.. as I said if the arms of the first person could hold up to the force of both people like a cell could definitely withstand... even if he is behind me pushing on my back, the two of us are still applying more force to that car than just one of us, same as 2 cells internal pressure would apply more force than one. As I said, it’s not twice as much (not compounding) force because he is behind me pushing on my back,, even with him pushing on my back, 2 people are still applying more force than one person.. yes if he was stronger than me than there would still be more force applied than I could apply myself and yes more force than 2 equally strong people if the person behind me was stronger. Not 3 times as much force but still more than somebody weaker than him pushing behind me.. but that is irrelevant because to keep it simple we should continue to compare equally strong people to equal cells..

 

[Cheap 4-life]

This is not my opinion, I have never said that. That is what the EVE document that was posted on here said. Im just trying to help you understand something that is escaping you.

Well if that’s what you think the EVE document implies than that’s your opinion. I do not agreee that it implies a fixed/rigid fixture is fine for our DIY packs. All I think the data sheet shows is how they tested one cell. That doesn’t make it correct for multiple cells long term or even for one cell long term or short term for that matter. It is simply how that cell was tested. The pressures that cell experience being in a rigid fixture might not be optimal for long battery life and might be overcompressing the cell and shortening its life..

 

[Cheap 4-life]

will cause someone else to read your explanations and get it wrong also. I don't want to have to explain it to someone else later on, so I am sticking with this until you get it.

This comment is exactly why I’m trying to make sure the correct information is on here.. now if you can explain how my car pushing logic is wrong, like how a person pushing on my back doesn’t make me push the car slightly harder, that would be great.. problem is I know for a fact that if someone is pushing on my back that I will absolutely be able to push harder, not twice as hard but none the less still harder. And if a person was added to his back pushing then he could push on my back harder which would make me push harder if my arms could handle the force...

 

[noenegdod]

I said he was equally strong similar to how each battery cell would apply the same force.. as I said if the arms of the first person could hold up to the force of both people like I cell could definitely withstand... even if he is behind me pushing on my back, the two of us are still applying more force to that car than just one of us, same as 2 cells would apply more force than one. As I said, it’s not twice as much (not compounding) force because he is behind me pushing on my back,, even with him pushing on my back. 2 people are still applying more force than one person.. yes if he was stronger than me than there would still be more force applied than I could apply myself and yes more force than 2 equally strong people if the person behind me was stronger. Not 3 times as much force but still more than somebody weaker than him pushing behind me.. but that irrelevant because we are comparing equally strong people to equal cells..

This comment is exactly why I’m trying to make sure the correct information is on here.. now if you can explain how my car pushing logic is wrong, like how a person pushing on my back doesn’t make me push the car slightly harder, that would be great.. problem is I know for a fact that if someone is pushing on my back that I will absolutely be able to push harder, not twice as hard but none the less still harder.

Here ya go

pushing a car is a bad example for a couple different reasons so try this instead.

If two people are lifting a 400lbs object and are standing side by side they are both supporting 200 lbs. Correct?

You have to ignore the weight of the second person. If instead of standing side by side, you picked up the second person who picked up the 400 lbs object. You now have to be able to hold 400 lbs and so does the second person. Does that make sense?

Side by side you both only have to be able to pick up 200 lbs. If you are in a row where you are picking up your weightless friend and he is picking up the object you both need to pick up 400 lbs. Please think this through. This is not opinion. it is fact. Simply the way the universe works.

 

[justgary]

I’m not saying ending up at the same psi. I’m saying the same amount of force.

Pressure in PSI (pounds per square inch) is equal to the force in pounds divided by the cross-sectional area in square inches. The same force exerted on the same cross section is the same pressure in PSI.

I can't find anything in the data sheet, it's quite relevant for creating fixtures.

Let's look at some datasheet values:
300kgf at 30% SOC. 300kgf equals 660 pounds.
7kN maximum under normal conditions. 7kN equals 1,573.7 pounds.

The cross-sectional area of an EVE 230 Ah cell is 204.6mm width times 173.93mm height. This is 35,586 square mm, which equals 55.16 square inches. To find the compression pressure, we divide the force in pounds by the cross-sectional area in inches. That gives us:

300kgf on the face of the cells = 660 / 55.16 = 11.97 PSI.
7kN on the face of the cells = 1,573.7 / 55.16 = 28.53 PSI maximum under normal conditions.

