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HP Forum Archive 13

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Battery questions
Message #1 Posted by Luk on 10 June 2003, 10:23 p.m.


I am new to calculators collecting and have the following newbie question. I own a few calculators mostly HPs but use regularly only one of them at one time for a couple of months and then switch to another one and so on. I am wondering what would happen to the batteries in the calculators that I do not use for a long time. Would they leak or get corroded? Is there any sort maintenance that I should do? I know if this is a car I would have to turn on the ignition once in a while do I have to do the same with calculators?

Thanks in advance. Luk

Re: Battery questions
Message #2 Posted by Randy Smith on 10 June 2003, 11:14 p.m.,
in response to message #1 by Luk

I would suggest when storing the calculators you are not currently using to leave the batteries out. That way, if anything does happen, you will only have to rebuild a battery pack or buy new batteries, not have a potentially dead calculator.

I can't speak to exercising calculators. Maybe someone else can chime in.

I second Randy, and I'd add...
Message #3 Posted by Vieira, Luiz C. (Brazil) on 11 June 2003, 12:46 a.m.,
in response to message #2 by Randy Smith

Hi Luk, Randy, guys;

First: what calculators do you have, Luk? Not necessarily their ID numbers and quantities, but their type: graphic, scientific, LCD or LED, or even better: Pioneers, Woodstocks, whatever. Batteries characteristics and their "risk" are not the same.

I agree with Randy about any sort of batteries and I'd add the following suggestion: shorten the calculator's batteries poles while they are resting for longer periods of time, mostly if they are newer, LCD type. Their susceptibility to ESD (Electro Static Discharges) make them potencial victims. The well know electrolytic capacitors leakage probably does not occur in SMT (Surface Mounting Technology) components in this case. I know about tantalum SMD capacitors and I want to ask: are there electrolytic SMD capacitors as well? Are they sealed the same way?

Using (exercising) calculators is something I do not have a "technical" position about. All I can see is that leaving batteries inside continuous-memory type (all new models and some "ancient" ones) will feed RAM, a few capacitors and keyboard sensing circuitry, what gives us a few tens of microamps (ľA), if not less than ten ľA. Replacing batteries with discharged capacitors, and I mean ALL MOS parasite capacitors, will cause a brief current surge through some parts of the circuits. I am not sure how dangerous it is, if it is. If a chip is burned somehow when a battery set is connected under normal to perfect conditions, I take as a weak link in a chain being broken: it would break someday.

Hope this helps. I'd like to read from others; maybe I added some wrong information here and did not realize it.

Luiz C. Vieira - Brazil

Re: I second Randy... - Thanks
Message #4 Posted by Luk on 11 June 2003, 1:11 a.m.,
in response to message #3 by Vieira, Luiz C. (Brazil)

Hello Randy and Luiz,

Thank you so much for the replies. I currently have the 12C, 15C, 16C, 10B, 17BII, 19BII and Casio CFX9850GB. I had always left the batteries inside the calculators even when they were not in use, but from now on I will take them out as you suggested.

The HP's always retain the memory and all the settings but the Casio always resets to default settings when turned on (after being unused for a while).

Cheers, Luk

SMD electrolytic capacitors
Message #5 Posted by Ellis Easley on 18 June 2003, 10:57 a.m.,
in response to message #3 by Vieira, Luiz C. (Brazil)

First, I want to say that tantalum capacitors are also electrolytic - there are aluminum electrolytic capacitors and tantalum electrolytic capacitors (and probably some other types - for instance, some other chemistry might be at work in the "supercaps" that go up to 1 farad and more in a small, low voltage package, they were intended to provide low current for memory backup as an alternative to batteries - I never actually saw them in any equipment, though). Anyway, I understand that in normal discussions, "electrolytic" means aluminum electrolytic and "tantalum" means tantalum electrolytic.

There are SMD (aluminum) electrolytic capacitors. They consist of a cylindrical can mounted on an SMD base. They are not as compact as the same value tantalum capacitor and are usually tall, since they are basically cylindrical cans with a seal at the bottom. I think aluminum electrolytics need to be built this way because they need a pressure relief valve (built into the rubber seal). Aluminum electrolytics have higher leakage and tend to "form" to the voltage they operate at: if they are used at a voltage much lower than the rated voltage, the dielectric tends to re-form in a thinner layer causing the capacitance to increase. If the applied voltage is increased, the thinner dielectric leaks more for a time until a thicker dielectric layer is built up - through "electrolysis" (that's why they are called electrolytic - there is no dielectric layer when they are first made, it is built up by application of voltage and current at the factory). As the dielectric layer becomes thicker, the capacitance decreases. If the voltage is increased too much-too fast, the leakage is so high that gas builds up to a high pressure in the can and the relief valve must vent it to the atmosphere.

Since tantalum capacitors are also electrolytic, they must have a dielectric layer formed by electrolysis also. One plate of the capacitor consists of a porous slug of powdered tantalum metal joined by heat and pressure (sintered) (BTW tantalum has a high melting point, ~3000 degrees C, it is so named because it tantalized metallurgists who tried to extract it from its ore). The other plate is the conductive electrolyte that saturates the slug and is in electrical contact with the metal container. Tantalum capacitors have much lower leakage and can be made with a glass seal (no pressure relief valve) so that's why they can be put in molded SMD packages and dipped wire-leaded packages.

Because of the sintered slug, all parts of the plate are electrically close together, compared to an aluminum electrolytic, where the plate is a roll of foil so the ends of the foil strip are electrically far from the terminal. This is why tantalum capacitors have lower inductance and lower ESR (equivalent series resistance - the resistance presented to an AC current).

There are aluminum electrolytic capacitors with extra-low ESR, these are important for use as filters in high frequency switching power supplies. I think they achieve the lower ESR by having multiple connections along the length of the foil strip to the terminal.

Re: Battery questions
Message #6 Posted by Alex on 11 June 2003, 4:27 p.m.,
in response to message #1 by Luk

Though avoiding battery contact corrosion is a good idea, one should also consider the effect of not having power applied to the electronics for a very long time. It is common for some electrolytic capacitors to fail if left uncharged for a very long time. Thus, the best way to long term store an HP is to periodically take it out and power it up to execise the electrolytic capacitors.

Re: Battery questions
Message #7 Posted by Luk on 11 June 2003, 8:11 p.m.,
in response to message #6 by Alex

Hi Alex,

Thanks for the information. How often do you think we should put the batteries back in and then power up the calculators? Would once every three months be sufficient? (Because of the nature of my job I only use one type of calculator for a couple of months and then switch to another).

Regards, Luk

Re: Battery questions
Message #8 Posted by David Smith on 13 June 2003, 4:49 p.m.,
in response to message #7 by Luk

The more often the merrier, but every three months should be fine.

If you have an HP91/92/97/82143A, etc with the printer make sure you run the printer also. This keeps the paper drive rollers from devloping flat spots, etc. Also run the card readers for the same reason.

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