re Computer PSU Conversion

[Rick Cole VK3YM]

I thought I would post my private reply to J.D. on this matter as somebody else might use the info..
         Rick

I would like to have a copy of page 35 in the may -2002 issue. of qst. it is
about using a computer power supply and converting it to a power supply for
the ham shak' thanks verry much. J.D.--KCØBD


FYI on converting ex Computer PSU's

You may use this info as you wish..ie give to other people or print copy
etc.

I have converted many computer power supplies and a very easy way to do it
is to use the h/d current +5vdc rail and use two psu's with the outputs in
SERIES...
the 5v rail can be modified to increase the voltage to 6.8vdc and the two in
series then adds up to 13.8vdc...

1]Find the TL494 ic or it's equivilent and from pin 1 find the resistor that
is in series to the 5vdc output...
...the other ic is usually a LM339 or Eqivalent

2]lift the end of the resistor on the side that is TOWARDS the 5vdc out and
place in series a 20k variable resistor..

3]adjust the v/r so that the 5vdc output rises to 6.8vdc..
    note...do this to both pcb's as individual units..

4]do this to two psu's then get rid of all the excess wires and put in new
heavy wires in the 6.8vdc [was 5vdc] position and the Negative lead.....wire
up the 110/240vac as required...just parralell the two

5]if you are using the original cases or remounting the PCB's in another
METAL case then you MUST locate the NEGATIVE rail on the pcb and ISOLATE it
where the track is conected to the MOUNTING SCREW of the pcb...do this by
cutting the track both sides of the mount screw and rejoining them using a
JUMPER WIRE...thus the screw{s} is now isolated from the pcb
circuit...usually only one {1} screw is connected...

6]remove the fans and REVERSE mount them so they are blowing INTO the case...

7]when the 5vdc rail is adjusted higher to 6.8vdc the 12vdc output also
rises and this makes the fans run a lot faster..too fast...the cure for this
is to put a 68 ohm resistor in SERIES with the + postive lead of the fan
wire..

8}run the -NEGATIVE lead of #1 pcb and join it to the POSITIVE lead of the
#2 pcb..

9}run the POSITIVE lead from the #1 pcb and join it to the NEGATIVE lead of
the #2 pcb

10}now use the POSITIVE & NEGATIVE ends to the output terminals on #2

Check the output voltage and because both psu pcb outs are in series the
total output voltage is 13.8vdc at X current...
X=Current of one of the psu pcb's

Try and use two identical psu pcb's as this makes it much easier...
CAUTION...the pcb has approx 110x1.414=155vac
                                              220x1.414=311vac
while the power is switched on..THIS IS LETHAL..

I am available for questions if needed
      have fun     Rick Cole  VK3YM

----- Original Message -----
From: "JD or Doris Linn" <dorisjd at GRAPEVINE.NET>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Friday, April 11, 2003 11:21 PM
Subject: power supply.


I would like to have a copy of page 35 in the may -2002 issue. of qst. it is
about using a computer power supply and converting it to a power supply for
the ham shak' thanks verry much. J.D.--KCØBD
__

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