HP-41 Batteries

[TASP]

I've looked in my EduCalc catalogs and don't see the charger I have.

I'm still unpacking the storage boxes, it's gotta be in there somewhere! It might have a brand or tag on it.

It is a wall transformer, a few feet of wire and a little console that holds 4 N-cells. I think it has a red LED indicator.

Except for my CX, all my HP stuff has been in storage since 1994, the last time I moved.

[TASP]

LOL, found the charger.

Label on the transformer says HP92266A. Pretty funny, it looks like a 3rd party aftermarket gizmo, but what do I know?

I do recall using it on NiCads and using it quite a bit.

Specs are

117v AC 60 Hz 3W
5.8 VDC 15 mA

It also says 5-84. Manufacturing date ??

[Dieter]

(03-01-2015 10:27 PM)TASP Wrote:  Label on the transformer says HP92266A. Pretty funny, it looks like a 3rd party aftermarket gizmo, but what do I know?

Ah, yes, this seems to be the official "external" HP41 battery charger for four N-size NiCd batteries.

(03-01-2015 10:27 PM)TASP Wrote:  Specs are
117v AC 60 Hz 3W
5.8 VDC 15 mA

This seems to be a very simple charger without any charge control that applies a more or less constant charging current of 15 mA. This was fine for the NiCds of the day, but current NiMHs have much higher capacities and thus require very long charging times. Take the battery capacity in mAh and divide it by 12 (=15/1,25). The result is the charging time in hours for an empty (!) battery. In the Eighties, regular N-size NiCds offered about 120–150 mA which means a 10–12 hour charge. But a current N-size NiMH has about 500 mAh, so this would require 40+ hours... #-)

I would strongly recommend a better charger with decent automatic charge control. There are several suggestions in earlier posts in this thread.

Dieter

[TASP]

Indeed.

Or maybe I rebuild it. The battery holder is fine, the transformer and electronics are too primitive for 2015, thats for sure.

Maybe put a plug on the wire lead, and make a nice little charger circuit in a handi-box. Good rainy day project.

I've found a heap of diodes, caps, resistors, x-formers while cleaning out the storage area, I might have most of what I need.

[Hans-Peter]

There are good variants to make a strong Power source even for a card reader. I have testetd a Lipo version and a double AAA version (for non card reader).
   
First preparation for all Versions:
First I took a 3mm playwood from a wooden giftbox. Then I took the spring contacts from a dead DECT phone. The best results with the glue are those with the "UHI Hart".
The small noses to hold the cover down, are replaces with a pice of alloy.
   
For the electronics I tried 5V and 6V mini step-up converters. The right one took only 7uA idle current. 5V version works but I would recomend the 6V versions (harder to find).
   
This module works from 0.8V to 5V. You can use a single cell but not with the card reader. I recomend the ENELOOP's as rechargeabel batteries.
   
If you like to use the card reader, then you have to give a higher voltage to the converter. I took a 240mAh 1S Lipo as a small Lipo chager. On the charger are two Led's. The red one means "charge" the blue one says "full". With a clear peace of plastic on the Led's, the color can be seen on the side.

Here is a Picture of the Lipo version. The AAA version is waiting for the 6V module.

The Lipo version has a charger plug on the right side of the calculator. You can use a micro charger cable to charge the Lipo.

Now, I take the HP41 to my work for a longterm test.

Best regards from switzerland