Puffed LiPo - when to start getting worried...? - Page 1
Forum section: electronics / general

author: darkstar49
author_rank: Frequent Contributor
timestamp: September 22, 2020, 02:57:24 pm
content: Hello,probably a stupid beginner's question, but I'd like to know when to start getting worried about a swollen LiPo battery.I've got two Turnigy 6A 3S Graphene batteries, that I use as a source for a spot welder. These are 75C continuous, 150C peak (i.e. 900A).I know that pulling nearly 1000A out of those is not their favorite exercise, no need to insist on that... yes, I've seen many funny (and some not so funny) videos on YT about exploding LiPo's... I just wanted to know if ANY puffing should be a sign to recycle the batteries, or if there is some 'margin' before throwing them away...According to the producer of the spot welder, car (lead) batteries are not a good option either, he recommended another type of LiPo that I couldn't source...These have made a few hundred welds each, which is not that much (at 2 welds per cell).See the pics, not yet a drama I think (but clearly not as when I received them), any comments welcome !

author: CoteRotie
author_rank: Contributor
timestamp: September 22, 2020, 04:21:26 pm
content: Personally I wouldn't take a chance with Lithium batteries of any sort. If the battery is expanding it has probably been stressed beyond its design parameters. The safety mechanisms built in to a well designed pack should prevent catastrophic failure, but there's a nonzero risk of fire. I'd dispose of it and get the recommended battery or equivalent that's spec'd for the job.

author: darkstar49
author_rank: Frequent Contributor
timestamp: September 22, 2020, 08:06:38 pm
content: Quote from: CoteRotie on September 22, 2020, 04:21:26 pmYep... just ordered 2 packs of 5.5A 140C that I'll use in parallel, they should have a lot less stress that way...

author: wraper
author_rank: Unknown
timestamp: September 22, 2020, 08:12:19 pm
content: Quote from: darkstar49 on September 22, 2020, 02:57:24 pmThis is firstQuoteSecond, waiting for pictures of your house going ablaze.

author: tom66
author_rank: Super Contributor
timestamp: September 22, 2020, 09:02:22 pm
content: LiPo cells puff because excessive oxygen is produced during the discharge due to the degradation of the electrolyte material into lithium dioxide, often because the cell is abused with high discharge currents. (The manufacturer may claim you can discharge 1000A from these packs, but the cell does have a reaction rate limit as well as thermal limits.)This puffing generally indicates that the cell has begun to catastrophically degrade, and as more lithium dioxide is produced the usable area of the cell falls. This will naturally increase ESR, decrease capacity and the result is a rapidly deteriorating battery cell.If you continue to use it, there is a high chance the cell will fail dramatically, with a large amount of heat and smoke, and possibly fire. As a bonus, the cell will contain a large amount of oxygen, which makes for a useful self-contained reaction...

author: sleemanj
author_rank: Super Contributor
timestamp: September 22, 2020, 09:41:03 pm
content: Quote from: wraper on September 22, 2020, 08:12:19 pmPoster is referring to battery tab welding, it is common to power with high current lipo. See kWeld developed right here on EEVBlog forums.https://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/

author: james_s
author_rank: Super Contributor
timestamp: September 22, 2020, 09:41:21 pm
content: I've flown packs that were more puffed than that for years without issues but YMMV. Any puffing indicates that one or more cells has been damaged. How much damage is hard to say, but I would keep a close eye on the individual cell voltage and stop using the pack if one or more cells is getting out of balance.

author: Whales
author_rank: Super Contributor
timestamp: September 22, 2020, 10:32:39 pm
content: I thought I read somewhere that some puffing in a lipo is normal and not a problem?IIRC during manufacture they also puff and have to be degassed as a step.

author: David Hess
author_rank: Super Contributor
timestamp: September 22, 2020, 11:16:58 pm
content: Quote from: Whales on September 22, 2020, 10:32:39 pmIf they puff up after construction, then they have been damaged which is hardly unexpected given the application.

author: wraper
author_rank: Unknown
timestamp: September 22, 2020, 11:25:38 pm
content: Quote from: sleemanj on September 22, 2020, 09:41:03 pmShorting LIPO is not something acceptable. Was discharge current ever controlled? I doubt that. Not to say don't believe those outrageous discharge ratings written on those batteries, it's a marketing wank. Batteries expanding after a few hundreds of welds certainly shows there is something wrong with such application.QuoteCommon for dumbasses.

author: james_s
author_rank: Super Contributor
timestamp: September 23, 2020, 05:13:39 am
content: Quote from: Whales on September 22, 2020, 10:32:39 pmIt's normal in that it often happens as a pack is nearing end of life, in the same way that an incandescent bulb blackens on the inside. It's not something that should typically be happening in normal use but it's one of the common failure modes.

