NiCad battery Questions



#8

I was in the process of rebuilding 5 82001A/B batttery packs this weekend and wondered if the replacement NiCads, which are rated for 700 milliamp-hours offer any improvement in operating time over the original ones. Does anyone know the ratings of the original AA NiCads?
I also have 2 batt packs from 1985 and one from 1989 that have not been used and appear to hold a charge like they were new. Is there any problem with using these or do the pose additional risk to the calculator because of their age. I am most worried aout leakge due to the early manufacture date.
And finally, will storing NiCads in the freezer when not in use prolong their life. I typically use 2 batteries and the other ones just sit on the shelf unused so I thought that perhaps they could be frozen when not used. Maybe this is a crazy idea but since the production of electricity in a battery is a chemical reaction it the colder temperature should slow down the self discharge but will this process prolong its useful life? Should the packs be frozen in a charged or discharged state?
Thanks in advance to your thoughts
Dale Richmond


#9

I think the original NiCd batteries that HP used on the Classics and Woodstock series were 500 mAH, so the newer 700 mAH batteries should offer some more operating time (one may assume that the time will increase as per the 700/500 ratio, but few things are linear these times...).

I think you should store your batteries charged and on fresh places, but never heard anything serious about freezing them, try to obtain credible advise on this!

#10

You might want to try these:

http://www.conrad.at/cgi-bin/conshop/ConShop.pl?TK_PAR[USER_ID]=0204052880982201667&TK_EV[SHOWPAGE]=&TK_PAR[PAGEID]=156900&TK_PAR[MEDIUM]=62

(sorry for the long link)

1000mAh min. isn't bad (Type P100 Mignon*).

You can take any battery, that's 50 x 14 in the "Abm. mm" column (This is AA for our U.S. friends).

You might also look around in model car stores. These need any capacity you can get and they maybe have even better NiCads. NiMh isn't recommended with "normal" NiCad chargers like in the HP calcs, because of their heat developed during certain conditions in the charging process.

I re-celled my 82161A cassette drive (82033A batt. pack) with Panasonic "RED-AMP" Nicads abt 15 years ago. These can live with the pulse currents draen by the drive motors (other NiCads died rather fast). The RED-AMPs were designed for model car applications.

This battery pack lasted til today (though I don't use the cassette drive too much nowadays).

Sure, that all these specialized accus are not too cheap, but if they save you opening the pack again in 3 years, you will be glad...


Sorry, no info about freezing Batteries. I think you should consult the datasheets. I'm pretty sure you can find them from the large companies, like Panasonic, Varta or Sonnenschein. There might be lot's of others manufacturers and I don't want to highlight some of them. These are just what I remembered in some seconds.

#11

I believe that storing alkalines in the fridge prolongs their life. I never tried the freezer.

NiCads are much less temperature sensitive. That's why I use NiCads in my camera outside in the winter. That might mean that the fridge or freezer will have little effect on their self-discharge rate and corrosion rate too. This is pure guessing though.

#12

I rebuilt a classic series battery pack a year ago. After ripping off the cardboard tube from around the dead batteries the writing on the side said 450mAh, I don't know when the original was made. One problem with higher capacity Nicads is the HP standard charger is now a bit slow and to get a full charge can take 24 hours (and my little transformer gets quite hot). Does anyone know what the charging rate is for classic series transformers? (I'd guess about 50mA)

As far a freezing the battery packs goes I would not do it unless the storage temperature range from the manufacturer indicates it is safe to go down to the lowest temperature of your freezer.

I have been told the best life can be extracted from Nicads by using them. I think this is because the self discharge will eventually kill the Nicad if it is not topped up on a slow charge every so often. So cycle the use of each battery pack in your calculator.

PS Books have been written on the care and use of batteries and I don't pretend to know what is best in each case. I use these simple rules of thumb for Nicads: Don't charge at too high a rate (especially repeatedly), don't leave them flat for too long, don't leave them in equipment that is not going to be used for a long time (month+).


#13

When simple charging circuits are used (I mean, there is no feedback mechanism that detects the battery status and adjust the charging current), the rule is to use a charging current that is 10% the rated capacity. So, for a 500 mAh battery, the charging current will be 50 mA, which is more or less what a typical HP 21/22/25 delivers to its batteries.

We may assume that, in such case, the charging time should be 10 hours, but things are not so simple. Fully charging a battery usually takes up to 40% more than such simply calculated value; on the other hand batteries are usually recharged while there still is some remaining charge on them. It usually ends in 14 hours for a fully discharged battery, and some 8 hours for a normal recharge.

If you replace the original batteries with newer, more capable units (700 to 1000 mAh), charging time will also increase.

#14

For what it's worth, all my HPs are running on Sanyo 1100AAU cells. These are 1100mAh AA sized cells. The cells I recently removed from an old HP-21 were 475mAh. In any case, I use both my HP-32E and 34C almost daily, and only need to recharge them about once a month.


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