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HP Forum Archive 08

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Alkaline batteris vs nickel cadmium
Message #1 Posted by Edwin Morales on 23 Mar 2002, 7:26 p.m.

My hp 31e and hp 34c are working ok with alkaline batteries: 3 volts, no 2.5 volts.

So, it was a hp business or AA batteries 1.5 volts does not exist in 1977 or 1979?

Re: Alkaline batteris vs nickel cadmium
Message #2 Posted by Chan Tran on 23 Mar 2002, 9:00 p.m.,
in response to message #1 by Edwin Morales

The old LED calculators run down battery pretty quick. I think you would have only about 10 hours of operating time with AA batteries on those calculators.

Re: Alkaline batteries vs nickel cadmium
Message #3 Posted by Andrés C. Rodríguez (Argentina) on 24 Mar 2002, 4:30 p.m.,
in response to message #1 by Edwin Morales

At least in my experience with an HP 25, alkalines are OK. I think that the circuitry allows for the not so large difference between a fully charged NiCD (perhaps 1.3V) and a regular alkaline (usually a little over 1.4 V).

The 1.5 V value comes from the old, zinc-carbon (non alkaline) batteries, and is used usually as a convention. A less than 10% tolerance seems almost logical.

While this makes sense to me as an Electronics Engineer, I can offer NO WARRANTY because I don't have any detailed data on the calculators circuitry and proprietary components HP used. This is just my personal opinion. The "C" models may be more sensitive to overvoltage because the batteries are supplying standby power to the memory chips when the calculator is off.

The alkalines may give you some 10 hours of service, while NiCd of the '80s offered about only 2 hours, but a 500 charge-recharge cycles' life. Rechargeables were usual at the time, they were what users tend to expect in the still infant calculator market. I don't think it was a HP business, since at the time HP earned its profit by offering unique and very well executed products at a premium price. The batteries will add little to such strategy. (Things have changed in the last decades...)

PS: Also see other threads and postings about this same matter.

Re: Alkaline batteris vs nickel cadmium
Message #4 Posted by Ellis Easley on 25 Mar 2002, 4:45 p.m.,
in response to message #1 by Edwin Morales

I have some TI calculators (2500, 2550, 2500II) from around 1973 on that give the user a choice of using NiCads or alkaline (or carbon-zinc) batteries. Apparently, TI shipped them with regular AA NiCads and a recharger. The 2500 and 2550 take 3 NiCads, the 2500II takes 2. If you want to use regular batteries, you put 4 in the 2500 and 2550, 2 in the 2500II but in two different holders. When the regular batteries are installed, since one or two additional holders are in use, an additional cell operates a switch. I don't know if this just disconnects the charger jack or if it conditions the power supply for a different voltage.

I think HP (and others) used NiCads because it was a fairly high drain application and having to buy batteries all the time would be an inconvenience. As for the special battery packs that HP used (and that TI went to) - I think that serves two purposes: controls the specification of the cells used (high capacity, and TI used the high charging rate), and also the plastic shell helps contain the chemicals when they finally leak. I fault both companies for encouraging people to leave the cells in the calculator in storage and leaving the calculators on charge indefinitely, but I guess they were still learning.

Re: Alkaline batteris vs nickel cadmium
Message #5 Posted by aruid on 25 Mar 2002, 7:51 p.m.,
in response to message #4 by Ellis Easley

I have 2500 that only has a built-in 3 cell ni-cad pack (it still holds good charge!). The charger plugs into a jack in the unit to charge the batteries. The only way to remove the batteries out of my TI 2500 is to remove 4 screws and seperate the two sections of the calculator then cut the two wires going into the battery pack.

I thought all of the TI 2500s were like this.

Re: Alkaline batteris vs nickel cadmium
Message #6 Posted by Ellis Easley on 26 Mar 2002, 3:35 a.m.,
in response to message #5 by aruid

The ones I have are the only ones I have seen, except I think a high school friend might have had a 2500 in the 70's! They all have the same battery cover except it goes on in the opposite direction on the 2550 vs. the others.

Here is an interesting difference: my 2500 display has LEDs that look like individual dots while my 2500II display has continuous segments. I have two 2550's and their displays are different as above. I guess this was a "running change" TI made.

First I got the 2500II by itself and later the 2500 with its booklet and was surprised to learn the "tricks" that TI described to extend the usefulness of the calculator, using the constant feature to re-use the first parameter as the second with "*" to square numbers or get higher integer powers; with "/", twice, to accomplish "1/x"; and finding square roots by repeatedly dividing by a guess, adding the guess, and dividing by 2 to get a closer estimate. That last one makes you appreciate the memory when it is available!

I had to read those tricks in the TI booklet, but when someone raised the issue of the changing accuracy (precision?) of "y^x" on HP calculators recently, I figured out how to do it on the 9100 on my own, re-acquainting myself with the slide rule in the process - y^x=e^(ln(y)*x) - and this lets you find 10^x, since the 9100 only has ln(x), e^x, and log(x). I first looked in the Museum 9100 article for this "workaround" because I thought I had read it there, but if it is there, I missed it.

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