please advice an EE idiot on using chargers

[vaklaff]

The other day I skimmed Converting HP-25 to NiMH batteries, possible? and learned, in essence, to never put a Woodstock on a charger. My question is, does it apply even the calculator is switched off?

And what's the situation with other models? I have a 55, 67 and two Spices. Are they safe when

• running on a charger with no accu
• running on a chager with a good accu
• being switched off but on a charger with a good accu to charge it
  

Many thanks in advance!

[Garth Wilson]

Note to Americans, or maybe to native English speakers in general: "Accumulator" (shortened to "accu" above) is apparently what Germans say when they mean "rechargeable battery."

[vaklaff]

Thanks, Garth. That’s really what I meant. My appologies. Languages are hard :-)

[teenix]

Best not to use chargers connected to any Woodstock calculator.

The Classics and 67 should be ok as long as the charger itself is ok. If it is faulty then it may cause problems.

Probably the best rule of thumb is charge all batteries externally to the calculator.

cheers

Tony

[Steve Simpkin]

(07-30-2022 10:30 AM)teenix Wrote:  Best not to use chargers connected to any Woodstock calculator.

The Classics and 67 should be ok as long as the charger itself is ok. If it is faulty then it may cause problems.

Probably the best rule of thumb is charge all batteries externally to the calculator.

cheers
Tony

Agree with Tony. When in doubt, consult the warning in the Owner's Handbook for your model regarding use of the AC charger and (good) batteries.

Per the HP-25 Owner's handbook (Page 102), "Attempting to operate the HP-25 from the ac line with the battery pack removed may result in damage to your calculator." A similar warning is in the manuals for the Woodstock series (HP-2x), Spice series (HP-3x), HP-65 and HP-67. Because of the risk of batteries that could fail open or have a poor connection, it is also not worth the risk to charge batteries in the calculator for any of these models. Models without Continuous Memory are not likely to be damaged if their power switch is Off, but why take the risk. Models with Continuous Memory have the batteries connected to the CMOS memory chips at all times so they can be damaged even with the power switch set to Off.

The Classic series models have a different AC charger design that has a regulated supply for the calculator and a separate unregulated supply to charge the batteries. Classic models without a card reader (HP-35, HP-45, HP-55, HP-70, HP-80) can be safely operated without the batteries installed. The HP-65 and HP-67 are a special case because the card motor and sense amplifier are connected to the batteries. Per their manuals, don't operate those two "Classic" models without good batteries in place.

[rprosperi]

(07-30-2022 09:00 AM)vaklaff Wrote:  My question is, does it apply even the calculator is switched off?

Just to add specific clarity, the same rules (never use the charger on a Woodstock) apply even when off.

Also, Spices have the same weakness, though it seems a bit fewer will be destroyed in plugged-in.

For Woodstocks, it's probably 95+ % will be killed, maybe only 85% for Spices, but you don't know which are/aren't safe until you try, then its 95% too late.

[vaklaff]

Thank you all for words of experience as well as the pointers to documentation (now I remember reading that bit on Spices, funny how memory works).

Well, I don't have any device to charge the batteries externally. Since I use those calculators just for fun - for occasional programming - maybe I would be better off with buying a lab power supply and just clip the crocodiles, does it make sense? If yes, any suggestion for a particular model or make, or more generally, is there anything I should pay attention to as a buyer? As I already admitted, I'm an EE idiot, I am not proud of it, it's just a sad fact...

Thanks in advance!

[Steve Simpkin]

Vaklaff,

For your HP-25 it may be easier to just use disposable AA alkaline batteries in the original battery pack than a lab power supply. I have been doing that for the last 36 years. I removed the thin center plastic post that was between the batteries in the original battery pack which then allowed me to then slip the batteries in and out when needed (see photo below). Be sure to observe the proper polarity! This is the easiest solution but beware that the raised part of the positive terminal on standard batteries may not make good contact with the terminal on the circuit board. The added length also makes it harder to remove the pack.

*Ideally* I would recommend using flat-top rechargeable AA batteries (NiCad or HiMH) similar to these: https://www.amazon.com/dp/B072KKCBVY

They can be recharged externally via a changer like this model: https://www.amazon.com/dp/B0721JP6FK
For rechargeable batteries, make sure the charger accommodates flat-top batteries like the above model does (many do not).


