2x 3S lipo problem

Hi, I have a problem with my battery’s i use two turnigy 3S 5000mah (40-50C) in series, but for some reason they start to puff up a bit, the batterys do not have many cycles on them. im still using them how they are now and still work, i do take care of them, balance charge them at 1C.

some of my parts: Motor: Turnigy Aerodrive SK3 - 5055, 70A, 5-8S lipo, 430kv, 1750W ESC: X-car beast 120A (burst 760A), 2-6S lipo

Here are some pictures, you cannot see it that well, buts its a slight bulge and can be pressed in a bit. IMG_6053IMG_1962IMG_4201IMG_4682IMG_5348IMG_2738

Not ideal, at least one of the cells in each pack is degraded. Sometimes it just happens. You’re probably going to need to replace them soon. Also if you’re going to use them have a fire plan in case they go nuts while charging or being discharged.

Please stop using that battery! Once they start puffing up the degradation accelerates. You’re liable to burst into flames at any point. What’s happening is that the electrolyte is basically evaporating and eventually the two electrodes can touch causing a short and a lot of heat. Toss it and eat your losses, seriously, don’t take battery safety lightly. These cells have a huge amount of energy stored in them and you don’t want to let it out uncontrolled. If the batteries are new-ish you may be able to get some sort of warranty on them. Not sure what Turnigy’s terms are though…

Edit: also I should note, take the C rating with a grain of salt, they tend to lie a bit. Which is why I have two 190A rated batteries in parallel.

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What’s your low voltage cutoff? Lipos are almost empty at 3.7v/cell.

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That is somewhat false. See image from http://learningrc.com/lipo-battery/. You can find others by searching “LiPo discharge curve” on your favorite search engine. image Under heavy loads the voltage drops to below 3.7V fairly quickly. Very light loads (less than 1C) will keep a higher voltage for longer and the battery may float back up when load is removed, but the float voltage is not a good indication of charge remaining.

You can safely cutoff around 3 volts (experienced users only!), not much lower though. That being said, over discharging your cells can cause damage, as can over charging. Check cell voltages after charging with an independent measurement device (multimeter). 0.01 volts over isn’t going to hurt, but 0.1 might.

Edit: Here’s a plot of low load discharge (not super realistic for our purposes either): image

that chart is 25c or more on a 1.7ah cell. 25c on a 5ah cell is 125a. I don’t think this is representative.

I do agree that voltage under load varies a lot. But if you want long healthy life from hobby packs, you want to stay far from the knee of the discharge curve, and also not leave the packs at full charge for more than a few hours. Well at least that’s what I’ve read on teh internets.

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I found that below 3.6 under load, a Lipo will heat up relatively quickly and you will shorten the lifespan significantly. Most will begin to puff.

That is based on destroying 12 packs a year for the past 4 years (Graphene packs - race drones).

ESK8 example. A couple of days ago, I had to make it back after a 35 km trip. The last two km I had to drop my cell voltage down to 3.5V. Puffed my lipos (granted, they were a year old but no issues before that).

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Bro. I would advise that whatever @deucesdown says should be regarded as an informed statement (especially when he’s helping me harrass @psychotiller lol). everything else that you mentioned in your reply is accurate, except the “discharging to 3v safely” part. It is safe to do this if you are testing the endurance/longevity of a battery (like, for science), but that’s only “safe” under controlled conditions, and with precision instruments. The original post-er has obviously puffed these packs under non-extreme conditions, and these are not batteries which are test-dummies, they’re for transportation (where loads change like the salmon of capistrano). As your other comments indicate, I’m respectfully assuming that you know what you’re talking about in regards to these chemistries, but I would also tend to advise a very generous safety-margin when publishing statements that may cause problems for other readers. My point here being, that in testing-scenarios you’re right. But eSk8 is real-world-scenario, and for someone who wants to keep their battery healthy, happy and slim, high amp discharging below a VERY conservative threshold (50%) isn’t good practice.

…aaand for a 40-50c lipo, a 25c load is probably way unsafe. Also, what @telnoi said. Please understand @AutoItKing , that I mean no rudeness or disrespect, but whith so many fires recently, CAUTION FIRST!! Heard?

Edit: having read some of your posts, it’s obvious that you know what you’re talking about. let me restate that my only concern with your above post is that kiddies may burn their stuff without the level of understanding that comes with in-depth research. Btw, just curious, what IS the nature of your extensive electrical experience @AutoItKing? your profile is vague but interesting

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And another thing: @SanderG , What the hell are you doing with such a small, and such a high-kV motor on an esk8 anyway?? without a ridiculously-low gear ratio you’re gonna puff ANY lipo at that low of voltage to do x-amount of watts (6s, right? tldr). go higher voltage, <190kV and a more gentile esc, and you’ll have less battery puffage :wink:

ps: output watts can be equated to the ability to do work over time (like horsepower for example). this is a generalization tho, and I’ve been drinking. while your esc can handle a shitload of amps, those batteries aren’t suited for it!!

Edit: no disrespect to YOU either, my b

Hey @PatRocks thanks but I mean it when I say I just read it on the internet. I’ve read a lot though with a focus on safety and longevity. I’ll instantly and always defer to those with experience.

Like this guy :slight_smile:

But, I’m stupid, 6s so those high amps are in the range of possible.

i charge them in a lipo safe bag…

how many cells do u use? 2X 6S in parallel?

my ESC cuts off at 3.7

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my battery’s are always charged to 4.2

The motor is 70A, my batteries can handle up to 250A no?

what is the best thing to do here? these are my second pair of batteries that puffed…

will something like this work better? (https://www.ebay.com/itm/90mm-dual-6364-hub-motors-drive-kit-for-electric-skateboard-longboard-part/302546262750)

there might be your problem. The highest Cutoff the X-Car is able to do is 3,4V general voltage. That means if you stress these lipos a bit, they decharge unevenly between the cells. So one cell could be at 3,0V when the ESC cuts off. 3,4V is already too low. So don´t rely on the X-Car cutoff!

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it cuts off when im giving full power when i have ridden for around 10km, so i think they go to that rate under heavy load, when i messure under no load they are 3.7V

They sag down under load and the ESC cuts off, after that the battery goes up again. Get a voltmeter to monitor your cells to know whats going on. If they sag too much down, they drift from each other and go bad over time.

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