 

[Cheap 4-life]

If two people are lifting a 400lbs object and are standing side by side they are both supporting 200 lbs. Correct?

You have to ignore the weight of the second person. If instead of standing side by side, you picked up the second person who picked up the 400 lbs object. You now have to be able to hold 400 lbs and so does the second person. Does that make sense?

Yes and yes.. but that still does not change the fact that if someone is pushing on my back like a cell is pushing on another, there’s is then more force.. you are adding gravity into the physics,, when it’s pushing instead of lifting then gravity is irrelevant other than the friction the weight has in the ground due to gravity but that's also irrelevant in my examples.

 

[justgary]

now if you can explain how my car pushing logic is wrong

First, you never explained why it is right. I don't feel like creating a force diagram for you just for you to refuse to accept it. How about you do it and show us?

pushing a car is a bad example for a couple different reasons so try this instead.

A very bad example, primarily because the car can move. If we can ignore friction for a moment, we would discover that the first person pushing the car will cause it to accelerate (and keep accelerating because he has constant force and F=MA). I didn't do the math, but I suspect that the second person would notice that even though it feels to him like he is pushing, the reality is that the first person is running away from him at the same rate the second is trying to run to apply force. The result is that the second person applies no useful force to the car.

 

[Cheap 4-life]

Pressure in PSI (pounds per square inch) is equal to the force in pounds divided by the cross-sectional area in square inches. The same force exerted on the same cross section is the same pressure in PSI.



Let's look at some datasheet values:
300kgf at 30% SOC. 300kgf equals 660 pounds.
7kN maximum under normal conditions. 7kN equals 1,573.7 pounds.

The cross-sectional area of an EVE 230 Ah cell is 204.6mm width times 173.93mm height. This is 35,586 square mm, which equals 55.16 square inches. To find the compression pressure, we divide the force in pounds by the cross-sectional area in inches. That gives us:

300kgf on the face of the cells = 660 / 55.16 = 11.97 PSI.
7kN on the face of the cells = 1,573.7 / 55.16 = 28.53 PSI maximum under normal conditions.

So your saying 28.53psi is fine to subject our cells in our packs to? I have to strongly disagree. That might be the maximum a cell will see under there normal operating conditions (tests they put the cell thru) in a rigid/fixed rig like the data sheet, but that does absolutely not mean that is ok to do to our cells.. and how you come up with they are implying that is fine pressures for our cells,, I can’t understand

 

[noenegdod]

Yes and yes.. but that still does not change the fact that if someone is pushing on my back like a cell is pushing on another, there’s is then more force.. you are adding gravity into the physics,, when it’s pushing instead of lifting then gravity is irrelevant other than the friction the weight has in the ground due to gravity but that's also irrelevant in my examples.

Quite to the contrary, it is a completely relevant example. I am sorry to sound harsh but you dont have the depth of knowledge to grasp the subject. You need to go get some basic knowledge and then you might have a chance of grasping this very simple concept.

 

[Cheap 4-life]

First, you never explained why it is right. I don't feel like creating a force diagram for you just for you to refuse to accept it. How about you do it and show us?


A very bad example, primarily because the car can move. If we can ignore friction for a moment, we would discover that the first person pushing the car will cause it to accelerate (and keep accelerating because he has constant force and F=MA). I didn't do the math, but I suspect that the second person would notice that even though it feels to him like he is pushing, the reality is that the first person is running away from him at the same rate the second is trying to run to apply force. The result is that the second person applies no useful force to the car.

The car can move but I also said now put the car against a concrete wall..and explained how there is still more force with him pushing on my back than I could muster on my own. again not twice as much but still more than I could force by myself.. Same as two cells pushing back to back..

 

[justgary]

again not twice as much but still more than I could force by myself.

If not twice as much, then how much? Please show your work. Conjecture and hypothecation aren't enough.

 

[Cheap 4-life]

Quite to the contrary, it is a completely relevant example. I am sorry to sound harsh but you dont have the depth of knowledge to grasp the subject. You need to go get some basic knowledge and then you might have a chance of grasping this very simple concept.

And I’m as sorry if I sound harsh same as you are, but go outside and push your car, now have someone push on your back when you are pushing. You will feel the extra force in your arms and if you both are strong enough y’all will move the car easier than if you were pushing by yourself.. now if you put that car against a concrete wall but put a pressure sensor between the wall and the car, you would then see that with the person pushing on your back there’s more force therefore there is more pressure created. If they stopped pushing on your back the force and pressure would slightly drop..