   

[AndiGer]

Vaklaff,
The above linked charger is just an example! It‘s suitable for US 110 volts but maybe not in Europe where you have 220 volts.

Just a warning to an EE idiot :-)))

[Steve Simpkin]

(07-30-2022 07:55 PM)AndiGer Wrote:  Vaklaff,
The above linked charger is just an example! It‘s suitable for US 110 volts but maybe not in Europe where you have 220 volts.

Just a warning to an EE idiot :-)))

True the above charger in the Amazon link is just an example but it uses power from a USB power source that you have to supply (or one you already have) so it does not plug directly in AC power. I picked it because it was inexpensive and appears to work with flat top AA batteries (NiCad or NiMH). Note I have not tested it myself.

[ijabbott]

(07-30-2022 09:35 AM)Garth Wilson Wrote:  Note to Americans, or maybe to native English speakers in general: "Accumulator" (shortened to "accu" above) is apparently what Germans say when they mean "rechargeable battery."

To be fair, "accumulator" is a correct scientific term in English too. (Also known as a "secondary cell".)

[vaklaff]

Thanks to all the suggestions, including those I received privately.

A side note first, I'm not German but Czech (*). I'm not sure what made the impression, if "accu" or my nick "vaklaff", it doesn't matter much anyway. I let it go at first not to distract from the subject but now I think it would be better to make it clear before it sticks. I've also added it to my profile. As for "Vaklaff", it's is my nickname coming from the way how native English speakers usually pronounce my first name "Václav", it somehow grew on me :-)

Now back to the subject. Having processed all the information, I see three options for me:

1. External chargers. Duane kindly pointed to Mark's USB boxes (Classic, Spice)
2. Holders for disposable batteries like these two: Classic, Spice
3. Using a regulated power supply (like this one) clipped directly to the calculators contacts.
   

I'm leaning towards the third option, unless I am advised against it. In that case I'd probably prefer the holders and use disposable alkalines, unless that's a bad idea too :-) I see the external chargers as the least suitable option for me because of the regular need to rebuild the battery packs. But still it's an option if it turns out the other two are bad.

What do you think?

(*) For non-Europeans, we Czechs are the beer brewing Slavic nation wedged between Germany and Austria

[Jim Horn]

I would recommend a combination of your choices #1 (external charger) and #2 (modified battery holder). The modified holder works well with today's much higher capacity NiMH cells so you can easily have one set charging while another is in use - and the charge will power the calculator far longer than the original battery packs would do. Double win!

Why I don't recommend your choice #3 is that lab bench DC supplies are more expensive, larger, can easily have their voltage accidentally turned too high, and connecting them to the calculator's battery contacts can damage them, risks reverse polarity, precludes portability, and is inconvenient.

Best to you!

[mfleming]

(07-31-2022 12:55 PM)vaklaff Wrote:  ... and use disposable alkalines, unless that's a bad idea too :-)

What do you think?

Alkalines, regardless of brand, will always leak if left long enough without replacing. They're the #1 killer of calculators

[vaklaff]

(08-01-2022 11:44 AM)mfleming Wrote:  Alkalines, regardless of brand, will always leak if left long enough without replacing. They're the #1 killer of calculators

Not a problem in my case. I use these historic calculators just occasionally, for fun. In the meantime they are stored without batteries.

(07-31-2022 08:42 PM)Jim Horn Wrote:  Why I don't recommend your choice #3 is that lab bench DC supplies are more expensive, larger, can easily have their voltage accidentally turned too high, and connecting them to the calculator's battery contacts can damage them, risks reverse polarity, precludes portability, and is inconvenient.

(emphasis mine)
Thank you Jim. I ruled #3 out and already ordered all battery holders I need.

I'm not sure if I really need chargers as well. If it's OK to use disposable AAs or AAAs then I think I'm good...

[Jim Horn]

(08-01-2022 12:56 PM)vaklaff Wrote:  Thank you Jim. I ruled #3 out and already ordered all battery holders I need.

I'm not sure if I really need chargers as well. If it's OK to use disposable AAs or AAAs then I think I'm good...

Glad to hear it. Do enjoy your fine machines!