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diy solar

Helicoils in Cell Terminals

I've been really annoyed about my terminal threads getting messed up.
And I was thinking "Why is this happening now? It didn't happen before"

I think it is from cells expanding and moving around with the tight busbars. :confused:

It could also be from torqueing or loosening my fixture with tight busbars. I am going to have to be more conscious of cells moving while busbars are tight.

I bet if I had used regular nuts and washers instead of serrated flanged nuts I wouldn't have this problem. ?
 
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You can modify your tap to allow make the threads deeper without the taper by cutting off a bit of the bottom of the tap. If you are using something like a drillpress to start the tap straight you can cut off quite a bit. If hand tapping you may need to buy a second tap, using the tapered one to start then switching to the cut off one to finish. In a blind hole you have to go slow and blow out the chips often. Most standard taps that you buy are taper taps.

img_5a1b10fbddbc2.png
 
Thanks somewhereinusa. I am going to do some experimenting until I get it right.

I noticed the helicoil has about 7 threads. It would be great if I can get it all the way in without having to cut it.
Probably not likely though. It needs to be at least a 1/4 turn below the top.

One weakness of helicoils compared to timeserts or keenserts is that the first couple treads can be pulled loose.
That won't be an issue with studs.
 
I did one helicoil in my spare cell that is no good. It was easy and I will fix my good cell next.
I put a couple washers and a nut on the stud and torqued it to 60 lbs no problem.
When I tried 80 inch pounds it tore the helicoil out.

I will never torque a good cell to 80 inch lbs.

I had to grind the end of the tap off.

before
1611862961865.png
after looks like 3-5 thread taper
1611863046895.png
new little HF grinder
1611863184668.png
sticking out
1611863342627.pngj
nipped off thread with dyke
1611863587528.png
 
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Bob B said:
In the spec sheet, it shows max torque on the threads would be 23 in lb. The original aluminum threads generally have 35 in lb or greater and they aren't working out very well.
Click to expand...
I think the issue with our soft aluminum threads is that the first time we remove a stainless thread from one, galling yo the aluminum has already occurred and we are removing some aluminum thread material along with the stainless thread...

Has anyone heard of anyone that has had a failure at 35 inch-lbs one one of these threads on the first and only time of use (stainless thread inserted only once and never removed?)?

The other thing I’m starting to get worried about now is stainless galling, even with stainless grub screws.

If a stainless nut falls into a stainless grub screw when tightened to 35 inch-lbs, it will take more than 35 inch-lbs to remove it, will degrade the threads in the process, and may twist the grubscrew out.

I’ve never experienced galling with SS bolts (that I know of) but I have with SS threaded piping and fixtures.

Is galling of SS nuts against SS grubscrews a concern at 35 inch-lbs?

Would another metal fit both grubscrews and nuts be better from that perspective?
 
ArthurEld said:
I did one helicoil in my spare cell that is no good. It was easy and I will fix my good cell next.
I put a couple washers and a nut on the stud and torqued it to 60 lbs no problem.
When I tried 80 inch pounds it tore the helicoil out.

I will never torque a good cell to 80 inch lbs.

I had to grind the end of the tap off.

before
View attachment 34919
after looks like 3-5 thread taper
View attachment 34920
new little HF grinder
View attachment 34921
sticking out
View attachment 34922j
nipped off thread with dyke
View attachment 34923
Click to expand...
Gotta say that looks pretty darned good!

Does anyone know whether stainless nuts can gall into stainless bolts/threads at torques of 35, 40 or 60 inch-lbs?
 
fafrd said:
From who? And for how much?
Click to expand...
I would have to check the specific vendor but they were the cheapest 200AH cells I could find on Ali Express. About $1,400 including shipping for 16 cells. To my surprise, they all check out with full capacity and look new.
 
Factory400 said:
I would have to check the specific vendor but they were the cheapest 200AH cells I could find on Ali Express. About $1,400 including shipping for 16 cells. To my surprise, they all check out with full capacity and look new.
Click to expand...
Sounds like you got a great deal. Under $90/cell with stainless threads and full capacity.

Didn’t notice they were only 200Ah however. I got 16 280Ah cells for about the same price so the ‘cost’ of your stainless threads was ~80Ah 29% of the capacity many of us 280Ah owners got with soft aluminum threads...
 
Factory400 said:
I would have to check the specific vendor but they were the cheapest 200AH cells I could find on Ali Express. About $1,400 including shipping for 16 cells. To my surprise, they all check out with full capacity and look new.
Click to expand...
I am curious about this. Are your cells prismatic cells or 200ah CALB cells? I have yet to see prismatic cells with threaded inserts installed at the price you paid. If you could find the vendor you bought from it would be appreciated. Thanks.
 
Gazoo said:
I am curious about this. Are your cells prismatic cells or 200ah CALB cells? I have yet to see prismatic cells with threaded inserts installed at the price you paid. If you could find the vendor you bought from it would be appreciated. Thanks.
Click to expand...

1611882532496.png

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fafrd said:
Sounds like you got a great deal. Under $90/cell with stainless threads and full capacity.

Didn’t notice they were only 200Ah however. I got 16 280Ah cells for about the same price so the ‘cost’ of your stainless threads was ~80Ah 29% of the capacity many of us 280Ah owners got with soft aluminum threads...
Click to expand...
lol, on the day I ordered - these were the lowest price I saw in the time alloted.

The size of the 200AH units was ideal for my setup so I probably still would have chosen them even if 280's were the same price. Ultimately, I was weight limited and the 200's were already a little over.
 
When I torqued the nut to 80 inch pounds and tore out the helicoil, the washer dented in the top of the terminal.
So, 80 inch pounds is too much even if the threads would hold.
These terminals are very soft even for aluminum and they probably were not meant to have threaded holes.

1611921494697.png
 
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