pjh@mccc.edu (Peter J. Holsberg) (06/15/91)
I have a 10 ohm 10 watt resistor connected to the terminals of a 7.2V 1000maH camcorder battery and the terminal voltage refuses to go below about 2.2V. Is this sufficiently low to be considered a full-discharge? If not, how can I drop the voltage even further. The resistor is slightly warm to the touch. Pete -- Prof. Peter J. Holsberg Mercer County Community College Voice: 609-586-4800 Engineering Technology, Computers and Math FAX: 609-586-6944 1200 Old Trenton Road, Trenton, NJ 08690 Internet: pjh@mccc.edu TCF 92 - April ??-??, 1992
mcovingt@athena.cs.uga.edu (Michael A. Covington) (06/15/91)
Full discharge for a 7.2-V NiCd is about 6 volts. Taking it below 6 volts can damage it by causing some of the cells to become reverse-charged. Because of electrochemistry, the voltage of a battery never falls to zero. As a battery discharges, the voltage charges somewhat, but the main change is that the internal resistance goes way up, so that the battery loses its ability to deliver substantial amounts of current. -- ------------------------------------------------------- Michael A. Covington | Artificial Intelligence Programs The University of Georgia | Athens, GA 30602 U.S.A. -------------------------------------------------------
fiedler@netcom.COM (David Fiedler) (06/16/91)
mcovingt@athena.cs.uga.edu (Michael A. Covington) writes: >Full discharge for a 7.2-V NiCd is about 6 volts. Taking it below 6 volts >can damage it by causing some of the cells to become reverse-charged. What *he* said. I believe the target voltage for discharging is .9 to 1.0 volts per cell. Find the number of cells in any NiCd battery by dividing by the NiCd cell voltage, 1.2. You don't want to go lower than 5.4 (better luck next time :-). -- David Fiedler UUCP:{ames,mrspoc,hoptoad}!infopro!david AIR: N3717R "Video for Computer Professionals" BIX: fiedler Internet: fiedler@netcom.com USMail:InfoPro Systems, PO Box 220 Rescue CA 95672 Phone:916/677-5870 FAX:-5873
john@qip.UUCP (John Moore) (06/16/91)
In article <1991Jun16.041527.3366@netcom.COM> fiedler@netcom.COM (David Fiedler) writes: ]mcovingt@athena.cs.uga.edu (Michael A. Covington) writes: ] ]>Full discharge for a 7.2-V NiCd is about 6 volts. Taking it below 6 volts ]>can damage it by causing some of the cells to become reverse-charged. ] ]What *he* said. I believe the target voltage for discharging is .9 to 1.0 ]volts per cell. Find the number of cells in any NiCd battery by dividing ]by the NiCd cell voltage, 1.2. You don't want to go lower than 5.4 (better ]luck next time :-). Better yet, don't discharge it at all. The most recent Gates application notes show that there is NO appreciable memory effect in modern NiCads - they ran a lot of experiments. Thus, there is NO REASON TO DISCHARGE NICADS! -- John Moore HAM:NJ7E/CAP:T-Bird 381 {ames!ncar!noao!asuvax,mcdphx}!anasaz!john USnail: 7525 Clearwater Pkwy, Scottsdale,AZ 85253 anasaz!john@asuvax.eas.asu.edu Voice: (602) 951-9326 Wishful Thinking: Long palladium, Short Petroleum Opinion: Support ALL of the bill of rights, INCLUDING the 2nd amendment! Disclaimer: The opinions expressed here are all my fault, and no one elses.
