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Dropping voltage from a Li-ion battery
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spec:

--- Quote from: 6PTsocket on December 26, 2018, 02:07:52 pm ---
--- Quote from: spec on December 26, 2018, 12:07:35 pm ---NimH batteries have been mentioned in this thread, so here is a point about them. Out of all the common battery technologies: lead/acid, NiCad, NimH, LiIon, NmH are the hardest to charge properly. And the reason is the very slight drop in voltage (-dv/dt) near the fully charged state. This means that you have to charge NiMH at a higher current than you would otherwise like to get a measurable -dv/dt, and even then it is missed. I have a top of the line NimH charger and even that gets the charging wrong from time to time. As for cheap chargers- forget it. :--

Of course, the easiest batteries to charge are the LiIon types. They have revolutionized battery power technology, in spite of some of the messages of doom you see on the net. ;D

--- End quote ---
Funny, I emailed Tenergy on that very subject and they assured me that my Tenergy smart charger, that predates the new batteries would have no trouble detecting the small voltage change. The fact is, there are a lot of devices that use drop in AA and AAA cells that are not easily converted to lithium. These new NiMh cells are something completely different than the older ones.
I never thought a cell that catches fire if it is over charged or is permamantly damaged if allowed to discharge too far, is a particularly simple technology. My interest started out when I had a problem similar to the OP. I had a 2.4 volt soldering iron that needed cells. As I do not use it a lot and NiCds do not hold a charge well, I thought of an 18650 but it seemed wasteful to lose1.2 volts of the 3.6 volts in a couple of diodes that also had to dissipate a lot of heat. I had to waste 1/3 of the cell's capacity. There is no room for a buck converter even if one existed for those specs and all that electronics just to change battery chemistry made no sense.
There is another lithium chemistry that is 2.4 volts per cell but there is not a lot of info out there. I would need control circuitry that is not on ebay.

Sent from my SM-G900V using Tapatalk

--- End quote ---
Don't get me wrong, nearly all of our domestic low-power devices, from TV controllers, to clocks, to radios, to garden lights, are powered by NMH batteries.

By new technology I assume you are referring to the Panasonic/Sanyo eneloop type which are excellent. But all the same, they do get into a state on occasions and I have to put them through a couple of discharge/charge cycles to get them 'standardized' again.

You do know that you can get LiIon batteries in all sizes, not just 18650. For small applications I use rechargeable CR123 types which are really handy and dirt cheap.
Cricri:
Yes, when NiMH came out, I thought they were God sent. I bought a bunch of Fuji ones on eBay, and gave all my NiCd to a flat mate. And that was more than 10 years ago!
Today, even my NiMH leave me unimpressed. My Fuji are long gone, and I swapped them for some Panasonic Infinium, which allegedly hold the charge longer when not in use (which is somewhat correct). But even then, I use them very little because they don't last that long, and they take several hours to charge properly. I used to have a Rezap charger (Australian I think?) and sold it off since I never recharged alkaline batteries. The few alkalines I tried to charge in there leaked soon after, wow, would have thought (besides everyone)? Now I've got a Tronic branded (=Lidl) slow charger, and that's pretty much the best charger I've ever had, but still I only use NiMH AAs in my son's toys because if it doesn't switch off the toy, I can blame it on him, delay changing the batteries ("they need charging") and save money on alkalines. Actually, I also have 4 in my scopemeter in C adapters because I don't use it much, so don't check it often, and I know NiMH won't leak!
So when I found these 2 Chinese device THIS YEAR that are still shipped with NiCd, I was at the same time annoyed and impressed that they still manage to source them.

Another funny thing about NiMH: people tell me "if the voltage drops very low, they're dead as a dodo". What I did on few occasions was "trickle"charge them in a cheap Sony charger that doesn't seem to do much checking before charging, leave them in there for like 10 minutes, then drop them in my Lidl charger which will then accept them. I know what you're thinking: they won't last. And actually I did have subsequent occasions of batteries in the same Infinium batch to go dead later. But, the weird thing is, I started marking them, and the ones which would later die were not the ones I resurrected! I mean, statistically, they could, but I still have some that I marked as dead years ago that still work like the rest of the crowd! Which suggests that NiMH going very low doesn't necessarily lead to long term damage, which I find puzzling and counter intuitive.
spec:
 + Cricri

:) Interesting. Before the arrival of LiIon batteries, rechargeable batteries always seemed to be source of problems, and no two batteries of the same type behaved the same. As you say though, NMH was a game-changer when it came out.

The NMH batteries around the house and garden often get discharged to a low voltage, but they appear to be working OK, although I have never checked what their actual capacity is. That dodge of forcing some current into a battery, with a low terminal voltage, made me smile- I do the same thing. In the old days I used to revive NiCad batteries that had shorted, and been ditched at work, by momentarily connecting them to a 50V 40A supply. In most cases, a few tries and they came back to life.

For new designs though, I now only use LiIon batteries of all sizes and silver oxide, non rechargeable, for micro power applications. I have two identical Casio fx-570W scientific calculators, bought in about 1981, and in nearly 2019 they are still going strong on the original  silver oxide batteries: that's 38 years.:phew:

The beauty of LiIon is its light-weight and relatively high terminal voltage range of 3V7 down to around 2V9, which means you can build circuits that run directly from a single cell. And if you need a higher voltage, or even split rails at a higher voltage, a simple switcher board does the job nicely. With the approximately 1V2 terminal voltage of NiCad, and NMH, it was difficult.

The other advantages of LiIon are its consistency, very low self discharge, and simple charging: if you do not need to squeeze the last 10% of capacity out of LiIon batteries, just stick a 4V current limited source across them.  This charging regime also extends the life of the batteries greatly.

Incidentally, as you probably know, LiIon batteries, unlike other batteries, do not use a chemical reaction to generate a flow of electrons. Instead they rely on ion entrapment.
spec:
 + Cricri

Do you have problems with batteries due to the low temperatures in the Antarctic?
james_s:

--- Quote from: 6PTsocket on December 26, 2018, 06:49:29 am ---In defence of NiCd's, I have them in a number of devices like an old 4.8 volt carpet sweeper, 7.2volt B&D dust buster, a 14.4 volt drill, an electric tooth brush and a beard trimmer. I may be stuck in the past but they all work and a few are on their second set of batteries. They are still used in many non critical, inexpensive applications.
According to Battery University, the educational site devoted to all things battery, the NiCd memory effect was a problem solved in the very early days of NiCd production and the real cause of the problem is something else entirely. NiCd's on trickle chargers are continuously over charged and loose capacity. Then again all rechargeable batteries loose capacity over time.
There is a new generation of low self discharge AA and AAA NiMh batteries with high capaity and high discharge rate ability that give lithiums a run for their money. I woukd use those for replacement of similar size NiCd's. They will work on the old NiCd/NiMh charger. One of the manufacturers is Tenergy, the other brand eludes me.

Sent from my SM-G900V using Tapatalk

--- End quote ---

There is a Dust Buster at our family cabin that was installed back in the 80s when they were a new thing. It has sat on the charging cradle ever since and I was surprised to find recently that it still actually works. Doesn't run very long, but it has 30+ year old NiCd batteries in it.
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