Testing Power Supplies! Re: Norsk Data Nord-10/S restoration

[John Lawson]

On Tue, 16 Nov 2004, Joe R. wrote:


>  OK I just picked up some computers with 150 Amp 5 volt supplies. Now 
> figure out the necessary resistrance and wattage and go find me a 
> resistor :-)


   Oh NO!! not (gasp!) OHM'S LAWWWW......

   Lessee - 5 times 150 is, um... 14.2 carry the three decimal 05, 
differentiating and simplifying - square root of of the product modulo 
3.14159265....   ummmm....

    oh yeah!   750 watts, give or take a microjoule.

    Okay, now 750 watts (plus/minus a microjoule) at 5 volts DC potential 
is...

[see procedure above, substituting dV/dT for all occurences of Zeta]

   ah, yes: 0.03333  ohms, but you could use a .1 1Kw unit and be fine.

   This is assuming you want to test the power supply at close to full 
load.  If you just want to see if it puts out current, then a smaller 
resistor, say .5 ohm, 200 W would do, if you limited the duration of the 
test so as not to fry the load.

  Actually for loads like this, a bucket of salt water with a couple of 
heavy metal bars dunked it it, connected to the PS, would also work - 
using an ammeter, vary the distance between the bars until the PS is 
putting it's rated current into the load.

   Also makes a nice amount of hydrogen and other interesting gasses.


   Cheers

John