mcovingt@athena.cs.uga.edu (Michael A. Covington) (06/17/91)
In article <6666@qip.UUCP> john@qip.UUCP (John Moore) writes: >In article <1991Jun16.041527.3366@netcom.COM> fiedler@netcom.COM (David Fiedler) writes: >]mcovingt@athena.cs.uga.edu (Michael A. Covington) writes: >] >]>Full discharge for a 7.2-V NiCd is about 6 volts. Taking it below 6 volts >]>can damage it by causing some of the cells to become reverse-charged. >] >]What *he* said. I believe the target voltage for discharging is .9 to 1.0 >]volts per cell. Find the number of cells in any NiCd battery by dividing >]by the NiCd cell voltage, 1.2. You don't want to go lower than 5.4 (better >]luck next time :-). > >Better yet, don't discharge it at all. The most recent Gates application >notes show that there is NO appreciable memory effect in modern NiCads - >they ran a lot of experiments. Thus, there is NO REASON TO DISCHARGE NICADS! >-- Not only that, but an article in Electronics World (London) says that a fast charge is better than a slow charge because it forms smaller (and more mixed-up) crystals. They advocate charging very fast (even 1-hour charge) if the temperature of the cell is monitored. Hmmm, anyone for a fast charger that you put into the refrigerator? Or one with a thermoelectric cooler? -- ------------------------------------------------------- Michael A. Covington | Artificial Intelligence Programs The University of Georgia | Athens, GA 30602 U.S.A. -------------------------------------------------------
gt0869a@prism.gatech.EDU (WATERS,CLYDE GORDON) (06/17/91)
In article <1991Jun15.023737.2673@mccc.edu> pjh@mccc.edu (Peter J. Holsberg) writes: >I have a 10 ohm 10 watt resistor connected to the terminals of a 7.2V >1000maH camcorder battery and the terminal voltage refuses to go below >about 2.2V. Is this sufficiently low to be considered a full-discharge? >If not, how can I drop the voltage even further. > Keep at it. Unless you COMPLETELY kill it it will still retain memory. You are probably at a charge region where some crystals inside are breaking down, at about the same quantum electric level. A friend of mine came up with an excellent way to completely drain these things. : Get 10 1157 dual element car light bulbs. Wire all 20 filaments in parallel. Then, hook up heavy lead wire (try 10g or so) to appropriate connectors to go to the battery. The neat thing about this is that the bulbs act like variable resistors. As the voltage across them decreases, the power decreases, the bulb cools down. The resistance of the elements then decreases, so the bulb still draws near the same current (loosely) Bulbs such as 1157's range from about .45 ohms cold to about 2.5 ohms hot. They will also have no problem dissapating power (they can't burn up). I think .045 ohms at a limit will have no problem in completely killing the battery! Regards, Gordon. -- WATERS,CLYDE GORDON-Georgia Institute of Technology Atlanta Ga 30332 ******<LANGUAGE IS A VIRUS! - Laurie Anderson-Home of the Brave>******* uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!gt0869a Internet: gt0869a@prism.gatech.edu
zimmer@calvin.stanford.edu (Andrew Zimmerman) (06/17/91)
In article <1991Jun16.215158.27005@athena.cs.uga.edu> mcovingt@athena.cs.uga.edu (Michael A. Covington) writes: >In article <6666@qip.UUCP> john@qip.UUCP (John Moore) writes: >>In article <1991Jun16.041527.3366@netcom.COM> fiedler@netcom.COM (David Fiedler) writes: >>]mcovingt@athena.cs.uga.edu (Michael A. Covington) writes: >>] >>]>Full discharge for a 7.2-V NiCd is about 6 volts. Taking it below 6 volts >>]>can damage it by causing some of the cells to become reverse-charged. >>] >>]What *he* said. I believe the target voltage for discharging is .9 to 1.0 >>]volts per cell. Find the number of cells in any NiCd battery by dividing >>]by the NiCd cell voltage, 1.2. You don't want to go lower than 5.4 (better >>]luck next time :-). >> >>Better yet, don't discharge it at all. The most recent Gates application >>notes show that there is NO appreciable memory effect in modern NiCads - >>they ran a lot of experiments. Thus, there is NO REASON TO DISCHARGE NICADS! >>-- > >Not only that, but an article in Electronics World (London) says that >a fast charge is better than a slow charge because it forms smaller (and >more mixed-up) crystals. They advocate charging very fast (even 1-hour >charge) if the temperature of the cell is monitored. > >Hmmm, anyone for a fast charger that you put into the refrigerator? >Or one with a thermoelectric cooler? > 1 hour to charge a battery, thats not a fast charge :-) I do 15-20 minute charges. (Oh course, that is for quick discharge NiCd's.) Truthfully, I abuse my NiCd's. I always charge them in 15 minutes, and I even charge them when they're hot. I have never had a problem with NiCd memory. I do try to discharge them completely, but I don't go to the extreme of hooking resistors or light bulbs to them. The above is just my personal experience. I am not saying that you should do quick charges, or that NiCd's don't have memory. Andrew zimmer@calvin.stanford.edu ---- My other car is radio controlled.
