Re: [Thinkpad] Re: External battery solution

At 06:19 PM 7/9/2005, you wrote:
>Well the t-23 battery is actually 10.8v, but since that battery pack
>uses the power adapter plug does it indeed need to supply 16v?
>
>mahto

I don't know the details of the TP charging circuits so the following
is a somewhat of a guess.

Typical lead acid rechargeable batteries require about 14 volts
(depends on the temperature of the battery) for changing a nominal
12 volt (6 cell) battery. Other battery types require somewhat
different voltages but still need higher charge voltages than the
nominal (a helicopter I used to fly that had a 24-V NiCad battery
(20 LARGE cells) for starting charged the battery at about 28 VDC).

So, depending on the charge requirements for LiIon batteries and
the amount of headroom the regulators in the charge circuits require,
I would expect that you would need a minimum of 13-13.5 V input to the
power jack to get much charge into a 10.8 V battery. To be safe
and charge at the nominal rate, you would need something on the
order of what the power brick supplies (16 V).

As for another question about running a TP on a solar cell, it
is possible but if you wish to provide the power that a typical
power brick does (72 watts for an A21p or T43p for example), the
solar cell might be bigger and heavier than you would wish to carry
around. For example, I found a 70 Watt panel that has the following
spec:

16.9 Volts (21.5 volts open circuit) 4.14 Amps (4.35 amps short
circuit) 34.1"x25.7"x2.2" 15.4 lbs

Note that the voltage under load may be low as it is for charging a
typical 12 Volt battery system but a custom panel could be
constructed to provide higher voltage at a lower current. Note that
the panel is almost 3 feet long and over 2 ft wide and weighs more
than double a large notebook! Note that the output is NOT regulated
and you would probably have to put in a regulator in-line to protect
the TP charge circuits.

A 40 Watt panel is listed at 20.7 by 25.7 inches. For "affordable"
solar cells, the power scales with area. There are higher power
density cells available (other types of semiconductors or with built-in
solar concentrators) but the costs are "interesting". The 40 watt
panel costs on the order of $200 (US) where the 70 W suggested
price is $400+.

Now, you might be able to get by on a lower power (smaller and cheaper)
panel but the charge time would go up and there is a lower limit
for current below which the notebook would have to be off to
charge (depends on the actual power consumption of the notebook).

Stuart

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Received on Sun Jul 10 09:19:16 2005