Yeah...very good point gazoo....We don't need to know the stripping point. We need to know how much torque it takes to make a good electrical connection between the busbar and the cell terminal and then we can work with that. @Bob B just posted in the other thread he thought he read somewhere 4nm.
I applied the loctite to the grub screws. The whole point of using it was to help prevent stripping of the cell terminal. I understand once it's cured it's supposed to be in a forever state. That's why I used it. I would think the torque applied to a nut screwed onto a grub screw would be the same as using a bolt in the cell terminal's hole?
Loctite is not a grease if allowed to cure properly. In my case is I did not use the primer. So maybe that one grub screw didn't cure.
I am referring to grub screws. I was hoping they would never come out. Nuts, ring terminals or whatever is not what I am referring to. I am only referring to the grub screw. The question still remains. How much torque is sufficient applied to the busbar to make a good electrical connection. You said you think you used 25 inch pounds. Is that enough? And is that enough to keep the screws or nuts tight enough so they don't come loose?
The EVE data sheet is pretty clear when it says "less than 8 Nm." I had my own idea that the term "... anti-torsion of pole is 8Nm" meant to be careful since I knew it had been translated from Chinese. We have heard earlier reports of people punching through the bottom of the terminal so I have enough data.I thought the 8nm point was because of what had been seen in the eve datasheet, but how do we know that in actual fact 6nm is the stripping point....as far as i can tell, we dont know for sure.
The point of the thread locker for me is more convenience to make sure the grub screw does not rotate when torque is applied to the nut above the terminal. On the one hand I don't want it punching a hole in the bottom of the terminal and two, I don't want it rotating out when reconfiguring the pack. If it inadvertently came out a turn or two then there would be a risk that it could strip out the next time it was torqued down because less threads were engaged.But you still can't use the same torque on a grub screw that has thread locker on it as you can on a dry grub screw. If you're doing the grub screw correctly, there shouldn't be any need for thread locker or even a torque wrench when inserting the grub screw into the terminal.
Sorry for being so stubborn, but I still don't understand why using a thread locker, JB Weld or whatever on the stud and terminal threads would have any effect on a "safe" torque applied to the nut. I would have thought more torque could be applied to the nut if using a thread locker.The torque to be worried about there is how much force is on the nut that holds the bus bar, ring terminal or lug down onto the terminal. You can still strip the terminal threads with a grub screw if you put too much force on the nut.
I think my answer to this is that you can't use the torque on the nut compensate for any curvature in your bus bar material. If the bus bar is flat and clean and the terminal is likewise, it won't take much pressure to create a good electrical connection. If the bus bar is trying to spring away from the terminal because it has a bend or curve to it, you'll likely strip out the threads before you get enough pressure on it to make a good connection.We are finding out these threads do strip easily. So....the question is how much torque needs to be applied to the busbar to ensure a good electrical connection.
Yes I would agree. I think the 8Nm refers to when the terminal pole will twist. Therefore I assumed the "less than 8Nm" meant exactly that as far as the safe torque for a nut.
Also it has been mentioned earlier that people have punched through the bottom of the terminal so I back off my grub screws 1/4 turn. I am not sure why @Darkstar feels it is necessary to put them in more than finger tight, especially when there is JBWeld at the bottom of the hole. I think that would put unnecessary pressure on the bottom of the terminal for no apparent benefit.
Sorry for being so stubborn, but I still don't understand why using a thread locker, JB Weld or whatever on the stud and terminal threads would have any effect on a "safe" torque applied to the nut. I would have thought more torque could be applied to the nut if using a thread locker.
We are finding out these threads do strip easily. So....the question is how much torque needs to be applied to the busbar to ensure a good electrical connection. If you are sure you used around 25in lbs, and you are not experiencing any issues then I know that would be good enough for me. There will never be more than 100 amps going through my busbars and it might end up being a lot less depending on the inverter I finally decide on. Does torque determine the amount of amps that can go through the bus bar? My thinking is good clean and flat terminals would not require much torque.
This is a good discussion. If we can determine a good torque value then we can help others to prevent stripping the cell terminals.
Yes it is and it deserves its own thread so it doesn't get buried. It applies to all of these LF280 cells, and perhaps to others with similar terminal construction.This is a good discussion. If we can determine a good torque value then we can help others to prevent stripping the cell terminals.
