Classic Battery Adapter

[bobwolfson@gmail.com]

For those owning Classic calculators (35, 45, 55, 65...), I sell an adapter that lets you power it with replaceable AAs. It's way more convenient than using the NiCad packs! $40



More pictures and details at:

https://sites.google.com/site/bobscalcul...ck-adapter

[rprosperi]

(01-21-2016 07:06 PM)bobwolfson@gmail.com Wrote:  For those owning Classic calculators (35, 45, 55, 65...), I sell an adapter that lets you power it with replaceable AAs. It's way more convenient than using the NiCad packs! $40

Can AA NiMH cells (mentioned on your site) be charged in a Classic HP Calculator safely?

[bobwolfson@gmail.com]

(01-21-2016 07:27 PM)rprosperi Wrote:  Can AA NiMH cells (mentioned on your site) be charged in a Classic HP Calculator safely?

I don't claim to be an expert in battery recharge technology. Indeed, it seems like a complex topic from what I've read. And I think it depends on what you mean by "safe".

But I think the answer is moot, because why would you bother doing this? If you use my adapter with NiMhs, you would charge them in their own charger outside the calculator. It will be safe, faster, and put no wear and tear on your calculator!

[rprosperi]

(01-21-2016 07:45 PM)bobwolfson@gmail.com Wrote:  I don't claim to be an expert in battery recharge technology. Indeed, it seems like a complex topic from what I've read. And I think it depends on what you mean by "safe".

But I think the answer is moot, because why would you bother doing this? If you use my adapter with NiMhs, you would charge them in their own charger outside the calculator. It will be safe, faster, and put no wear and tear on your calculator!

I may charge them in the calculator (assuming it is truly safe) so that I don't have to buy a charger for the NiMH cells. I have some of these now, as they are used in devices that charge them directly (mice) and I could use them, as I agree the NiCd charge time is a pain, though I suppose it would be similar (or longer!) with the NiMh cells, so maybe a charger is a good thought after all.

Anyone know if charging NiMh cells in a classic calc. is "totally safe", "recommended against", or the dreaded "it depends" ?

[Katie Wasserman]

(01-21-2016 11:34 PM)rprosperi Wrote:  Anyone know if charging NiMh cells in a classic calc. is "totally safe", "recommended against", or the dreaded "it depends" ?

Totally safe. I used to do it regularly in all my HP calculators before I switched to primary lithium cells -- so that I would not have to recharge them at all. (Of course many NiMh cells today have very good self-discharge characteristics.)

Many here will advise against charging cells inside a Spice or Woodstock because your calculator might not have good battery contact, then turning them on while charging would expose the circuit to higher voltage, pulsating DC current. Just don't turn them on while charging and you'll be fine.

[bobwolfson@gmail.com]

(01-22-2016 04:29 AM)Katie Wasserman Wrote:  Many here will advise against charging cells inside a Spice or Woodstock...

I can also mod a Woodstock pack to use any AAs. $32.50
Then you don't have to worry about charging in the calculator at all.



See more here:

https://sites.google.com/site/bobscalcul...y-pack-mod

[Sadsilence]

(01-21-2016 07:27 PM)rprosperi Wrote:  Can AA NiMH cells (mentioned on your site) be charged in a Classic HP Calculator safely?

Agree with Katie. I have been using Texcus 3AA NiMH 2100 mAh packs with low self discharge characteristics within Classic calculators for a long time now and charge them with orginal ac adapters. Checked packs externally regularly at the beginning. No desease of pack after 10 - 20 cycles. LSD cells have the great advantage, that they hold charge for 1 year and more with only 20% loss, compared to normal NiCD/NiMH cells who loose 100% after 3 - 6 months (and leak after some more time).

Charge current is around 60 mA with classics AC adapter so modern NiMH cells with capacity C >2000 mAh simply cannot be overcharged no matter how long you charge them. Typical datasheet information of cells states no damage of cell when charged with C/10 for one year. C/10 would be 210mA in my example.

Senseful charging time for low charge currents (C/10 or less) can be selected with following rule for empty NiMH/NiCD cells:
Take REAL capacity of cells * 1.6 / low charge current.

e.g. 2100 mAh * 1.6 / 60 mA = 56 h

To be on the safe side (printed capacity often exceeds real capacity) I would choose 48h. It is easy to remember and NiMH/NiCD cells need a lot of time to get in last few percents. I checked and get 95% of real capacity out of cells.

Anyway that is a lot of charge time but 40 years old clip holders of battery doors for classics are a weak point of case and I try move them as little as possible. Of course it is possible to charge an empty pack outside with around C/2 charge current for 135 min using a matching charger.

To be honest there is another drawback. Charging modern NiMH cells with such low currents all the time let vanish their high current capabilities. No real problem, as 100 - 200 mA supply current for classics do not count as high current ;-).

