Sanity check my terminal nut security plan

[SlimyLemur56]

I have 4x 3.2v 105AH cells, and I will be pulling a small amount of current from them (generally <5A@12v with a 15A breaker). The studs are M8, that I had to put in myself after the M4 terminals stripped out immediately when I got them. The battery will be compressed in a pelican case I have built out with padding on the inside, as part of a travel kit.

To paint a picture of the lifestyle it will live: it will sit on the concrete in my garage unused, and then a few times a month, get picked up, put in the car, taken out to a field, set on the earth over night, back in the car to the garage. So it will not be subject to ongoing vibration, but occasional weight-shifting transport within it's padded home. It will be moved carefully by me, so not post-office-banged-around, just regular I-tried-not-to-bang-it-around-banged-around.

Because of the low amount of amperage I will be pulling from it (with a breaker also), and to reduce the chance of weird stresses put on the terminals when the weight shifts, in lieu of traditional bus bars I am using flexible, short, double-runs of 12awg wire between the cells.

Now that I have my studs glued in (https://diysolarforum.com/threads/cleaning-the-terminals-after-jb-welding-studs-in.48723/) I have some final question about nuts, lock washers, and torque.

My plan is to put the ring terminals on, then put on lock washers like these

Then put an M8 hex nut on. Tighten it enough to flatten the lock washer. Then put another hex nut on as a lock nut over the first to lock it like this

And usr blue loctite on the locking nut for extra security.


Does this seem sane?
If I am using this type of springy lock washer, is it good enough to tighten the nut down until the washer is flat, or do I need to be concerned about precise numerical torque?

 

[400bird]

The originals were m4? That's tiny, I haven't heard of any cells with terminals that small.

My concern with m8 lock washers is that they take more clamping force to flatten than the m4, possibly even more force than stripped out the m4.

In the end, yes I would recommend using a torque wrench. I might skip the split lock washer and some of the softest thread locker.

 

[Supervstech]

I have 4x 3.2v 105AH cells, and I will be pulling a small amount of current from them (generally <5A@12v with a 15A breaker). The studs are M8, that I had to put in myself after the M4 terminals stripped out immediately when I got them. The battery will be compressed in a pelican case I have built out with padding on the inside, as part of a travel kit.

To paint a picture of the lifestyle it will live: it will sit on the concrete in my garage unused, and then a few times a month, get picked up, put in the car, taken out to a field, set on the earth over night, back in the car to the garage. So it will not be subject to ongoing vibration, but occasional weight-shifting transport within it's padded home. It will be moved carefully by me, so not post-office-banged-around, just regular I-tried-not-to-bang-it-around-banged-around.

Because of the low amount of amperage I will be pulling from it (with a breaker also), and to reduce the chance of weird stresses put on the terminals when the weight shifts, in lieu of traditional bus bars I am using flexible, short, double-runs of 12awg wire between the cells.

Now that I have my studs glued in (https://diysolarforum.com/threads/cleaning-the-terminals-after-jb-welding-studs-in.48723/) I have some final question about nuts, lock washers, and torque.

My plan is to put the ring terminals on, then put on lock washers like these
View attachment 116413
Then put an M8 hex nut on. Tighten it enough to flatten the lock washer. Then put another hex nut on as a lock nut over the first to lock it like this
View attachment 116414
And usr blue loctite on the locking nut for extra security.


Does this seem sane?
If I am using this type of springy lock washer, is it good enough to tighten the nut down until the washer is flat, or do I need to be concerned about precise numerical torque?

I don’t understand what you will be doing with the nuts and the bolt in relation to the terminals.

 

[time2roll]

I put mine at 3nm torque with nothing else.

 

[SlimyLemur56]

The originals were m4? That's tiny, I haven't heard of any cells with terminals that small.

My concern with m8 lock washers is that they take more clamping force to flatten than the m4, possibly even more force than stripped out the m4.

Yes, the M4 was ridiculous. At the time when I bought them it didn't occur to me to even consider screening products for the terminal screw/stud size. Not only were they M4, but they were tapped like trash, only half of the screws would even go in properly, the other half either went in at a funny angle, went in only half way, or not at all. The ones that stripped happened when I was just simply (and carefully) trying to get the screws to go in -- no busbars or anything clamped at extreme pressure, just trying to get the screws into the terrible threads the very first time. Unfortunately I had let too much time pass by then to try to return them. The cells were also mislabeled as 75AH and I had contact the seller who told me based on the weight they were the right cells just labeled wrong, quality was apparently not a priority.

Interesting point about the clamping force on the split lock washers...

In the end, yes I would recommend using a torque wrench. I might skip the split lock washer and some of the softest thread locker.

Sorry, I don't follow the last sentence: Skip the lock washer and [also skip?] some of the "softest thread locker"? Do you mean skip the lock washer and the loctite?

 

[SlimyLemur56]

I don’t understand what you will be doing with the nuts and the bolt in relation to the terminals.

This is what I was proposing, although reconsidering now

Looking at it drawn like this it does look like a lot of things with the word Lock in them...

My reasoning for the lock washer was actually not the normal reason. Since I had to redrill/tap the holes myself some of them did not come out exactly dead nuts square and maybe have a few degrees tilt on them. They are pretty close to square since I drilled them on a drill press, but in the process of tapping them by hand it was (slightly) thrown off. I wanted something between the nut and the ring terminal to sortof even out the pressure on the ring terminal if the stud was not exactly robotically square. Maybe a lock washer like this is not the best solution for that anyway. What if the split lock washer was a nylon washer instead?