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Loctite install process for studs

blutow

Solar Enthusiast
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Dec 20, 2020
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I've seen much debate on Loctite vs. helicoil, etc. to strengthen studs. I'd say helicoils are the way to go if you want the strongest option, but I decided to go with red loctite since my threads seemed pretty good.

I did my first 4 cells and ended up making a bit of a mess of the terminals. The challenge is that the loctite pushes out the top of the hole as it goes down (hydraulic pressure). The loctite mess was causing poor connections and it was a pain to remove.

The process I used on the rest of my cells worked very well. As follows:

Cleaned terminal top and threads with acetone and q-tips, blow dry.

Apply a small piece of electrical tape to each terminal. This will prevent loctite from contaminating the terminal surface and allows generous use of the loctite.

Use a large drill bit to cleanly cut out the terminal hole. If you spin the bit backwards by hand, it cuts out the electrical tape and doesn't do anything to the aluminum. (edit - the drill bit should be much bigger than the hole, it's cutting on the top, doesn't go into the hole)
IMG_0464.jpgIMG_0465.jpgIMG_0467.jpg

Apply primer (improves bond/strength with aluminum and stainless). Rather than spraying, I just shoot some in the cap and use a q-tip to apply to the terminal threads and studs. Let it dry for 5 minutes. I used a little compressed air to make sure the holes are dry.
IMG_0488.jpgIMG_0485.jpg

Apply loctite generously to threads in terminal hole and just a little on the first couple threads of the stud. Screw the stud into the terminal slowly, rocking it as you go. You can see the bubbles work themselves to the surface. Take it to the the bottom of the hole and back off just slightly. You end up with extra loctite around the based of the stud that needs to be wiped up carefully so that you don't get any on the exposed stud.
IMG_0468.jpg

After wiping up the extra loctite, I put a bus bar on with a couple washers and nut to properly seat the stud. I think this step is important because there is some slop in the threads and you want it to set up in a nice straight position with threads fully engaged. I let it set for at least 12 hours before removing the bus bar and tape. Use acetone to clean off any residual adhesive from the tape and then good to go. They say 24 hours for complete cure.
IMG_0487.jpg

So far, so good. I'm assembled and disassembled one of my packs at least 5 times with 35 in/lbs of torque and they seem really solid. I guess it always seem solid until it's not.... Time will tell how things hold up.
 
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I've seen much debate on Loctite vs. helicoil, etc. to strengthen studs. I'd say helicoils are the way to go if you want the strongest option, but I decided to go with red loctite since my threads seemed pretty good.

I did my first 4 cells and ended up making a bit of a mess of the terminals. The challenge is that the loctite pushes out the top of the hole as it goes down (hydraulic pressure). The loctite mess was causing poor connections and it was a pain to remove.

The process I used on the rest of my cells worked very well. As follows:

Cleaned terminal top and threads with acetone and q-tips, blow dry.

Apply a small piece of electrical tape to each terminal. This will prevent loctite from contaminating the terminal surface and allows generous use of the loctite.

Use a large drill bit to cleanly cut out the terminal hole. If you spin the bit backwards by hand, it cuts out the electrical tape and doesn't do anything to the aluminum. (edit - the drill bit should be much bigger than the hole, it's cutting on the top, doesn't go into the hole)
View attachment 39460View attachment 39461View attachment 39462

Apply primer (improves bond/strength with aluminum and stainless). Rather than spraying, I just shoot some in the cap and use a q-tip to apply to the terminal threads and studs. Let it dry for 5 minutes. I used a little compressed air to make sure the holes are dry.
View attachment 39464View attachment 39463

Apply loctite generously to threads in terminal hole and just a little on the first couple threads of the stud. Screw the stud into the terminal slowly, rocking it as you go. You can see the bubbles work themselves to the surface. Take it to the the bottom of the hole and back off just slightly. You end up with extra loctite around the based of the stud that needs to be wiped up carefully so that you don't get any on the exposed stud.
View attachment 39465

After wiping up the extra loctite, I put a bus bar on with a couple washers and nut to properly seat the stud. I think this step is important because there is some slop in the threads and you want it to set up in a nice straight position with threads fully engaged. I let it set for at least 12 hours before removing the bus bar and tape. Use acetone to clean off any residual adhesive from the tape and then good to go. They say 24 hours for complete cure.
View attachment 39468

So far, so good. I'm assembled and disassembled one of my packs at least 5 times with 35 in/lbs of torque and they seem really solid. I guess it always seem solid until it's not.... Time will tell how things hold up.
Really nice description, thanks! And the ‘drilling a hole in electrical-tap-terminal-cover’ is brilliant!

