The Museum of HP Calculators

HP Forum Archive 08

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Leaving batteries in
Message #1 Posted by David Ramsey on 2 Aug 2002, 5:45 p.m.

I used to delight in showing people my collection, turning each calculator on in sequence to show that they all worked.

Of course, I now keep the batteries out of all my calculators with rechargeable batteries.

What's the consensus on calculators that use the button batteries? I know the "N" cells used in some calcs can leak; have anyone ever seen damage from leaking button cells?

On another subject: what's a good source of calculator display stands?

      
Re: Leaving batteries in
Message #2 Posted by David Smith on 2 Aug 2002, 5:48 p.m.,
in response to message #1 by David Ramsey

ALL batteries have seals that can leak. Exceptions are hermetic batteries for implants and really expensive equipment (think hundreds of bucks each). Consumer alkalines and nicads are just about guaranteed to spew at some really inappropriate time in the future.

            
HP42S - won't work after empty batteries replaced
Message #3 Posted by Sandor Spruit on 5 Aug 2002, 7:06 a.m.,
in response to message #2 by David Smith

I own a HP42S that I got as a present when I got my BSc. in electrical engineering, years ago. I've been moving towards software engineering ever since, so the calculator has been laying around for quite a while.

Problem: the device won't work after I've replaced its empty batteries, even though there's no sign of any damage or leaks. Does this mean it has broken down, or could it be I've used the wrong batteries (I've noticed there are lots of different types) ?

                  
Re: HP42S - won't work after empty batteries replaced
Message #4 Posted by David Smith on 5 Aug 2002, 10:26 a.m.,
in response to message #3 by Sandor Spruit

The HP manual suggests shorting the ends of the battery contacts with a piece of wire or paper clip for a couple of seconds WHILE THE BATTERIES ARE INSTALLED IN THE CALCULATOR. Strange, but it does work.

                        
Re: HP42S - won't work after empty batteries replaced
Message #5 Posted by Vieira, Luiz C. (Brazil) on 5 Aug 2002, 11:46 a.m.,
in response to message #4 by David Smith

Hi;

should I suggest a brief short circuit? A single touch (less than a second) would be enough. I have experienced a total loss of memory (more than 3/4 of available 7200K in programs... Sob!) when replacing batteries. There is a way you place them (edgess first, middle last) that may shorten two of them in a flash, and the calcualtor circuitry is fed with only 1.5 Volts. So, Memory Clear becomes today's special. (S......). After testing masny forms, the one with less failures (for me) is placing the two batteries that go with minus pole (-) first, and place the last one as the being the positive pole (+). The risk is having the ciruitry fed with 3.0 Volts, and I did not have troubles since than.

Hope it helps.

                              
Re: HP42S - won't work after empty batteries replaced
Message #6 Posted by Sandor Spruit on 8 Aug 2002, 6:05 a.m.,
in response to message #5 by Vieira, Luiz C. (Brazil)

Well, very strange suggestions indeed :) It's sure worth a try to fiddle with the batteries before giving up on the calculator entirely. Thanks for the suggestions, I'll definately report back what happened ....

Sandor

                                    
Re: HP42S - won't work after empty batteries replaced
Message #7 Posted by Vieira, Luiz C. (Brazil) on 8 Aug 2002, 8:16 a.m.,
in response to message #6 by Sandor Spruit

Hi;

when I first read them, I also thought they were strange (must confess I still do), but there is some sort of reason on this procedure. (Voyagers' Manuals suggest this brief short-circuit as a "last chance")

By keeping batteries in their compartment and connected to the calculator circuitry, you avoid increasing the voltage in their terminal; if there is a chance that electrostatic charges are the problem, MOS internal circuitry could be easily damaged IF batteries are removed (they ensure low voltage at the mains source poles). Also, the brief short circuit will discharge the first electrolytic (or tantalum) capacitor, that keeps the main voltage for a few minutes when changing batteries; this is more than a reset: it's an HW reset, and might clear all user (RAM) memory contents. If the calculator will not switch ON for SW, HW or ESD causes, this procedure is enough for all of them.

If the calculator still does not respond, I would also suggest that, AFTER briefly short circuiting the terminals with the batteries on, remove them and let it rest for, say, one day long. Then you replace the batteries for NEW, unsuspicious ones and try again.

I sincerely hope you have success.

Best regards.

      
Calculator Display Stands
Message #8 Posted by Victor on 2 Aug 2002, 7:38 p.m.,
in response to message #1 by David Ramsey

I use those clear plastic picture frames that are roughly in an L shape. This gives me a wedge shape that I can set my calculator on top of. The frames cost about 99 cents each.

