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isanchez · 02-17-2016, 11:39 AM

Hi everybody,

As you all know it was considered to implement a direct power supply connection to HP41 series by mean of the two small golden balls present in early 41c. This was abandoned and the side conector was used to direct feed the rechargable battery pack. The rechargable battery packs are all dead and are not easy to rebuilt.

Despite the golden contacts are present or not, in the keyboard card you can still see the two connection points.
My question is simple: does it work? Are they functional?
If yes, would it be possible to charge four N-size rechargable batteries?, or is it just to power on the calculator?

I was thinking that, if functional, could be useful to design a connector (using 3d printing capabilities and adding the corresponding metal parts) to connect 41 series to a USB port...at least to use 41 on the desk without batteries...

Kind regards
Ignacio

Massimo Gnerucci · (This post was last modified: 02-17-2016 12:02 PM by Massimo Gnerucci.)

(02-17-2016 11:39 AM)isanchez Wrote: Hi everybody,

As you all know it was considered to implement a direct power supply connection to HP41 series by mean of the two small golden balls present in early 41c. This was abandoned and the side conector was used to direct feed the rechargable battery pack. The rechargable battery packs are all dead and are not easy to rebuilt.

Despite the golden contacts are present or not, in the keyboard card you can still see the two connection points.
My question is simple: does it work? Are they functional?
If yes, would it be possible to charge four N-size rechargable batteries?, or is it just to power on the calculator?

I was thinking that, if functional, could be useful to design a connector (using 3d printing capabilities and adding the corresponding metal parts) to connect 41 series to a USB port...at least to use 41 on the desk without batteries...

Kind regards
Ignacio

If only to power up the calc you can use one of Diego's USB power modules (or make one by yourself).

I have one and it works quite well; thanks Diego!

Artur - Brasil · 02-17-2016, 06:16 PM

Hi,

These days I was playing with my 41 connected to a wall power supply that I have made but, it's really anoying can't move to other rooms with it.
So, I'm studying construct one step-up internal power supply, that could transform a single 1.5V cell (AA) in 6V, using discrete components, as I don't know if I'll find such ultra small step-up ICs by here.
I have been studying the old charges and internal circuits of some even older HP calculators that used such circuits to generate other voltages from some power supply.
Any ideas?

wojtek · (This post was last modified: 02-18-2016 12:53 AM by wojtek.)

(02-17-2016 11:39 AM)isanchez Wrote: Hi everybody,

As you all know it was considered to implement a direct power supply connection to HP41 series by mean of the two small golden balls present in early 41c. This was abandoned and the side conector was used to direct feed the rechargable battery pack. The rechargable battery packs are all dead and are not easy to rebuilt.

Years ago I was using a set of 4 AA batteries connected to the 41c via its side connector with a short cable about 15cm, at least it was giving a kind of mobility. Then I improved this and build a kind of a box for the batteries which was attached to the 41c in a way the card reader is attached.
Anyway I like most the idea of Artur, the one of voltage multiplier 1.5 to 6V.
I have such a multiplier, bought as the phone camping power supply, which is fed by a single AA battery or nimh accu and gives 6V. Perhaps it would be possible to adapt it to power the 41c

4ster · (This post was last modified: 02-18-2016 05:34 PM by 4ster.)

(02-17-2016 11:39 AM)isanchez Wrote: As you all know it was considered to implement a direct power supply connection to HP41 series by mean of the two small golden balls present in early 41c. This was abandoned and the side conector was used to direct feed the rechargable battery pack. The rechargable battery packs are all dead and are not easy to rebuilt.

It's not what you are asking, but a pack rebuild is really easy. I recently used Helmut Wabnig's instructions for using two Varta Ni-MH 2/V150H in an original rechargeable pack. I free-styled the rebuild a little bit since my soldering skills are atrocious, but the rebuild was easy. Google "HP41 Rechargeable Battery Pack Refurbishment" to locate Helmut's write up in PDF.

My other two 41s have the N cell holder. I recently won the bid on a lot that included another 41 and a printer with the item I was interested in. The seller was quite clear that the extra items were not working. When I got the stuff, I was surprised that the 41 was in great shape, except for a dead rechargeable battery. I considered buying the 3D printed battery holder mentioned on another thread here, but decided to try a pack rebuild instead since this 41 didn't have a charge port cover either. I was really pleased it was so easy to get the "bonus" 41 running so easily. (And the printer was an easy fix as well.)

Nate Martin · 02-18-2016, 05:23 AM

Greetings all,

I have a couple of battery cases uploaded to shapeways ( http://www.shapeways.com/search?q=nmartin&type= ), and a couple others have them also. The 41 n-cell and rechargeable housings work OK, and I currently use both. Just need a source for the 'guts' (springs, circuits, and such). The 41 LiPO housing is a work in progress with the prototype sitting on my desk waiting for a rewiring. All the parts fit and are a little tight which resulted in me breaking a wire. But, the LiPO pack dropped in priority as I found NiMH rechargeable N cells and made a charging adapter sleeve to use in a AA cell charger. Also reading the design specs on the 41 made me worry a little that the voltage may be too high with 2 LiPO's in series.

