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On 30 Dec 2003 10:32:28 -0800,
Dan wrote:
"Fred Miller" wrote in message ...
Slightly Off topic but I know someone here can answer the question.

I am trying to run a Dell Inspiron 5100 in my truck using a small inverter
but all I do is blow fuses in the truck. This is a 6 month old Chev 1500 in
excellent condition.

My "brick" 110 V power supply reads:

AC 100-240 V - 103-109 VA 50-60Hz
DC 20 V 4.5 A

What size inverter in watts do I need to use with this power supply?
Can a cigar lighter outlet supply the required power?

TIA for your help.

Whether in a truck or a boat, it's inefficient to convert DC to AC
back to DC. You'd be better off powering a tower or laptop computer
directly from the DC off the vehicle. A trip to Radio Shack should
provide all the parts needed. An AT power supply for a tower computer
has +12V, -12V, +5V, -5V, and ground. For the +12V and -12V, you will
need to filter and regulate the DC feed from your battery bank. The
+5V and -5V can be derived from your filtered 12V side, just step the
voltage down via a stepdown transformer and regulate it. Make sure to
filter the ground as well or gremlins will get your electronics. Now
take the wires from your existing PC power supply and connect them to
your new power supply. This is overly simplified, but I think the
whole project can be built from schematics found in the Radio Shack
project books. Laptops are a little bit trickier. Find the voltage
rating of the battery, then step the 12V DC of the vehicle to the
proper voltage. The tricky part is determining if the voltage
regulator is built into the battery or the laptop itself. You may
have to make the voltage regulator yourself. If you don't need the
regulator, connect your new power supply to the battery contact pads
on the laptop. Just remember that you will definately void any
warranty doing this.

Dan Schiro
M/V Sea Ranch
Pensacola Sail and Power Squadron


In order to use a transformer to step the voltage down, you must by
definition be using AC. A transformer doesn't work with a DC level.


Rather than go to the hassle of designing and building your own
powersupplies, you can buy std AT style supplies that take 12VDC as an
input, but usually in limited power forms, don't try powering your 500W
game monster machine from one. Expect to pay $200 and up for one.

For the laptop, most manufacturers make a 12V car powersupply as an
option. If not, then Targus among others, will happily sell you one.

The downside to low voltage DC of course, is the I2R losses in the
cables, 120VAC may lose some in the translation from DC-AC, but it has
the advantage of low loss with relatively small gauge wire.



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--
Jim Richardson http://www.eskimo.com/~warlock
Those who live by the sword are shot by those who don't.