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Hi,
I have HP-65, HP-67, HP-35 and Hp-25.
I also have a TI-58.

I have spare battery packs and power supplies for all of these, but since they're only collectors items they don't get used that much and I'm not good at pulling out the calculators to maintain a charge in the batteries.

Instead of continuing with the old rechargeables, I'd like to find a way to use alkalines when I pull out my calculators.

Were battery holders ever made for these calculators or does somebody make them today? I can find loads of rechargeable packs on eBay, but that's not what I'm looking for.
(11-29-2014 07:40 PM)pocketRockets Wrote: [ -> ]Were battery holders ever made for these calculators or does somebody make them today? I can find loads of rechargeable packs on eBay, but that's not what I'm looking for.

I never heard of battery holders for the 25, 65/67 or TI-58. Regular Alkalines have somewhat higher voltages than rechargeable batteries: a freshly charged NiCd or NiMH cell may exceed 1,4 Volts, so I would expect the internal electronics to handle this voltage. 1,4 V seems to be not too much different from the 1,5 V nominal voltage of Alkalines, but fresh Alkalines may also exceed this value. Which leads to the question whether Alkalines can be used safely in the calculators you mention.

But maybe there is another solution. There are NiMH batteries with extremely low self-discharge rate. In other words: charge them now, put them in a drawer (or in a calculator with no power drain) and they will still be close 100% in 2016. The leading manufacturer, Sanyo/Panasonic, even claims 70% after 5 years (!).

However, there are some problems on the practical side. Assembling a battery pack from these cells is not easy as they are hard to get as flat-tops and/or with soldering tabs. I use two Sanyo Eneloops in my 34C instead of the regular battery pack. The calculator is used only once in a while, and I even cannot recall the last time I had to charge its batteries (in an external charger). Finally the Eneloops even have roughly 5x the original capacity. ;-)

Dieter
Thanks,
The eneloops look like a good solution if they have good shelf life. I still need to figure out a way to create a battery pack from them though as I'm hoping to not have to solder them together at all.
I "built" a new battery pack for my TI-58C a few months ago using a 3xAAA receptacle from Radio Shack soldered directly to the battery contacts on the board. Modern NiMH AAAs probably have comparable capacity to the NiCd AA-size cells that were used when the calculators were originally produced, and the smaller AAA receptacle was easy to fit inside the battery bay without any elaborate plastic fabrication. It's also easy to pop out the cells and stick them in a standard charger, which I prefer to do, as I don't know how the calculator would handle directly charging NiMH chemistry.

For cosmetics, I modified the original battery pack into a plain battery door to hide everything away. A Dremel works well for that step.
Thanks,
No Radio Shack on this side of the pond, but ebay might have something suitable.
(12-01-2014 08:50 PM)Dave Britten Wrote: [ -> ]Modern NiMH AAAs probably have comparable capacity to the NiCd AA-size cells that were used when the calculators were originally produced.

They are even better. Around 1980, standard AA NiCds usually had a capacity of about 450 mAh. The mentioned Eneloop NiMHs are rated with typical capacities of 800 mAh (standard type) or even 950 mAh (Eneloop Pro). So you can expect about twice the original operating time.

Standard NiMHs offer even higher capacities – but without the special benefits of the Eneloops: 90% charge after a year or 70% after five years, according to the manufacturer. So even if they sit in a drawer for five years after charging they still should have significantly more capacity than a freshly charged original NiCd pack. ;-)

Dieter
(12-01-2014 09:34 PM)Dieter Wrote: [ -> ]They are even better. Around 1980, standard AA NiCds usually had a capacity of about 450 mAh. The mentioned Eneloop NiMHs are rated with typical capacities of 800 mAh (standard type) or even 950 mAh (Eneloop Pro). So you can expect about twice the original operating time.

Even better still - I bought some Eneloops a few weeks ago, and the spares on my desk, labeled BK-3MCCE, are rated at "1.2V min. 1900 mAh (HR6)". I haven't even had to recharge them yet.
(12-01-2014 09:43 PM)Les Bell Wrote: [ -> ]Even better still - I bought some Eneloops a few weeks ago, and the spares on my desk, labeled BK-3MCCE, are rated at "1.2V min. 1900 mAh (HR6)".

