Increase voltage using capactior etc

The current handling for those ports will not supply a fan..

You'd be luck if you didn't short the port.

since this is a laptop, you must have access to the power plug ?

"

The serial port has no 5V output, you are measuring a data line. As you are seeing more than 5V between it and the PS2 port which *does* have a

5V line, it must be negative, not the +5V you think it is!

As expected, see below under 'Modders'.

One can double a voltage using a switched capacitor converter but not easily for the sort of current a fan needs. Mistaking -5V for +5V does not lead to confidence in your skills with a multimeter and unless you *have* basic electronics skills, building a boost converter, (even from a kit) is not going to go too well. It would use an inductor for energy storage and voltage conversion, not a capacitor. Caps are good for keeping the voltage nearly the same while the current varies a lot, more or less the opposite of what a boost converter has to do. Anyone who's learnt network engineering can learn electronics if sufficiently motivated but this particular part of your project is not a good place to start.

Small kit projects where failure only smokes a few cheap and easily replaceable parts or building circuits from components on a solderless breadboard is a good start, not a project you've already invested a lot of time into where you are risking a laptop main board that you cant easily replace (unless you've got another identical laptop) and whatever camera card or USB stick you are planning to load the photos from).

What is the power supply voltage of the laptop? (I'm assuming you have removed the battery.) With no battery to charge, it should have plenty of spare current for fans, you just need to (A) switch them on when you have +5V on the PS2 port and (B) regulate the voltage so you don't blow them and they aren't too noisy. It may even be possible to wire your fans in series if they are identical and the PSU is in the 18 to 24V range (with a smoothing capacitor across each fan to keep them happy). Linear regulators convert excess voltage into heat so if they can be avoided when you are trying to reduce the heat, it would be nice.

A simple transistor switch in the ground wire to the fan or fans, controlled by the +5V you found on the PS2 port, would switch them on and off with the main power button. You also need a couple of resistors to make the transistor switch operate correctly. More details if/when you reply with the PSU voltage.

*DONT* COPY THE MODDERS, if there isn't enough load on the 5V rail to handle the extra current from the 12V rail via the fans it will blow the board. Its normally OK on a desktop PC, but I'd still not recommend it. On a laptop its criminally stupid to do it that way, so always run fans between a proper supply and ground. You got lucky the serial port couldn't sink any significant current . . .

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Ian Malcolm.   London, ENGLAND.  (NEWSGROUP REPLY PREFERRED)
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Not really.

Your meter with a >1Mohm input impedance was a poor model for what you connected to those points. Measure it again with the actual load connected.

Ah. The old >100% efficiency ploy.

As Ian noted, you probably integrated a pulse train as you already *had* capacitance in your hi-z measurement which gave you the reading you did see.

An oscilloscope and some (load) resistors would be good things to have to sort this out. If all you have is a meter, you can see which lines **aren't** DC lines by putting a capacitor-coupled AC voltmeter on a point.

not really good, the serial port cant supply much power.

with just the 5V supply from the ps/2 the fans will spin slowly and probbly start themselves. if you need more voltage look at using a LM7812 (or just a resistor) to reduce the DC that the laptop runs off down to

12V