Ok, I am definately starting to look for parts for my upcoming MP3 system. I found a
p-133 laptop w/ a broken lcd for a bargain price. My question is: If I am not mistaken, laptops run on DC power (it has an
AC adaptor). It seems kind of crazy to run an inverter to take the DC to AC and then plug in an adaptor to take the AC to DC. Would it work to somehow wire the notebook more directly? (don't bust my balls if this is a stupid question, I am much better w/ computers than w/ electricity - I will be getting help in that dept. ;)
All computers run on DC power, so it's generally just stupid to use an inverter anyway, so congratulations for not wanting to go the WTS (white trash solution) route. Now then, for your question: What you need to do is figure out what kind of power the laptop takes. There should be a DC power in, and if you're lucky, it'll say right there what input it takes. Then it's just a matter of stepping the voltage from the car battery up or down to match that voltage. I'm not the person to ask on this, as I'm not an AC/DC expert either. One thing you can do that would probably be easier, but may or may not be cheaper, is buy a car adapter for your laptop. If you know what brand the laptop is, you may be able to find an adaptor, so look around.
I have never heard of a laptop using AC power.. they usually come with a transformer that converts the AC power from the wall to 12VDC... or something similar.. I suggest you do that Jupiter said and just buy a car adapter for the laptop..
Oh yeah.. and jupiter.. although DC-DC power supplies are better, you can't really label someone that uses a DC-AC power supply stupid.. I know I used one because it was neater and I could remove the computer and use it in the house quite quickly.. its not as if the conversion is inefficient and looses a great deal of power... there is only a slight power loss from DC-AC conversion and thats through heat.. which is very minimal..
I suppose my judgement was a bit hasty, but I still think that the DC-AC-DC method is impractical. First of all, a good DC-DC <a href="http://scott.kincaid.net/needpwr.htm">power supply</a> is available for $35 ($10 less if you care to build it yourself), which is about the same as you'd expect to pay for an AT power supply (not including the inverter), so that eliminates any cost concerns. Here's how it works out: An AT power supply plus an inverter will run you at least $90. An AT power supply (for indoor use) plus a DC power supply (for car use) will run you about $65. Second, AC power supplies are, in comparison, embarassingly large, and when you add an inverter, that just increases the amount of wasted space that much more. I do plan to use my player inside, but by simply having the board's power in easily accessible, and keeping the AC supply next to my home stereo, and the DC supply behind me car stereo. Just snap & go.
OK I've got an accessory (as opposed to battery) to +12V DC regulator (my board regulates +12 down to 5, 3.3, and processor voltage) so I don't have to remember to turn off the system with the car. The problem is that I can't listen to the system without actually starting the engine because with the key in the accessory position, but no alternator turning, you only get the +12 off the battery, which immediately drops the system out of regulation (even with the LDO regulator). I am trying to figure out an efficient way of doing this, but I need roughly 5+ Amps at startup (mostly due to HD spin up). I was thinking of using a relay, but that is soo ugly. Any ideas?