As for a USB connection, I made one from a memory module to plug into the back of the 41 to power it, works well but I did not consider reverse power to batteries and only use it without a battery pack installed. If there is demand, I could model the module housing so we don't have to destroy good modules.

Artur - Brasil · 02-18-2016, 05:05 PM

Dave, what a great job with 3d printers!
Why not new HP41 back cases? Just wondering ....

Well, I believe that using new standard batteries - like AA or, even better and small, cell phones, and a converter to 6V would be a better solution, as N-cells on some places are difficult to find; using a USB or wall power supply will hook you near it - no mobility - an hp41 is a portable calculator, not a desktop calculator ...
With your battery cover already modeled for shapeways, I believe it would be simple to remove the inner battery separators and model a new one that could hold in one AA, or two AAA in parallel, or a cell phone battery, and the converter to 6V, as the one bellow:

http://www.ebay.com/itm/DC-DC-0-8V-6V-to...781?_ul=BR

or

http://www.aliexpress.com/item/1Pcs-High...71671.html (just asking for a 6V output instead of 5V)

The 1.5 cell get weak, just throw it and go to the pharmacy and buy another...

Artur - Brasil · 02-18-2016, 05:15 PM

Another solution, with simple parts:

Code:

 +--------+------------------------------------+-----------------------------+

 |        |                                    |                             |

 |        \                                    /||                           |

 |        / 1k                                 /||  470uH                  -----

 | +      \                                    /||                 2x 1.5V  ---

---       |                              470pF |       /        (parallel?)----- 

---       +---------+-------\            -||---+------>|-----+----o +       ---

 |1000uF  |         |         \         /      |       /     |               |

 |        |         \  2.2K     \     /        |      zener  |+              |

 |        |         /               /          |            --- 100uF        |

 |        |         \             / \          |            ---              |

 |      c |         |           /     \        | c           |               |

 |         \|_------+---/\/\/-/        \----_|/              |               |

 |      e </|                  1k            |\> e           +----o  -       |

 |        | bc547                              | bc547       |               | 

 |        |                                    |             |               |

 +--------+------------------------------------+-------------+---------------+

quantalume · (This post was last modified: 02-18-2016 07:53 PM by quantalume.)

Another possibility to consider is NiZn batteries. They provide 1.6-1.7 volts under light load, with a fairly flat discharge curve, so three of them would provide around 5 volts. Three AAAs would fit nicely in the space available.

Dave Frederickson · 02-18-2016, 07:56 PM

(02-18-2016 05:05 PM)Artur - Brasil Wrote: Dave, what a great job with 3d printers!
Why not new HP41 back cases? Just wondering ....

Thanks, but Nate created all the 41 models and Hans the FRAM71 bezel. I simply set up the Shapeways shop. Note that the rechargeable battery housing is available from Nate's own shop, wants_beer.

Dave

wojtek · 02-18-2016, 08:50 PM

(02-18-2016 05:15 PM)Artur - Brasil Wrote: Another solution, with simple parts:

Code:

+--------+------------------------------------+-----------------------------+ | | | | | \ /|| | | / 1k /|| 470uH ----- | + \ /|| 2x 1.5V --- --- | 470pF | / (parallel?)----- --- +---------+-------\ -||---+------>|-----+----o + --- |1000uF | | \ / | / | | | | \ 2.2K \ / | zener |+ | | | / / | --- 100uF | | | \ / \ | --- | | c | | / \ | c | | | \|_------+---/\/\/-/ \----_|/ | | | e </| 1k |\> e +----o - | | | bc547 | bc547 | | | | | | | +--------+------------------------------------+-------------+---------------+

What should be the breakdown voltage of the zener diode here?

Artur - Brasil · (This post was last modified: 02-19-2016 01:53 AM by Artur - Brasil.)

Good question! I take a look at the circuit again and the parte is 15mq040, which, actually, is a scotky diode, not a zener.
A zener in that position, I believe would have no x-function as voltage limiter....
So, it would be neccessary a voltage regulator too...
Its getting complicated....

Dieter · (This post was last modified: 02-19-2016 08:19 PM by Dieter.)

I'm a bit late to the party, but let me add my 2 cents anyway. ;-)

(02-17-2016 11:39 AM)isanchez Wrote: Despite the golden contacts are present or not, in the keyboard card you can still see the two connection points.
My question is simple: does it work? Are they functional?
If yes, would it be possible to charge four N-size rechargable batteries?, or is it just to power on the calculator?

As far as I know the HP41s do not contain any charging circuitry. That's why the 82120A pack had its own PCB, and later external chargers for N-cells were offered.

Alternative battery solutions for the HP41 have been discussed here several times – obviously this is a topic that shows up every few years. Maybe the last threads (in the old forum) may give some additional insights, e.g. on possible battery options. Cf. this thread which also links to that one.

