bernie@DIALix.oz.au (Bernd Felsche) (02/15/91)
In <1437@tau.sm.luth.se> d90-usn@sm.luth.se (Ulf Sundelin) writes: >sed@sppy00.UUCP (DRISCOLL STEVE) writes: >>The title says it all. My '59 died and I need to run a queueing simulation. >>Hopefully some of you hp-48 owners will have some pity on an an old TI'er >>who would LOVE to be using an HP, but must make do with what he has. If you >>know of any place that carries battery packs for the TI-59 please e-mail. >You don't really need any batterypack,I had the same problem,and I >got rid of the old batterypack and plugged in the adaptor,and it >worked..... [ ramblings about HPs deleted ] Here are two ways to delay your quest for a new battery pack: If you are adventurous, and confidently wield a soldering iron (or spot-welder), then the cells in the battery pack can be replaced with standard 1.3 V (or thereabouts) NiCds. You will need a lot of patience, and a steady hand. More later. Often, you can "rejuvenate" the NiCds by individually charge cycling them. To do this, you charge them up as far as they will go, and then rapidly discharge them using a 10W 0.3R resistor. DO NOT SHORT CIRCUIT THE TERMINALS. Then recharge them individually at about 300 mA, for an hour. If you have access to a constant-voltage charger, use that, setting it to about 1.35V. The charge current should never be higher than 500 mA, so the initial voltage setting may have to be lower. You will notice the charge current drop as the cell reaches capacity. Charge cells individually, not in series. Discharge the cells again, and individually recharge them again, this time limiting the current to 30 to 50 mA, for about 10 hours. Sometimes, NiCds lose their sense of polarity, typically after prolonged total discharge. They cannot be recharged until they have a small polarity in the right direction. To re-polarise, a small, high voltage charge needs to be applied to the NiCd. I do this by setting up a current-limited (2A) power supply to 12V, (well, that's high enough) and then striking the end of the NiCd contact with the supply connection. The polarity is checked after each strike. Brave people have used car batteries in much the same way, but the thought of gases exploding, and acid melting my skin leads me to advise against that practice. A car battery can produce more than 300A, for several seconds. A NiCd about 60A for a split second. Rejuvinating NiCds like this gives you another 50 to 100 charge cycles, more if the cells is fairly new. Don't expect miracles though. They don't have eternal life. CHAPTER 2 :-) The following is an overview of what's needed to change the cells. It is by no means comprehensive or definitive. Use with care and intelligence. This is not guarranteed to work! The top of the pack can be broken open at the weld. You can then remove the three cells. Take note of the polarity of the cells, and which pad is +. The tough bit is removing the stainless (?) steel contacts from the cells which have been spot welded to the cells. A pair of pliers and a twisting motion on the weld should crack the contact strips off. (welds are weakest in shear) You only really need the two contacts from the end cells, which form the pads on the top of the battery pack. Other connections can be made with any thin, flat connection. If you have a spot welding facility, you're in luck. It's a real pain getting a good solder joint onto the end of a NiCd. The heat-sink capacity is enormous. DO NOT overheat the cell. If you can't hold onto it, it's too hot. DO NOT block the vent(s) on the cells. Cells will explode if you re-charge them quickly. When you have assembled the cells, make sure that they will still fit in the pack. Make sure (with a voltmeter) that the cells are correctly oriented. If you find that one of the cells is low on voltage at this stage, charge it up a little. You can do this with a small lab. power supply on which you can vary the charge voltage/current. A few minutes at 300 to 500 mA will top up the cell nicely. Cells which are low on voltage, tend to act as resistors if you try to charge them in series with others. I don't know why. Please don't ask me. A difference of less than 0.1 V between cells can be ignored, for the purposes of this exercise. When you're happy with the state of charge, re-assemble the battery pack. It can be glued with urethane, solvent plastic cement, or similar. Check the pack voltage and polarity. Make absolutely sure. My TI-59 has a + near one of the pack contacts, on the PCB. -- ________Bernd_Felsche__________bernie@DIALix.oz.au_____________ [ Phone: +61 9 419 2297 19 Coleman Road ] [ TZ: UTC-8 Calista, Western Australia 6167 ]
jsims@vuse.vanderbilt.edu (J. Robert Sims) (02/16/91)
Most of this article is accurate, but I see a few potential problems. Some of the charge/discharge rates are quite high. Unless a NiCd is designed for a quick charge, the charge rate should not exceed the amp-hour rating (i.e. rapid charging should happen in one hour). Discharge rates should not exceed this value by much (for a long period of time). The internal resistance of these batteries can cause them to overheat and be destroyed. I have seen Nicads catch fire from being overcharged. Trickle charge rates are capacity / 10 (what almost all chargers with one charge rate use) and C/20 for maintaining a battery. The caution about soldering quickly should also be heeded; Nicad manufacturers say to never solder, to always spot weld; I haven't had problems (other than adhesion) with quick soldering. Digi-Key will make custom battery packs for a reasonable price (I think in single quantities, too). If their number isn't 1-800-digikey, it's in the 800 directory. Rob jsims@vuse.vanderbilt.edu
tomm@voodoo.UUCP (Tom Mackey) (02/19/91)
In article <839@DIALix.oz.au> bernie@DIALix.oz.au (Bernd Felsche) writes: [chapter 1 deleted] >CHAPTER 2 :-) [portions of chapter 2 deleted, too] >The tough bit is removing the stainless (?) steel contacts from >the cells which have been spot welded to the cells. A pair of >pliers and a twisting motion on the weld should crack the contact >strips off. (welds are weakest in shear) >You only really need the two contacts from the end cells, which form >the pads on the top of the battery pack. Other connections can be >made with any thin, flat connection. I tried to reuse the pads for the first pack I rebuilt... I never did get the pads re-soldered, so discarded them completely in favor of the following hack: Use fine wire (I like the individual wires in 4/8/etc. telephone cables) and solder the batteries together as mentioned by Bernd. Then just solder two additional pieces of wire to the end battery contacts and solder the wires directly to the contacts inside the calculator (make it fast, do it with a steady hand, and apply as little heat as possible). Try to solder to a portion of the contacts that was not used to make contact with the original battery pack, just in cast you ever find a good one. As an improvement on that scheme, solder wires to the calculator contacts as before, but solder them to the wires coming off the new battery package, so if you have to change them out, you don't have to probe the calculator innards with a soldering iron again! With this plan, you can even use non-rechargable batteries in a pinch. Just don't try to recharge them. I do this for an old calculator that one of my daughters is fond of, but for which we don't have a recharger. >>>>> wear safety glasses or goggles when soldering batteries! <<<<<< >When you're happy with the state of charge, re-assemble the battery >pack. It can be glued with urethane, solvent plastic cement, or >similar. Another thing that works is the strapping tape (heavy duty super sticky transparent tape with embedded filiments of nylon). Just be careful not to put it somewhere where the extra thickness makes it impossible to fit the pack back in. I now have a half dozen or so calculators (including a TI59, but mostly HP's) that are now productive again owing to my battery transplant surgery. >-- > ________Bernd_Felsche__________bernie@DIALix.oz.au_____________ >[ Phone: +61 9 419 2297 19 Coleman Road ] >[ TZ: UTC-8 Calista, Western Australia 6167 ] -- Tom Mackey (206) 865-6575 tomm@voodoo.boeing.com Boeing Computer Services ....uunet!bcstec!voodoo!tomm M/S 7K-20, P.O. Box 24346, Seattle, WA 98124-0346