HP-41 rechargeable battery pack repair

[Benoit Maag]

I am trying to refurb an HP-41 rechargeable battery pack but could not find any information on how to crack open the pack, or which batteries to use for replacement
Is there any information about that somewhere?

Thank you

[AndiGer]

Try the google search not the search function here for 1/3 AAA
1/3 Aaa site:hpmuseum.org

[Massimo Gnerucci]

(07-16-2018 03:44 AM)AndiGer Wrote:  Try the google search not the search function here for 1/3 AAA
1/3 Aaa site:hpmuseum.org

Or, alternatively,
1/2 N site:hpmuseum.org

[Benoit Maag]

Thank you both
There is indeed a lot of information available on hpmuseum.org

[damaltor]

Also, have a look here for two-pin packs
http://www.keesvandersanden.nl/calculators/hp82120A.php
and here (my personal page) for three-pin-packs
http://malte.deringenieur.net/wiederbele...ks-82120a/

[burkhard]

(07-16-2018 09:03 AM)damaltor Wrote:  Also, have a look here for two-pin packs
http://www.keesvandersanden.nl/calculators/hp82120A.php
and here (my personal page) for three-pin-packs
http://malte.deringenieur.net/wiederbele...ks-82120a/

A few questions:
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.

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?

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?

Thanks!

burkhard

[AndiGer]

Burkhard,

Regarding to use this as a spare? Ships (nearly) worldwide. Seems to be easier to refurbish than using single cells.
https://www.ebay.com/itm/Akku-Pack-82120...1929950942

(I am not in concern with this seller)

[burkhard]

(07-16-2018 03:58 PM)AndiGer Wrote:  Regarding to use this as a spare? Ships (nearly) worldwide. Seems to be easier to refurbish than using single cells.
https://www.ebay.com/itm/Akku-Pack-82120...1929950942

Yes, I've seen that akku-wechsel eBay ad (are they 1/3 AAA?) and have been tempted. I was considering that seller if somebody had good experience using them.

It seems (per the keesvandersanden site) that some batteries don't really fit all that well inside the pack housing and require some significant modification or the spring function itself might be compromised (which could possibly cause damage to the calculator power posts). Do the akku-wechsel packs fit well?

1. So, my first preference is somebody who has a "ready-to-drop-in-calculator" completed pack supplier they like.
2. If not that, perhaps somebody has experience with these akku-wechsel assembled base packs. Are these built from 1/2N, 1/3AAA, or some other base cells?

Thanks again!

[Massimo Gnerucci]

(07-16-2018 03:27 PM)burkhard Wrote:  A few questions:
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, they are an "early production thing". I can confirm this since I bought mine in 1980. And you can check this old thread too.

[Neve]

(07-16-2018 02:40 AM)Benoit Maag Wrote:  I am trying to refurb an HP-41 rechargeable battery pack but could not find any information on how to crack open the pack, or which batteries to use for replacement
Is there any information about that somewhere?

Thank you

I have refurbished quite a few. If you need help PM me.

[burkhard]

(07-16-2018 07:13 PM)Massimo Gnerucci Wrote:  

(07-16-2018 03:27 PM)burkhard Wrote:  A few questions:
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, they are an "early production thing". I can confirm this since I bought mine in 1980. And you can check this old thread too.

Great information! You guys are amazing---Thanks!

[rprosperi]

(07-16-2018 04:20 PM)burkhard Wrote:  1. So, my first preference is somebody who has a "ready-to-drop-in-calculator" completed pack supplier they like.

This listing on eBay:

https://www.ebay.com/itm/Rebuilt-82120A-...3098071409

is available from a reliable vendor. Jerry has been repairing and rebuilding 41 equipment for many years, and I've had excellent results buying from him. Of course rebuilding yourself is a lot cheaper, but that ignores the value you place on your own time, so this may be just what you are looking for.

Good luck, and let us all know how it all turns out so the next guy looking has some recent experience to go on.

[Neve]

(07-16-2018 07:59 PM)burkhard Wrote:  

(07-16-2018 07:13 PM)Massimo Gnerucci Wrote:  Actually, they are an "early production thing". I can confirm this since I bought mine in 1980. And you can check this old thread too.

Great information! You guys are amazing---Thanks!

No it’s not the Euro thing. It’s an earlier production model.

[Neve]

I’ve always used this, and they are quite cheap and great.

https://rover.ebay.com/rover/0/0/0?mpre=...1929950942

It’s quite simple to open the pack with a sharp blade.

[Massimo Gnerucci]

(07-16-2018 09:08 PM)Neve Wrote:  

(07-16-2018 07:59 PM)burkhard Wrote:  

(07-16-2018 07:13 PM)Massimo Gnerucci Wrote:  Actually, they are an "early production thing". I can confirm this since I bought mine in 1980. And you can check this old thread too.

Great information! You guys are amazing---Thanks!

No it’s not the Euro thing. It’s an earlier production model.

Repetita iuvant, it seems... ;)

[Neve]

(07-16-2018 09:59 PM)Massimo Gnerucci Wrote:  

(07-16-2018 09:08 PM)Neve Wrote:  No it’s not the Euro thing. It’s an earlier production model.

Repetita iuvant, it seems...

Sorry, I didn’t quote the right person.

[rprosperi]

Benoit,

Here's a refurbished battery and charger (and even a 'manual'), selling auction style on eBay but starting at only $0.99:

https://www.ebay.com/itm/HP-82120-HP-CALCULATOR-RECHARGEABLE-LIFETIME-BATTERY-PACK-WORKS-PERFECTLY/362388647020

The seller, vintagecalculatorsinc, is fully reliable, has been selling these for many years, and even offers a LIFETIME WARRANTY on the unit, so it's hard to go wrong.

[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.