BTW, has anyone ever thought of using a 2CR5 Lithium battery? These were quite common in photo cameras, they are as small as 17x34x45 mm and offer 6 V nominal voltage with 1200...1500 mAh capacity. Which is almost twice as much as an N-size Alkaline cell. Or 20x that of the original 82120A pack. ;-)

For my 41s I sometimes use a custom-made connector that fits the battery compartment. A short cable ends in a button-type connector (the one that is also used on 9 V batteries) which fits on various battery holders, e.g. for 4x AA. Or even 4x D if you think that up to 20 000 mAh are required. ;-)

Dieter

Artur - Brasil · 02-24-2016, 12:27 PM

Hi, I found one converter, in the format of a very small module. It's rated from 2V to up 18V!
Great for my pourposes! I'll receive it these days and will work on what I'm saying: having a portable calculator with simple batteries in it.

TASP · 02-24-2016, 02:22 PM

Probably just my native paranoia, but having an actual conducting piece of wire from any of my precious HP41s to an electrical outlet (regardless of the intervening electronics) in my rural backwater here, with lightning storms, neighbors with great big 3 phase farm irrigators, neighbors with AC powered fence chargers connected to miles of fences, and a 450 foot communication tower 1/2 way between me and the power company sub-station just isn't going to happen.

I'll plug in the printers and the video interface, and other HP accessories as there is not a real alternative, but except for HP battery chargers, I just try real hard not to leave items from my collection plugged in if I'm not actually using them.

And yes, the house has an electric panel installed surge suppressor, but I'm out in the boonies here, and I'm not inclined to trust the power company with the crown jewels.

Artur - Brasil · 02-24-2016, 03:11 PM

Great! One (or tons) of new motives for not wiring it to any external power source.

It would be great for you if HP had used coaxial wires to their power suppliers and good surge and electrical/magnetic suppressors inside it!

wojtek · 02-24-2016, 05:06 PM

(02-24-2016 12:27 PM)Artur - Brasil Wrote: Hi, I found one converter, in the format of a very small module. It's rated from 2V to up 18V!
Great for my pourposes! I'll receive it these days and will work on what I'm saying: having a portable calculator with simple batteries in it.

Me too :-) I ordered 3 different converters, still waiting for the package to arrive.
At the moment I have only one converter, which gives stable 5.5V with input in 0.8 to 1.5V range
The closer look at the shape of the output waveform on a scopemeter showed that it is of ramp shape of about 20mV peek-to-peek at 5.5V level, about 1kHz frequency, but the single capacitor some 10 uF should do.
You better inspect the waveform on an oscilloscope.
Important is how the converter will behave under very small load, some 20 uA, necessary to provide power for continous memory of 41c, will it start at all?. I checked mine and it seems to be OK

Artur - Brasil · 02-24-2016, 05:26 PM

Wow! 5.5V from 1.5V is great!
About the ripple, I believe you should try a bigger capacitor - 10uF is too low.
If at calculators power off state the converter doesn't work, what to put a resistance that keeps the current around 100uA? Do you believe this would dry out the battery?

TASP · 02-24-2016, 05:56 PM

LOL, generally in the sparky world you don't worry about a power supply misbehaving at low loads, but I could see down in the micro-amp region, things might get a little unspecific.

I recall back in the 80s an engineer friend of mine noting nearly unloaded, or lightly loaded generators on aircraft engines can be a problem since what little load there is might 'hunt' between paralleled generators on the plane, and in the case of a 4 engine plane, as the load 'moves around' the plane can experience slight changes in engine speed if the load shifts from, let's say #1 to #3, and that can make for slight, and annoying, changes in the direction the plane is flying. The autopilot (or the real deal behind the yoke) can compensate, but having a plane with perceived directional instability is comparable to a car with loose steering.

wojtek · (This post was last modified: 02-24-2016 08:28 PM by wojtek.)

(02-24-2016 05:26 PM)Artur - Brasil Wrote: Wow! 5.5V from 1.5V is great!
About the ripple, I believe you should try a bigger capacitor - 10uF is too low.
If at calculators power off state the converter doesn't work, what to put a resistance that keeps the current around 100uA? Do you believe this would dry out the battery?

In fact it gives 5.5V out of 0.8V, enough to use badly dried nimh accu. It is from a telephone backup power source.
As for a resistor to keep a small load in case the converter won't start it certainly would dry the battery sooner. But just count, on average 1800 mAh for a single nimh accu would give 1mA for some 500 hours till the voltage drops to some 1V from 1.2V. With 100uA the accu would last for 5000 hours or 200 days. So perhaps it would not be so bad.
But, this quick calculation does not allow for the self discharging of the accu and efficiency of the converter. So the real values certainly would be much smaller (with the efficiency of some 25%, what seems to be reasonable, we would get 50 days instead of 200 what still would be good enough to consider).