Only one more hint: Within AC adapters of classics are some electronic parts that convert AC into DC (later AC adapters for woodstock/spice/HP-41 and peripherals have an AC only output). One key element for conversion is a 400uF capacitor which more often than not is dead to due age. Other components like diodes and transformer are normally made for eternity. As a result both adapter outputs have a more or less ac ripple which reduces charge current for battery pack even more and can influence calculator functionality when it is switched on at the same time. AC adapter supplies calculator completely in that case. A typcial sign are fllickering LED digits at start until AC adapter reaches operating temperature. Replace mentioned capacitor with a modern 470uF/25V type and be happy again ;-).

[rprosperi]

(01-22-2016 04:29 AM)Katie Wasserman Wrote:  Totally safe. I used to do it regularly in all my HP calculators before I switched to primary lithium cells -- so that I would not have to recharge them at all. (Of course many NiMh cells today have very good self-discharge characteristics.)

Many here will advise against charging cells inside a Spice or Woodstock because your calculator might not have good battery contact, then turning them on while charging would expose the circuit to higher voltage, pulsating DC current. Just don't turn them on while charging and you'll be fine.

Thanks Katie and Sadsilence, for confirming my suspicions. For both Woodstock and Spice machines, I use external chargers due to the risk, but have always thought the Classic machines were more robust.

I've given much thought about giving up on rechargeables totally and getting a bunch of Lithium cells, but haven't made the leap yet. At some point, convenience will indeed win out over old-school use-it-like-it-was technology appreciation, but just not quite there yet.

[HP-Collection]

(01-22-2016 05:06 AM)bobwolfson@gmail.com Wrote:  

(01-22-2016 04:29 AM)Katie Wasserman Wrote:  Many here will advise against charging cells inside a Spice or Woodstock...

I can also mod a Woodstock pack to use any AAs. $32.50
Then you don't have to worry about charging in the calculator at all.



See more here:

https://sites.google.com/site/bobscalcul...y-pack-mod

Sorry, but $32.50 for what? You only cut away the mittle bridge and glue some contacts in the shell?
The classic adapter is much more interesting for me, even the price is very high, I think. maybe someone publishes a 3D printer layout on the Shapeways shop?

[bobwolfson@gmail.com]

(01-23-2016 11:10 AM)HP-Collection Wrote:  Sorry, but $32.50 for what? You only cut away the mittle bridge and glue some contacts in the shell?
The classic adapter is much more interesting for me, even the price is very high, I think. maybe someone publishes a 3D printer layout on the Shapeways shop?

It's more than cutting away the bridge. It's also cutting one of the slanted sides. And it's doing it carefully. But I don't mind if it's not worth it to you.

As to the classic adapter, I actually do print the plastic parts at Shapeways these days. Costs about $12. Then I have to cut and solder contacts from brass sheet, and glue assemble/glue the parts so the contacts are embedded inside the plastic frame.

It takes a couple hours to do one, plus there's the fact that I put all the time into figuring out how to make them and into designing the 3D model. It may be pricey to you, but I've made many people happy with them.

[d b]

I'm sure that to a woodstock owner missing a batt box; that was the best 32 bucks he ever spent.

[Dave Frederickson]

(01-27-2016 09:25 PM)Den Belillo (Martinez Ca.) Wrote:  I'm sure that to a woodstock owner missing a batt box; that was the best 32 bucks he ever spent.

The $32.50 is to modify a battery pack, not to purchase.

[d b]

That explains why the more complexly shaped part is cheaper. For people unlike us, who don't have a drawer of exacto knives, little files, and a Dremel; it may be worth it. I did mine myself. I bet you did too.

[HP-Collection]

I did, yes.
As explained, the classic shell is a nice feature and is worth some money. I would prefer doing the electical part myself, so $12 for the 3D print is ok.....

[bobwolfson@gmail.com]

(01-28-2016 06:29 PM)HP-Collection Wrote:  $12 for the 3D print is ok.....

LOL! That was $12 it costs ME to print one, after which I fashion the contacts, assemble the parts, fit, test, box and mail for $40.

I don't think it's so much when you consider all I've done in terms of design and development, and all I do in terms of production.

But for the do-it-yourself-er, I've put the adapter shell on sale at Shapeways for $25. Adapter On Shapeways

[Steve Simpkin]

Bob,

Thank you for the work you have done in crafting this classic battery adapter and thanks for giving us the option of buying just the adapter shell.

[James P.G. Sterbenz]

I've got three of these on the way for my HP-35 (which I just inherited from a friend with a bad pack), -45, and -55 (for which I'd gotten rebuilt NiCd packs. Thanks Bob!

Is it really safe to use alkaline batteries given the higher voltage (3*1.5=4.5V vs. 3*1.2=3.6V)?