HP Forum Archive 06

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External charger Message #1 Posted by Arthur Bullard on 19 Sept 2001, 2:54 p.m. Hi, I unearthed an HP65 a little while ago at work, and today I discovered an external battery charger (with battery) for it. I've not seen one of these in the museum, and wondered if anyone could shed any light on it - are they common? Of course, I could be being dim and the charger is already in the museum, in which case sorry :-) Cheers, Arthur

Re: External charger Message #2 Posted by Erik Wahlin on 19 Sept 2001, 3:50 p.m., in response to message #1 by Arthur Bullard The battery charger for the HP-65 is the same as that used for the HP-35,45,55,65,67,70, and 80. They are fairly common.

Re: External charger Message #3 Posted by Arthur Bullard on 19 Sept 2001, 5:07 p.m., in response to message #2 by Erik Wahlin Thanks, I suspected that was probably the case. I wonder if the fact that my 65 is German (the instruction label on the back is in German) is much rarer than the US versions.

Re: External charger Message #4 Posted by Tony Duell (UK) on 19 Sept 2001, 5:44 p.m., in response to message #1 by Arthur Bullard They're not that rare (at least the one for the 'classic' battery pack is not rare) -- I've managed to get 3 of them without really trying (I am _NOT_ a collector). One interesting thing, though. Take it apart (4 screws on the bottom and carefully separate the case). Inside are 4 components -- 2 resistors, a transistor and an LED. It works like this : The classic series mains adapter has a constant-current output. This is connected to the battery pack (to charge it) with one of the resistors in series. The base-emitter junction of the transistor is connected across that resistor, so that when the battery is in place and charging, the transistor turns on. The LED and other resistor are in series between the collector of the transistor and the constant voltage output of the adapter (the line that would supply the calculator logic normally). So that when the transistor turns on, the LED lights up. So far, so good, it's all what you'd expect. The odd part, though, is the construction. There is no PCB. Nor even a tagstrip. The transistor is placed in a cylindrical post moulded in the base of the housing. The LED fits over a plastic riddge with one lead each side. And the whole thing is assembled by just soldering the component wires together. It's a 'birds nest' of components -- the sort of thing you'd find in an experimental setup but not in a production device, normally. These HP 'reserve power packs' must have been hand-built -- I can't think of any machine available at the time that could wire like that. I would have thought it would have been cheaper to use a PCB, though.

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