Building a car-laptop power adapter

[jeana]

As if I didn't have enough projects to keep me busy, I've become interested in building a car lighter-socket to laptop power adapter.

I know that these exist already, but the ones "for laptops" cost $80 or more! Any good reasons why it costs so much or why I shouldn't build my own?

Though I don't know much about electronics yet, this seems like a very basic project. Suggestions or warnings are welcome!

Jeana

[nilknarf]

I bought a AC-DC power inverter to take care of that. It didn't cost anywhere near $80. The manufacturers just want you to pay more for their proprietary power supplies. You can sometimes find generic adapters that work.

The main issues you have to deal with in building an adapter are,
1. - The actual connection to the laptop
2. - The right voltage on all the pins and making it a steady voltage.

No, there are no really good reasons for them to cost so much.

Being an electronics person myself, I would build one if I had the time.

This isn't exactly a basic project, as you are dealing with something which must be stable or it will fry the laptop. Such power supplies can become very complex, very quickly. If you haven't done much with designing and building electronic circuits, this is definitely a good place to seek advice and possibly get some circuit designs.

To help, we will probably need the output specs of the AC adapter or the power input specs of the laptop, as well as what type of connector is on the laptop or the make/model.

Still want to try this? If you do, we'll certainly help.

Tim

Darn KB

[This message has been edited by nilknarf (edited 08-02-2000).]

[barry glisson]

It is not unusual for alternator out put to vary from 13.2 to as high as 14.8 volts on a lot of cars check yours with a/c on and off lights etc also while adding or removing load. Tthis could save you some grief. barry

[jeana]

Muchas gracias for the input, nilknarf and Barry!

I guess this weekend I'll figure out what I can about the input/output specs, at least... maybe draw up a play schematic based on one published in "The Art of Electronics." Actually, this would be my first experience designing an electronic circuit and perhaps I'd better not start out by frying a laptop http://sysopt.earthweb.com/forum/frown.gif I need a lot of basic equipment, too...seeing how things go, I'm pretty sure I'll end up spending way over $80 on equipment! (but in my household we call that "investment" http://sysopt.earthweb.com/forum/wink.gif) On the other hand, I don't see how I'll ever learn if I don't jump right in.

Well, after I do my homework for this I'll write in again to this thread (probably a couple of weeks.)

-J

[Bovon]

Jeana, just as Nalknarf said, a direct converter would have to be highly stablized-regulated. This means you would have to first up the voltage from 12 -14.8 or so to somewhere above the voltageneeded for the laptop. Using my Dell as an example, it uses 18.?? volts. So, in order to build a regulated supply, I would first have to generate something on the order of 25 volts, then cut it down to size, using regulating circuits. Probably a switching circuit to start with to generate the necessary voltage above the needed voltage, then a well filtered (alternator whine, ect) regulator circuit following. This is the basics. The way I would do it is, build a DC-AC converter, this would produce 120 volts @ 60 cycles, square wave, which any 120 volt device will work with. Sence most Lap Tops do not require heavy current, the design wouldn't need to be really heavy duty, just design it about 50% above the current requirements, at least...the more, the better, given size limitations. Then, just plug your Lap Top adaptor in, and let it work/charge away. This feature also will be beneficial for other purposes also...like charging up a rechargeable flashlight, ect.

Bovon