That's the AA version. The question was about 1980's AA NiCds compared to today's AAA (!) Eneloops. Despite the smaller size they still offer twice the original capacity.

But of course you are right: if you compare same-sized batteries the current versions actually offer five times (!) the capacity of the old NiCds. However, the point here was that even the smaller AAAs (as suggested by Dave) perform better than the much bigger AAs from 1980.

Dieter
I did this to virtually all the rechargeable calculators in my collection (abut 200 of them). Take a look at the bottom of this post from a couple of years ago.
(12-02-2014 04:42 PM)Katie Wasserman Wrote: [ -> ]I did this to virtually all the rechargeable calculators in my collection (abut 200 of them). Take a look at the bottom of this post from a couple of years ago.

Thanks, exactly what I was looking for!
Found some on dx.com for $7.47 for a 10-pack ;-)
(12-02-2014 04:42 PM)Katie Wasserman Wrote: [ -> ]I did this to virtually all the rechargeable calculators in my collection (abut 200 of them).

Alkaline batteries have a slightly higher voltage than NiCds or NiMHs. So I wonder if there is a maximum battery voltage that is known to be safe with the good old Classics, Woodstocks and Spices.

Dieter
(12-03-2014 02:35 PM)Dieter Wrote: [ -> ]Alkaline batteries have a slightly higher voltage than NiCds or NiMHs. So I wonder if there is a maximum battery voltage that is known to be safe with the good old Classics, Woodstocks and Spices.
Dieter

Dieter;
There was a thread about possible problems in using 1.5v alkalines in place of 1.25v nicads around ten years ago. Someone who knows more than I do thought there *could* be a problem so he installs slightly used disposable cells in his. There's always some from tv remotes or flashlights laying around. Since "they don't make 'em like this any more" ; I figure it's a small bit of trouble to do this to not stress my irreplaceable old Woodstocks There is no reason for any mod more involved than the cut you would need to change out the nicads in them anyway. The same is true for Spices that have broken tabs, but I keep a set of rechargables around for those and my Classics.
(12-03-2014 02:35 PM)Dieter Wrote: [ -> ]
(12-02-2014 04:42 PM)Katie Wasserman Wrote: [ -> ]I did this to virtually all the rechargeable calculators in my collection (abut 200 of them).

Alkaline batteries have a slightly higher voltage than NiCds or NiMHs. So I wonder if there is a maximum battery voltage that is known to be safe with the good old Classics, Woodstocks and Spices.

Dieter

I use Energizer lithium cells in and they're up to 1.7 volts per call, so quite a lot higher than nicad's. I've never had a problem doing this with any HP calculator: classics, woodstocks, spicse, stings, etc.
(12-03-2014 11:16 PM)Katie Wasserman Wrote: [ -> ]I use Energizer lithium cells in and they're up to 1.7 volts per call, so quite a lot higher than nicad's. I've never had a problem doing this with any HP calculator: classics, woodstocks, spicse, stings, etc.

Thank you very much, and sorry for my late reply. Finally I would like to add two remarks:

According to the graphs in the Energizer L91 datasheet the voltage almost instantly drops to 1.5 Volts or below if the load is 10 mA or higher. All LED calculators should exceed this load, so I wonder if the actual voltage applied to such a calculator really is not much higher than these 1.5 Volts, even if a fresh set of batteries is used.

Finally I would like to ask if someone has looked at the schematics of a Classic, Woodstock or Sting series calculator, especially at the voltage supply, and may dare an educated guess from there regarding the maximum "safe" battery voltage. I understand that even Lithium cells obviously do no harm, but maybe this observation can be confirmed by a closer look at the schematics. ;-)

Dieter
(12-11-2014 08:08 PM)Dieter Wrote: [ -> ]
(12-03-2014 11:16 PM)Katie Wasserman Wrote: [ -> ]I use Energizer lithium cells in and they're up to 1.7 volts per call, so quite a lot higher than nicad's. I've never had a problem doing this with any HP calculator: classics, woodstocks, spicse, stings, etc.

