[Jolly-Swagman]

Jolly Swagmans Mods
AT- PSU Coversion to Lab bench PSU

ConversionI am going to Mod an old ATPSU
for use as a Lab bench PSU
using a 230 Watt ATPSU,
and will have output voltages of,
+12v 12v
+5v 5v
& Ground
things needed are
1 x AT PSU
2 x Red bannana Terminal Posts
2 x Yellow bannana Terminal Posts
1 x Blue bannana Terminal Posts
1 x White bannana Terminal Post
1 x Black bannana Terminal Post
1 x (120mm x 70mm x 40mm) Hobby Box
2 x Panel Mount Fuse holders (Small)
2 x 5mm LED's (green + amber)
2 x 120ohm .75watt resistors
1 x 2amp small glass fuse
1 x 5amp small glass fuse
2 x 10 Ohm 10 Watt Load resistor
1 x 16Amp 240volt DPDT toggle switch
10 x 4mm ring crimp lugs
1 x 20mm Blank pvc plug
Zip ties for wire management ect.
1 x SPST small toggle switch (optional)
1 x 3pin Fan header (optional)
A soldering iron, Solder, Shrink tube various sizes,
Heat Blower to use on shrink tube, Multimeter

*** CAUTION Should be used when working on PSU make
sure it has been turned OFF or not used for at least a day
before attemping this MOD as PSU capacitors retain residual
HIGH Voltages and Will give you a nasty SHOCK if touched ***


STEP 1
Take off the PSU cover and check all wiring and components are OK,



STEP 2 (Optional)
This part may be Optional if you wish to have an easier accesable
240/110 Volt 5 Amp fuse, as most PSU,s have one on the circuit board
either as a clip in or are soldered in.
I chose to Remove the soldered fuse and replace with Two wires going to
a Small Glass Fuse Holder mounted on the case panel, with 5 Amp Fuse.

The Fuse mounts in right Cable slot in below pic



STEP 3

Now Cut 1 Red +5Volt wire and 1 Black Ground wire (about 150mm)

Enough to attach to the 10 ohm 10 watt Resistor.

Slide on some shrink tube of correct size to the legs of Load Resistor

And shrink leaving 10mm of wire for soldering.

Also slide some tubing on the Red & Black wires that you have just cut

And strip ends pre solder both wires and resistor and then attach one wire

at either leg of Resistor, Slide the Shrink tubing over the

Soldered joint and Shrink



Now mount the Resistor to the side of case as per above picture as

this will provide some sort of cooling and act like a heat sink

as the resistor will get rather warm, Also I have used some AS5

Thermal compound added to the back of resistor to aid in Cooling.

Attach using zip ties.

1 10 Ohm 10 Watt Resistor should be enough as a latching load on

the 5-volt side without this the PSU wont start, you can also join

another in series if this is not enough.

STEP 4

Now I have chosen to use a Hobby Box for my Terminals and Switches

to be mounted, you can if there if sufficient room mount these into the

case side, but I proffered to isolate them in box.

Plan out where you want the power switch and Terminals, ect to go and

Drill appropriate size holes for mounting, and 20mm hole in rear of box

for wiring loom to pass through.

Continued Post #2

[Jolly-Swagman]

Continued

he box has been mounted to the lid part of the PSU just above the

Ventilation slots, you may choose to mount where you prefer.



STEP 5

Cut the Power Switch cable to length to reach new switch, Solder wires,

AS per wiring diagram as shown in STEP 1 pic. And shrink tube wires

and power switch to make sure is double insulated from low voltage side.

Cut the 3 Black Ground wires to length and terminate at one of the terminals

on the Fuse holder mounted on your switch panel, and then a Black wire from

the other terminal of this fuse holder to the black Banana Post using crimp

ring lugs, The remain Black wires can be trimmed short near circuit board

and a piece of shrink tube placed over them.

