HP Forum Archive 03

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help with 29c please Message #1 Posted by john on 5 Sept 2000, 6:37 p.m. i have an extremely dumb question. i am disgustingly fanatical about older hp's like all the rest of y'all, but i am NOT an electronics person--at all. so, here's my question. the 29c uses rechargeable nicads for a voltage of 2.5 V. could i still put two DEAD alkaline AA's in the battery "holder" and run it off the power cord/charger?

Re: help with 29c please Message #2 Posted by Ron Ross on 5 Sept 2000, 9:29 p.m., in response to message #1 by john Yes, but be warned that dead alkilines wont explode ( a warning they always post so people won't try to recharge). However, they can and will leak corrosive fluid into your battery compartment and cause you damage and grief. Buy rechargeables for about $5 for a pair. The 29c deserves that. It would be very costly to replace.

Re: help with 29c please Message #3 Posted by Andrés C. Rodríguez (Argentina) on 5 Sept 2000, 10:39 p.m., in response to message #1 by john At your own (but low) risk, I suggest you can run it from two FRESH alkalines and WITHOUT the AC Adapter any near! Options: Rebuild the battery pack with new NiCd AA batteries, then (and only then) use the Adapter with the batteries inside. Run from a REGULATED DC source (not merely rectified and filtered), delivering 3.2 Volt DC at the AC connector on the calculator. Since you are not electroncs oriented, I suggest the alkalines as a good solution for you. The voltage will be about 2.8 V instead of 2.6 from fully charged NiCd, but it should be within tolerance. I have done similar arrangements with non-continuous memory models (HP 25), but I haven't had the chance on a 25C or 29C, so I could offer these suggestions but no warranties.

Re: help with 29c please Message #4 Posted by john on 5 Sept 2000, 11:28 p.m., in response to message #1 by john thanks to both of you

Re: help with 29c please Message #5 Posted by Les Bell on 6 Sept 2000, 1:45 a.m., in response to message #1 by john A better option: use NiCd's. Either rebuild the battery pack yourself, or have it rebuilt. There are lots of companies around who routinely rebuild NiCd battery packs for all kinds of devices. I just used the online Yellow Pages and in short order found a company near me (Sydney, Australia) who did an excellent job of rebuilding battery packs for my 82143A printer and an Icom hand-held radio. I'm about to send them the battery pack of my 41CX. Best, --- Les [http://www.lesbell.com.au]

Re: help with 29c please Message #6 Posted by john on 6 Sept 2000, 6:53 a.m., in response to message #5 by Les Bell i went to the store and bought a pair of eveready nicads. they are good for only 1.2v each (instead of 1.25). so far there is no problem. does that .05v matter?

Re: help with 29c please Message #7 Posted by Glynn on 6 Sept 2000, 7:36 a.m., in response to message #6 by john No, it is more of a manufacturer's admission of inefficiency than a practical matter of concern. Eveready, in fact, makes a good battery; what they state may be a touch on the "conservative" side, to allow for per-battery variations. NiCads are essentially alike, in their per-cell storage. They have, due to certain methods of manufacture, slightly different internal resistances. This translates to getting a bit warmer during charging, perhaps; but it doesn't affect you in a practical way (especially: you indicated you would be operating this from line-voltage most of the time-- meaning the charged NiCads won't be charging and discharging much). Remember: the best the battery can do is at the "topped out", fully-charged condition. The whole rest of the time you are operating the device, it is getting less than the stated voltage, and yet operates on this downward sloping curve, to some point at which the voltage is TOO low-- and the device does not operate, at which time you recharge or replace batteries. Ya done good, go ye and calculate, my son.

Re: help with 29c please Message #8 Posted by Viktor Toth on 6 Sept 2000, 8:37 p.m., in response to message #7 by Glynn A couple of comments, in the hope that it'll reduce the number of freshly killed HP-29Cs out there... A new alkaline "AA" battery can deliver a voltage as high as 1.6 Volts, which means 3.2V for a pair of them. I would think that this is within tolerance, but I've heard horror stories that this was enough to kill continuous memory models. A fully charged NiCd battery can deliver as much as 1.45V briefly after the end of the charging cycle. During charging, the voltage on the terminals may even be higher than that, so the 25C/29C were obviously capable of accepting an input voltage of 2.9V or a bit more. Using alkaline batteries and the charger may indeed not cause a spectacular explosion but the results won't be nice no matter what. "AA" size NiCd cells are easy to find, they're cheap, and can be used with the same ease as alkaline cells, once you cut the plastic case of the battery pack open. Because of corrosion on Woodstock battery contacts, I am hesitant these days when it comes to using the charger on 'C' models even with a rebuilt battery pack. Remember, in these models the RAM is always under power! If the battery doesn't make good contact, the calculator may momentarily receive a voltage far in excess of 2.9V (10V or more!!!), which is enough to kill the RAM and perhaps other chips. It is best to charge the batteries in a non-CMOS model (e.g., an HP-25) and avoid turning the calculator on while the charger is in. Viktor

Re: Help with 29c please Message #9 Posted by Andrés C. Rodríguez (Argentina) on 7 Sept 2000, 7:55 a.m., in response to message #8 by Viktor Toth 100 % agree

Re: Help with 29c, please Message #10 Posted by Andrés C. Rodríguez (Argentina) on 6 Sept 2000, 10:07 a.m., in response to message #6 by john 1.2 Volt is OK, 1.25 is nominal. Be sure about the polatity and absence of dirt or corrossion on the contacts, to be sure that the batteries and the calculator have good connections. It is of utmost importance on a AC-run HP29C. Good luck!

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