Hearing tales of people getting bad quality cells in a group buy has got me shaking in my boots. I really appreciate the peace of mind of molicel and I weigh that when making my cell choices. Doesn’t mean it will always be the best option like you stated.
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Just received this used battery I bought. Found this damage in the pack. Wondering what you all think of this, next steps to do etc.
This is a eve40pl cell. Wondering how damaged this truly is. Got as close of an image as possible
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@Battery_Mooch help us out
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Looks like hit with a small meteorite. How does the cell do?
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Kind of looks like some welding was going on nearby and an ember burnt through.
The risk is if the can is punctured.
Can you smell any sickly sweet smell of electrolyte?
The one picture looked like rust but the others look like clean steel.
If no electrolyte smell is present I’d clean it, carefully razor some mechanical tooth cross hatching adjacent to crater, and cover that with a dollop of 24 hour JB weld, rewrap it and use it.
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Great close-ups!
For me though it’s too hard to tell what the condition of the can actually is. Carefully cut the wrap back from that spot a bit to expose the surrounding metal, clean the spot with something slightly dampened with IPA, and photo the spot again.
@SternWake had a good recommendation too…take a close whiff. Electrolyte has a strong and very distinct sickly-sweet solvent odor. If you can smell that then the cell is ruined and must be replaced or return the pack.
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tell me if I’m wrong but if there’s any damage to the cell it will show when comparing it’s voltage to the others or from being warmer when in use. It’s hard to recognize a hole or a smell. I’d charge while checking it’s temp and if it stays balanced through charging n discharging it’s good
The resting voltage probably wouldn’t change if some electrolyte had evaporated but performance would fall and temps rise if the cell had dried out enough and was being used hard enough (not advisable!).
Balancing might eventually be affected, and changes detectable, depending on the number of cells in the p-group.
Cycling a pack, hoping to detect a temp change that could be very small now (but significantly increase later as the cell dried out), wouldn’t be something I recommend. It’s the long term reliability of the pack that’s my concern and the temp change (if any) could be small. But even the tiniest hole is a big concern.
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I had a 5.2AH 3S lipo pack start emitting a very distinct sweet smell on my last few welds.
Concerningly weaker welds.
I discharged it through a wattmeter, and it delivered over 5 AH powering a 12v fan.
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I smell possibly a musty smell but I’m not 100%.
More close ups here with wrap removed. accidentally deleted reply.
Man, it is hard to judge. Looks less like the dents ive seen and more like a burn/arc. Looks like material is missing from the cell can. If not a burn then like a screw or something was tightened into it. The crater ish look of the close macro photos are very suspicious to me.
Was the shrink on it just compressed or was it melted back a smidge? If it was on a pack i was selling to someone i would fix it by replacing that cell.
If it was on a pack i was repairing i would replace it with the caveat that depending on the current cycle life it may need attention in the future if ir cant be matched and that group may wear faster due to mismatch but likely fine because of the batching on these cells is still so small.
If it was mine i would replace that cell and sleep easier. It seems like a big enough deformation that I wouldn’t trust it and long term MAYBE be a problem and maybe is too much risk for me. I am very risk averse and especially with other people’s risk.
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Thanks. Sounds like this pack may be going in for evaluation and repair
Appreciate the help guys!
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Oops…you posted while I was composing…
I’ll keep my post up anyway. Sounds like a good plan!
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The liquid is also very slippery so you can check the wrap and any fishpaper that was over/near that spot for stains or a slippery coating. It’s a very strong and unique odor though so the cell probably hasn’t been pierced.
But in my opinion, judging by the last of photos, that hole is very close to piercing the can. Could it eventually open up? I don’t know. Lots of pressure can build up in a round cell during normal operation but I have no idea what is needed to get through that last bit of metal.
You could epoxy/jb-weld over that point and hope for the best or arrange to return the pack. Unfortunately it’s going to have to be your call. Just not enough info for us to judge the integrity (or lack thereof) of that spot. Sorry for the extra work in getting those additional photos.
If you’re using that pack hard then definitely keep an eye on that cell’s voltage and temperature. Maybe even move a temp sensor to that cell, near that spot. Tape the sensor down hard and well with a high-temp (Kapton or similar) tape or use neutral-cure RTV/silicone with the sensor pressed firmly against the cell while the stuff cures. Epoxy might be better since you can use any tape to hold the sensor down and then remove the tape when it’s cured.
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It’ll keep chugging away until enough (flammable and toxic) electrolyte evaporates out. Temps will rise though along with internal resistance (more sag) so high power use exposes it earlier.
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It looks not only like there is metal removed, like perhaps a walking drill bit, but that there is a slight dent in the can surrounding the central crater.
If that slight dent is not just a trick of the light, I’d probably replace that cell, as I’d assume uneven jelly roll compression, and perhaps a pressure point on the separator.
If there is no can deformmtion inward and no Stink, I’d likely prep the surrounding area of can for maximum adhesion, and a strip of Nickel plated steel, with sharp razorblade cross hatching on it for maximum mechanical tooth, and JB weld that over the area. Perhaps I’d put a K-type thermocouple into the JB weld, but not under the NPS reinforcing strip, just right next to it.
I had an electrode slip off my Nickel plated steel onto 0.1mm copper when the welder fired automatically, and blew a hole through the copper. I couldn’t smell any electrolyte. I could not see any obvious damage to the cell below. I cleaned it well and razored opposing cross hatching and 24 hour JBWelded a piece of similarly prepped Nickel steel over the area.
That battery was built in May this year, and is performing very well with rarely less than 10 miles a day on it.
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Best sensor to use but unfortunately none of the BMS’ support thermocouples.
But some multimeters do and, of course, dedicated digital thermometers. A thermistor can be okay for tracking trends and max temps if not doing insane power pulses.
Yep that was my experience.
After the fan stopped spinning arounf 6 volts or so, I put it on a 100 watt 10 OHM resistor for a few days outside on some pavers and underneath a pot lid. When I lifted the pot lid the aroma of electrolyte was very noticeable, outside, and it was not perfectly sealed to the pavers.
Try tightly taping a piece baggie of plastic baggie tightly over the crater giving it a pretty wide berth, and enough area to expand. if you see it expand on its own like a balloon, she be done for. If it does not, then stick your nose close to it and peel off the tape and give a sniff.
I have punched a hole in cans testing welding copper strips with no sandwich and the smell was different from the Lipo, but still strong. I have a little plastic 18650 cell holder and did a few more test welds on the other end of the cell. The plastic near the hole in the cell turned the plastic white the same way super glue turns some plastics white.
Debated using just a piece of copper instead of the braid but decided on aesthetics. The heat is pulled out so fast and distributed quickly enough that i cleaning up the flux is more difficult - gets cold faster than i can get my iso rag on itand is touchable immediately after putting down the iron. Running a fat chisel tip at 800f (450c) to get a good thoroughly wetted joint.
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Where the braid haters at
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