Now cut 3 Red (actually you only need 1wire, 3 wires will give you

extra load current) to length and terminate at the +5 Volt

Red Banana Post terminal, (I have used 2 terminal posts +5Volt

This will be optional if you want)

Now cut 3 Yellow wires and terminate these to the Yellow +12Volt Banana

Post terminal (I have used 2 terminal posts +12Volt

This will be optional if you want)

The remain Yellow wires can be trimmed short near circuit board

and a piece of shrink tube placed over them. (Optionally you may want to keep

1 of these Yellow +12Volt wires for cooling Fan for Resistor see later)

Now Cut the Blue and the White and if there is 1 Orange wire to length

And terminated the Blue wire to blue Banana Post Terminal and the white

To the White Banana post Terminal.

The Orange wire if present is the PG line (Power Good) this may be used to

Connect to the Amber LED +leg and the -leg to 120ohm resistor then too

Black Ground Post

Now Optionally I have put in Fan header and Small toggle switch, for Fan testing

This is entirely up to you wether you want this.

Connect a Green LED +leg with a wire to Yellow +12volt Post and the -leg

to the 120ohm Resistor then to the Black Ground Post, this will then sow that

Your 12 volt line is UP /ON

STEP 6 (Optional)

Now for added Cooling of the Load Resistor I have placed a 80mm 12v

Fan mounted on a Bracket to aide in cooling this would be connected to a black ground and one of those Yellow +12volt wires we saved earlier.

See picture below, and also shrink tube wires.



Picture above also shows where the 20mm Blank plug goes to block the

hole the original wiring loom came out before we modded the PSU,

And the 240/110volt 5Amp Fuse holder where the old power switch

Cable came from.

The 2Amp Fuse we place in the Fuse Holder in the Terminal panel this

Protects the -Ground from any short Circuit mishaps for anything

that is connected to the terminals.

Continued Post #3

[Jolly-Swagman]

Continued

So there we now have a Lab Bench PSU to use for all those Hobby projects

Or just simply to test out Fans ect







Also the Feet are another Optional extra just some MDF pieces

Covered with non-slip mat.


*********DISCLAIMER*********

This Mod is what I have done to make a Lab PSU from an old AT-PSU

Jolly Swagman takes NO Responsibility if you undertake to do or

Replicate this MOD and something goes wrong as working with 240/110Volt

Circuitry is Dangerous if you DONT know what you are doing.

I am a Qualified Electrical “A” Grade Special Class Electrical Mechanic.

I hope all goes as well for you, as it did for me.

Jolly Swagman

************************************************** *********

[Jolly-Swagman]

Continued

This Mod can also be found on My Blogger Page here http://jolly-swagmans.blogspot.com/

And for those that Dont have an old AT-PSU and wish to use a ATX-PSU see links below as that is where I got the idea from

http://www.wikihow.com/Convert-a-Com...b-Power-Supply

http://web2.murraystate.edu/andy.bat...OWERSUPPLY.HTM


Hope this has been a helpful insight for those wanting A Lab Bench PSU

Jolly Swagman

[nd4spdbh2]

a suggestion, run the psu fan off the 5v line to load it so that it starts up, thats what i do to allow my bench psu to start without anything hooked to it.

[Crazy Jayhawk]

Is that enough of a load to keep all the voltages where they need to be?

[Jolly-Swagman]

Originally Posted by nd4spdbh2

a suggestion, run the psu fan off the 5v line to load it so that it starts up, thats what i do to allow my bench psu to start without anything hooked to it.

I did think of doing that but the PUS fan is a really low rpm fan and wont run @ 5volt, but I could have swapped the fan I put on the front as it is a higher RPM. and they are both very quiet dont even notice them on.

Crazy Jayhawk
Is that enough of a load to keep all the voltages where they need to be?

Yeah with the load resistor the voltages are fairly stable remember this is only an AT-PSU, you may need 20ohm's for an ATX-PSU