Drilling and tapping REPT 100Ah cells?

[Ogre]

I have two prototype LFP batteries each made up of 16 new REPT 100Ah cells. The company that made them did a poor job at laser welding the busbars on top and they’ve come off many of the cells. I’d like to save these 10Kwh of cells, but to do so I’ll have to somehow attach studs or busbars to them. Any suggestions?

 

[NVS]

I think I would have someone mig welder the studs back on vs drilling and tapping them.

 

[Luk88]

I think I would have someone mig welder the studs back on vs drilling and tapping them.

I'm not sure I'd like to ARC weld these. This generates lots of heat and aluminium requires lots of current. I believe they must use alternate welding methods in production of packs. Laser comes to mind, also spot.

Depending on how deep these terminals are I'd feel much better drilling and tapping.

A common "rule of thumb" is that 3 good threads reach the strength of the bolt. Tapping into a blind hole till the end, even with a bottoming thread you can get up to 1.5 "bad" threads at the bottom (not fully cut). So I'd go for at least 4.5 threads.

If you're planning to use M6x1 bolts that would be (obviously) 4.5mm plus whatever your bottoming tap requires to engage. May be as much as 2mm. I have cut taps and made a "more bottoming" tap that got all the way. I wouldn't try that if you're not quite experienced in hand tapping, but if you are, maybe you can make just 3.5 threads ending on the bottom work. If you do that, don't forget to grind the bottom of the bolts too.

The key question is, how deep can you drill these? You may need to sacrifice one to find out.

 

[MattiFin]

A common "rule of thumb" is that 3 good threads reach the strength of the bolt. Tapping into a blind hole till the end, even with a bottoming thread you can get up to 1.5 "bad" threads at the bottom (not fully cut). So I'd go for at least 4.5 threads.

Rule of thumb works for steel or similar materials on both nut and bolt.
In soft aluminium you need something like 20-30 turn engagement to reach ordinary 8.8 bolt strenght.
3 turn thread engagement in soft aluminium strips extremely easy

 

[Quattrohead]

There is a thread on here about the Envision 280 cells from 18650.com.
I ended up drilling and tapping four of them as an experiment and if I remember correctly 6 mm was the absolute maximum depth you could go.

 

[AntronX]

My have to sacrifice one cell to drilling depth experiment.