mingmar@cs.mcgill.ca (Ming MAR) (06/18/91)
In article <1991Jun17.092406.11386@neon.Stanford.EDU> zimmer@calvin.stanford.edu (Andrew Zimmerman) writes: > Truthfully, I abuse my NiCd's. I always charge them in 15 > minutes, and I even charge them when they're hot. I have never > had a problem with NiCd memory. I do try to discharge them > completely, but I don't go to the extreme of hooking resistors or > light bulbs to them. Well, I hooked 'em up to light bulbs. I though I was doing them a favor, but they were dying like flies. What happened was I had discharged them to the point where they had _reverse polarities_. I later found out that reversing polarities destroys them. Now, I no longer try to discharge them completely before recharging.
pjh@mccc.edu (Pete Holsberg) (06/19/91)
In article <1991Jun17.092406.11386@neon.Stanford.EDU> zimmer@calvin.stanford.edu (Andrew Zimmerman) writes:
=1 hour to charge a battery, thats not a fast charge :-) I do 15-20 minute
=charges. (Oh course, that is for quick discharge NiCd's.)
=
=Truthfully, I abuse my NiCd's. I always charge them in 15 minutes, and
=I even charge them when they're hot. I have never had a problem with
=NiCd memory. I do try to discharge them completely, but I don't go
=to the extreme of hooking resistors or light bulbs to them.
=
=The above is just my personal experience. I am not saying that you
=should do quick charges, or that NiCd's don't have memory.
How do you accomplish discharging them completely?
Pete
--
Prof. Peter J. Holsberg Mercer County Community College
Voice: 609-586-4800 Engineering Technology, Computers and Math
FAX: 609-586-6944 1200 Old Trenton Road, Trenton, NJ 08690
Internet: pjh@mccc.edu TCF 92 - April ??-??, 1992myers@hpfcrlm.HP.COM (Bob Myers) (06/19/91)
>>I have a 10 ohm 10 watt resistor connected to the terminals of a 7.2V >>1000maH camcorder battery and the terminal voltage refuses to go below >>about 2.2V. Is this sufficiently low to be considered a full-discharge? >>If not, how can I drop the voltage even further. >> >Keep at it. Unless you COMPLETELY kill it it will still retain memory. ABSOLUTELY NOT! As previous posters have mentioned, 2.2V is already VERY low on the curve for this battery; a 7.2V battery is six NiCd cells, each with a nominal voltage of 1.2V. IF each cell were to discharge equally, 2.2V across the battery means each cell is only at a little over 0.3V - which is definitely "deep discharge" for this technology! But - as has also been mentioned - it is very unlikely that the cells will discharge at exactly the same rate, to exactly the same level; this sort of "very-deep- discharge" is likely to wind up with one or more of the cells in the stack being reverse-charged, which is a Bad Thing for NiCds. The real lesson to be learned here, though, is that such intentional discharging is completely unnecessary - there is NO reason to be concerned about "memory" in NiCd cells/batteries. For all practical purposes, it doesn't exist. It's a myth. A phantom. A falsehood. A misconception. (Get the point yet? :-)) What has been mistakenly labelled "memory" in consumer electronic application is almost without exception actually a phenomenon called "voltage depression" which results from improper or excessive CHARGING, *not* from anything having to do with how the cell is discharged. Bob Myers | "There is a law of inertia. And I have found that of myers@fc.hp.com | all the inert substances, the most inert is the | human brain." - Edward Teller
mike@abekrd.co.uk (Mike Quinn) (06/21/91)
