18650 batteries not charging - Page 1
Forum section: electronics / projects

author: sdancer75
author_rank: Frequent Contributor
timestamp: August 17, 2021, 02:55:17 pm
content: I replaced my old Pb batteries from my vacuum cleaner with four 18650 batteries 14.4v in total. I added also a 4s BMS overcharge protection circuit. The original power supply is 18v / 150mA but it seems that it couldn't charge the batteries. From 12.50v at the beginning, it stopped charging around 13.50v after 1 day in the power.I connected the circuit with external power supply 18 / 1.5A. After about 20 minutes it jumped at 14.30v and still charging.What is wrong with the original power supply? Is it too slow for charging? Does it affect the batteries that the new power supply outputs 1.5A?

author: madires
author_rank: Super Contributor
timestamp: August 17, 2021, 04:02:09 pm
content: Have you checked the output of the wallwart? DC voltage and ripple under load?

author: tooki
author_rank: Super Contributor
timestamp: August 17, 2021, 04:33:17 pm
content: 1. Is that board just a balancer and protection, or does it actually contain a charger IC?Edit:No, it does not. You need to get an actual charger, too. Very little is available on AliExpress as boards. The BQ24650 boards are the only ones I see, but you’d need to modify the configuration resistors to the correct charging current, since they’re all sold configured for 5-10A, too much for single cells.2. If it does not contain a charger IC: are you then just relying on the protection IC to stop charging? That’s a very, very bad idea, since it’s not intended to be your everyday control, it’s the safety backup. Besides, LiIon do not like being trickle charged indefinitely.3. 150mA is a quite low charging current for 18650 cells. A modern 3000mAh cell would take over 20h to charge, longer than the default safety timer on many charger ICs. A more typical current would be around 1.5A (1/2C), with 1C usually being possible, if not optimal. But then the charger needs to switch to constant-voltage charging (usually down to 1/10C).

author: sdancer75
author_rank: Frequent Contributor
timestamp: August 18, 2021, 11:28:17 am
content: It seems a cold joint at the pcb board was the root of the problem. Thanks to all.The BMS is the one below.https://m.banggood.com/4S-40A-Li-ion-Lithium-Battery-18650-Charger-PCB-BMS-Protection-Board-with-Balance-For-Drill-Motor-14_8V-16_8V-Lipo-Cell-Module-p-1405559.html?createTmp=1&utm_source=google&utm_medium=cpc_ods&utm_content=ana&utm_campaign=ana-sds-15cov-top30-210510&ad_id=520376153942&gclid=Cj0KCQjwvO2IBhCzARIsALw3ASrDXKK3RXP8yRU0y1WWQoubck165Y05HL0i2gnFiAV0BBdkRP6nvwwaAg0tEALw_wcB

author: tooki
author_rank: Super Contributor
timestamp: August 18, 2021, 12:48:05 pm
content: Quote from: sdancer75 on August 18, 2021, 11:28:17 amThat’s only a protection board. You still need an actual LiIon charger (not just a power supply!) to properly charge the battery pack. While using the 150mA charger is very unlikely to cause a fire, it’s not the right way to charge LiIon, and you’ll end up reducing the lifespan of the batteries.

author: sdancer75
author_rank: Frequent Contributor
timestamp: August 18, 2021, 05:57:39 pm
content: Quote from: tooki on August 18, 2021, 12:48:05 pmHi,Can you point me one?

author: tooki
author_rank: Super Contributor
timestamp: August 18, 2021, 06:05:39 pm
content: If you want a bare board from AliExpress, read my prior post, where I explained it already.If you want a device, look at the chargers sold for radio control (RC) cars, drones/quadcopters, etc.

author: sdancer75
author_rank: Frequent Contributor
timestamp: August 18, 2021, 07:09:47 pm
content: Thanks,I am still wondering, why this BMS is not good for LiIon batteries.... As you already said, it protects from overcharging (why you say that is a backup solution???) and keeps the balancing, what else a charger would offer more than this? This BMS is supposed to do exactly this and nowhere says as far as I know/read that it needs and extra charging board.So the question is: what the extra charging board will offer to the circuit?

