Most of the computers that I use have at least 2, and often up to 4
power supplies. Some have 6! Since computers are thrown out by the millions, it is
usually very easy to get used power supplies. At first I used the old
AT type from 286, 386, and 486 computers. These are getting difficult
to find now, so that I now use ATX power supplies.

To use an old AT type, you simply wire in a 12 volt relay, usually free from
automobile scrap, or from microwaves, or some TV sets, to the 12 volt
yellow wire on the first power supply, and ground. All added AT supplies go to the
output contacts on the relay, so that when the first power supply puts
out 12 Volts, the relay closes, and the contacts power the 110 volt wires
on the other AT power supplies. You have to add a diode BACKWARDS
across the 12 Volt pins on the relay , that is, + to ground, and ground to + 12 volts,
because, when the relay turns OFF, the magnetic field on the relay collpses
creating a spike of high voltage and high amperage electricity, that will go backwards
through the wires into the first power supply, damaging the circuits. ANY
relay, if you look at the circuits in a microwave or TV, etc, has a diode across

ABOVE:  You can see the white ( Neutral or ZERO volt, and BLACK, 110 VOLT power wires
connect to the POWER SUPPLY INPUT, then go through capacitors and a CHOKE to stop the
400 Cycle Chopped Transformer wave noise from travelling backwards, out the power supply, and
feeding the 400 Cycle noise into the Household wires, causing noise on Radios, TV/s etc. Then the
power goes through a FULL WAVE BRIDGE RECTIFIER, that takes the + /- Alternating electricity
and makes it always + on one side, and - on the other, to feed into two CAPACITORS, which store
the 110 Volts into a more EVEN, Direct Current ( D.C. ) power, much like a BATTERY.
A capacitor, typically is two sheets of metal rolled up, and separated by paper soaked in an oil that
stops the Positive sheet from sparking over to the Negative sheet.


This Direct, 110 Volts, is then CHOPPED up into 400 pulses a second, by two POWER TRANSISTORS,
which are bolted to the aluminum HEAT SINK, right in front of the FAN, which takes away the HEAT.
Then the chopped pulses of 110 VOLTS are fed into 3 TRANSFORMERS, that put out +5 volts,
+12 Volts, and - 12 Volts, that are used to power the Mother Board, and the Floppies, CDs, and Hard

ABOVE: you see a single black module which has 4 DIODES in it, that change +/- A.C. ( Alternating
Current ) into a pulse of D.C. at 110 Volts, to feed the two CAPACITORS. On some computer power
supplies, they use 4 round barrel diodes, instead of one module. The two BLUE wires
go to the back of the power supply box, where the typical 110V / 220V switch connects, or disconnects
the wires. I always remove the wires ( In North America ) and just connect the pins together. This makes
the suppy ALWAYS 110 Volts. In a part of the world where you use 220 Volts, you just REMOVE
the wires completely, leaving the two connection pins NOT connected.

ABOVE: You see the two POWER Transistors that switch the D.C. 110 Volts that is "smoothed out"
by the two big CAPACITORS into what looks like a smooth 110 Volt "Battery" output , and make
a "chopped" 400 times a second ( 400 HERTZ ) chopped pulse of electricity that is fed into the 3
TRANSFORMERS, seen below with YELLOW tape wrapped on them.

ABOVE: After lowering the 110 Volt, Chopped electricity at 400 pulses a second, the 3 transformers
send the low voltage +5 and +12 Volts etc. through DIODES, to turn the chopped spikes back into
smooth Direct Current (D.C.), needed by the computer. Two very large, high Amperage ( high current)
Fast, "switching" power diodes can be seen above, bolted to a large aluminum heat sink that takes
away the heat. These black modules "LOOK" like transistors, but inside, there are two diodes, called
SCHOTTKY diodes, that turn the power into D.C.... On some computers, they use round "barrel"
diodes instead, and there are TWO of these , wherever they replace one "module".

