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+--- Thread: Woodstock battery modification (/thread-6818.html)
Woodstock battery modification - AndiGer - 09-10-2016 08:19 AM
Lately bought a HP-25 with an interesting mod of the battery case done by a previous owner (hardware and software specialist).
[attachment=3901]
[attachment=3902]
Anybody aware of that?
I took the risc and hook the calc to the power adapter.
It worked perfectly.
RE: Woodstock battery modification - damaltor - 09-10-2016 10:34 AM
interesting. I wonder what the diodes are for. they might protect the caps from overvoltage?
RE: Woodstock battery modification - Maximilian Hohmann - 09-10-2016 10:59 AM
(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...
RE: Woodstock battery modification - Nate Martin - 09-12-2016 01:01 AM
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.
RE: Woodstock battery modification - Nate Martin - 09-12-2016 01:19 AM
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/CT8EMAFQH/woodstock-bottom-std
Top:
https://www.shapeways.com/product/ZKFJHGDJM/
RE: Woodstock battery modification - rprosperi - 09-12-2016 02:26 AM
(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?
RE: Woodstock battery modification - Sadsilence - 09-12-2016 06:04 AM
(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...
RE: Woodstock battery modification - Adam Vaughn - 09-13-2016 02:58 AM
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
RE: Woodstock battery modification - Nate Martin - 09-13-2016 04:03 AM
(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.