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HP Forum Archive 10

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Woodstock (HP-25) battery packs
Message #1 Posted by Robert Burnham on 23 Feb 2003, 5:05 p.m.

Got the battery pack apart and the leaky pair of NiCds removed. I notice that one end of the batteries has been soldered together with a strip to connect + to - .

When I reload the pack with new batteries, is it necessary to have the new batteries similarly connected? In other words, will the tensioning spring at the foot (non-contact end) of the pack work as an electrical bridge between the two batteries by itself -- or must the strip also be attached to guarantee good electrical connectivity?

Second, if the connecting strip is needed, what's a good material to use? And is there a non-soldering way to attach it? I'm afraid of cooking the battery, since my soldering skills are about zip (last experience: a botched Heathkit roughly 40 years ago).

Third, what's a good solvent or cleaner for the contacts on the calculator itself? And also for the tensioning spring, which has picked up a bit of goober from the battery?

(Sorry for the newbie questions. At least I got the polarity business straight...)

Thanks!

      
Re: Woodstock (HP-25) battery packs
Message #2 Posted by Dave on 23 Feb 2003, 5:46 p.m.,
in response to message #1 by Robert Burnham

You do not need the soldered connector. Just get the polarity right.

      
Re: Woodstock (HP-25) battery packs
Message #3 Posted by Gordon Dyer on 23 Feb 2003, 6:20 p.m.,
in response to message #1 by Robert Burnham

I use a rebuilt HP-25 battery pack with just the spring fitted and NiMH batteries.

      
Re: Woodstock (HP-25) battery packs
Message #4 Posted by David Smith on 23 Feb 2003, 8:38 p.m.,
in response to message #1 by Robert Burnham

You really are better off with the strap... if the spring alone does not make good contact, the pack open circuits, the internal machine voltage rises to potentially destructive levels when connected to the charger.

Some early HP packs just use the spring. Later ones added a tight fitting strap. Finally they went to a strap with some play in it. The cells need to be able to move independently to assure good contact with the potentially uneven battery contacts in the machine.

One should NEVER solder to the batteries... it can damage them and a damaged battery can lead to a dead machine. Best to get them spot welded together at a battery store.

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