ABOVE: Once the low voltages are fed through the Schottky diodes, they go out through CHOKES
and capacitors, to smooth out any SPIKES in the 400 CYCLE chopped electricity. The CHOKES are
just a wire wrapped around a FERRITE ( iron dust baked into a ceramic shape ) CORES, and any
spikes are cancelled out by waves (between any two adjacent wires) hitting each other. The Capacitors act as
very short timed batteries, and bridge the drops in electricity between the 400 pulses a second.
By using capacitors, then chokes, then capacitors again, the power coming out looks just like the smooth
power coming from a BATTERY...

FINALLY, Above, the nice, regulated, D.C. power goes out to wires to the motherboard and the
Harddrives, CDs, and Floppies. NOTE: on AT power supplies, there is one wire, ORANGE, that
does not go OUT of the power supply, but actually comes FROM the Motherboard. This is the PG
or Power Good, wire, and it feeds BACK +5 Volts TO the power supply, to let the power supply
know that there is NOT a SHORT or problem with the Motherboard. If you use an "AT" power supply
( or 2, or 3 or 4 AT supplies ) you must connect the POWER GOOD feedback wire to the RED
+ 5 VOLT wires, so that the "AT" supply will stay in the "ON" mode ! Once you do this, the "AT"
supply will instantly turn on when you connect the 110 Volt power, by using a 12 VOLT RELAY
which is powered by the MAIN, ATX supply on your computer !

It is easy to tell if the power supply ( ABOVE ) is the old "AT" type, since, first, it will have heavy,
110 VOLT wires that would go to a heavy duty, large, 110 VOLT POWER Switch on the Front
of the computer...

ABOVE: you can tell an old "AT" power supply, since it has two MOTHERBOARD PLUGS, that
bring power from the supply to the MB. Note that the BLACK WIRES, GROUND, Zero Volts,
are beside each other in "standard" AT motherboards, and it is possible to plug the TWO connectors
in WRONG, and blow up the power supply ! As shown above, the ORANGE, PG wire, inside
the power supply CASE, should be connected to ANY red +5 Volt wire, to turn the AT supply "ON".
Since I cut OFF all motherboard connection wires INSIDE the "AT" supplies that I add to my computers,
the ORANGE wire is simply jumped over, inside the AT supply to the most convenient spot..

For the ATX power supplies, you do not need a relay, just two diodes of
almost ANY kind, again, these can be found in scrap TV's, microwaves, power
supplies, radios, - just about everywhere, and they do not need to be very
big or powerful. I just take two glass, silicon, typical diodes, usually with red
paint, and a black stripe, and wire them together on the GREEN wire going to
the computer motherboard ATX power plug. A typical ATX motherboard, turns on the
power supply, by SHORTING the GREEN wire to GROUND ( Zero, 0 volts ),
so that I just connect all the new, added power supply's GREEN wires, to the
first GREEN wire. To keep electricity and noise and transient spikes from going
from one power supply to another, I add a DIODE on each power supply,
with the BLACK BAND ( Ground, Zero Volts, Negative ) end pointing down
to the motherboard - which, when it wants to turn on all the power supplies,
will connect the GREEN wires to Ground ( Zero Volts, Negative, 0 Volts ).
The diodes allow all the green wires to "see" the motherboard, but the GREEN
wires cannot "see" each other. It works great.

As you can see from the picture above, I cut the first power supply's GREEN
wire, and to add a SECOND power supply, I add two diodes - one for the
first power supply, and one for the second -- you would add a third diode if
you want a third power supply.

Above, you can see how I slide heat shrink tubing over the bare wires, and heat up
with a flame proof cigarette lighter, to shrink the tube over the solder joints. ( note
that you have to remember to slide the tubes on to the wires BEFORE you solder the wires !)
If you do not have heat shrink tubes, carefully use black electrical tape.