author: darkstar49
author_rank: Frequent Contributor
timestamp: September 23, 2020, 06:56:59 am
content: Quote from: wraper on September 22, 2020, 08:12:19 pmkWeld, battery spot welder, Lipo Battery recommended by the manufacturer...

author: darkstar49
author_rank: Frequent Contributor
timestamp: September 23, 2020, 07:11:22 am
content: Quote from: wraper on September 22, 2020, 11:25:38 pmSome R/C applications are also using hundreds of amps out of these packs... and getting rude rarely helps much

author: Siwastaja
author_rank: Super Contributor
timestamp: September 23, 2020, 08:23:12 am
content: Slight amount of puffing - completely normal, even in A brand products.Too much - sign of serious degradation, possibly (but not necessarily) dangerous.Where to draw the limit? This is a tough question.In any case, all these hobbyking products are crap cells to begin with, and likely lack safety mechanisms compared to top brand products.Nothing fundamentally wrong in using li-ion cells to power a spot welder, stay well within specs and it's a load like anything else, obviously you need active power conversion instead of rednecking it without current limiting. The point is, you can easily get multiple kilowatts of peak power from a small pack. Large bank of electrolytics, or a smaller bank of ultracaps are the other typical options.

author: darkstar49
author_rank: Frequent Contributor
timestamp: September 23, 2020, 08:34:24 am
content: Quote from: Siwastaja on September 23, 2020, 08:23:12 amas stated, I'm using the kWeld (www.keenlab.de), they have indeed a (super)capacitor supply, but that one in turn needs a current-regulated (20A max) supply. All in all, given the relatively light usage (and the price of the capacitor option), I thought that the LiPo option would be OK (as stated, I bought 2 packs, but was stupid enough not to use them in parallel... I think dividing the current by 2 will help a lot).

author: wraper
author_rank: Unknown
timestamp: September 23, 2020, 01:21:47 pm
content: Quote from: darkstar49 on September 23, 2020, 08:34:24 amTrash without any current limiting. It simply short circuits the battery. Also:Quote

author: Siwastaja
author_rank: Super Contributor
timestamp: September 23, 2020, 05:10:26 pm
content: Quote from: wraper on September 23, 2020, 01:21:47 pmAlso the 300A fuse as shown is way, way too big. They have no idea about the I^2t ratings or curves of the fuses. That thing could work out if something like a 30-50A, maybe 100A fuse was to be used, limiting current a bit with its resistance, yet not blow during normal operation because the pulses are so short; yet blow quickly enough if the MOSFETs blow short or the software malfunctions anyway. A 300A fuse would take minutes to blow even at 600A, and this level of current may never be reached with the li-ion battery, or the wiring, before the battery or the wiring insulation bursts into flames. All of this would be easy to fix with good passive safety including understanding fuse ratings. (I'd go so far to say that passive safety based on proper fuse selection is #1 safety feature on any battery-powered project.)But I guess they are running successful business in any case. Even marginal designs sometimes work out in practice.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 23, 2020, 05:30:35 pm
content: These batteries are warning you. But everyone has their own risk tolerance. And I am not aware of any good metrics or algorithms to tell you how much risk you are taking.My personal experience is that slightly puffed batteries have never gone up on me, but are already showing degraded performance. I have had batteries go up, and if they were giving any warning it wasn't something I recognized. I have also found that these batteries add to the realism of model airplane crashes (smoke and fire). While I haven't had any of the really extreme events you see on YouTube, even a "mild" battery meltdown is "exciting".If you want to continue using LiPo batteries in this application I recommend that you use precautions such as working outdoors or other extremely well ventilated location, using a battery bag, and listening to your gut. If you are worried it is time to move on from that set of batteries.

author: james_s
author_rank: Super Contributor
timestamp: September 23, 2020, 08:21:36 pm
content: Quote from: CatalinaWOW on September 23, 2020, 05:30:35 pmSomeone crashed a 700 size heli at the field I fly at a couple years ago, I heard the thud from a few hundred feet away, glanced over to see a fireball that was probably 3 feet around and then after I landed the plane I was flying I walked closer and there were several guys picking debris out of a smoking depression in the grass. It was pretty impressive.I always make sure I have the balance leads connected when I'm charging, never do so indoors unattended and I never leave packs sitting around fully charged. That tends to make them puff up, especially if they get a bit warm while sitting fully charged.

