HP-67 Battery Pack



#7

Hi everybody, Can I use NI-HM Batteries (Panasonic HHR-P401 3.6V 1150 mAh) instead of the standard Ni-Cd pack? Does this option produce damages in the calculator? Thanks. ATE.


#8

Absolutely, just a couple of points:

1 you will have to modify the connection as the unit you
mention, the Panasonic HHR-P401 3.6V 1150 mAh has a standard
home wireless telephone plug.

The metal contacts found on the HP-67 match two metal strips on
the original battery pack mount and the Panasonic does not have
these.

2 A better option, if you want to purchase a unit, is to search on
EBay for Classic Battery pack. Check this link for the battery
pack: ebay link

I am not affiliated with the seller but the price is lower and the added benefit of a correct contact not requiring modification.

As an aside I am doing a section on how to modify the classic case to accept the new style battery packs the telephones have. This modification is for the calculators that have been restored but have had severe damage done to the two spring metal contacts found inside the battery compartment. The mod is simply attaching the male receptacle in a milled portion of the battery compartment and then just plugging the battery into the receptacle as seen in modern wireless home phones.

Cheers, Geoff

P.S. the NiMH batteries will take twice as long as the NiCd batteries to charge while using a standard NiCd battery charger. If you use the HP-67 to charge the NiMH batteries be aware of this limitation.


Edited: 7 Oct 2009, 6:35 p.m.


#9

Quote:
As an aside I am doing a section on how to modify the classic case to accept the new style battery packs the telephones have. This modification is for the calculators that have been restored but have had severe damage done to the two spring metal contacts found inside the battery compartment. The mod is simply attaching the male receptacle in a milled portion of the battery compartment and then just plugging the battery into the receptacle as seen in modern wireless home phones.

Cheers, Geoff

P.S. the NiMH batteries will take twice as long as the NiCd batteries to charge while using a standard NiCd battery charger. If you use the HP-67 to charge the NiMH batteries be aware of this limitation.


I look forward to seeing your phone-pak mod. Sounds nice!

When I put NiMH in my 67, charge times were way more than "twice as long." (The original NiCd were only 450mAh, the smallest capacity AA NiMH I had on hand was some NexCells at IIRC, 1800mAh, maybe more.) A full charge now takes 2+ days before the batts start getting warm.

sdb


#10

The charge rate of the 82002 is approximately 55ma which puts it at .03/C for an 1800mah cell, a perfect trickle charge rate.

At that rate, 50 to 60 hours would be normal for a full charge but you might encounter problems should the cells ever discharge fully, the trickle rate most likely will not be enough to bring the pack back to life.

Because of the simplistic design and low current of the HP chargers, I avoid using Nimh in pack rebuilds since they seem to fail sooner, rather than later. Sanyo makes an 1100mah AA nicd so why switch chemistries if you don't have to?

PS: You'll find those eBay batteries are nicd's as well. Ask the seller why... :^)


Edited: 10 Oct 2009, 1:34 p.m.


#11

Quote:
you might encounter problems should the cells ever discharge fully, the trickle rate most likely will not be enough to bring the pack back to life.

Because of the simplistic design and low current of the HP chargers, I avoid using Nimh in pack rebuilds since they seem to fail sooner, rather than later. Sanyo makes an 1100mah AA nicd so why switch chemistries if you don't have to?


Interesting. For 30+ years I have never had acceptable results with NiCd cells. Now I switch every pack I own to NiMH at the first failure and for many years I've been happy with that approach.

NiMH is a very robust chemistry if you avoid 1C or faster charging and the super high capacity cells. (The jury is still out on the low self-discharge variety, e.g. Sanyo eneloop.)

I'm even experimenting with switching out lead-acid (e.g. a UPS) and it seems to be working very well (but probably not cost effective). I'm watching for some surplus (read: cheap) flooded NiMH for my main UPS system. The cycle life and voltage curve should beat the flooded lead-acid, but since I don't care about energy density (volume or weight) the economics thus far have not worked.

Should I run into problems with a specific pack not charging (e.g. my 67 or the 25) I do have a generic NiMH fast charger which will charge anything from 2 to 12 cells in series (disconnected from any electronics and if I bypass any electronics in the pack). So far I've only used it when I did not have a charger for an application, or when I was in a hurry.

(It does up to 2amps into a pack with very good delta-V detection. Of course, delta-V into NiMH does not work very well below about C/5, but that's OK, at that rate my fingers safely detect the temperature rise in order to terminate charging.)

#12

Quote:
A full charge now takes 2+ days before the batts start getting warm.

To add a data point... The same day I posted that, I used the 67 down to the point the display would blank and all would reset when trying to read a card (wouldn't even pull the card in). It would still do simple calculations, but that's it. Probably had no more than a few minutes left of that before it wouldn't do more than power up.

I plugged it in that evening (the 10th). Just unplugged it an hour or so ago (the 14th). The batteries had no detectable warmth this morning, but tonight they seemed just a bit above ambient (66 there now, but it varies +10/-2f or so over the past few days -- it's by a south facing wall near a poorly weatherstripped wooden door opening onto a large concrete patio).

After four days on charge, all's well for another three to six months (depending on how much I use it, with no use the charge is still usable after six months).

sdb


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