            
Re: Calculator Display Stands
Message #9 Posted by David Ramsey on 2 Aug 2002, 8:29 p.m.,
in response to message #8 by Victor

I think I've seen the frames you're talking about, but the ones I'm thinking of hold the calculator at a very shallow angle-- I need something more upright.

                  
Re: Calculator Display Stands
Message #10 Posted by Ellis Easley on 3 Aug 2002, 9:46 p.m.,
in response to message #9 by David Ramsey

I got a calculator stand from calcpro.com recently. It is made for Pioneers but they advertise it for "graphing calculators" and the 48G and 49G sit on it well. It is a simple piece of molded plastic with a hinge and an adjustable support. The highest angle, which I find best for use, is about 25 degrees. It is their item number PA30001 and sells for $7.95

                        
Re: Calculator Display Stands
Message #11 Posted by David Ramsey on 3 Aug 2002, 10:13 p.m.,
in response to message #10 by Ellis Easley

Thanks, you'd think I'd have tried CalcPro since I just ordered an HP-40 from them!

                              
Re: Calculator Display Stands
Message #12 Posted by Ellis Easley on 5 Aug 2002, 11:50 a.m.,
in response to message #11 by David Ramsey

I measured the highest angle of the calculator stand more carefully and it is closer to 30 degrees. [ atan(2.75/4.875) = 29.4 degrees ] I thought calcpro.com had a section for calculator accessories and that was where I found the stand in the first place, but now I don't find such a section, but using their search for "stand" found it (although the search strangely returned a list of calculators and other things as well!)

      
Re: Leaving batteries in
Message #13 Posted by Glynn on 3 Aug 2002, 2:19 a.m.,
in response to message #1 by David Ramsey

David Smith's response is correct: just about ANY cell CAN leak, and probably will, given time. Careful manufacture can minimize the tendency, of course. But consumer cells just aren't so high-tech as to be totally leak-proof.

A separate but equally important issue is not leaking, per se, but Venting. Rechargeables in particular can do that, and that leads to battery compartment problems as well.

In FACT, if you look at a NiCd or NiMH rechargeable cell. (say a AA size) you will sometimes see the HOLES, usually at the positive terminal cap. All cylindrical rechargeables have holes; some are visible and some are just hidden by the label area. These are to vent off a gas buildup in the electrolyte that occurs while charging, and especially if overcharging. As a battery "ages", its electrolyte is more likely to dry out and this outgassing increases. So terminal corrosion in the form of "hazing" is very common, and gold plating is recommended in applications where outgassing is possible.

Since gold is expensive, most manufacturers use a "corrosion-resistant" bright-metal alloy instead. It looks a lot like gold, but can still haze up pretty badly. When "hazed", they are not as good at conducting, and so you want to keep them shiny. Polish these contacts with #2 plastic polish and a small felt wheel or vigorous q-tip.

In a LEAK situation, real corrosion of the metal results, even on gold, and you will lose metal... so it is important to clean up a leak immediately and thoroughly. Towel and q-tip and cotton-ball clean every bit of electrolyte; follow up with isopropyl alcohol wipes. When your battery compartment is clean and dry, any corroded spots on the metal contacts or springs need to be scrubbed (an old dry toothbrush works well).

Inspect the metal; green or blackened areas need to be worked on further. Very very fine (000?) steel-wool of the sort used by furniture refinishers can clean contacts very well, BUT in doing so realize that the sheddings of this stuff are a danger to circuitry, so shield your calculator well prior to working on it this way.

Do button-cells leak? Sometimes, yes. More likely, you've seen a button cell swell (take on a convexity). If they do so, replace them IMMEDIATELY *no matter if they still work*.

Zinc-air cells leak notoriously. They need those holes to activate; but those holes are an achilles heel. I do not recommend zinc-air cells in any calculator application anyway; but they've found their way into pagers and the like and are the de facto standard in hearing-aids. If you use zinc-air in a calc, take them out if you won't be using the calculator for more than a week.

Much speculation about making "pseudo" batteries run by AC to power your displayed calcs... hmm, simpler to me is to SEPARATE battery from calc with a length of WIRE. Attach wires to contacts on calc, attach to a battery pack of proper voltage SOMEWHERE ELSE, and you'll never, never have calc damage. Even AC adapters and charging circuits will be properly fooled if you do this right.

            
Re: Leaving batteries in
Message #14 Posted by David Ramsey on 3 Aug 2002, 11:43 a.m.,
in response to message #13 by Glynn

Glynn,

Thanks for that long, informative message on battery stuff!


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