Power supply for HP computers with Woodstock case

[Tom Flatterhand]

As part of my recently purchased HP-25 and HP-29C, I've been looking into the future power supply for the two calculators. Probably most of you here already know the best way to do this. But in case you don't, or for newbies, I'll summarize here what I found out:

For 3D printer owners, Thingiverse has an STL file for a battery/battery case that fits the Woodstock case very well:

https://www.thingiverse.com/thing:1276886

Presumably based on this STL file, you can order this case in different variants at Shapeways:

https://www.shapeways.com/product/6NQAST...ery-holder

The 'problem' of this case, just like the original case, is the fact that modern batteries like Eneloop only fit in very tightly and therefore put a lot of mechanical stress on the case. This is because many AA batteries are around 50 mm long. Eneloop for example 50.5 mm.

Instead, I found a battery (NH GP 130AAM) at the German company Reichelt, which fits perfectly into this case with only 48.2 mm:

https://www.reichelt.de/de/en/nimh-indus...os_0&nbc=1

Moreover, it has with 1300 mAh about twice the capacity of the original battery!

At least 2 levels further is the solution from 'pwr', who has developed a battery/battery case suitable for the Woodstock case, which allows wireless charging and contains a modern lithium battery. Unfortunately, probably not so easily doable for most of us:

https://partsbox.com/blog/wireless-charg...-2021.html

Bilder:

Das weiße Gehäuse ist das von Shapeways. Das graue und das goldene Gehäuse habe ich selbst ausgedruckt.

   
   
   
   
   

[rprosperi]

For people that don't have 3D printers, a very nice replacement battery holder for Woodstocks is available here; this case is nearly the same color as a Woodstock case and it's easy to snap batteries in and out:

https://hp4171.com/shop/ols/products/hp-...ery-holder

The proper cells to use are called "flat-top" cells as they don't include the small button on the top (+) end of the battery found on consumer variety cells. These are less easily found in retail stores, but not too hard to find online. One of the best quality and longest charge cells are made by Tenergy:

https://www.tenergy.com/Tenergy-NiCd-AA-...op-Battery

[mfleming]

There are a fair number of posts about Woodstock battery holders as you can see from this search list

https://www.hpmuseum.org/forum/search.ph...order=desc

An alternative battery choice is a 4/5 AA size battery, which works well for the more restrictive Spice battery case. I've used them myself.

The Shapeways case you linked to is just the Thingiverse design minus the retaining tab that was rejected by Shapeway's design checker. Part was added for the convenience for others, with no markup.

~Mark

[David Hayden]

(04-30-2022 11:24 AM)rprosperi Wrote:  The proper cells to use are called "flat-top" cells as they don't include the small button on the top (+) end of the battery found on consumer variety cells.

You can get flat-tops at Batteries+Bulbs. One downside is that some chargers don't make contact with the them because of the missing tabs. I use a folded bit of aluminum foil to bridge the gap. Just be careful not to short anything out.