author: james_s
author_rank: Super Contributor
timestamp: September 23, 2020, 08:25:00 pm
content: Quote from: Siwastaja on September 23, 2020, 08:23:12 amI haven't found this to be the case. I have a bunch of HobbyKing packs that I've been using for quite a while, the oldest ones I bought in 2014 and many have hundreds of flights on them. The only ones I've had fail are the tiny little gumstick cells used in micro planes and quads, and a couple larger ones that were my fault, I over-discharged them and one I left in the hot sun. The high drain LiPo packs don't really have any safety features to speak of, other than the balance taps to monitor cell voltage. There is no BMS of any sort.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 24, 2020, 06:53:02 am
content: Look, the fact a few packs haven't gone up in flames for you, doesn't mean the product safety is at a good level.0.1% failure rate would be a total disaster yet you would be unlikely topersonallyhave a product fail.Roughly speaking, the difference between crap and good products is 0.1% vs. 0.00001% failure rate.(talking about catastrophic failure rate. non-dangerous failure is more common, in both crap and good products.)

author: bdunham7
author_rank: Super Contributor
timestamp: September 24, 2020, 05:45:26 pm
content: Quote from: darkstar49 on September 22, 2020, 02:57:24 pmI'd like to know the reason lead-acid is not a good choice. I use one medium-sized starting (not deep cycle) battery and don't see any reason to use anything else. I leave a charger connected to it for some extra surface charge which means its internal impedance for a pulsed output is very low.

author: james_s
author_rank: Super Contributor
timestamp: September 24, 2020, 05:49:54 pm
content: Quote from: Siwastaja on September 24, 2020, 06:53:02 amCould you provide some data to back this up? It's not just me, there are thousands of people flying models with LiPo packs, a handful in the community have had fires, about 90% of those occurred while charging and almost all of those that I've seen were charging without the balance leads connected. I personally have seen no correlation between the brand of the pack and the failure rate. I want to see data that shows the orders of magnitude difference in failure rate you quote and would like to know which brands you sourced that data from.

author: darkstar49
author_rank: Frequent Contributor
timestamp: September 25, 2020, 05:11:35 am
content: Quote from: bdunham7 on September 24, 2020, 05:45:26 pmI don’t really know... but honestly, on my bench, I prefer a Lipo or something smaller...The battery type doesn’t matter much I think, the point being more what current it can deliver, can a (typical) lead-acid battery deliver in excess of 800A ?

author: james_s
author_rank: Super Contributor
timestamp: September 25, 2020, 06:02:54 am
content: Quote from: darkstar49 on September 25, 2020, 05:11:35 amYes, a starting battery certainly can, especially the sort that would be used in something like a diesel pickup truck, even a conventional medium sized car battery can likely manage though. The downside is that lead acid is bulky and very heavy and they can be dangerous, flooded cells will leak acid if tipped and they give off corrosive vapors and produce hydrogen when charging. They are extremely robust and can take a lot of abuse though.

author: Berni
author_rank: Super Contributor
timestamp: September 25, 2020, 06:58:01 am
content: Yeah if its puffed its on its way out.But it doesn't mean that it will spontaneously catch fire when left alone on a shelf. But if you continue stressing it so much it might puff up even more and at some point cause enough of a current concentration inside to create a hotspot and start the runaway self destruction. Tho physical damage tends to be a much easier way to start this self destruction process.In any case even a brand new perfectly fine looking LiPo pack should be treated with care, especially these RC packs that are protected by nothing else than foil. All it takes is dropping a heavy or sharp object on it and it has a pretty good chance of suddenly catching on fire.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 25, 2020, 11:47:19 am
content: Quote from: james_s on September 24, 2020, 05:49:54 pmNote that "a handful" out of "thousands" is roughly 0.1% meaning you are agreeing with my numbers! You just need to apply logic instead of emotion.A proper cell does not typically go up in flames while charging, even if electrically abused. They have passive safety layers; which are not perfect, of course, but make a big difference between a cheap Chinese product made in a no-name factory vs. a Panasonic or Samsung cell with decades of R&D and responsibility by the manufacturer.It's hard to protect against physical damage, like a copter crash; but during charging, having catastrophic failure is almost inexcusable, even if the charger does something wrong. Yet as you say, these crap cells fail while charging. It's a clear sign of lack of passive cell-level safety including shutdown separators, CIDs and PTCs (and likely modern and proprietary things I'm not even aware of).The fact the same people who sell these crap cells, also sell fire-proof sacks and stainless steel bunkers for charging, tells the whole story. They make a business out of the well-known unsafety of their own products.No one has actual data about this, obviously. The many orders of magnitude difference in safety between proper cells insidehunderds of millionsconsumer device, vs. "almost everybody has seen or heard about someone (2nd or 3rd hand) having a fire" in the Hobbyking hobbyist scene, should be evident.Similarly, it's very typical that when a phone goes up in flames generating headlines, it's almost always a cheap replacement cell that was used; even if the percentage of such replacement cells inside the devices is minuscule. Hence many orders of difference in safety. But again, no one has hard data on this.Do note, I have absolutely nothing against these Hobbyking products and do use them myself, they have their place. I just don't like mental dishonesty.