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12V Auto power converter schematic needed for laptop

My laptop which is a Lenovo (IBM) T41 needs a 12V auto power adaptor.
I've been using a 200W inverter, but that thing likes to run my car
battery dead, not to mention that it is constantly screetching an
alarm as soon as the car battery is not fully charged. I have never
understood why it drains my battery when it's just charging the
computer battery, (with computer shut off), but it does.

Anyhow, I was told that I need to get a direct 12V charger for the
computer and eliminate that annoying inverter. I was shocked when I
saw the price for this charger at $140. (Almost as much as I paid for
the computer). Screw that, I already have a cig lighter socket and
the plug for the computer on a wire. All I need is the schematic to
step the voltage to whatever it needs to be. (which I still have to
find out). Anyone know where I might locate such a schematic online?
I'm sure it's a very simple circuit.

Thanks
 
R

Rich Grise

My laptop which is a Lenovo (IBM) T41 needs a 12V auto power adaptor.
I've been using a 200W inverter, but that thing likes to run my car
battery dead, not to mention that it is constantly screetching an
alarm as soon as the car battery is not fully charged. I have never
understood why it drains my battery when it's just charging the
computer battery, (with computer shut off), but it does.

Anyhow, I was told that I need to get a direct 12V charger for the
computer and eliminate that annoying inverter. I was shocked when I
saw the price for this charger at $140. (Almost as much as I paid for
the computer). Screw that, I already have a cig lighter socket and
the plug for the computer on a wire. All I need is the schematic to
step the voltage to whatever it needs to be. (which I still have to
find out). Anyone know where I might locate such a schematic online?
I'm sure it's a very simple circuit.
Adapters for the 12V lighter socket are off-the-shelf these days.

Good Luck!
Rich
 
M

mike

My laptop which is a Lenovo (IBM) T41 needs a 12V auto power adaptor.
I've been using a 200W inverter, but that thing likes to run my car
battery dead, not to mention that it is constantly screetching an
alarm as soon as the car battery is not fully charged. I have never
understood why it drains my battery when it's just charging the
computer battery, (with computer shut off), but it does.

Anyhow, I was told that I need to get a direct 12V charger for the
computer and eliminate that annoying inverter. I was shocked when I
saw the price for this charger at $140. (Almost as much as I paid for
the computer). Screw that, I already have a cig lighter socket and
the plug for the computer on a wire. All I need is the schematic to
step the voltage to whatever it needs to be. (which I still have to
find out). Anyone know where I might locate such a schematic online?
I'm sure it's a very simple circuit.

Thanks
If you have the skills to (successfully) implement a voltage converter,
you have the skills and equipment to diagnose the problem.
Do the math. I'm too lazy to look up the numbers your your particular
machine,
but, to use round numbers, if your battery is 60WH, it might take
120WH to charge it from 12v stepped up to 120v, stepped down to 18V,
stepped again by the internal charging inverter.
That's 10AH, which is a significant percentage of your car battery when
it was new.
200W inverters come in various efficiencies. Get out your meter and
determine the efficiency of yours...as well as the standby consumption.
You can't leave the/any inverter connected and running over night.

Best one I've seen draws 140mA unloaded. Most are 5x that or more.
Turn it off when not in use.
And the wall charger uses standby juice, as does the internal charging
circuitry.

The screeching is more likely caused by using wire that's too small.
Your meter will tell you how many volts at the inverter input.
It should be
almost the same as at the battery under load. If it's not, fix that.

Building a car inverter is a difficult problem for at least two reasons.
1) The input can go from 10V to 15V or so. That's too close to the required
output voltage for a simple regulator. Designs exist, but they're not
as simple.
2) The auto electrical system is an EXTREMELY hostile environment.
It takes a lot of design effort to keep it from blowing up.
Read this:
http://www.littelfuse.com/data/en/Application_Notes/an9312.pdf

If you're using any of the hardware ports on your computer, like audio
out, ground loops exist that can fry your laptop with voltage spikes.

So, if you take a random design off the web, build it without paying
attention
to all the subtle effects of the physical wiring, ignore the hostile
environment and don't thoroughly test it under conditions likely to
exist in the electrical system, you're asking for a fried laptop.
YMMV

For most of us, the 120VAC inverter is a good solution that will work
on your next computer and the one after that.
Just fix the voltage drop problem and turn it off when not in use.
 
M

Michael Karas

Adapters for the 12V lighter socket are off-the-shelf these days.

Good Luck!
Rich

And low cost models are available from eBay as pointed out by another
poster. Some models are universal in that they come with a set of eight
or nine adapter plugs that permit use with virtually all main stream
laptops. The universal ones also have a slide switch available that
allows setting the output voltage to be compatible with the particular
laptop. All that for just a few $$$ US.
 
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