From: W. Sierke (ws_at_senet.com.au)
Date: Wed Sep 03 2003 - 22:42:49 PDT
Hi,
New eMate user, here. Well, almost. I recently bought one for my partner to
use for her University studies, thinking she would be able to use it like a
small laptop, which is indeed how she has been using it. Prior to this my
only
awareness of the Newton series of devices was by virtue of its infamous
handwriting recognition inability. Despite only having had contact for a
short time with an eMate device and not an actual Newton, I realise now what
an unfortunate result it is that Apple's creativity and ingenuity wasn't
properly recognised by a larger audience. All the more so since I myself
recently became the owner of an iPaq 5455 (inbuilt 802.11b, Bluetooth). The
Pocket PC OS pales in comparison. I could list all the problems and
annoyances I have discovered with the iPaq in the short time I've owned it,
but this message is turning out quite long enough as it is!
Anyhow, so much for the introduction. I wanted to relate my experience with
restoring the eMate's battery pack in case it may be of use to others with
failing battery packs.
The eMate was purchased from a school and I have no idea how it was
maintained - mostly run on power or regularly used on battery, etc. The main
problem was that while it appeared to charge up ok, it wouldn't run for very
long on battery. I researched the options for replacing/repairing the
battery pack and of course found Frank Gruendel's excellent material on the
matter and so resigned myself to replacing the cells in the battery pack.
Following Frank's advice I was determined to use cells with solder tabs but
it was turning out to be a little problematic to locate some quickly.
Meanwhile my partner was anxious to have the eMate ready for use, having
been somewhat embarrassed when her first attempt at using it at a lecture
resulted in her powering it on and briefly seeing the message I'd left on it
the night before: "I think the batteries are a bit stuffed! Better take a
notepad!" (I thought she would power it up briefly before she left for Uni
that morning! :).
As I was not having much success locating the tabbed cells, after a few days
I thought I might at least start disassembling the pack, ready for repair,
with the idea that that might inspire me to put a bit more effort into
finding some cells and getting the job finished. I got to the point where
I'd removed all the exterior packing from the battery pack and was left with
just the cells themselves, still assembled, the lead and connector and a now
floating thermistor.
Out of interest (I'm an electronics engineer by trade) I thought I'd just
check what state the individual cells were in, since the eMate seemed to be
happy to charge them, and would report them to be at full charge for a short
while after which the charge level would rapidly decline (over about 5
minutes) until it shut itself off. I made an opening in the remaining
plastic covering each pair of cells and checked the voltage on each. Three
of them seemed to be at full charge (around 1.3V) while the fourth read
zero.
The zero Volts result gave me a glimmer of hope, at least the cell hadn't
become reverse-charged. Next I thought I'd see what that cell would do under
a light charging current. I grabbed a 5V power pack and applied it to the
cell via a 100 ohm resistor to give me a 50mA current limit. I monitored the
cell's voltage and watched it slowly rise and before long it had levelled
out at about 1.35V. I removed the charging circuit and checked the terminal
voltage and it held up at around 1.2V. Next I decided I would try and give
the cell a full charge and see how well it would hold up under load, so I
used a 33 ohm resistor to charge at about 110mA and left the cell charging
for about 12 hours or so. I removed the charge circuit and applied a 2.5 ohm
load (4 x 10 ohm in parallel) as a (approx) 500mA load to the cell. I
monitored the cell's terminal voltage and it held at around 1.05V, dropping
to about 1.0V after 30 minutes. I missed the other interim readings I'd
meant to take and when I next checked about 90 minutes later the reading was
down to 0.25V. When I removed the load, the voltage read as nearly 1.3V. I
thought that wasn't too bad a sign.
Next I did some more googling and found a site that suggested a
reconditioning technique for nickel-based batteries: a 1C discharge to 1.0V
terminal voltage, then a lower rate (not specified) discharge to 0.4V. First
I grabbed a 3.3 ohm 5W resistor and gave the cell a quick charge at about
1.1A for about an hour (being careful not to overcharge the cell at such a
high charge rate). Then I used a 1 ohm 5W resistor and individually
discharged all the cells down to around 1.0V, followed by a 10 ohm until
they were each down to about 0.4V under load. This was followed with another
quick charge (carefully monitored) for each cell. Then the pack was
reassembled and reinstalled into the eMate.
Lo and behold! We had the eMate running for hours and hours (with lots of
backlight usage) before the battery level indicator dropped it's first
"notch". It took a few more hours usage to get the level indicator to drop
down to around 60-70%. At that point I decided to give the batteries a
recharge in the eMate so in went the power lead. My partner wanted to use it
the next day so it has been back in her hands since.
I hope to have the chance to do some more battery performance checks soon
and report them here if people are interested. I'm certainly pleased to have
been able to recover the battery pack to some kind of usable state. Still,
we'll have to see how well it holds up. I'm still tempted to replace the
cells, particularly in order to get some 1800mAh cells in there (ooh, 50%
longer usage! :) but at least it's not currently on my list of "get this
done or suffer the consequences" tasks! :)
Wayne
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