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Helicoils in Cell Terminals

Sillyputty

Solar Enthusiast
Joined
Jul 21, 2020
Messages
188
An update on my helicoil adventures: I got in on a Michael B. Caro battery group buy a while back, and the 4 - 280AH cells arrived dented, etc. To his credit, at that time Michael was prompt in contacting the supplier and ultimately giving me a full refund. At that time the cells were tapped for the shorter bolts which on most of the cells stripped out during assembly, even using a torque wrench to specs, so I decided to tap and install helicoils and studs on the ones that were stripping out, which was a majority.

Following the methods here, all the re-threaded terminals worked out fine, and the battery was in service in my camp trailer for a few seasons, along mostly bumpy gravel roads. Recently however I noticed a cell that was intermittently showing ~500mv fluctuation from the others, that would even out when the terminals were tightened. Eventually the terminal bolt stripped and wouldn't remain tight enough. This was on one of the untapped and un-helicoiled terminals, so having had such good luck with the previous terminal gave me confidence in drilling and tapping this one as well.

Unfortunately, in the end the the drill bit ended up grabbing into the aluminum, at very close to the depth I'd previous used with no problems, with the following results:

1.JPG4.JPG2.JPG3.JPG

The good news: Nothing caught on fire. & 911 was prompt. Once the drill bit broke through into the internal part of the cell there were a very few sparks and a small candle-sized flame at the hole, which extinguished easily just blowing it out. The cell started slowly out-gassing, increasing in speed and intensity after 30 seconds or so, billowing huge amounts of smoke straight up like a mini-volcano and completely filling the trailer in moments. You can see the black soot on the ceiling in one of the pics. I sprayed the battery with a fire extinguisher even though there were no flames apparent by then, and after the smoke stopped billowing out, the fire dept. donned masks and safely removed the battery from the trailer.

The melamine did get charred near the offending cell, while the fiberglass (?) reinforced silicone mats I used between the cells held up fine. The bottom of the battery box beneath the damaged cell did partially melt through, but thankfully did little damage to the trailer flooring. The damaged cell's temperature after being removed and sitting for several minutes was ~195 F with the adjoining cells less than 100 F.

Another good thing: the damaged cell did exactly as described on YouTube when damaged this way: lots of very hazardous outgassing and smoke, but with no fire or explosion.

All in all I got off lightly with a smoked-out, stinky trailer, a now-unusable battery that, even though it cost me nothing, ended up providing a harrowing learning experience and lessons for the future: 1) Probably don't drill into the aluminum cell terminals. Sure, 6 times it may work perfectly, but the odds of it going wrong outweigh the benefits, and 2) If you do decide to drill and tap them, remove the battery from the trailer and separate the cells from each other and do the drilling in a safe, clear area (outside would be ideal) with proper safety and fire suppression equipment on hand; there's much less potential for collateral damage if things do go wrong.

Thanks for all the help and input from all the contributors on here - I'd not have learned how to to any of this properly nor known what to do in the event something went wrong without all your input.

Stay safe!
 
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Thanks for posting, thats good info for all of us, though its an unfortunate turn of events.

If I am ever drilling something sensitive like this, I make a drill stop from a piece of pvc/pex pipe, or I get a locking collar on the drill bit.
 
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Yes - I should have used a solid depth-stop - however: I used the same depth gauge (tape with a small part left hanging to brush the metal particles aside as it neared the desired depth) ) as I used on the other cells, and although it grabbed a bit at the last, it never seemed to go farther than the others, although that's likely what happened. The other possibility is that that particular cells terminal depth was shallower than the others, resulting in the puncture. I'll never know for sure.
 
Any chance the terminal spun? Probably not worth it, but you could cut the can off the cell if you still have it.

BTW the electrolyte is toxic when it comes into contact with moisture, so wear gloves, and use copious water to wipe down any surfaces.
 
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Any chance the terminal spun? Probably not worth it, but you could cut the can off the cell if you still have it.

BTW the electrolyte is somewhat toxic when it comes into contact with moisture, so wear gloves, and use copious water to wipe down any surfaces.
No indication that the terminal spun. There are no visible traces of liquid electrolite - it appears to have all out-gassed and turned to white smoke during the eruption. Remarkable: the inside of the trailer is a lot less affected by the smoke and smell than I'd feared. I'm still removing items and vaccuming up the fire extinguisher residue, but at this point it only smells a bit like someone lit-off a firework or two in there.
 
UPDATE: The trailer has been completely washed and the smell is almost unnoticeable. The paint on the ceiling area was not damaged in any way, just discolored with small bits of debris that washed off almost completely. There was no sign of heat damage anywhere aside from the battery cells and the battery case.

None of cells pressure relief valves were activated; one cell had more outward damage than the others and had voltage readings which fluctuated. The other two had similar voltage that was steady @ ~ 3.3V.

