LiOn charging cutoff? - Page 1
Forum section: electronics / projects

author: jitter
author_rank: Frequent Contributor
timestamp: July 30, 2016, 07:27:12 am
content: I was under the impression that all LiOn batteries need protection circuits to prevent overcharge and overdischarge, overcurrent, etc.Recently I boughtthishair trimmer that is equipped with a 600 mAh LiOn battery.The manual clearly states that charging must be done for a maximum of 90 minutes. But it also states that when the charge is completed, the display will show that.Now this has me wondering if the manufacturer is just covering their ass or that this trimmer will actually stop charging when full and there won't be any damage to the battery from overcharge if you forget to unplug the unit from the charger... Any insight?

author: Kilrah
author_rank: Unknown
timestamp: July 30, 2016, 07:35:08 am
content: It will of course stop charging as it should, otherwise you'd already have read about an outbreak of house fires in the news...Likely CYA, not being very confident in their charge circuitNote that it is also in "NOTES", not in the many other "DANGER!!!!" categories.

author: Ian.M
author_rank: Super Contributor
timestamp: July 30, 2016, 07:38:24 am
content: Sounds like it may use a fairly dumb CC/CV charge controller. If so, holding it at the peak voltage for an extended period will certainly shorten the battery life, although it wont kill it immediately.I agree its also probably a large amount of ass-covering to further reduce the risk of fires and >1% warranty failure rate, and give their lawyers grounds to argue improper use if they have to!Unless you are prepared to do a teardown and temporarily patch in a couple of wires to let you log the charging voltage over a full charging cycle, you wont know for sure.

author: tatus1969
author_rank: Super Contributor
timestamp: July 30, 2016, 09:53:41 am
content: right, sounds somewhat contradictory. But I wouldn't place a bet on that they have done it right (and safe). I had almost lost my house because of a (Chinese) Lipo balance charger that just wasn't one.They'll probably have done that CC/CV charging profile right, but to be safe you also need a temperature monitor and an undervoltage cutoff. If you don't have that it could be a time bomb, as problems will probably not show up until the battery is worn and has started swelling (if it is a flat cell).Would also be interested in a teardown.

author: jitter
author_rank: Frequent Contributor
timestamp: July 30, 2016, 10:52:07 am
content: I tried a teardown, but it's not going to be non destructive, so I stopped. The rear part of the back is held on by clips and a single screw. But as I tried to split the housing open, it became clear that the business end (near the blades) isn't going to be released without tearing stuff irreparably. It's been intentionally designed so that the battery can be taken out before disposal, but not for replacement, so battery EOL means device EOL (unless you don't mind using it on the adapter).The Dutch and German sections of the manual confirm that the removal procedure kills the device. AFAIK, it's an EU requirement that the battery can be reasonably easily removed by the end user before disposal. A similar thing can be seen with those popular Braun electric toothbrushes Dave did ateardownon. You can easily take the bottom off the brush, but taking out the battery results in destruction of the internals.Through the crack I could see a lightgreen round LiOn cell with a small pcb under it. Unfortunately, that's where the teardown ends.

author: Pjotr
author_rank: Frequent Contributor
timestamp: July 30, 2016, 11:39:56 am
content: Quote from: tatus1969 on July 30, 2016, 09:53:41 amDon't think it is that bad. This kind of things is usually single cell which avoids the hassle of cell balancing. Simple current limited CV charging is fine and safe then. Only thing, leaving the battery at max allowable voltage shortens its life. Over max allowable voltage simply damages the cell and must be avoided at all times.Batteries "on fire" is a result of too deep discharging and then charging them again. So this things have anyway a controller to watch deep discharging (sometimes within the cell itself) to cut off.Selling stuff with Li batteries without minimal safety precautions can be considered a crime. Don't think Lidl as seller of the product will/can afford that.

author: jitter
author_rank: Frequent Contributor
timestamp: July 30, 2016, 12:00:07 pm
content: Quote from: Pjotr on July 30, 2016, 11:39:56 amNo, I don't think so either. If have several electric and electronic things sold by Lidl (usually temporary, but recurring) and they have some of the most elaborate (and ass-covering) manuals you have ever seen.But having said that, the stuff looks good and never gave the idea of questionable safety. It's usually built down to a price AND up to a standard... guess high volume can make that possible.

author: tatus1969
author_rank: Super Contributor
timestamp: July 30, 2016, 01:50:50 pm
content: Quote from: jitter on July 30, 2016, 12:00:07 pmI would have signed that without seeing until some years ago, when China were only manufacturing cheap stuff, that was designed elsewhere. The problem has evolved when they have starteddesigningelectronics. Of course there are also certainly many good design examples, but the number of carelessly designed stuff, neglecting all safety rules, faked EMC compliance and CE approvals and squeezing out everything in terms of absolute maximum ratings and lifetime, is increasing faster and faster. I even have one case now where the Chinese (TUEV certified!) approval lab definitely has issued faked reports.As these units are sold at unbeatable prices, I can imagine that also renowned resellers like Lidl are tempted to grab such offers.

author: amyk
author_rank: Super Contributor
timestamp: July 30, 2016, 03:16:54 pm
content: There are some very informative posts in this thread:https://www.eevblog.com/forum/projects/diagnosing-lithium-cells/Keeping cells fully charged may not be that bad, as long as the voltage remains within tolerance.

author: jitter
author_rank: Frequent Contributor
timestamp: July 30, 2016, 05:17:31 pm
content: I glanced through that thread, but I was already aware of the fact that LiIon cells may live longer when stored in a partial state of charge rather than fully charged. Though, it's good to know that storing them fully charged isn't much of a problem because that's what I like to do. A camera or cordless drill is no good if the battery is almost flat, and usually, I don't know beforehand when I need them and they may have been idle for quite a while.I think everyone has the experience of getting the cordless drill that had been stored unused for a couple of months and finding that the NiCd battery was flat and refused to take a (full) charge ever again. Luckily no more of that with LiIon cells (i.e. no high self discharge). But it must be said that I found that a totally flat NiMH cell, which was in that state for several years, happily accepted being charged again.More and more wireless stuff seems to switch to LiIon. My previous trimmer had a NiCd battery, and my previous electric toothbrush had a NiMH cell, both replacements use LiIon. I don't need to tell you about phones, only my Garmin outdoor GPS (GPSmap 62 st) still relies on "old" technology, but then its batteries are not built in but replaceable primary or rechargeable AA cells. I don't count low power devices such as clocks or remote controls, they work best on primary cells.