Agreed. You can reverse bias the weaker cells in the pack that way and bugger them up real good.The "memory effect" with nicads is a much overated problem. About the only times it really comes into play and reduces the capacity of the battery is with devices like cordless phones, when they are used in a mode where they get put back on the charger after each short phone call and never really get discharged very much at all.
Jeff
Jeff
Actually, it really is a standard AA size. I expected to see a sub-C or something when I opened it up. I had some good AA NiCd batteries laying about, so I soldered one in. It didn't have the solder tabs, but I was able to get a blob of solder to stick to each end without cooking the battery with heat.
Ken
Ken,
Without getting into the chemistry of ni-cads, keep in mind these facts:
(New) ni-cads are typically good for about 1000 charge / discharge cycles. Shelf life depletes the charge about 1% a day. Occasional deep discharge does help you get your 1000 cycles. Batteries may be kept on the charger continuously in some cases. Let me explain.
Assume your "AA" battery has a listed current rating of 1100 milliamp hours (Mah). This means it should deliver 1100 milliamps for 1 hour or 110 milliamps for 10 hours or 11 milliamps for 100 hours. You get the idea. The
1 hour rate (1100) is known as it's "1R" parameter.Now, regarding chargers, you can charge a totally dead cell at the 1R rate (1100 milliamps) and expect a complete charge in just over 1 hour. You can also charge at the 1/10R rate for about 14 hours and get the same results. The important factor to remember is that once a cell is completely charged, a high charge rate will cause it's temperature to rise and that's a "bad thing". The trick is to know when a cell is "full" so the charger current can be reduced or stopped. Two ways exist to determine a full charge. Carefully monitor the cell voltage or carefully monitor the internal temperature (rectal and oral have no meaning here).
In specialized cells (think Motorola commercial walkie-talkies) where quick charging is desirable, custom batteries are built with internal temperature sensors. That's why these batteries have more than two contacts. Customized (smart) chargers use these sensors to know when to reduce the high charge rate (1R) to the 1/10R rate.
Finally, a ni-cad cell can be left connected to a 1/10R charger indefinitely with no ill effects. The off-gassing that occurs is offset by the re-combining chemistry within the cell so overheating does not occur at the
1/10R rate. How do you know if your wall wart is designed to deliver at the 1/10R rate? Easy. If the owners manual indicates a complete charge may take 14 - 16 hours, you have one. If it says it can charge a dead battery in substantially less time, you don't.Nickel metal hydride (Nimh) and lithium ion cells have different rules. Another time, perhaps.
"Craven Morehead" wrote in news:OJDne.38744$ snipped-for-privacy@bignews3.bellsouth.net:
I do not believe this to be true. Digi-Key lists NiCds *specifically designed* to be left on the charger when not in use. If what you said was true,this would not be necessary. My own experience also shows it to be false.
Same with mine, but I bought a new NiCd and for 25¢ they spot welded the tabs.
I've read this isn't a good idea. Sometimes one cell goes weak before the others, and then you get voltage reversal on the weak cell.
Agree. I don't believe in total discharge. I was involved with recharging banks of NiCad batteries. We never deeply discharged and had them last for
20 years or more. Of course those were big commercial units. We never let them get below 50% state of charge.My theory is that memory only shows up if you repeatedly discharge to the same level of state of charge. Varying the depth of discharge or even just one deep one with wipe out any accumulated memory effect.
I think more important is the number of discharges.
For tools and the like I keep them on a curcuit where I turn on a switch occasionaly for a few minutes. A timer would work too.
There may be something to that. I will add one additional personal observation. It appears that the earlier (like 1970) NiCds did suffer from the memory effect much more than today's do. It may be due to different chargers, but I suspect they made some improvement to battery formula and design over the years. Those old NiCd batteries in the flashes for the Polaroid 100 cameras all seemed to have the problem. I recovered many of them for irate customers back then. Two or three deep cycles did the trick. That and instructions to allow them to discharge fully from time to time, seemed to make happy customers out of un-happy ones.
With the charger attached to the battery, 1.55V isn't a bad estimate for the voltage you'll see at full charge. With the charger detached, 1.325V is a decent estimate for the battery voltage.
Thanks for all the info. I don't recall the exact number, but I do recall the manual saying something about the charge taking the better portion of a day. Basically, I try to trim my beard some morning, find that it is dead, plug in the charger, and then unplug it either that night or else the next morning if I forget.
Ken
Digi-Key does not make the batteries; they only sell them. This claim of unique capability is only sales talk. They claim a special benefit which is, in fact, common to all ordinary NiCads -- a widespread practice with sales people.
SJF
Cool! Thanks. :-)
Being a cheap basthud I'd check the battery by subjecting it to a quick shot at a higher voltage then check to see if the cell is still dead. I've zapped apperently dead cells back to stretch the life a bit. I hit a cell with the 12v battery charger (i said quick- a touch ) then I checked to see if the battery is still dead. Leave it sit for perhaps 6 hrs and see if it is still holding a charge. About 1/3 of the time , I can manage to get the dead cell to hold the charge for a while, then I go to a complete slow charge (a typical 500-740 aa cell) will be charged at 50mah overnight.If you already have the cel why not give it a shot. I just retired a 500mah aa nicad that had a 1974 manufacter date. Course it was down to mebbe 40% of capacity for the last year, but I did get some work outa the battery. Pat
"SJF" wrote in news:d0Ine.56$xr.35@fed1read05:
Bulls..t. It's not "sales talk",it's in their printed catalog.
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