After getting a refund for these shipment-damaged cells from Michael Caro, I ordered another set of the 280AH EVE cells from @Amy Wan. These cells had the M6 studs already installed/welded and it was a breeze to assemble. After top balancing them, that battery had been sitting unused in my office for about a year. Upon installing that battery and allowing it to charge with the solar panels on the trailer up to ~ 90% I ran a a test discharge using a heat gun, the TV/Computer system in the trailer, and the trailers refrigerator running on AC provided by the 2200W Giandel inverter, with the remaining loads being the DC side such as fans and a few LED lights. The total load fluctuated between 1200W - 1750W @ between 100A - 135A for twenty minutes. Everything went well, with the inverter getting up to about 102F and the battery cables near terminals reaching about 109F. Ambient temperature was 85F. There was no indication of any diddimilar voltage difference between cells while under load, and they were within about 2mv of each other afterward.

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Yes. Drill stop or drill press. You got lucky.
Indeed. Even with a drill press and/or physical stop I'll not be drilling cells again. Getting the right depth to drill was already basically a hazardous guess, and with the inconsistency of these lower priced cells even having accurate information for doing so may be wrong given the poorer quality control during manufacturing.

For any $150+ battery cell, it's simply not worth it.
 
I hope you're not getting additional damage.

By the images it looks like a powder fire extinguisher. That powder is bloody aggressive and, overtime, will destroy everything and somehow gets into everything (just like the fine dust while grinding concrete)
 
@Sillyputty , thanks for posting. I would not have expected such a catastrophe from drilling through the cell terminal. I won't be volunteering to drill any cell terminals now. (y)
@Sillyputty , thanks for posting. I would not have expected such a catastrophe from drilling through the cell terminal. I won't be volunteering to drill any cell terminals now. (y)
For sure. The less robust terminals on the earlier, less expensive cells were problematic enough. Quite thankful to be getting away with as little damage and down-time as I have. It could have been a more immediate 'volcano' of gassified electrolyte which likely would have hit me in the face as I was using a handheld drill with only minimal eye protection.

Replacing them promptly after getting a refund from Michael Caro with EVE cells from @Amy Wan was a good move: excellent customer service, great battery quality, with robust cell terminals and no issues with voltage fluctuations whatsoever.
 
I hope you're not getting additional damage.

By the images it looks like a powder fire extinguisher. That powder is bloody aggressive and, overtime, will destroy everything and somehow gets into everything (just like the fine dust while grinding concrete)
Thanks for bringing this up. It was promptly cleaned, with the inverter and other electrical components exposed blown out with high pressure air. It does look to be a good idea to go back and use elctrical contact cleaner on the components as well.
 
Well, so far what i'm getting is its easier to do thread repair on these cells than on side post car batteries! That crap is ludicrously hard, and i'm an experienced auto tech with plenty of thread repair experience. My V10 rv has.. 10 thread inserts in the spark plug holes! That sucked..

Glad you got off lucky. I agree with everyone else about the drill stopper although im perhaps one of the most guilty people in history when it comes to not using them.

I'm new to this scene but i have already noticed that the threaded terminals on some of these powerful cells/batteries range from 'i wish it was better' to 'this is actual crap'.
 
My supplier sent my calb cells with all of the posts already drilled and heli-coiled and I have not had a single issue with them from jump sometimes it’s better to be lucky than smart I guess. With all the scam artists out there it’s easy to get burned
 
Unfortunately, in the end the the drill bit ended up grabbing into the aluminum, at very close to the depth I'd previous used with no problems, with the following results:

Can you clarify what you mean by grabbing above please? Was it a drill press or hand held drill?
 
Can you clarify what you mean by grabbing above please? Was it a drill press or hand held drill?
Does not matter, the bit grabbed and self pulled into the material. Common issue when using a hand drill or a cheap drill press. The correct answer is stop using shit to do precision work.
 
Does not matter, the bit grabbed and self pulled into the material. Common issue when using a hand drill or a cheap drill press. The correct answer is stop using shit to do precision work.
Ok thanks. I was asking because one of my Lishen 272Ah cells has stripped a thread (my fault of course) and I was expecting to have to put an M6 helicoil in. Having taken it to a local machine shop though they advised a better and stronger fix will be to drill out to M8 1.0mm fine thread, which I’ve left in their hands to do (with clear warning to use an end stop to drill no lower than existing hole depth).
 
Ok thanks. I was asking because one of my Lishen 272Ah cells has stripped a thread (my fault of course) and I was expecting to have to put an M6 helicoil in. Having taken it to a local machine shop though they advised a better and stronger fix will be to drill out to M8 1.0mm fine thread, which I’ve left in their hands to do (with clear warning to use an end stop to drill no lower than existing hole depth).

You'll find out one way or another if it's a quality machine shop! ?
 
I didn't follow why the heli-coil wasn't used on that cell as well? I was planning on doing that for one of my cells (also from same person).

Also makes you realize having these batteries in a fixture/compressed would make it impossible to get rid of a single cell in a hurry.
 
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