How to charge a LiPo battery safely? - Page 1
Forum section: electronics / projects

author: miketan3904
author_rank: Contributor
timestamp: September 29, 2021, 08:16:31 am
content: I have a 3S 8000mAh 35C LiPo battery and a 20W charger (specification provided by seller: 110-240V AC Input, 3 x 1600mA Output). I have a few questions as follow:1. At what battery voltage should I start to recharge the LiPo battery?2. How long does it take to charge a battery?3. Is there any other safety precaution that I should take?

author: drakejest
author_rank: Regular Contributor
timestamp: September 29, 2021, 08:27:23 am
content: Quote from: miketan3904 on September 29, 2021, 08:16:31 amThat depends if you want you battery to last, 3.2v per cell should your absolute minimum be. but discharging that low would degrade the battery faster. My personal sweet spot is 3.5v and maximum voltage of 4.1Quote from: miketan3904 on September 29, 2021, 08:16:31 amThat also depends on how much current you are pushing through the battery if you can provide the specific BMS you are using that would be nice. In a perfect case and assuming your battery is really 8000mAh(which i doubt is true, its probably MUCH lower than that) and you are charging at 1A. It would take you 8 Hours to charge that battery, again assuming everything is perfect. The formula is Ah capacity divided by charging current. T= Ah/AQuote from: miketan3904 on September 29, 2021, 08:16:31 amYes there are a few, especially if your BMS dont have them. Such as overvoltage protection, undervoltage protection, over temperature protection (yes you dont want your batteries getting too hot), over current protection

author: tunk
author_rank: Super Contributor
timestamp: September 29, 2021, 10:23:14 am
content: Quality of the charger, it should follow CC/CV/cutoff. And does it have balancing?Photos of the battery and charger may help.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 29, 2021, 06:13:21 pm
content: Q: How to charge a LiPo battery safely?A: You use a LiPo battery charger, if you don't know what you are doing / don't know much about charging LiPo's in the first place.Quote from: miketan3904 on September 29, 2021, 08:16:31 amYou don't start at a given voltage.Proper Li-ion/LiPo charging starts with a constant current phase, not a constant voltage phase. So the battery voltage will start at whatever it is, and will increase as the charging proceeds, at a constant current. During that phase, the voltage is monitored. When it reaches a given voltage - usually the 4.2V max voltage for a LiPo - the charging circuit should switch to a constant voltage mode, at this voltage. Note that this must be very accurate - even just a few tens of mV over 4.2V, and it can damage the battery. OTOH, it is safe to choose a lower maximum voltage, at the expense of a (slight) decrease in usable capacity.During the constant voltage phase, current should be monitored. The usual end-of-charge condition is determined when the current during this phase drops below C/10. This is what most chargers do, and what is considered safe.Now that's the basics of LiPo charging. A decent charger should also implement additional safety features, such as:- Refusing to charge if the initial battery voltage is below a given threshold (usually 2.8V or so);- Start with a low charging current (to "precondition" the battery) if the initial voltage is between the above threshold and something like 3.0V to 3.1V, and until it reaches the latter;- A time-out;- Ideally monitoring the battery's temperature.Now all of this is usually properly handled by most decent charging ICs. Use one. Don't attempt to implement this with discrete components, unless you have a very good reason for doing so, and know very well what you are doing.Quote from: miketan3904 on September 29, 2021, 08:16:31 amIt depends on the battery, its "health", the initial state of charge, the charging current, and the end-of-charge condition (see above)."Typical" charge time for a typical charging current of C/2 is between 2 hours and 3 hours. It's always more than 2 hours, as the charging process is not 100% efficient from the battery's chemistry POV.Quote from: miketan3904 on September 29, 2021, 08:16:31 amSee above.Last note is that a a 3S 8000mAh contains a significant amount of energy, and can be a real hazard when mishandled. And the 35C parameter means that it has fairly low internal resistance when charged, so can deliver a lot of current. Any improper handling could lead to explosion and/or fire. This is serious stuff.Note: the voltages I gave here are for a "1S" battery. Yours is a "3S", meaning it has 3 cells in series - actually it's probably a combination of cells in series and parallel, to yield low internal resistance and high voltage output. For a 3S battery, voltages must be multiplied by 3. But, there will be other things to consider that I didn't mention: ideally, 2S/3S/... batteries should be balanced. The commercial chargers usually have that feature. But if you're designing one, that may be one more thing to take into account...

author: miketan3904
author_rank: Contributor
timestamp: October 03, 2021, 09:00:14 am
content: What kind of mishandling would lead to explosion? And how should I handle the battery in case it explodes?

author: tooki
author_rank: Super Contributor
timestamp: October 03, 2021, 11:20:40 am
content: Quote from: miketan3904 on October 03, 2021, 09:00:14 amOvercharging. Charging at too high a current. Charging at far too low a current. Charging after very deep over-discharge. Overheating. Charging when too hot. Charging when too cold. Short circuiting. Connecting them backwards. …Lithium ion batteries are divas. Youhaveto treat them properly, which is why properly designed systems use dedicated charger ICs, temperature monitoring, protection ICs (either in the charger and/or in the battery pack), and proper load disconnection at the right voltage.What SiliconWizard is talking about, balancing of series cells, is important, because if you don’t balance, you can end up overcharging cells or even forcing voltage through in reverse, which are… bad.The chances of a fire or explosion when abused aren’thigh, but the consequences can be catastrophic (since lithium fires are almost impossible to extinguish), so you really need to treat them with respect. If you are unable or unwilling to do that, choose a more tolerant battery chemistry like NiMH (also needs careful charging, but the only consequence of abuse is ruining the battery, it’s not going to set your house on fire) or lead-acid.Quote from: miketan3904 on October 03, 2021, 09:00:14 am1. Don’t let it get that far.2. Throw it in a (metal!) bucket of sand. (Cellphone repair shops often have a bucket of sand or a dedicated lithium ion safety bag/container in case a battery is catastrophically damaged during a repair.)3. Call the fire department.

author: DuPe
author_rank: Regular Contributor
timestamp: October 05, 2021, 06:08:13 am
content: There is very comprehensive Information on batteryuniversity on how to charge several lipo chemistry.https://batteryuniversity.com/article/bu-409-charging-lithium-ioncheersPeter