11 Apr
2001
11 Apr
'01
7:29 p.m.
At 08:00 PM 4/11/01 +0100, you wrote:
Tony's right. You should have the battery in place when trying this.
You'd probably be safe leaving the battery out if you used a power supply
with the output set at a safe voltage (~ 1.2 to 1.5 Volts/cell) but don't
try this with a standard charger. They're seldom regulated and you could
fry something. Leaving the dead battery out and trying to run a HP 2xC
calcualtor on the charger alone is THE biggest cause of dead HP 2xC
caculators.
Bill,
It will probably work since the charging voltage of the battery is
certainly higher than the 15 volts that you would get from using alkaline
or carbon-zinc batteries.
Some machines use the battery as a shunt regulator -- that is to say they
rely on the fact that the voltage across the battery pack, even when
charged from a supply _capable_ of giving out a higher voltage, will be
limited. This is one reason why many HP and TI calculators may be damaged
if you connect the charger without a battery pack in place.
For the original poster, if you insist on using normal primary batteries
(1.5V each), I would start with only 8 of them in series, which should
give you 12V. I would not put 10 in. I have seen devices made with a
battery holder that will take 10 AA cells, and which are supplied with 2
dummy batteries (plastic rods the size of a AA cell, with metal contacts
at the end that are shorted togehter). If you use primary batteries you
use 8, and the 2 dummy batteries to fill up the empty slots. If you use
NiCds, you use 10 of them.
I am told that some HP calculators (the Woodstock HP21 series, for
example) can be damaged if you put primary batteries into the battery
pack. Now, I know how the Woodstock PSU should work (it's a little
transformer-based transistor oscillator with regulation taken from one of
the outputs), and I don't see why it wouldn't regulate properly at 3V
input rather than 2.4V input. But I certainly am not going to risk it :-)
FWIW I don't recommend it but I've run Woodstocks at 3 VDC and even a
little above. A FULLY CHARGED GOOD NiCad will often put out up to 1.55
volts/cell when they're new therefore a new Woodstock battery pack can have
up to 3.1 VDC.
Joe
-tony