Power for Desktop PC??

Hi Geen,

While what you suggest is very possible the need for positive and negative supplies and multiple voltages will probably make your power adapter not that much different from the PSU and not that inexpensive. What I have done in my lab is to remove the small 12 volt battery from my inverter and install car batteries to the side. This gives me many hours of use if the power is down. In my case this doesn't happen often and the trickle charger in the inverter usually recharges the car battery over a days time. If you have a situation where the power is off more often you could use a regular car battery charger to speed up the process when power is available. Don't forget you will also have to power your screen and any internet interface device that you may be using.

John

Power is becoming a real pain lately, and moving to another country is a bit extreme... Here is the thing to consider. the "negative voltage" how on earth does that work I mean how do you get a negative voltage to begin with?

Maybe the best way to go about this is get a PSU hook it up to a multi meter and find the components that are responsible for the "negative voltage" and see how it looks and what components are being used. Maybe even take it out make it stand alone "maybe" or not...

That said some boards don't actually need those voltages but again I am not willing to burn a board to find out.

I will look into it some more...  

Hi Geen,

Here is a quick description of how there can be positive and negative voltage in a circuit. I have made a drawing of (2) 12 Volt batteries that are hooked in series. We call the connection between the two batteries the 0 volt point and we make all of our measurements from that point. The top of battery B1 becomes +12 and the bottom of battery B2 becomes -12. Many circuits like to operate with this split or double supply and if the circuit is designed for it there is really no way around it.

John

Hi John

thank you for explaining it to me, I will do a test and see what happens on smaller batteries and then work from that point forwards. Really thanks for the drawing!! It helps a a lot!! 

Much appreciated 

Well illustrated, John.  It seems you are really raising your game.  Let me put it in verbal terms:  If you have a DVM and putting the leads across a battery causes it to register, say, seven-and-a-half volts, interchanging the leads will cause it to register minus-seven-and-a half-volts.  We are keeping the mantissa and inverting the signum.

This is a basic example of Gustav Kirchoff's law.

We measure current through a point.  We measure potential across two points.  This causes us to arbitrarily label some node in the circuit as zero.  Spelling out the acronym, it is a Differential Volt-Meter.  Properly stated, 'voltages' or potentials are always measured at a point with respect to another point.  It's just that EEs have gotten tired of saying 'with respect to ground' all of the time.  Sometimes they abbreviate:  'WRT Gnd.'

Logic guys often assign the lowest potential to zero.  Stereo guys often assign the middle potential as zero.

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Few PCs use the -5, many don't use the -12, some just use the 12V and buck down for the local supplies which are often 3.3, 2.5 or 1.8 volts, nowadays.

So, to illustrate, it we had a 10V supply, and a string of ten equal-valued resistors across it, the difference across each resistor would be one volt, 10/10.  We could measure many different voltages.  Reading across a pair of connected resistors would generate two volts, signum dependant upon which way the leads were applied.  If we were to sum the net of all possible readings, the result would be zero.  If we bump the supply to 20V, then each R would feature a 2V drop.

This allows your beloved 555 to be a relatively stable timer WRT delta supply voltage.  The reference string (three equal resistors, giving us a tap at 1/3 and 2/3 [0/3 and 3/3 at the ends]) is ratiometric.  A higher supply potential both raises the rate at which C is charged and the threshold it must reach in order to switch the output of the 555, keeping the timing relatively constant.  Meditate on the diagram.

When I go camping, sometimes I bring my 1KW pure sine gasoline-powered generator.  I can power both my lappy and a projector and speakers with me so that we can watch art film in the evenings.  Yamaha and Honda both make them, mine's blue, so IIRC it's a Honda.  It's small, about the size of a sewing machine.

Still somewhat noisy.  I isolate it with a couple of extension cords intended for electric lawn-mowers.

Sometimes others at the campsite audibly murmur something about my bring tech along with me camping, calling it contradictory or counter-productive or insomniac.  They have never known the thrill of watching a film like Satyricon or Battleship Potemkin when a storm is brewing.  I find turning up the sound a little helps with this.