Charging a protected Li-Ion cell with a protected charger - Page 1
Forum section: electronics / beginners

author: PinheadBE
author_rank: Regular Contributor
timestamp: January 12, 2019, 08:36:42 pm
content: Hi,I just wondered if it is ok to charge a protected 18650 cell with a charger that also has protections.Something like this:https://www.aliexpress.com/item/12V-Charging-UPS-Uninterrupted-Protection-Integrated-Board-18650-Lithium-Battery-Boost-Module/32892470149.htmlAren't the two protection circuits going to pose problems ?I suppose it will be ok, but, better be safe than sorryThanks

author: spec
author_rank: Frequent Contributor
timestamp: January 13, 2019, 08:22:36 am
content: Quote from: PinheadBE on January 12, 2019, 08:36:42 pmHi PinheadBE,Never heard of any problems charging a protected LiIon battery with a normal charger.From a theoretical point of view there will not be a fight between the two protection schemes because the scheme with the most stringent settings will function first and the other protection scheme will not be triggered.The only area where the built-in protection could get triggered is if you had a fast charger with a very high charge current.By the way, I understand that all first-tier manufacturer's large LiIon batteries have a built-in thermal fuse.

author: PinheadBE
author_rank: Regular Contributor
timestamp: January 13, 2019, 06:19:55 pm
content: Thank you for your reply

author: Daixiwen
author_rank: Frequent Contributor
timestamp: January 14, 2019, 09:27:01 am
content: Quote from: spec on January 13, 2019, 08:22:36 amNo it's usually a circuit breaker triggered by an increase of the internal pressure. But you shouldn't consider this as a replacement for a safety mechanism. There are ways to provoke a fire without triggering the circuit breaker, by example by very slowly charging the battery slightly above the thermal runaway voltage with a very small current. Low temperatures make this easier too. So don't count on that safety as the only one against a defective charger.By the way battery manufacturers don't like using the words "fire" or "explosion" so I should probably say "fast uncontrolled disassembly with high temperature degassing"

author: PinheadBE
author_rank: Regular Contributor
timestamp: January 14, 2019, 05:40:57 pm
content: Quote from: Daixiwen on January 14, 2019, 09:27:01 amThank you: You just made my day !

author: spec
author_rank: Frequent Contributor
timestamp: January 15, 2019, 04:11:27 pm
content: Quote from: Daixiwen on January 14, 2019, 09:27:01 amHmm, interesting. My understanding was that there is a thermal fuse (and I may have got that wrong). In addition the battery has a strong case with blow off vents to release excessive pressure.Quote from: Daixiwen on January 14, 2019, 09:27:01 amI see we have the usual 'end of the world' stuff every time someone mentions LiIon batteries. It used to be lead acid at one time, then NiCad, and then NMH.

author: Daixiwen
author_rank: Frequent Contributor
timestamp: January 16, 2019, 10:10:20 am
content: The problem is that people that know a bit about the internal construction of batteries have often worked on safety too. I have done what we called "abusive tests" for 3 years on Lithium-Ion cells, finding all possible ways things could go badly, and this kind of work tends to make you paranoidQuote from: spec on January 15, 2019, 04:11:27 pmYes that's true. Often when there is excessive pressure there is also a thermal runaway going on and it's not just gas that comes out, it's a flame that can be 10 times longer than the cell itself.I know that I sound "end of the world" but when you are working on something that can potentially burn your house down, take a few precautions. Protection circuits for Li-Ion are dead cheap, there is no reason for not using them, at least for charging. Please use them. Thermal runaway on a Li-Ion cell can start at a voltage as low as 4.35V, all it needs is a badly calibrated power supply.

author: spec
author_rank: Frequent Contributor
timestamp: January 16, 2019, 09:24:36 pm
content: Quote from: Daixiwen on January 16, 2019, 10:10:20 amYes, I know you mean well, but safety is not what the OP asked about.But as we are on the safety track, you are right, the switch is operated by internal pressure. Here, AFAIK, are the safety measures that are on top tier batteries.Pressure switchPTC to limit current if overtemperatureStrong case to contain pressureBlow-off vents to release pressureInhibiting mat which melts on over temperature and prevents ion exchangeLimit the amount of Lithium in a battery cell