The next step is to connect the ORANGE or sometimes BROWN, feedback, voltage
SENSE wire, on pin 13 of the ATX connector, to any ORANGE, 3.3 volt power connection.
This extra wire going from PIN 13 on the ATX Motherboard plug, feeds BACK the voltage
from the plug, into the ATX power supply, to check to make certain that exactly 3.3 Volts are
being delivered through the Orange wires to the PLUG. If you cut off the Motherboard plug
wires, you have to connect this 3.3V SENSE wire back to 3.3Volts, so that the power supply
"sees" 3.3 Volts, properly, and continues to work.
If you DO NOT cut off the UNUSED MotherBoard plug and wire bundle, and just wrap it with
black electrical tape to keep it from accidentally shorting, then you do not need to worry about
the SENSE wire, since if it exists on pin 13, it just remains connected as normal. Power would
go from the +3.3 volt bundle on the ower supply, down to Pin #13, and then back on the SENSE
wire to the power supply SENSE circuit. It would have no Idea that it was not connected to the
motherboard. Cutting the UN-used wires creates a bit of extra work, but in my computers there is
rarely enough space just for the devices that I "do" want, and big bundles of extra wires block the
air flow, and just are too difficult to cram into the space. It is always a good Idea to open the
2nd ATX power supply and just check to see where PIN #13 on the connector actually goes to
inside the power supply!

ABOVE, I usually just cut a short section of the Orange SENSE wire, and loop it over to the
most convenient spot on or near the bundle of 3.3 Volt Orange wires. Note that on older ATX
supplies, this wire can be brown, but is easy to identify, since it will always be on PIN 13 of the
newer 24 Pin MB connector, and on PIN 11 of the older, ATX revision 1, 20 pin connectors.
See, near the end of this document, PHOTOGRAPH # 59, of the two types of ATX MB
connectors. NOTE: the top 20 pins of both connectors are IDENTICAL! Really
cheap ATX supplies did not use an extra wire at all, and just shorted the SENSE wire over to
3.3 Volts in the first place. Just check to see where the wire on PIN 13 of the ATX connector
actually goes. If it goes to ALL the other 3.3 Volt bundled wires on the supply, and there is no
extra smaller feed back wire, then the feedback is already shorted to 3.3 Volts on the board, and
you do not have to do anything. This modification is ONLY done on the "ADDED" ATX supplies,
since the MAIN ATX supply just goes to the motherboard, and has the SENSE wire already
properly connected to the motherboard PLUG.

The RULE for using more than one ordinary power supply, is that the OUTPUT wires
CANNOT connect together-- that is, the first power supply could, for example, go
to a CD or DVD, and the second could go another CD or DVD, but you cannot have
both supplies EVER go to the same place - both supplies are constantly checking to see
if +5 volts is exactly right and +12 volts is correct, etc, and if two different supplies
ever had the wires for + 5 volts connected, both power supplies would try to raise or
lower the voltage at the SAME TIME, and they would be fighting each other, and
one would blow up first, and the second one would then get the full load, and overload,
blowing it up as well...
To separate them, I put the first power supply ONLY to the motherboard. I cut off
all the wires that do not go to the motherboard plug. In the example here, the
power supply states on the label " 450 Watts ", but this is a fake, instantaneous value
which is put out during testing, for a fraction of a second as the LOAD is increased
from 100 watts, to 200 watts, to 300 watts etc., until the supply reaches 450 Watts,
and blows up. The CONTINUOUS, real rating is probably more like 285 Watts!
285 Watts is more than enough to power a standard motherboard and the motherboard

While I have the power supply apart, I clean up a few things, first by cutting the
two wires to the 120/ 200 Volt case switch, and in North America ( 110 Volts )
I just connect the two wires together permanently. In Japan or England, you would
just REMOVE the wires, which permanently adjusts for 220 Volts power.

