Hurricane II: An HP-41C Battery Pack w/ USB

[Hans Brueggemann]

with its anemic energy content, utterly long charging time, short lifespan, and inability to supply the card reader about just every time you would need reading a magnetic card, the HP 82120A Hurricane truly belongs into the "most disappointing HP accessory of all times" category. imho, of course.

when reviving my HP-41CL's configuration for the umpteenth time after an unforseen power loss (or getting an unresponsive HP-41C just because CLONIX is a tad picky when it comes to inrush current), i was no longer having it and decided to do my own rechargeable battery pack. here's my take on it.

instead of using an LiIon type pack, i opted for three ENELOOP AAA cells that would just so fit into the battery space of the calculator and still have some room for the converter circuitry. being at it, i opted for an USB-C connector that allows me to use any USB-charger that i have in my household.

rechargeable battery packs for the HP-41 have been done before, so why re-invent the wheel? the one thing that i was really missing in existing LiIon battery packs was the fact that they by design disable the LOW BAT warning on the HP-41. also, they would require some extra circuitry to take care of the LiIon's characteristcs in order to play safe. hence, i decided to implement a converter that would actually boost the ENELOOP's voltage to the desired level that the calculator requires and at the same time would track the ENELOOP's voltage during discharge. thus, the HP-41 is still able to report a LOW BAT condition to remind you of connecting an USB charger.
the charging circuitry itself clamps the max charging current to very low levels, so it takes quite a long time (approx. 8 hrs) to recharge the pack. at that point, the charging circuitry goes into a kind of "super low trickle charge" mode that allows you to have the charger permanently connected without damiging the battery cells. the boost circuitry is in fact quite beefy and has no problems feeding the high inrush current of the card reader, even if the card gets stuck for some reason.
so, finally, say bye-bye to your HP-41 falling into coma just because you didn't get notified on LOW BAT in time!

for now, this is for information only, as you can imagine i'm currently busy with testing something else. however, i'm eager to hear what you think about this approach!

[Massimo Gnerucci]

(12-11-2020 06:39 PM)Hans Brueggemann Wrote:  with its anemic energy content, utterly long charging time, short lifespan, and inability to supply the card reader about just every time you would need reading a magnetic card, the HP 82120A Hurricane truly belongs into the "most disappointing HP accessory of all times" category. imho, of course.

when reviving my HP-41CL's configuration for the umpteenth time after an unforseen power loss (or getting an unresponsive HP-41C just because CLONIX is a tad picky when it comes to inrush current), i was no longer having it and decided to do my own rechargeable battery pack. here's my take on it.

instead of using an LiIon type pack, i opted for three ENELOOP AAA cells that would just so fit into the battery space of the calculator and still have some room for the converter circuitry. being at it, i opted for an USB-C connector that allows me to use any USB-charger that i have in my household.

rechargeable battery packs for the HP-41 have been done before, so why re-invent the wheel? the one thing that i was really missing in existing LiIon battery packs was the fact that they by design disable the LOW BAT warning on the HP-41. also, they would require some extra circuitry to take care of the LiIon's characteristcs in order to play safe. hence, i decided to implement a converter that would actually boost the ENELOOP's voltage to the desired level that the calculator requires and at the same time would track the ENELOOP's voltage during discharge. thus, the HP-41 is still able to report a LOW BAT condition to remind you of connecting an USB charger.
the charging circuitry itself clamps the max charging current to very low levels, so it takes quite a long time (approx. 8 hrs) to recharge the pack. at that point, the charging circuitry goes into a kind of "super low trickle charge" mode that allows you to have the charger permanently connected without damiging the battery cells. the boost circuitry is in fact quite beefy and has no problems feeding the high inrush current of the card reader, even if the card gets stuck for some reason.
so, finally, say bye-bye to your HP-41 falling into coma just because you didn't get notified on LOW BAT in time!

for now, this is for information only, as you can imagine i'm currently busy with testing something else. however, i'm eager to hear what you think about this approach!

I'd say it's very promising and really interesting!
Keep us posted about development and availability, thank you.

[Sylvain Cote]

(12-11-2020 06:39 PM)Hans Brueggemann Wrote:  however, i'm eager to hear what you think about this approach!

I am very interested, I am using the card reader often, enough to always carry with me a battery holder with Alcaline batteries.
Each time I need to read or write cards, I swap the battery holder, read or write cards, then swap again the holder to put back NiMH cells.
I also carry the USB-power-module adapter (Diego design) for when I have a USB plug near.
Sylvain

[Massimo Gnerucci]

(12-11-2020 07:39 PM)Sylvain Cote Wrote:  I also carry the USB-power-module adapter (Diego design) for when I have a USB plug near.

Ditto! ;)

[JurgenRo]

(12-11-2020 07:42 PM)Massimo Gnerucci Wrote:  

(12-11-2020 07:39 PM)Sylvain Cote Wrote:  I also carry the USB-power-module adapter (Diego design) for when I have a USB plug near.

Ditto!

Same here! Another great design by Diego!

[PeterP]

Awesome. All I can say "Can I get three please?"

Great stuff,

[rprosperi]

(12-11-2020 06:39 PM)Hans Brueggemann Wrote:  [snip]
i'm eager to hear what you think about this approach!

Great solution Hans, I'm glad you were annoyed enough to fix this long standing problem. I agree this is the worst (least satisfactory) HP accessory; one of these is the only HP accessory that I purchased that was so useless I threw it away.

As for what I think: I think I want one. Ok, a couple. Maybe even 3 like Peter.

[Ángel Martin]

Two for me as well...

[MeindertKuipers]

Cool! I have another solution with a rechargeable cell, but the lack of BAT indication has always been troubling me.

[twoweims]

I will be buying two or three when the time comes!

[rocket.scientist]

Count me in for three, please. These are going to be awesome!

-Pat (KG5YPQ'

[BruceH]

Yes please. Two probably.

[Hans-Peter]

My design has no BAT control but a power-off switch in case a hard reset is necessary.
       
This version has a diode between LiFePo4 battery and the charger module, so I can use a normal 4.2V charger.
The second module is the step up converter to 5V.

[Mark Power]

A couple for me as well please Han.

[EricB]

Yes please. One for me.

[HP-Collection]

Seems to become a new mass product:
I suggest:

Maybe there is a nice 3D printer where the PCB and the recharging batteries fits perfect, contacts between the batteries and to the calc can be done by old Siemens Gigaset Battery springs (at least that's my best goal)

[jch]

Two for me, please.

[BobVA]

Nice! I particularly like your use of AAA cells.

What do you estimate the standby time of the pack will be?

[Craig Bladow]

Very cool! I would be interested in one if/when they become available.

[Hans Brueggemann]

(12-13-2020 06:11 PM)BobVA Wrote:  Nice! I particularly like your use of AAA cells.

What do you estimate the standby time of the pack will be?

for an HP-41CX w/ CLONIX,
12000 hours STANDBY and 25 hours RUN.
(typical values w/ 700 mAh ENELOOPs, after 10 hours charging time)