Re: [NTLK] eMate Battery Project

From: Frank Gruendel (newtontalk_at_pda-soft.de)
Date: Wed Jan 04 2006 - 16:25:47 PST


> 1. What happens when the batteries short out, fire, explosion,
> ***out-of-body experience ?

Each of this can happen. I do not have personal experience with
out of body experiences, but I'd think that if you were very close to
four AA cells exploding simultaneously you might be out of your body
quite fast ;-)

> 2. I wonder if early eMates were designed without the PolyCell
> and they added it later out of experience ?

To the best of my knowledge, no. All eMate batteries I have ever seen
had the polyswitch.

> 3. I used RadioShack(TM) 2500 mAH AA cells. I think the original
batts
> were only like 1500 mAH or so but my old ones were unmarked, so do you
> see any issues with using the higher mAH's ?

The original cells are 1200mAh. It is not a problem whatsoever to use
cells with higher capacity as long as the cell technology remains the
same. In other words, only replace NiCad cells with NiCad cells and
NiMH cells (as in your eMate's pack) with NiMH cells.

The charge circuitry of the Newton 2000/2100 and the eMate can handle
higher capacity cells easily. The only difference you will notice is
that
charging 2500mAh cells will take more than twice as long as charging
an original pack.

> 4. Why the variation between 1.2 vs. 1.5 VDC in rechargable
> vs. standard batteries,

This is a chemical issue. NiCad and NiMH chemistry will only be good for
1.2 Volt, Alkaline chemistry will be good for 1.5 Volt. As a matter of
fact
a fully charged cell can often put out a voltage that's a bit higher
than
1.2 Volt.

> and is this going to be a charging problem form me to use the
> RadioShack batteries with the standard eMate or Newton charger?

No, it's not. Voltage-wise the cells you used are identical to the
originals. Just make sure you won't accidently put alkalines into your
battery holder unless you have a spare Newton and a spare life at your
disposal.

> I'm wondering what
> is the "purpose" of the black plastic sleeve with the two metal
> retaining clips is for into which the green shrink-wrapped original
> batteries are housed?

No idea. I have seen eMates whose batteries did not have that sleeve.
Maybe Apple thought that a mere layer of heat shrink tubing wasn't
enough protection. Or maybe US laws require battery packs to have some
kind of protection against force from the outside (or exploding cells).

> I wonder if the early eMates were catching on fire or something, and
the
> black sleeve was intended to contain the temperatures of the batteries
> more accurately ?

I consider this hardly likely. If they actually were catching fire at
some time, adding a polyswitch with an appropriate temperature value
would have solved this problem for good.

Frank

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