HHC 2014

Roger Hill rhill at siue.edu
Sat Jul 12 18:14:12 MDT 2014

Hi Richard S and all,

I don't know about probabilities outside of [0,1], but I do remember
rejuvinating NiCad cells from my HP-41 printer.  Seems that the cells
developed internal conducting filaments and gradually shorted
themselves out.  The battery pack had to be taken apart enough so
that one could get at each individual cell (I believe each cell was
about 1.5V).  I used a model train power supply that would supply 12V
DC at around 3A (didn't have a circult breaker but it did have a
current limiter) and **momentarily** touched wires from the terminals
to the ailing cell (+ to + and - to -, as if you were trying to
charge the cell).  The idea was that the zappings would "burn out"
the filaments.  After a few zappings I would measure the voltage of
the cell and see if it it stayed steady or slowly dropped to zero; if
the latter I would repeat the zappings.  If the cell held its voltage
I would put everything back together and charge the pack normally.

(WARNING: Usual warning and disclaimer; wearing glasses at least
would be a good idea...  I would also be wary of using fancy modern
solid-state model train power supplies.  My power supply was an old
toy train transformer with selenium rectifier, in series with an auto
headlamp buib for a current limiter.)  

There was a period of some years where I only used the printer about
once a year, and each time I found one or more cells that needed
zapping.  I was always able to get the cells going again, at least
for the time I needed to use the printer.

I don't think I ever tried it with HP-67 cells, but I would imagine
it ought to work -- but I don't know after how many years of

-- Roger

------------ On richard nineteenfortyone's message ------------
> Is 100% the best you could do?   I heard that there is some kind
> of meaning associated with probabilities outside of [0, 1], but I
> am not advanced enough to know about stuff like that.   I
> certainly plan to be there.
> Another matter: does anybody remember the procedure for restoring
> NiCad cells from the HP-67 days?  This is an ongoing problem with
> old ham radios, and a bit of technology transfer is in order.

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