srm@dimacs.rutgers.edu (Scott R. Myers) (03/14/91)
I have a Panasonic Transportable phone. I know about the problems
associated with NiCads when you try to recharge them before they've
been totally depleted. How can I discharge the battery beyond the
handset just cutting off. I figured something like a light bulb and
some leads to connect to the battery terminals but that seems crude
and slow. Any suggestions. Thanks in advance...
Scott R. Myers
Snail: 26 Stiles Street Phone:(908)352-4162
Apartment 18
Elizabeth, NJ 07208
Arpa: srm@dimacs.rutgers.edu Uucp: ..!dimacs!srmdplatt@apple.com (Dave Platt) (03/16/91)
In article <telecom11.203.5@eecs.nwu.edu> Scott Meyers writes: > I have a Panasonic Transportable phone. I know about the problems > associated with NiCads when you try to recharge them before they've > been totally depleted. How can I discharge the battery beyond the > handset just cutting off. I figured something like a light bulb and > some leads to connect to the battery terminals but that seems crude > and slow. Any suggestions. Thanks in advance... What you've suggested is crude and slow ... and, if you're talking about a typical NiCd battery pack, it can damage the cells. The _only_ safe ways to discharge NiCd cells are either [a] one at a time, or [b] with the cells connected in parallel. In either case, a light bulb or a resistor does a fine job. This is easy to do if you have single 1.2-volt cells (e.g. AA or C or D size); you can home-brew up a discharging fixture with a battery holder, light, and resistor from Radio Shack. Discharging NiCd cells that are connected in series (e.g. when they are wired up in a battery pack) is a BAD idea. The reason is that it's quite common for one cell in the pack to have slightly less capacity than another (manufacturing differences, etc.). If you try to discharge the battery all the way to zero, the weakest cell will reach zero volts while the other cells are still "live". As the remaining cells continue to discharge, the current will be flowing through the dead cell ... in effect, trying to "charge" it in reverse (as if you'd put the cell into a charger backwards). This will damage the cell ... it may lose some of its ability to store electricity, and/or develop an internal short. Because the cell has been weakened, it will run down even sooner the next time you use it ... and if you then attempt to drain the whole battery, you'll damage the weakened cell even sooner. Eventually the cell may short itself completely, and your battery pack's output will be 1.2 volts below what it should be ... your phone will probably reject it. It's true that some NiCd cells have been shown to exhibit a "memory" effect, if you repeatedly discharge them to an identical point and then recharge them. I've heard that modern NiCd batteries have pretty much eliminated the memory effect. In real-world use, the memory effect is likely to do much less damage to the cells in your battery than over-discharging them will. NiCd cells have a very flat voltage output ... they deliver very close to 1.2 volts until they've almost completely discharged, at which point the voltage drops off very rapidly. This is unlike the behavior of lead-acid, carbon-zinc, and alkaline batteries, whose output voltages drop off more gradually and smoothly as they discharge. Well-designed NiCd-powered equipment will detect the voltage dropoff, and will shut down immediately to avoid over-discharging the cells and damaging the battery pack. So, your best bet is probably to keep a spare well-charged NiCd battery with your phone. When the phone reports "Low battery" and shuts down, it means that the battery you've been using has only about 5% of its capacity left and should _not_ be discharged further. You can then swap in the new battery, and recharge the old one without worrying about the memory effect. Dave Platt VOICE: (415) 813-8917 UUCP: ...apple!ntg!dplatt USNAIL: New Technologies Group Inc. 2468 Embarcardero Way, Palo Alto CA 94303
bruce@camb.com (Barton F. Bruce) (03/17/91)
In article <telecom11.207.6@eecs.nwu.edu>, ntg!dplatt@apple.com (Dave Platt) writes: > In article <telecom11.203.5@eecs.nwu.edu> Scott Meyers writes: >> handset just cutting off. I figured something like a light bulb and >> some leads to connect to the battery terminals but that seems crude >> and slow. Any suggestions. Thanks in advance... > What you've suggested is crude and slow ... and, if you're talking > about a typical NiCd battery pack, it can damage the cells. Somewhere I ran into a reference to a special charging circuit that obviates the need for full discharge to prevent shallow discharge memory. This charger also recharged VERY fast from whatever state the battery was in and there was something about high current short pulses and blowing away whiskers. A custom module was needed for each battery size to 'tune' the charger's action properly. It sounded like a wonderful device, but was several hunderd dollars. Some HAM, maybe Pennsylvania area??, was making them. Does anyone know if this sort of charger really works, and if there is a more affordable universal one with built in ability to do any size battery? Perhaps one is now mass produced, and 'hand built' prices can be avoided.
jgd@gatech.edu (John G. DeArmond) (03/19/91)
> handset just cutting off. I figured something like a light bulb and > some leads to connect to the battery terminals but that seems crude > and slow. Any suggestions. Thanks in advance... I missed the first part of this thread but since it is apparent by the title that we're discussing Panasonic portable batteries, a slight misconception needs to be corrected. The battery in the the old style Panasonic portable (and I believe in the new style also) is NOT a NiCad battery. It is a Gell-cell-type lead-acid battery, as is the same battery used in the Panasonic Cam-corders. Using a Ni-cad-style charge cycle and/or deep discharging these batteries will RUIN them, as I found out by experience. I smoked my first battery in a few weeks; the second has lasted several years. The way to make these batteries last is exactly the same technique you use to preserve ordinary car batteries. Store them charged, maintain a trickle charge whenever possible and never deep discharge. There IS a reason why the Panasonic phone dumps you so fast when the battery is going down. John De Armond, WD4OQC Rapid Deployment System, Inc. Marietta, Ga {emory,uunet}!rsiatl!jgd
droid@uunet.uu.net (Marty Brenneis) (03/20/91)
bruce@camb.com (Barton F. Bruce) writes: > Somewhere I ran into a reference to a special charging circuit that > obviates the need for full discharge to prevent shallow discharge > memory. > This charger also recharged VERY fast from whatever state the battery > was in and there was something about high current short pulses and > blowing away whiskers. A custom module was needed for each battery > size to 'tune' the charger's action properly. This sounds like a "Negative Delta V" charger from Alexander Battery Company. They make a line of rapid chargers that monitors the battery voltage while charging it. It is not as harsh as a timed charge or a simple voltage sensitive charger. For more details see below. They can be aquired from Alexander Battery in San Diego, CA. Tha phone number is 800-327-0814 in CA and 800-421-1108 elsewhere. I always talk to Pat Huberty there, he is a cool guy. Tell him Marty from ILM sent you. Here is how it works for you technoids: The charger pushes a high current into the battery at the start. It does this for a minute or so. It then switches in a small load and measures the voltage. It keeps pushing hard and stopping to measure the progress until it gets to the proper terminal voltage for that cell size. It then switches to a trickle mode to maintain that. The trick here is the charger is measuring the battery condition rather than charging until it heats up to 41 degrees C like most rapid chargers. It won't overheat the cells and cook the chemicals. This translates into more charge/discharge cycles. The drawback is the battery must be directly connected to the charger, you can't use the regular charge contacts. They have holders that take the battery and charge thru the output contacts. The cost of these is around $125 for a single unit charger. Have fun! Marty the Droid Industrial Magician