Re-celling



#2

Having replaced the AA NiCds in my HP-45, HP-33E, SR-52, SR-56, and TI-59, I thought I should try some more modern battery technologies. I put 2 AAA NiMHs in a BP7 for my TI-55, -57 and MBA. It works well with the stock TI charger. Then I put a 3.7 V Li Ion battery from a broken cell phone into a modified TI-58. It works well but I have not installed an internal charger.

Have any of you used other battery types to replace NiCds in your LED calculators?


#3

I use Sanyo Eneloop AAA cells in 50G and bought some NiMh with welded tabs to replace nicads in a cell phone. The Sanyo cells have a very low self discharge rate, and have been recebtly improved. The voltages seem to match a nicad cell. I use the Sanyo cells in shavers, toothbrush, flashlights, radios. I used to keep 2 chargers busy replacing the self discharge loss, now I seldom use one. I use the AA cells in a holder to substitute for D cells and get good life. Sam

#4

Quote:
Have any of you used other battery types to replace NiCds in your LED calculators?

Yes, I use my good old 34C with two standard Sanyo Eneloop NiMHs. Since the regular HP battery pack uses two NiCds connected with welded tabs, the new solution has to provide some kind of connection as well. I simply use a short piece of metal, or even a piece of aluminium foil folded several times to give the required thickness, fitting snugly into the battery compartment.



Using NiMHs replacing NiCds usually causes no major problems - this was one of the key features pointed out by the battery manufacturers in the early nineties when NiMHs became available to the average consumer. As with NiCds, the standard charging method applies a constant current, charging the battery with a similar efficiency of roughly 80% (for lower charging rates). This means that, in many cases, old LED-calculators with their low-current unsophisticated (and uncontrolled) simple not-exaclty-constant-current chargers can be used for NiHMs as well. However, the same charging time still gives the same operating time. So a full charge of the new cells means that a capacity four times as high also requires four times the charging time. Or four times the charging current for the same time as before. That's one of the reasons why I usually charge my NiMHs in a decent external processor-controlled charger.



NiMHs with low (virtually nonexistent) self discharge are available from several manufacturers, e.g. from Sanyo as "Eneloop" but also under different brand names. As far as I know these cells are not available with welded soldering tabs, at least not from Sanyo. The standard type has a capacity of 2000 mAh, giving 4x (!) the operation time of the original NiCds. Since there is virtually no self-discharge this kind of battery also is perfect for infrequently used devices. A set of four low-self-discharge NiMHs with a decent four-channel -dU processor-controlled charger can be had for less than 30 EUR/USD.


More information, including several brand names, can be found in this Wikipedia-article.



Dieter


#5

Quote:
... As far as I know these cells are not available with welded soldering tabs, at least not from Sanyo.
Dieter

I took some low self-discharge button-top cells to a local battery shop ("Batteries Plus" for USA readers) and had them spot weld and shrink wrap a couple of packs for me for about USD 10 each. Resulting packs are a bit taller than flat-tops with solder tab, but may work for some applications.


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