Also, my interpretation of the 8Nm limit is that it is the limit of torque you can put on the terminal before you risk damage to the connection between the terminal and the battery internals. I don't think it has anything to do with thread strength.
Sorry for being so stubborn, but I still don't understand why using a thread locker, JB Weld or whatever on the stud and terminal threads would have any effect on a "safe" torque applied to the nut. I would have thought more torque could be applied to the nut if using a thread locker.
We are finding out these threads do strip easily. So....the question is how much torque needs to be applied to the busbar to ensure a good electrical connection. If you are sure you used around 25in lbs, and you are not experiencing any issues then I know that would be good enough for me. There will never be more than 100 amps going through my busbars and it might end up being a lot less depending on the inverter I finally decide on. Does torque determine the amount of amps that can go through the bus bar? My thinking is good clean and flat terminals would not require much torque.
This is a good discussion. If we can determine a good torque value then we can help others to prevent stripping the cell terminals.
Not arguing about the thread locker on the bottom threads of a grub screw. As long as you insert the grub screw into the terminal by hand (no tools) you'll never strip the threads in that step.
My issue is with the tightening of the nut on top. If someone isn't doing this right, they can certainly strip the terminal threads. The right way is to hold onto the grub screw with one tool and tighten the nut with a second tool. Even with that technique, you can still put too much force on the terminal threads, pulling the grub screw out of the terminal.
I agree completely and that is something to be mindful of when using thicker buss bars. Laminated or double buss bars would mitigate that.I think my answer to this is that you can't use the torque on the nut compensate for any curvature in your bus bar material. If the bus bar is flat and clean and the terminal is likewise, it won't take much pressure to create a good electrical connection. If the bus bar is trying to spring away from the terminal because it has a bend or curve to it, you'll likely strip out the threads before you get enough pressure on it to make a good connection.
Yes that was my interpretation as well. That is why I particularly paid attention to the following "less than 8Nm" sentence. Fortunately my torque 1/4" socket driver does not go beyond 6 Nm.Also, my interpretation of the 8Nm limit is that it is the limit of torque you can put on the terminal before you risk damage to the connection between the terminal and the battery internals. I don't think it has anything to do with thread strength.
I think my answer to this is that you can't use the torque on the nut compensate for any curvature in your bus bar material. If the bus bar is flat and clean and the terminal is likewise, it won't take much pressure to create a good electrical connection. If the bus bar is trying to spring away from the terminal because it has a bend or curve to it, you'll likely strip out the threads before you get enough pressure on it to make a good connection.
Also, my interpretation of the 8Nm limit is that it is the limit of torque you can put on the terminal before you risk damage to the connection between the terminal and the battery internals. I don't think it has anything to do with thread strength.
I know and you got that number from HRTKD....same here.When I said I saw no issues at 25 in/lbs I was only referring to no more problems with stripping.
Yup...I am thinking the same. No more than 4nm's. One can always use double nuts to keep the nut at that torque.As a side note about another comment, my gut feeling is that at 6NM you may start seeing some stripping of threads. I think 5 and 6NM may still be too much torque. I stripped every hole I tried at 8NM. I stopped at 3 attempts...
I think if properly clamped and using braided busbars, and insulators they would be fine in mobile applications. I noticed my cells expanding even though they are clamped with 5/16 threaded rod and 1/4 inch plywood. Whoever said threaded rods act like springs was right. I think it was @Luthj? In light of all of this I have been thinking that only braided busbars should be used whether mobile or not. But that's another subject.I now see why these cells would not work in any sort of mobile application. They are too fragile.
That's the way I would prefer to do it .... I did some searching for an open end torque wrench so the 2 wrench method could be used and know what the torque is ... but I didn't find anything I liked the look of.
Some BMSs can give you IR readings of the cells in a pack and in some cases a weak or higher resistance connection can show up there as an added diagnostic before it shows up as heat.I am awaiting parts to complete the battery pack before I can test all the connections for conductivity. I guess that would just involve making sure I have full voltage at 16s and then checking for overheating during charge/discharge.
I now see why these cells would not work in any sort of mobile application. They are too fragile.