I just bought some Panasonic 3400s and found that they are larger than other 18650s (as I have read). The fit is pretty tight in my charger, I have noticed the tops can move around. Is this to be expected? Is it safe? Should I send them back?
Thanks,
John!
I’d say while it’s not going to explode immediately, it may be a short/failure hazard.
Where did you purchase them? Do you have a link?
If it’s worth your time, send it back.
Edit: Your photo was working a second ago but it failed to load just now.
I agree, the top should be well secured in place. If it ever managed to get in contact with the battery tube, it would be a short which would not be protected by the protection circuit.
I would contact the seller to see about replacement or refund.
Those loose button tops, being that they're under the heatshrink & insulator, are VERY CLOSE to the outer shell of the cell, which is the negative pole. I would carefully move the loose tops back to the center, tape over them well to keep them in place, and store them outside until I found a way to dispose of them safely, the only other alternative is to peel off the original heatshrink, remove the tops somebody forgot to weld, then re-wrap with new heatshrink.
They are not safe to send through the mail like that for a refund, if you decide to go that route make sure you let the seller know they're not safe to ship in their present condition.
Thanks for the info guys. I will contact the Amazon seller for a refund.
I had a similar problem once with some OG Trustfire flames and didn’t know how dangerous the “situation” was. I actually tried to fix it with some tape but (I guess it’s a good thing now.) they just wouldn’t charge at all. What Comfy is saying makes me realize how dangerous this stuff is.
One question though: I heard that even the unprotected NCRs have some kind of primitive “protection”. Would that apply to this problem at all?
If its a tight fit, my guess is that the tops moved because you pushed too hard.
Pretty much al 18650 are built like that. The top is welded but still can move around if you apply some pressure. See this thread for pictures:
I'd say that contact with the negative parts of the cell is pretty much impossible because of the extra insulation layer.
@Anzy: NCR cells have an additional safety feature, the HRL (heat resistant layer) that prevents internal short circuits in the cell. Wont help you in daily use and when it triggers, the cell is usually dead.
Almost all cells have a PTC that disconnects the positive pole from the inside of the cell once the temperature gets too high preventing overheating.
I agree that button tops (like these) are built like that. That is not an actual part of the cell though. It was added after manufacture by a third party.
You are correct that the original insulating layer is still there, so the button part should not contact the cell case. Since I have not seen a cell do this before, I err on the side of caution.
If the button continually moces around, it could weaked the welded metal tab. It may already be broken, causing a poor contact.
Even with the safety risk mostly eliminated, these seem defective after the top has moved around.
If they were mine, I’d remove the outer layer and remove the button top, and hope the protection circuit tab was welded directly to the cell top. Then, I would rewrap the cell. Not everyone is that comfortable modifying Li-Ion cells so do this at your own risk, of course.
Just out of curiousity, what charger are you using?
NightCrawler, thanks for the informative link. Based on moving the tops back to center with my fingernail, I think my tops are attached with the tab. Maybe they aren’t unsafe then?
Ruffles, I have a 4x 18650 case I have for the moment. I’m planning to get a balancing cable and magnets soon.