With total discharge, sulphation can set in that quickly.
There's various methods for reviving sulphated cells, but you have to act fast or the sulphate steals a big chunk of capacity.
And as already mentioned, most SLA become marginal at best if discharged below about 11V.
The story I first read that was NASA discovered memory effect - apparently solar charged satellite batteries got charged on a very regular cycle when the panels could see the sun, and the daily discharge pattern was always the same - eventually the cells developed only having that much capacity.
Aggessive pulse charging is spectacularly good at curing memory effect in Ni-Cd cells - my experiments with Ni-Mh were somewhat less impressive.
Motorola introduced a pulse charger for Honeywell Strobonar electronic-flash packs back in the '60s. "Modern Photography" hailed it as a miracle -- it could actually bring near-dead packs back to life, and significantly increase the capacity of "wilted" packs.
Several years later, I asked Bert Keppler why the product had disappeared. "Uh... the battery packs blew up too often."
You could use them in Renee Everhart's alarm system. Nobody cares if she gets burnt up in a fire.
You sound so much like a Jew when you say, "I'm not going to pay so and so for such and such."
Oh, wait you are a Jew.
Tell the Jew that it's two thicker issues and you might have a sale.
I have a pulse conditioner for Ni-Cd published in the current July/August summer circuits issue of Elektor.
Its somewhat less aggressive than my original converted AT PSU, but the cells remain cool throughout the treatment.
Congrats on getting an article published, but I'm not going to pay $13 to download the issue: What's an "Acupuntural NiCd Battery Conditioner"? Anything to do with acupuncture? Push needles into the cell? Feel no pain?
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
The summer issue traditionally was the best, lots of circuits rather than multipage articles. So you'd get more for your money (plus, it was a thicker issue, instead of two issues).
Michael
I may have noticed that, I can't remember if the summer issue is on the newsstand here yet. I know I looked at the current issue recently, and soemthing made me wonder if I "knew" the writer. But I can't remember what the project was, or if I saw a name I wondered about.
This isn't the first time a denizen of this hierarchy made it into Elektor. Andre somebody who used to be a regular in sci.electronics. basics had a simple project, I can't remember what.
Michael
Over the years I've had a couple of bicycle lights published.
Hopefully the July/August issue also includes; my take on what might be in the house coded chip in a 2D LED flashlight and an E-cigarette battery charger.
Thanks for the info about memory effect, much of that was new to me.
So, what is it that kills laptop batteries? I've had to replace several on the kids's laptops.
If there's no memory effect, and much of the damage is caused by overcharging, is that the problem with laptops? Should I be retrofitting a better wallwart to these?
Laptop batteries are LiIon and do not have anything to do with the mythical NiCd memory effect. Three things will help kill LiIon batteries:
The details:
Let me guess(tm). You left the charger plugged into the laptop 24x7?
It's almost impossible to overcharge a LiIon battery. There's plenty of electronics between the charger and the cells to prevent that. It's also fairly easy to tell if a LiIon battery has been overcharged. They just roll over and die with a shorted cell in a few hours.
However, leaving the battery on 99.99999% of capacity forever is just as bad, but takes longer to trash the cells. See the aformentioned URL's.
No. You should be using the one that came with the laptops or an equivalent replacement. Plugging in the wrong charger is more likely to kill the laptop charging circuit than the battery.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
However remote - there's a possibility the wrong charger could over volt the charge cut off chip in the laptop.
That would lead to full on over charging, thermal runaway and venting with flaming gas.
What is "full" charge?
----------------------------
I mentioned a few weeks back that my HP notebook won't charge its battery if its "charge state" is 95% or higher. This prevents the battery from receiving a "full" charge until the charge state has dropped below 95%.
I normally leave the unit on charge, knowing that it can't be "overcharged". I checked earlier today, and sure enough, the charge system reported 97% -- and the battery wasn't being charged. That's as it should be.
At least one poster has stated that leaving a Li-ion battery at continual full charge will damage it. But what is full charge?
According to this Battery University article, "full" charge occurs at a nominal 4.2V/cell. At this point, the charger is supposed to completely shut off, with no trickle charge (not unlike a lead-acid battery).
It would appear, then, that with a /properly/ designed charger, overcharge is impossible. It's safe to leave the charger plugged in indefinitely.
The following remarks seemed pertinent, though...
"If a lithium-ion battery must be left in the charger for operational readiness, some chargers apply a brief topping charge to compensate for the small self-discharge the battery and its protective circuit consume. The charger may kick in when the open-circuit voltage drops to 4.05V/cell and turn off again at a high 4.20V/cell. Chargers made for operational readiness, or standby mode, often let the battery voltage drop to 4.00V/cell and recharge to only 4.05V/cell instead of the full 4.20V/cell. This reduces voltage-related stress and prolongs battery life.
"Some portable devices sit in a charge cradle in the on position. The current drawn through the device is called the parasitic load and can distort the charge cycle. Battery manufacturers advise against parasitic load while charging because it induces mini-cycles, but this cannot always be avoided; a laptop connected to the AC main is such a case. The battery is being charged to 4.20V/cell and then discharged by the device. The stress level on the battery is high because the cycles occur at the 4.20V/cell threshold.
"A portable device must be turned off during charge. This allows the battery to reach the set threshold voltage unhindered, and enables terminating charge on low current. A parasitic load confuses the charger by depressing the battery voltage and preventing the current in the saturation stage to drop low. A battery may be fully charged, but the prevailing conditions prompt a continued charge. This causes undue battery stress and compromises safety."
Some years ago when I worked in the television industry, portable cameras of the day were powered with Ni-Cad battery packs. I recall reading a white paper from Anton Bauer about this only somewhat true memory effect. According to the paper a good battery cell that had an apparent memory problem would still deliver the total amp hours expected from the cell but at a reduced voltage of around .1V per cell.
The actual problem stated was manufacturers going the cheap route and using too few cells for a given voltage...like using 10 cells to get a nominal 12 volts. In this case that .1V per cell could add up to a full volt. The solution used in high dollar cameras was to make the battery packs using 12 cells and then using voltage regulation in the camera to produce the needed 12V. Then even if a memory effect existed causing the
12 cell battery to lose a nominal 1.2V, there was still enough voltage to regulate down to the required 12V.I never made a huge personal study/experiment on this and it could have just been marketing by the battery company because they always put 12 cells in their 12V batteries but it did make sense to me at the time.
I'm old enough to remember reading about this, circa 1959.
At that time, my father had an appliance store in Towson, MD. He got a number of industry publications, including "Merchandising Week" (later "Electrical Merchandising Week"). * These included articles discussing memory effect.
According to these articles, memory effect had reared its ugly head with rechargeable electric toothbrushes. Users commonly put the handle back on the charger after every use. So, unless a lot of people used the toothbrush every day, it went through a shallow discharge/charge cycle. The result was that the batteries lost their ability to hold a "full" charge.
The solution was discovered when people took their electric toothbrushes on trips, and the toothbrush's power switch was accidentally turned "on" in the suitcase, causing a "hard" battery rundown. When the battery was recharged, it got most of its capacity back.
Now... //This is what the trade publications said.// Whether it is the truth about "memory effect", I don't know.
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