I then, in the picture above, add a 110 volt wire to the 110 volt input connector, and the
110 volt switch, so that the added power supplies are turned OFF at the same time as the
first power supply. I use the old ATX, shielded 110 volt cables if I can find them, but in
the example above, I am using very heavy duty 3 conductor wire from a refridgerator.
White ( Neutral ) goes to white, Black ( 110 volt power ) goes to the OUTPUT side of
the switch ( which goes to the power supply board as well ), and the green wire ( GROUND )
goes to the ground post on the power plug.
You can see where I cut off the two wires on the 110 /220 switch.
Also note that the fan, which is turned around to blow INTO, and OVER the aluminum
heatsinks ( vastly increasing the cooling capacity ), has the black and red wires on the
inside face- this is usually a quick way to tell which way a fan is blowing, since the wires
are usually on the side that is the Exhaust or Blowing side.

When you turn around a fan so that it blows fresh air over the cooling heatsinks, you cannot
have ANY metal near the tips of the blades ! ! !, this will produce huge amounts of noise.
As well, by removing all the metal, you increase the flow, typically by 4 times as much, so
the power supply is much cooler, and will last much longer - power supplies like this that I
made 10 years ago are still running just fine. I often use part of the case metal to make a bit
of a protector on the back, as you can see in the picture above. All my case fans blow IN
to the computer, and the exhaust is usually a large hole at the front, top, where I remove the
dead plastic cover plates for extra CD's and DVD's. This generally proves to be extremely
On the second, added power supply, I cut off all the wires that go to the motherboard plug,
and then my harddrives and CD's and DVD's and case fans, are all powered by the
second power supply - which is not connected to anything on the first supply. Again, I cut
off the 120 /220 switch wires and permanently connect them. I then connect the 110 Volt
power wire that I added from the first power supply switch, to the black, white and green
power wires, and finally, I wire in the GREEN ATX PLUG wire to the remaining diode, going to the
GREEN ATX PLUG wire on the motherboard connector. If I have room, as in the picture below,
I put the second power supply on the case, front, bottom, just in front of the CASE fan,
which, again, blows IN fresh air over the power supply. I often have to take the case
plastic Front, Bottom, and drill in dozens of holes to make certain that the area of the
holes equals the area of the fan, so that it is not starved for air.

In the photo above, I have taken the trusty Tin Snips or Metal Cutters, and cut away the
case on the second power supply to make it easier to fit in the case. The bottom sheet of
the supply can be seen with the green 110 volt GROUND, green wire attached. The
bottom plate allows me to mount the 4 corner screws on the power supply circuit board,
to connect the ground screw, and to give me a place to drill holes to put in metal screws
to hold the power supply on the computer case, bottom.
You may also notice, that I have used high- temperature hot melt glue to add cut up pieces
of aluminum heatsink, on top of any chips or transistors that are running hot,
on the motherboard. After running a computer about 1/2 hour,
I use the baby finger test to see if any components are too hot to touch- if so, I use
heatsink paste and put on a chunk of aluminum. After adding the aluminum heatsinks,
I test again, and normally I will not be able to feel any heat at all - if I do, then I replace
the heatsink with a bigger one, until the chip is running cool. Motherboards like this will
run for years with no problems, as long as they are cleaned periodically of dust,
that clogs the fans and covers the heatsinks.
As you can see in the photo above, the first power supply ONLY has the connector
to the motherboard, and the second power supply ONLY has the Yellow ( +12 volt)
Black Black ( Ground, Negative, Zero Volt ), and RED ( +5 Volt ) wires, running up
behind the harddrives and CD/DVD's.

As I add the PCI ethernet, the Sound Card, memory, AGP Video card, Fans, cables, etc,.
the case is getting full, and a lot of power is being used. Note that on the bottom, the aluminum
heatsink behind the two large black capacitors reads over +178 volts - when the power is OFF!
If you remove the case like I do, you have to be careful of the capacitor charge! It drops to ZERO after a while.