The only thing I didn’t understand is why you backed off a bit after bottoming the grubscrew - are you hoping from some extra adhesion by a thicker layer of Loctite down there?
 
You do realize that Loctite is an insulator, and you're just creating a high resistance barrier between the stud and the post? The place where you want the least resistance and most contact?
 
You do realize that Loctite is an insulator, and you're just creating a high resistance barrier between the stud and the post? The place where you want the least resistance and most contact?
You do realize that 99.9% of the conductance is through the aluminum surface of the terminal.

Conductance trough the post is utterly immaterial.
 
You do realize that 99.9% of the conductance is through the aluminum surface of the terminal.

Conductance trough the post is utterly immaterial.

Yep, there’s a chance the ring terminal might not even be touching the stud after assembly.
 
Really nice description, thanks! And the ‘drilling a hole in electrical-tap-terminal-cover’ is brilliant!

The only thing I didn’t understand is why you backed off a bit after bottoming the grubscrew - are you hoping from some extra adhesion by a thicker layer of Loctite down there?

I just slightly backed them off, so they were not "captive" on the bottom. If the stud was tight against the bottom, it's possible it could cause it to skew one way or the other. By making the stud only stressed between the threads and the the nut at top (when you have a flat busbar/terminal under it), you improve the chance that the stud is perfectly perpendicular to the bus bar (and terminal) surface.

That's my theory anyway. In practice, it's probably not going to make a measurable difference either way. But there are no threads near the bottom of the hole so you aren't losing any thread contact or strength by backing it off a smidge.
 
Has anyone isolated the terminal top face with electrical tape or equivalent and done a test on conductance/ampacity of just the threaded grubscrews and nuts/washers to busbar connection? My terminal screws are just as conductive as the flat terminal face when I test voltages, but I've not seen any data on them not being able to carry a load due to increased resistance or other losses.
 
I just slightly backed them off, so they were not "captive" on the bottom. If the stud was tight against the bottom, it's possible it could cause it to skew one way or the other. By making the stud only stressed between the threads and the the nut at top (when you have a flat busbar/terminal under it), you improve the chance that the stud is perfectly perpendicular to the bus bar (and terminal) surface.

That's my theory anyway. In practice, it's probably not going to make a measurable difference either way. But there are no threads near the bottom of the hole so you aren't losing any thread contact or strength by backing it off a smidge.
Thanks for the answer - now I understand your rationale.

I’ve glued in about 12 studs using JB Weld and had the same concerns regarding being straight.

The way I handled it was to apply force downwards while tightening and forcing JB Weld to ooze out, then, after bottoming, I’d use an inverted socket holding a nut to tighten down on the grubscrew and assure that it was vertical. I used my maximum force by hand which I later measured to be ~20 inch-lbs. My goal was to move the grubscrew from being in contact with aluminum threads at the bottom surface of the stainless threads to switching to being in contact along the upper surface of the stainless threads (a very slight ‘backing off’ similar to your idea).

My experience has been that the aluminum threads themselves dictate the position of the grubscrew and so far, I’ve had no issue getting my grubscrews perfectly vertical (probably because the aluminum threads were tapped perfectly vertical).

I think you certainly don’t want a grubscrew placing stress on the bottom of a terminal, so from that point of view, either bottoming gently or backing off a smidge probably works...
 
Has anyone isolated the terminal top face with electrical tape or equivalent and done a test on conductance/ampacity of just the threaded grubscrews and nuts/washers to busbar connection? My terminal screws are just as conductive as the flat terminal face when I test voltages, but I've not seen any data on them not being able to carry a load due to increased resistance or other losses

An unloaded voltage test is meaningless. That's like saying you are showing the same volts at the end of a 22 gauge wire as the same length 4/0 wire. Yes, they will measure the same volts at no load, but that doesn't mean you can run the same load through them.

