# Stripped LiFePO4 cell



## Ziggythewiz (May 16, 2010)

IIRC Jack R had stripped a bunch of his early cells and the solution was to re-thread them all (as opposed to not overtorquing them), but looks like you've tried that already.


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## racunniff (Jan 14, 2009)

Ziggythewiz said:


> IIRC Jack R had stripped a bunch of his early cells and the solution was to re-thread them all (as opposed to not overtorquing them), but looks like you've tried that already.


I don't have a good suggestion for already-stripped threads (maybe bore them out and re-thread to a larger size?). However, for new installations, I recommend threaded rod and nuts, instead of bolts, for terminals where cable lugs will be installed. Using a typical rotary tool (i.e. Dremel) one can both cut the rod to appropriate length as well as notch the top end so you can hold it steady against torque with a flat-head screwdriver.

Using threaded rods does several things. First, it allows you to insert the rod all the way to the bottom of the terminal threads, which will reduce the probability of stripping. Second, it allows for longer thread extension above the terminal, which is good for the thicker cable lugs. Finally, it allows you to "hang" the lug onto the terminal while you install the BMS connection / washer / lock washer / nut combo, which is useful in case you don't have three hands (one to hold the cable & BMS connection, one to put the bolt through the lug into the terminal, and one to grab the torque wrench).

Regardless of bolt or threaded rod, one should be careful to observe the torque specifications of the battery manufacturer. The terminals are made of very soft metal (copper and aluminum), and it is easy to over-torque hard steel fasteners, damaging the threads of the terminal.


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## pm_dawn (Sep 14, 2009)

why don't you just add a coil insert. like helicoil.

The thread is actually going to be stronger if you do that.
I talked a lot to a bolt securing expert when I tried to establish the best way to secure the terminals on my Thundersky 160ah in the car. I tested the amount of torque I could apply to a terminal before the threads came out. The cell I tested was a dead cell so I could do some destructive testing on it.
But the best way to secure the terminals would actually be to do inserts, like helicoil in the terminals, both to get a better thread and also to get a smaller bolt dimension. So it would be better to use m6 instead of m8 to get closer to optimum ratio between the diameter of the bolt and the length of the unengaged part of the bolt, for getting optimum clamping force for that bolt.
And also a thread insert is always stronger than the soft materials that is used in the battery terminals. 

regards
/Per


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## crackerjackz (Jun 26, 2009)

pm_dawn said:


> why don't you just add a coil insert. like helicoil.
> 
> regards
> /Per


Second that  those helicoils have saved my butt very often ...


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## GizmoEV (Nov 28, 2009)

You could also take it to a machine shop to see if someone there will tackle it.


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## kchiangusa (Mar 28, 2012)

Thanks for the helicoil suggestion, I didn't think of that. I do have someone that thinks that he may be able to retap it. I will post pictures when it is fixed.


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