Finally I would like to ask if someone has looked at the schematics of a Classic, Woodstock or Sting series calculator, especially at the voltage supply, and may dare an educated guess from there regarding the maximum "safe" battery voltage. I understand that even Lithium cells obviously do no harm, but maybe this observation can be confirmed by a closer look at the schematics. ;-)

Others can add more insight on this subject, but from what I know from my HP-25, the IC's runs on higher voltages than the one supplied from the batteries, and to achieve this, a regulated DC-DC converter is employed.
It means that the input voltage is not that critical at it seems at first look.

In this example, the nominal supply input voltage is around 2.5VDC when using the original two NiCd rechargeable batteries, while using replacement nominal 1.5VDC non rechargeable cells gives about 3VDC. We are talking here on a excess of just 0.5VDC.

Considering that the average input current on these LED calculators is around 140mA to 170mA (from it, one not so small part is wasted in the DC-DC converter due to efficiency limitations), a little more input voltage is even welcome.

Jacques Laporte shares plenty of insight on these classic machines that I enjoy to revisit from time to time.
This thread us is quite old, but appears to be the most recent in-depth discussion of voltage for HP battery packs. Having just received three of Bob Wolfson's battery adapters, and only owning 2 HP NiCd packs to share across my HP-35, HP-45, and HP-55, I wonder if there are any updates to this?

In http://www.hpmuseum.org/forum/thread-5570.html Bob suggests that it is safe to use 1.5V Alkaline cells. Do people still think it safe to run a classic on 4.5V? Did anyone ever manage to check against original schematics?

I've got some NiMH cells charging now, but would like to know if Alkalines or Li-ion cells are safe. I certainly don't want to damage my classics!
Waterhosko (on TAS) has been making and selling Battery packs for the classics for a number of years. He makes a variety of rechargeable packs. He also builds alkaline battery packs for the classics. Although he can rebuild OEM battery packs, he doesn’t have to because he makes complete packs that fit perfectly.

Over the years I have bought several of his products (including alkalines) and I highly recommend them. His workmanship is excellent.

A fully charged niCAD is 1.4volts. A fully charged alkaline is 1.55 volts, a difference of less than 10%. I do not believe that is enough difference to cause a problem. Anecdotally, I have used alkalines on all the classics that I own including 35, 45, 80, and 65. It is anecdotal, but I have had no problems.

John
(Wonderful those time machine links to older threads)
About the size of everyday AA cells:
In a fit I filed off the button terminals from two NiMH batteries today.
Now the battery pack of an HP21 is far more easy to remove.

When I finally acquired a long admired HP67, it came without batteries or charger.
With some modifications i fitted in a Li-Ion battery (samsung galaxy s2) and used a Li-Ion charger from a camera. The modified battery looks very much like the padded AAA pack that Katie made.

I guess I should write a little text and make some photographs...

Robert
Thanks all!

Alkaline cells work just fine in Bob Wolfson's adapter in my HP-35. For some reason NiMH cells weren't making good contact, but they are fairly old, and may have crud on the contacts, even though my DVM was reading ~1.3V, but the Fluke probes are nice and sharp.
(03-26-2018 03:40 AM)John Cadick Wrote: [ -> ]Waterhosko (on TAS) has been making and selling Battery packs for the classics for a number of years. He makes a variety of rechargeable packs. He also builds alkaline battery packs for the classics. Although he can rebuild OEM battery packs, he doesn’t have to because he makes complete packs that fit perfectly.

Over the years I have bought several of his products (including alkalines) and I highly recommend them. His workmanship is excellent.

A fully charged niCAD is 1.4volts. A fully charged alkaline is 1.55 volts, a difference of less than 10%. I do not believe that is enough difference to cause a problem. Anecdotally, I have used alkalines on all the classics that I own including 35, 45, 80, and 65. It is anecdotal, but I have had no problems.

John

I've used several of the rechargeable packs from Waterhosko as well. They are excellent. Although he doesn't advertise them as suitable for TI calculators, I've found that the three-cell packs fit nicely inside an eviscerated BP-1A battery pack. I use a three-cell NiCd pack in an SR-52 and a three-cell NiMH pack in a TI-58C (the NiMH pack won't quite fit into the SR-52, for some reason). Both fit securely.

Nigel (UK)
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