I’m not sure why stainless is used so much in these lifepo4 battery applications. If the conditions for dissimilar metal corrosion are present in the place where the batteries are installed your other equipment is going too be damaged anyway. If I understand correctly standard issue nuts and bolts are only slightly more reactive with aluminum than stainless and when such corrosion does occur the aluminum is only affected visually. I can understand why stainless is used in outdoor applications with aluminum to avoid rust streaking on the aluminum and seized bolts but in a non acid battery application in the same room as electronic equipment I can’t see corrosion being an issue as the catalyst for corrosion can’t be present without endangering the connected equipment. Am I missing something?
Broken welded stud
- Thread starter neil_99
- Start date
neil_99
New Member
I believe they drilled it out with a drill press to open the hole. They said they were going to use the CNC for cutting the threads. I'm not sure how a CNC would help with that.
neil_99
New Member
Good questions. They said they got three turns in when they retapped. I may use thread locking glue like you suggest on the stud. I would be interested in someone spot welding everything, but this machine shop didn't have that ability. I didn't contact Eve because I didn't think they would respond, but I probably should have.
They have not used a CNC for retapping based on the pictures. And CNC or drill press would be a lot more precise for removing the stud leftover, but for retapping it would be a challenge to get it right.
Regarding the stainless steel vs steel - the main goal I think is to protect the cell terminals. This is the reason why copper busbars are tinned. The tinned layer prevents the electrochemical (galvanic) corrosion that would otherwise "eat" the cell terminal. I suppose I'm missing part of the theory here, but on my cell terminals, I have a zinc-plated spring washer. Time will show if it is an issue.
On the 105Ah EVE cells, the tread depth is ~7mm. In your case it is ~3mm. Be extremely careful with the tightening torq.
Regarding the stainless steel vs steel - the main goal I think is to protect the cell terminals. This is the reason why copper busbars are tinned. The tinned layer prevents the electrochemical (galvanic) corrosion that would otherwise "eat" the cell terminal. I suppose I'm missing part of the theory here, but on my cell terminals, I have a zinc-plated spring washer. Time will show if it is an issue.
On the 105Ah EVE cells, the tread depth is ~7mm. In your case it is ~3mm. Be extremely careful with the tightening torq.
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Tapping with CNC would not help, but thread milling with a single form thread mill would get full threads to the bottom of the hole.
neil_99
New Member
There was a bit of a language barrier, so it's possible things got garbled in the conversation.
Xhumeka
Off-Grid'er
I had this happen to me just the other day - I was building a pack for use boondocking that would be subject to a lot of vibration while travelling, so I thought I would try "Self-Locking Nylon Insert Hex Lock Nuts" to help prevent loosening.
Everything went fine for assembly and BMS testing, but when I unscrewed the positive terminal's nut to attach a battery cable (to attach to external post on box) it started to get fairly tight near the very end. I was using a very small socket wrench (4") and I wasn't even using the handle, I was just turning the head of the wrench to make sure I wasn't using too much force.
I should have applied some oil, because all of a sudden - SNAP! The nut broke the last bit off the stud (almost the same size as the nut) - and I KNOW I was much under the torque specs. China QC like you said!
At least in my case I still have enough stud left to attach a regular nut, but I've learned my lesson... NO LOCK NUTS on these cells!!
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