forrette@sim.berkeley.edu (Steve Forrette) (07/17/90)
Can someone recap the discussion of "memory" in nicad batteries? I'm having a problem with my HT5300 AT&T cordless phone. I had it unplugged for about two months, and like a dummy didn't disconnect the battery in the handset. So, I assume that it was on standby (since it was off the base for awhile), and totally discharged the battery. This is bad news, right? It's been charging for over two days, and reads only 2.65 volts. The battery is rated at 3.6V, 720mAh. When I take the handset off the base, the LO BATTERY light comes on, and none of the keys do anything. Any thoughts?
rpw3%rigden.wpd@sgi.com (Rob Warnock) (07/19/90)
In article <9807@accuvax.nwu.edu> forrette@sim.berkeley.edu (Steve Forrette) writes: | Can someone recap the discussion of "memory" in nicad batteries? I'm | having a problem with my HT5300 AT&T cordless phone. I had it | unplugged for about two months, and like a dummy didn't disconnect the | battery in the handset. So, I assume that it was on standby (since it | was off the base for awhile), and totally discharged the battery. This is not the "memory effect" (which is something completely different), but a case of your causing a "cell reversal". When you completely discharge a multi-cell NiCd battery, *some* cell is going to go all the way to zero volts first, and then as the other cells continue discharging they're going to back-bias the one that zeroed first, and start charging it "the wrong way". | This is bad news, right? Yup! The reverse current causes chemical changes in the cell which can permanently damage it. Among other things, rumor has it that conductive "whiskers" grow across the cell. There is urban legend to the effect that you can cure a back-biased NiCd cell by zapping it with a very strong (but brief!) forward charging current (as from a large capacitor), supposedly to "blow the whiskers", but as I said, I consider this in the urban legend category. | It's been charging for over two days, and | reads only 2.65 volts. The battery is rated at 3.6V, 720mAh. When I | take the handset off the base, the LO BATTERY light comes on, and none | of the keys do anything. Any thoughts? I think you need a new battery. Sorry. Rob Warnock, MS-9U/510 rpw3@sgi.com rpw3@pei.com Silicon Graphics, Inc. (415)335-1673 Protocol Engines, Inc. 2011 N. Shoreline Blvd. Mountain View, CA 94039-7311
kaufman@neon.stanford.edu (Marc T. Kaufman) (07/19/90)
In article <9888@accuvax.nwu.edu> Rob Warnock <rpw3@sgi.com> writes: >...There is urban legend to >the effect that you can cure a back-biased NiCd cell by zapping it >with a very strong (but brief!) forward charging current (as from a >large capacitor), supposedly to "blow the whiskers", but as I said, I >consider this in the urban legend category. Not an urban legend. *I* have done it several times. Just use either the charge from a large capacitor, or (better) a current limited power supply. I have a supply I can limit to 3 amps with an 18 volt maximum. Attach it to the battery in charging configuration and slowly turn up the juice. The current will go up rapidly (into the shorting whisker) until it fries, then drop back to a more reasonable value (100 ma or so). At that point I revert to standard charging techniques. I can't tell you about the _ultimate_ service life of a recovered battery, but it is certainly longer than the remaining life of an unrecovered cell. Marc Kaufman (kaufman@Neon.stanford.edu)
elliott@uunet.uu.net (Paul Elliott x225) (07/21/90)
In article <9888@accuvax.nwu.edu>, rpw3%rigden.wpd@sgi.com (Rob Warnock) writes: > In article <9807@accuvax.nwu.edu> forrette@sim.berkeley.edu (Steve > Forrette) writes: > | Can someone recap the discussion of "memory" in nicad batteries? I'm > | having a problem with my HT5300 AT&T cordless phone. I had it > | [description of battery problem] > [reverse-charging, etc] There is urban legend to > the effect that you can cure a back-biased NiCd cell by zapping it > with a very strong (but brief!) forward charging current (as from a > large capacitor), supposedly to "blow the whiskers", but as I said, I > consider this in the urban legend category. This isn't really a legend; it does work. Unfortunately, It doesn't work often or well. You will occasionally get lucky, but my experience has been that the restored cell is not reliable, and will likely have excessive leakage (self-discharge), and will probably short out again. If you want a battery you can depend on, just replace it. > | It's been charging for over two days, and > | reads only 2.65 volts. The battery is rated at 3.6V, 720mAh. When I Definitely a shorted cell. NiCd cells charge up to about 1.3 to 1.45V when they are charging and fully charged (in the "overcharge" state), so the voltage you are measuring corresponds to two fully-charged cells and one shorted cell. Paul M. Elliott Optilink Corporation (707) 795-9444 {uunet, pyramid, tekbspa}!optilink!elliott
tad@beaver.cs.washington.edu (Tad Cook) (07/25/90)
In article <9807@accuvax.nwu.edu>, forrette@sim.berkeley.edu (Steve Forrette) writes: > Can someone recap the discussion of "memory" in nicad batteries? I'm > I had it unplugged for about two months, and like a dummy didn't > disconnect the battery in the handset. > This is bad news, right? It's been charging for over two days, and > reads only 2.65 volts. The battery is rated at 3.6V, 720mAh. When I > take the handset off the base, the LO BATTERY light comes on, and none > of the keys do anything. Any thoughts? This is not a case of nicad memory, but reversed polarity. The batteries have disharged so far that they have probably reversed, and may be non-recoverable. Its time for new batteries. Tad Cook Seattle, WA Packet: KT7H @ N7HFZ.WA.USA.NA Phone: 206/527-4089 MCI Mail: 3288544 Telex: 6503288544 MCI UW USENET:...uw-beaver!sumax!amc-gw!ssc!tad or, tad@ssc.UUCP
ge@phoibos.cs.kun.nl (Ge Weijers) (08/06/90)
forrette@sim.berkeley.edu (Steve Forrette) writes:
]Can someone recap the discussion of "memory" in nicad batteries? I'm
]having a problem with my HT5300 AT&T cordless phone. I had it
]unplugged for about two months, and like a dummy didn't disconnect the
]battery in the handset. So, I assume that it was on standby (since it
]was off the base for awhile), and totally discharged the battery.
]This is bad news, right? It's been charging for over two days, and
]reads only 2.65 volts. The battery is rated at 3.6V, 720mAh. When I
]take the handset off the base, the LO BATTERY light comes on, and none
]of the keys do anything. Any thoughts?
This has nothing to do with the 'memory' effect. The NiCd battery has
been 'shorted' too long, i.e. drained to much. Replacing it is your
only option. (A better-designed phone would stop drawing current when
the voltage drops below a certain limit. It should NOT light a
battery-low LED until no charge remains. Never discharge below the
1V/cell level, 3V in your case.) The memory effect comes into play if
you never fully discharge a battery.
Ge' Weijers Internet/UUCP: ge@cs.kun.nl
Faculty of Mathematics and Computer Science, (uunet.uu.net!cs.kun.nl!ge)
University of Nijmegen, Toernooiveld 1 tel. +3180612483 (UTC+1,
6525 ED Nijmegen, the Netherlands UTC+2 march/september