>> You wouldn't be able to load the tray with cells like that. State of the
>> art these days is 1.8 Ah for NiMH AA size cells. Maybe 2.0 Ah (= 2000
mAh)
>> by now, but certainly not 6-7 Ah).
> that was a total, frank! i mean 4 x state of the art cells of course
I see your point. However, you can't assume a total like that. 1800 mAh
means
"This cell will provide a current of 1800 mA for one hour before its
voltage drops below the discharge voltage (usually 1.1 volts or so)".
Serially-connected cells do neither provide a longer time nor a higher
current, but a higher voltage. Thus the mAh remain the same and the 4 cells
in the pack will last just as long as one cell would if
your Newton was able to work on a diet of 1.2 volts.
Theoretically you can provide a longer time for a given current or a higher
current for a given time (and thus more mAh) by connecting
cells parallel, but this is nothing I'd recommend unless you can
guarantee they are from the
same manufacturing batch and they will always have the same
charge state. Connecting a fully charged and a fully
discharged cell that way can harm or even destroy the cells.
>wait a sec, wasnt there a hack for that? i mean, my question was - can you
>alter the charging mechanism to accept the re-charging of cells in a
battery
>tray? will the unit melt or will it cope with the heat?
As to heat, there's no problem. There wouldn't be much more heat than what
you have in the original rechargeable pack.
To make the Newton charge cells in the battery tray,
you need to add two contacts which it
doesn't originally have and connect a temperature-dependant resistor to
the new contacts. It is mandatory that this resistor has *exactly* the
same specs as the original one, otherwise the charge control electronics
inside the Newton would be misled and it would charge too much or too
little.
There is a page somewhere with german instructions of how to do this, I
dimly remember it was somewhere at www.newton-lifestyle.de or so. However,
I think they didn't use the oringinal type resistor, so I'd proceed with
care.
Still, even if you manage to do this, you'd give up your second line of
defense. The original MP2k and eMate battery packs have a thermistor
connected serially between two cells that will effectively stop all current
into and out of the pack if a certain temperature is reached. A thermistor
is something like a gremlin with a thermometer in one hand and a switch
in the other hand. The switch is set to "off" if the temperature is
reached and back to "on" when it falls below that value.
Electrically the packs look like what you see below (you might want
to set your font to a non-proportional one like Courier to view this
in all its beauty).
Whatever modification you do to the battery tray, this is what should
be the result if you plan to remain on the safe side of life:
+----------+ +----------+
+-------| + Cell 2 |--------| + Cell 1 |------+----( GND
| +----------+ +----------+ |
| +----( A
| |
+---+ +---+
| T | | R |
+---+ +---+
| |
| +----( B
| +----------+ +----------+
+-------| Cell 3 + |--------| Cell 4 + |-----------( +
+----------+ +----------+
GND: Negative battery contact
A: Resistor contact 1, electrically wired to GND
B: Resistor contact 2
+: Positive battery contact
R: Temperature dependant resistor
T: Thermistor
Good luck!
Frank
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