In <17660174@hpfcrlm.HP.COM> myers@hpfcrlm.HP.COM (Bob Myers) writes: >The real lesson to be learned here, though, is that such intentional >discharging is completely unnecessary - there is NO reason to be concerned >about "memory" in NiCd cells/batteries. For all practical purposes, it >doesn't exist. It's a myth. A phantom. A falsehood. A misconception. >(Get the point yet? :-)) What has been mistakenly labelled "memory" in >consumer electronic application is almost without exception actually a >phenomenon called "voltage depression" which results from improper or >excessive CHARGING, *not* from anything having to do with how the cell is >discharged. Okay, I'm a consumer I spent $50 (35 UK Pounds) on a consumer NiCad pack for my camcorder. Originally it gave me 40 minutes recording time, but now it's down to 15 minutes and falling fast. What do I have to do to get back to 40 or so minutes? Or do I just throw away $50? To me that's a lot of money and I'd like to get proper use. If you can be fairly specific (remeber I'm a peasant consumer, not an electrical engineer), I would be grateful. I could manage with a circuit diagram and a list of parts or even a Radio Shack part no. Sorry to go on, but my system says I must post more than I include ;-( Mike Quinn. Abekas Video Systems Ltd. Reading. United Kingdom. net: mike@abekrd.co.uk UUCP: ...!uunet!mcsun!ukc!abekrd!mike He is BOB, eager for fun. He wears a smile, everybody run.
pjh@mccc.edu (Pete Holsberg) (06/22/91)
In article <17660174@hpfcrlm.HP.COM> myers@hpfcrlm.HP.COM (Bob Myers) writes:
=What has been mistakenly labelled "memory" in
=consumer electronic application is almost without exception actually a
=phenomenon called "voltage depression" which results from improper or
=excessive CHARGING, *not* from anything having to do with how the cell is
=discharged.
So? Are you just going to stop there? :-) Seriously, what should I be
concerned about in using/charging my camcorder batteries? Should I use
a battery until it will no longer run the 'corder and then charge it, or
can I just throw it on the charger after each use? Should I remove the
battery from the charger as soon as there's an indication of full
charge, or can I leave it there until I need it to run the 'corder?
Thanks,
Pete
--
Prof. Peter J. Holsberg Mercer County Community College
Voice: 609-586-4800 Engineering Technology, Computers and Math
FAX: 609-586-6944 1200 Old Trenton Road, Trenton, NJ 08690
Internet: pjh@mccc.edu TCF 92 - April ??-??, 1992dorton@dri.com (David Orton) (06/23/91)
In article <1991Jun21.180435.2415@mccc.edu> pjh@mccc.edu (Pete Holsberg) writes: >In article <17660174@hpfcrlm.HP.COM> myers@hpfcrlm.HP.COM (Bob Myers) writes: >=What has been mistakenly labelled "memory" in >=consumer electronic application is almost without exception actually a >=phenomenon called "voltage depression" which results from improper or >=excessive CHARGING, *not* from anything having to do with how the cell is >=discharged. > >So? Are you just going to stop there? :-) Seriously, what should I be >concerned about in using/charging my camcorder batteries? Should I use >a battery until it will no longer run the 'corder and then charge it, or >can I just throw it on the charger after each use? Should I remove the >battery from the charger as soon as there's an indication of full >charge, or can I leave it there until I need it to run the 'corder? > Use the battery until it won't run the camera, then charge it 'til it "gives an indication of full charge". Take if off the charger, and if you don't use it for a while DISCHARGE it(either running the camera or with a homemade discharger), and charge it again. This will help remove any memory(if you decide to belive that it exists), and supposedly keep things in good shape. Geez guys, I'm only 13 and I know this stuff! ;-) Will Orton "It makes me wonder how I keep myself so slender"-Matt Groening -- Dave Orton dorton@dri.com (uunet!drivax!dorton)
myers@hpfcrlm.HP.COM (Bob Myers) (06/25/91)
