Woodstock battery modification

[AndiGer]

Lately bought a HP-25 with an interesting mod of the battery case done by a previous owner (hardware and software specialist).
   
   

Anybody aware of that?
I took the risc and hook the calc to the power adapter.
It worked perfectly.

[damaltor]

interesting. I wonder what the diodes are for. they might protect the caps from overvoltage?

[Maximilian Hohmann]

(09-10-2016 10:34 AM)damaltor Wrote:  they might protect the caps from overvoltage?

Rather the calculator! This looks like a fairly primitive circuit for smoothing the current (capacitors) and limiting the voltage to the calculator (diodes, maybe one of them a Zener-diode?). I would not want to use any of my woodstocks like this, rather connect them to a properly regulated and protected power supply set to 2.5V. Or, as I prefer, use it with externally charged batteries and hide the original chargers very deep inside some drawer...

[Nate Martin]

I have just been rebuilding the power circuits in a bunch of HP-21's and this looks like the substitute for batteries circuit from http://www.cs.ubc.ca/~hilpert/eec/calctd/HP21.pdf.

The Si diodes each have ~07.V drop which get you up to the 2.1-2.8V range.

[Nate Martin]

BTW, I just prototyped models for the woodstock battery case at shapeways. They seem a little rough but work.

Bottom:
https://www.shapeways.com/product/CT8EMA...bottom-std

Top:
https://www.shapeways.com/product/ZKFJHGDJM/

[rprosperi]

(09-12-2016 01:19 AM)Nate Martin Wrote:  Top:
https://www.shapeways.com/product/ZKFJHGDJM/

This link seems to be bad; at least it was for me.

Once released, will you add these into the existing store that has the 41C and 71B parts?

[Sadsilence]

(09-10-2016 10:59 AM)Maximilian Hohmann Wrote:  

(09-10-2016 10:34 AM)damaltor Wrote:  they might protect the caps from overvoltage?

Rather the calculator! This looks like a fairly primitive circuit for smoothing the current (capacitors) and limiting the voltage to the calculator (diodes, maybe one of them a Zener-diode?).

Agreement. It is a workaround as woodstock's power adapter delivers ac and too much output voltage for directly driving calculator. Some capacitors and diodes can do ac/dc conversion and voltage cut. Nevertheless curcuit looks frightening simple ;-).

P.S. Found a similiar curcuit in an HP19C (Only 1 capacitor and 1 diode ;-)) and it is (after remodifcation) still alive...

[Adam Vaughn]

IMO, those capacitors should be replaced before you use that calculator much longer. They look rather old, and electrolytic capacitors don't have an indefinite lifespan (often 10-20 years, sometimes 30-40 if you're lucky). Use values as close as possible to the existing caps, to be safe. Might not be a bad idea to replace the diodes, while you're at it. Make sure to match the polarity of the new parts to how the old ones were wired in.
-Adam

[Nate Martin]

(09-12-2016 02:26 AM)rprosperi Wrote:  

(09-12-2016 01:19 AM)Nate Martin Wrote:  Top:
https://www.shapeways.com/product/ZKFJHGDJM/

This link seems to be bad; at least it was for me.

Once released, will you add these into the existing store that has the 41C and 71B parts?

I am doing small adjustments to the bottom, once I have them working well I will open up to everyone.