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isanchez · (This post was last modified: 07-08-2016 07:52 AM by isanchez.)

Dear friends,
just a few words to share my last project I have been working on.

I have refurbished an HP41c battery pack with new batteries and what makes it more special is that it can be connected to any mobile phone charger or to a laptop through a micro USB connector implemented. As I have removed all the circuit stuff, there is room for the new batteries, keeping the originals (circuit opened) for aesthetic & structural purposes.

I share some pictures.

Hope it is useful for you.

Kind regards

Ignacio

Ángel Martin · 07-08-2016, 07:24 AM

A great idea, and very nicely done. Congrats!

'/AM

Massimo Gnerucci · 07-08-2016, 07:31 AM

Well done Ignacio!!

isanchez · (This post was last modified: 07-08-2016 12:41 PM by isanchez.)

Thanks, Ángel & Massimo! Very proud to recieve your congrats!

On the other hand, and following with the "avoid batteries and chargers" philosophy, I have done a similar project for HP 41C printers and HP97 family calculators...

In both cases, the solution is the same: I have added a discreet coaxial "5.5mm barrel type" plug in the back of the Printer/HP97.

Using a cable with "Barrel Type" connector and with a conventional USB at the other end (easy to find in amazon).. This gives power to the HP97 and printer without the need of a battery pack installed or a original charger. It can be plugged to any Ipad/mobile charger or to a USB 2.0/3.0(better) laptop port.

As an altenative, a conventional 5V regulated charger can be used (with 5.5 mm coaxial end)

It is important to remark that the old powering system is not lost at all: you can use this new standard system, as an alternative system to power your printer/calculator.

If any detailed information required, please ask me!

I enclose some pictures.

Regards

Ignacio

Dieter · (This post was last modified: 07-08-2016 07:10 PM by Dieter.)

(07-08-2016 07:14 AM)isanchez Wrote: I have refurbished an HP41c battery pack with new batteries and what makes it more special is that it can be connected to any mobile phone charger or to a laptop through a micro USB connector implemented. As I have removed all the circuit stuff

OK, but where is the charging circuit then? Connecting the batteries directly to the 5 V of an USB port is not a good idea at all as there is nothing that sets the correct charging current and you also do not know the charging time for an empty pack.

After all there was a reason for the "circuit stuff" inside the original 82120A. ;-)

USB ports or USB AC-adapters are not chargers. They just provide a voltage and a certain maximum current. Also 5 V are not sufficient to charge a pack of four NiMH batteries. This means that as soon as the cells reach 1.25 V each there is no current that could charge them. Compare this to a freshly charged NiMH which will read about 1.4 Volts and more.

Sorry if this sounds a bit sceptical, but I am curious how you did it. Maybe there is something I overlooked here?

Dieter

Massimo Gnerucci · 07-08-2016, 07:21 PM

(07-08-2016 06:55 PM)Dieter Wrote: 5 V are not sufficient to charge a pack of four NiMH batteries.

Something like this maybe?

klacombe · 07-08-2016, 08:40 PM

Great idea! Could you post internal photos? I had looked at options for doing something similar with 2/3 AAA so I'm curious what you did for charging circuitry.