author: tunk
author_rank: Super Contributor
timestamp: August 18, 2021, 09:28:14 pm
content: Usually li-ion charging is done in three stages:1. Constant current (CC) until set voltage is reached (usually 4.2V per cell).2. Constant voltage (CV) until the cut off current is reached.3. Charging cut off (usually 10% of CC value).A BMS does none of this, it only cuts off charging when 4.2-4.3V per cell is reached.I.e. you're loosing one level of protection, and you risk overcharging to 4.3V.

author: sdancer75
author_rank: Frequent Contributor
timestamp: August 19, 2021, 11:58:30 am
content: Thanks for the info !!!The 4.3v is considered as an overcharged for 3.7v 18650 batteries?

author: tunk
author_rank: Super Contributor
timestamp: August 19, 2021, 12:39:10 pm
content: For the majority of 18650s 4.2V is the fully charged voltage,and 4.3V is overcharging. A few 18650s have a higher chargevoltage. I suggest that you look up the specs for your cells.

author: Gregg
author_rank: Super Contributor
timestamp: August 19, 2021, 09:40:09 pm
content: Search for a iMAX B6 charger. They have provision for individual cell equalization. They are also very inexpensive for their capabilities. I have one that I bought from Banggood several years ago and it seems to do the job as well as any other charger I have. If you buy one, get a set of the plugs for the equalization ports. Theses are pretty standard in the world of drones and RC models.

author: tooki
author_rank: Super Contributor
timestamp: August 19, 2021, 11:58:59 pm
content: Quote from: sdancer75 on August 18, 2021, 07:09:47 pmA backup is intended as just that: asecondarylevel of protection in case the primary protection fails. By using the secondary protection only, you havenoprotection if it fails.The issue with LiIon is not that they fail catastrophically often (they don’t), but that when they do, you suddenly have abigproblem. They are high-capacity, high-current cells that, frankly, are not the kind of cells to be played with before understanding them properly. You cannot just treat them like substitute lead acid cells (which is literally what many AliExpress “LiIon” chargers are: lead acid chargers). I’m not scared of them, but I definitely respect them.Anyhow, I don’t know you, but I care about you enough that I don’t want your house to burn down and kill you and your family. Not a common outcome, but one that literally can happen with an abused rechargeable lithium battery.That a Banggood/AliExpress/eBay listing doesn’t provide proper documentation is, well, indicative of nothing at all. The Chinese vendors use terminologyveryloosely, unfortunately requiring a lot of knowledge on the part of the buyer. Then again, some of these are the same people literally selling mains-powered “18650 chargers” that are nothing more than an unregulated capacitive dropper: if one of those caps fails short, one could be putting mains AC straight across the cell!Tunk did a great job explaining how LiIon charging works. If you do notfullyunderstand the process, I urge you to stop now and research it more until you do.Quote from: sdancer75 on August 19, 2021, 11:58:30 amFor most, yes. You need to look at the datasheet for your battery, as it can vary. Note that rechargeable lithium cells are fairly picky: a typical datasheet will specify a termination voltage to ±0.05V. So you can’t just say “eh, close enough!”That’s afartighter tolerance than typically found in non-lithium chemistries, and part of why lithium rechargeables are generally always charged with a lithium-specific charging IC. (NiMH is the other common battery chemistry that requires precision voltage measurement for proper charging. These are actually arguably even harder to charge properly. But an abused NiMH cell simply suffers damage to itself, without risking harm to you.)

author: sdancer75
author_rank: Frequent Contributor
timestamp: August 20, 2021, 08:09:50 am
content: Quote from: tooki on August 17, 2021, 04:33:17 pmYou mean a board like this? As far as I can see it takes as an input 18v from solar panels output. Does this it means I can directly connect the output of the conversational charger and then directly to the BMS?https://m.aliexpress.com/item/32875926007.html?trace=wwwdetail2mobilesitedetail

author: tooki
author_rank: Super Contributor
timestamp: August 20, 2021, 01:12:03 pm
content: Quote from: sdancer75 on August 20, 2021, 08:09:50 amYes. But you will need to change some resistor values to set the correct charging current, since 5A is far too much for most 18650 cells.A charger like the imax one mentioned by Gregg will be much easier to deal with.