Stainless just isn't near as good a conductor as aluminum or copper. Yes, it can conduct electricity, it's just not great at it. You could test your theory without doing the electrical tape by just putting a nut on the terminal, followed by a bus bar, followed by another nut. You'll get the added benefit of the conduction through both the nut and the stud, but I think you will find things heating up in a hurry if you push any watts.
 
they will measure the same volts at no load, but that doesn't mean you can run the same load through them.
That's why I asked for actual data to confirm the extent of this using the typical hardware that is being used with these cells. Have you done this and recorded your data, or do you have a link to data on this? Thanks!
 
No, I have not run any tests. I doubt you'd find much on people testing stainless as a conductor.

I guess it would be an interesting experiment, but are you questioning whether a stainless stud is making a significant contribution to the current flow in a battery? Stainless isn't like half as conductive as aluminum or copper, it's like 1/30th as conductive. Is a stainless stud contributing at all? Technically, the answer is probably yes. Is it a material contribution? I seriously doubt it, but I'll concede that I don't have any data.
 
Thanks for the reply. Also, great write up on your battery build - the battery box build is phenomenal, with your top-compression/hold-down mechanism providing an elegant solution to a problem I've been considering in my build.
 
This is nice info and I'm interested in other peoples' long-term bolt-tightness reports, but I think if you're putting enough Loctite that it spills out the top and the tape is at all necessary, then you're using too much.
 
This is nice info and I'm interested in other peoples' long-term bolt-tightness reports, but I think if you're putting enough Loctite that it spills out the top and the tape is at all necessary, then you're using too much.
Better too much than too little...
 
Better too much than too little...
I don't know why you think that. If the resistance is too high from too much loctite or it is too high from something coming loose, the result is the same. I would say too much and too little are equally bad.

So if they can stay tight with no Loctite and proper torque (or periodic maintenance) that is a preferable solution.
 
This is nice info and I'm interested in other peoples' long-term bolt-tightness reports, but I think if you're putting enough Loctite that it spills out the top and the tape is at all necessary, then you're using too much.
Give it a shot and let me know how it turns out. The problem isn’t the amount, it’s the hydraulic effect with a closed hole. You can put the smallest amount at the tip of the stud and you will still have loctite pushing out the top. At that point, you might as well load it up and try to get best possible coverage.
 
Give it a shot and let me know how it turns out. The problem isn’t the amount, it’s the hydraulic effect with a closed hole.
Yeah, maybe I'm engaged in armchair commenting; I will try it out and let you know. With studs I don't think you should bottom them out anyway as the pressure at the tip has a huge mechanical advantage to strip the threads or blow out the bottom, in addition to being a motive force to "undo" the bolt. Loctite is supposed to be applied to the side of a bolt (the threads), and not the tip, so I don't know where this hydraulic pressure would come from: surely the threads are not that precise and there is some play between the tap and die parts, right?
 
Yeah, maybe I'm engaged in armchair commenting; I will try it out and let you know. With studs I don't think you should bottom them out anyway as the pressure at the tip has a huge mechanical advantage to strip the threads or blow out the bottom, in addition to being a motive force to "undo" the bolt. Loctite is supposed to be applied to the side of a bolt (the threads), and not the tip, so I don't know where this hydraulic pressure would come from: surely the threads are not that precise and there is some play between the tap and die parts, right?
Yes, there is play. That is why you want to have a small reservoir of Loctite at the bottom of the hole and have hydraulic pressure force it up the thread gap and out the top.

If you don’t see liquid oozing out of the top around the grub screw, it means you have thread surface which has not been coated with Loctite.

The Loctite is there merely to keep the grubscrew from turning (and shearing off the fragile aluminum threads).

The aluminum threads are there to hold the grubscrew down and from pulling out.

The grubscrews is there to provide a clamping force on a busbar or terminal lug using a nut.

All of the necessary conductance occurs between the top surface of the aluminum terminal and the bottom surface of the lug/busbar (which is why you want sufficient clamping force pressing them together...).
 
Thanks fafrd, I get the idea of nuts and bolts. I'm standing by my sort of tautological assertion that "if you squeeze a bunch out you have probably applied too much" for keeping the stud from getting loose.
 
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