HP-41 rechargeable battery pack repair

[damaltor]

Please excuse my late answer...

(07-16-2018 03:27 PM)burkhard Wrote:  1. So, why does your pack have 3 pins? Is that a "Euro thing" or a "late production thing"? The packs I have myself and seen in the US (admittedly not a whole lot) are all 2-pin.

Actually it is an early-production thing. The Tab and the third pin bridge a small diode when operating in battery mode so that the full battery voltage is supplied to the calculator. when the charger is inserted, it does not (!) connect to the third pin but lifts the connection with the tab, so that there is a diode after the rectified charger output, so that the calculator gets supplied directly from the charger. no idea why they made this overly complicated circuit, as the later two-pin battery packs work just fine.

(07-16-2018 03:27 PM)burkhard Wrote:  2. The base battery pack you sourced from akkuplus was NiCad rather than NiMH. Wouldn't the pack capacity have been a lot higher with NiMH, offsetting the smaller size of the 1/3 AAA? You mentioned a couple of upsides for NiCad, but it seems that NiMH is a better battery chemistry choice today. Am I overlooking something, or does your opinion still favor NiCad?

The original hat NiCd, so i thought i could simply use the same again. partly to nostalgia, partly to make sure that charging works exactly the same (though the charging circuit is so dead simple that it would work with NiMh just fine). There is no real reason to stick with NiCd. I one cread that NiMh leakages are worse that NiCd leakages, but neither do i know where, nor do i know if that is really true.

(07-16-2018 03:27 PM)burkhard Wrote:  3. In addition to your site, the Dutch page above has a bunch of other nice links at the bottom. Lots of people of done these pack updates via a few different techniques. It doesn't seem too tough and I am pretty handy with such stuff, but I've got a *ton* of projects already, up to my chin, and I'm at the point I'd rather just buy one from some expert. Is there a "favorite vendor" people have who does a nice job and just sells them?

Try ebay. There are already some links in the posts over this one.