HP Forum Archive 13

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1600 mAh 1.2 V NiMH Batteries for an HP-25C Message #1 Posted by Albert on 12 Sept 2003, 2:59 p.m. Hi all, I know, this issue was already asked long time ago and far away; unfortunately, I don't remember when and where... Let's go: Are 1600 mAh 1.2 V NiMH Batteries dangerous for an HP-25C? I mean, only use; recharging will be performed outside calculator. Original pack is Ni-Cd 1.2 V 750 or 600 mAh. Thanks, Albert

Re: 1600 mAh 1.2 V NiMH Batteries for an HP-25C Message #2 Posted by Randy Sloyer on 12 Sept 2003, 7:38 p.m., in response to message #1 by Albert To quote the Nike ads, Just Do It. You already know the #1 rule - never charge in the calculator. With that law of calculator preservation firmly established, any 1.2-1.5 Volt AA sized source will do fine. The calculator doesn't know and doesn't care, but you will when they last two times longer...

Re: 1600 mAh 1.2 V NiMH Batteries for an HP-25C Message #3 Posted by PeterL on 14 Sept 2003, 12:46 p.m., in response to message #2 by Randy Sloyer Hi there, ...never charge in the calculator.... Since I didn' knew that rule, it killed my HP25 after three Years charging them in the calculator. :-( 73 Peter

Re: 1600 mAh 1.2 V NiMH Batteries for an HP-25C Message #4 Posted by David Smith on 13 Sept 2003, 12:45 p.m., in response to message #1 by Albert Yes, they will work just fine. Even better are the 1800maH cells. There are some supposedly 2100-2300maH AA cells out there, but testing and users seem to indicate that they are no better than the 1800 maH... must be marketing milliamp hours (2300 mmaH). Although they will charge just fine in the machine, we all know that it is best to avoid connecting your Woodstock machines to the evil power plug. If you MUST do it, try to make sure that the battery pack is making contact (LEDs light up) and leave the machine on while charging. The increased load will help keep the voltage down. Remember that these batteries require 3 times as long to fully charge as the originals.

Re: 1600 mAh 1.2 V NiMH Batteries for an HP-25C Message #5 Posted by Tom Scott on 13 Sept 2003, 2:02 p.m., in response to message #4 by David Smith Sorry if this has been discussed many times before, but what is the problem connecting a Woodstock to the power line? Thanks, Tom Scott

Re: 1600 mAh 1.2 V NiMH Batteries for an HP-25C Message #6 Posted by Albert on 13 Sept 2003, 5:41 p.m., in response to message #5 by Tom Scott Let's see, Internal Integrated Circuits (IC) of calculator are connected directly to the power supply. If you forget batteries out while power supply is connected, the ICs will be fried. The reason is the following: in woodstock calculators , the AC power supply adapter doesn't have the rectifier itself, instead of that, it is the machine with a single diode and a resistor who converts AC voltage in order to charge the battery pack. Unfortunately, the same circuit is connected to the whole ICs set of calculator without any kind of protection. In fact, battery pack must play the capacitor role. Without batteries, internal circuits are exposed to high voltage/current combination, very dangerous and lethal gift. Regards, Albert

Re: 1600 mAh 1.2 V NiMH Batteries for an HP-25C Message #7 Posted by George on 14 Sept 2003, 10:09 a.m., in response to message #6 by Albert Does this "rule" also apply t the classics?

Re: 1600 mAh 1.2 V NiMH Batteries for an HP-25C Message #8 Posted by Albert on 14 Sept 2003, 11:45 a.m., in response to message #7 by George More or less ... Not 100 * 100, but I suggest you to follow that rule always if possible. Classic AC power adapter has a diode bridge rectifier inside. In addition, classics are protected because they are 3 input contacts (2 positives (+) and Ground - GND). First (+)ve with 15 Vdc or V= to charge batteries and the second one with 3.6 Vdc to operate with the machine safely. Therefore, charging battery pack circuit is isolated from internal machine ICs. For more information, please see explanations on the following HP Museum link: http://www.hpmuseum.org/batts/battery.htm -> Classics. Anyway: Avoid charge battery pack without batteries in! Albert

Re: 1600 mAh 1.2 V NiMH Batteries for an HP-25C Message #9 Posted by George on 14 Sept 2003, 1:44 p.m., in response to message #8 by Albert Thanks for the info. I have been selling off some of my collection of HP calcs. and would like to get a HP45 or HP55 to "play" with. Hence my interest in this thread.

Re: 1600 mAh 1.2 V NiMH Batteries for an HP-25C Message #10 Posted by Albert on 14 Sept 2003, 2:58 p.m., in response to message #8 by Albert Misprint: Wrong: "Anyway: Avoid charge battery pack without batteries in!" Right: "Anyway: Avoid use the machine without batteries in AND AC Power Adapter connected!" Sorry, Albert.

Re: 1600 mAh 1.2 V NiMH Batteries for an HP-25C Message #11 Posted by David Smith on 14 Sept 2003, 3:07 p.m., in response to message #7 by George The classic chargers have a dual supply/volatge regulator built in. You can run them just fine without the battery pack installed... except for the card reader machines. These machines have a direct connection to the unregulated battery supply to the card reader chip. Also they need the extra current from the battery to run the reader motor.

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