>Okay, I'm a consumer I spent $50 (35 UK Pounds) on a consumer NiCad pack for >my camcorder. Originally it gave me 40 minutes recording time, but now it's >down to 15 minutes and falling fast. You didn't mention how old (either in months/years or charge/discharge cycles) the pack is, so I'm assuming that you think it's dying before its time. (These things DO NOT have an infinite life, but I'm guessing that you expected a lot more life than you got.) Also, how are you charging the pack? IS IT definitely a NiCd battery (many of the camcorder packs are lead-acid gel cells, and these behave differently)? Has the pack ever been exposed to temperature extremes or very excessive charging? Are all the cells mechanically intact (no dents, holes, etc.)? Without knowing this, it's hard to be specific about this particular case, but I'll at least post some further general information: The "voltage depression" phenomenon I mentioned (the one which is mistaken for "memory) happens if a NiCd cell/battery is overcharged; should overcharing occur, the cell's output voltage will be decreased on the next discharge. This occurs solely due to the overcharge, regardless of the previous discharge cycle, and so is not what we'd call "memory" - however, overcharging IS more likely after a short discharge, due to the way most people recharge NiCds (put 'em on the charger and leave 'em until the next morning or whenever, regardless of how long they were discharged). This explains the belief in "memory" - many people DO see an apparent loss in capacity after a short discharge cycle - but it wasn't the short discharge that caused it; it was the excessive charge. They've just picked the wrong cause. Unfortunately, most consumer gear and chargers don't treat NiCds very well. The simplest way for a camcorder, say, to figure out how much battery capacity remains is to monitor the cell voltage, and trip an indicator when this falls below a certain level. Unfortunately, that's a bit simplistic - in the case of voltage depression, the "LOW BATTERY" indicator will come on fairly early in the discharge cycle, even though the cell has capacity remaining - it's just brainlessly looking at an absolute level. Similarly, the chargers usually have no means for monitoring the progress of a charge - they don't watch either the battery voltage or temperature (two important things to look out for, the latter especially important if "quick charging" the cells), and so don't know when to quit. They will very happily drive the cell into an overcharged state. NiCds have a very distinctive discharge characteristic - the discharge starts with a short, rapid drop from, say, 1.4V or so down to the nominal cell voltage of around 1.2V. Here it will stay for most (about 80% or so) of the cycle, dropping very slowly. As the cell nears the end of the cycle, a sudden drop begins again - this time, it'd go damn near all the way to 0V if you let it. (And in a battery, there is at least one really good reason for not letting this happen - you don't wanna reverse charge any of the cells.) These two "knees" are an important clue to where you are in the curve. You should stop charging soon after reaching the upped "knee" (or if a similar rise in cell temperature is seen), and stop the discharge soon after the lower knee is reached. In your case, I don't know if the cell is really low (reduced capacity), or if it's just the camcorder SAYING it's low. Here, I would suggest a forced discharge, but only because it'll get the pack into a known state. Discharge it until you're down to around 0.8-0.9V/cell - for a six cell (nom. 7.2V) battery, this would be a battery voltage of about 4.8-5.4V. Then charge it until you see no more than 1.4V/cell - again, a six-pack would be then at 8.4V. Try the pack then, and see if it gives "normal" service. If you cannot restore the pack to normal operation after a couple of these cycles, there is something wrong - you have a shorted cell, one or more cells have vented, etc.. It would then have to be replaced. Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers@fc.hp.com | sentient life-form on this planet.