As you can see in the picture above, I often have to drill air holes in the front case to allow the bottom, front
case ( and power supply ) fan to get enough air to work properly. Almost all computer cases have a cut out
for a bottom fan, but almost none have enough holes. Here also I remove ALL the metal from the fan hole,
to remove noise, and to allow up to 4 times as much air.
This computer is specifically made just to run UBUNTU, 10.4, which is a FREE, Linux, version, with
thousands of programs available in the library. For example, there is OPEN OFFICE, which replaces
the typical Microsoft Office, and free drawing programs, that replace the typical Adobe Photoshop. The
free web browser, FIRE FOX, is included in the operating start up, and is faster and more virus proof
than most other programs. The case, the power supplies, the harddrives, the motherboard, CD/DVD's,
the floppy, the monitor, the keyboard, the mouse, the RAM memory, all were thrown out. I used my old
ATHLON CPU from my upgraded computer ( although I could have used thrown out CPU's- mine was a
bit faster ! ) . Generally, it is a FREE computer, running free software, for FREE. Since both power
supplies are labelled "450 Watts " I have the equivalent of a new, typical 900 Watt power supply as well,
( noting that the "typical" 900 Watt label is probably more like 550 Watts "TRUE" continuous rating!
A "REAL" 900 Watt or 1000 Watt, continuous, high quality, power supply can cost $200 - an old ATX
350 Watt or 400 watt is free, by the dozens...)

In the simplified diagram above, you can see where the wires go to.
If you want to add MORE power supplies, you just chain them along !

The question remains, since it is assumed that you have lots of spare old, small power supplies
how do you know which diodes will work? Where do you get them?

In the picture above, I grabbed a few diodes that I had in my toolbox. These are bulk purchase,
inexpensive diodes from electronic sources, like an electronic store, or , in my case from the
Electronic Flea Market, every 3rd Saturday on Aviation Boulevard near Los Angeles. If you
look on the web for the PRICES of typical diodes, like the ones above, you find that in quantity,
they cost $00.0009 each ! If you buy 10 in a bag, with fancy packaging, they can cost 10 cents each!
Also shown in the photo is a typical motherboard battery, a CR2032 ( 20 is 2 centimeters across,
and 32 is 32 millimeters thick ), and it is 3 Volts, which is exactly the right value to TEST most
LEDs. The battery and LED are all you need to test a typical diode to see if it works on the GREEN
"POWER ON " lead from a typical ATX power supply ( not to be confused with the 110 Volt

It is easy to see which wire on a TYPICAL  LED is positive or negative, by just looking at which
side has the CUP which holds the LED CHIP, and which side has the post. The post is usually POSITIVE,
+3 Volts, and the CUP side is usually negative. 99% of LEDS are made this way, although I have
found some backwards, over the years. Just recently I found an entire string of Christmas LEDs, all white,
and ALL had the poles REVERSED, so you do have to check !
To quickly test if a DIODE that you find is a typical diode, you just connect the battery and the
LED through the DIODE. If the LED lights up, then you are probably will be able to use the diode
to connect a power supply.

In the photo above, I just SET the LED on top of the diodes I was testing, and the LED lit up - no soldering
or expensive laboratory equipment needed! - You can just hold the battery and the DIODE in your fingers
an touch the LED to test !
If you really want to be certain about a DIODE that you find, you can use a magnifying glass to read the printing
on the side, and look up the diodes on the web... The two bulk Diodes that I have in a clump from the photo
earlier, are labelled 1N4148 and 1N914. I looked up the data on the web and found pages of specifications,
but you usually only need the FIRST little chart, seen below:

The two important things to note are the VOLTAGE, forward or reverse, (the maximum DIGITAL
voltage used that we need is only 5 volts!), and the Amperage or milliAmperage, A, or mA,
( we need 2 or 3 milli amps ) so the specifications above, of 75, 100, and 200 VOLTS is huge
compared to the 5 volts needed, and the the Amperage listed above of 150, 200, 300 and 500 mA,
is way over the 2 or 3 milliamps that we need. So ANY of these diodes would be vastly over-
qualified to use!
If you have a pile of old power supplies ( they are usually free from computer repair shops ! )
you can just take pairs from the power supplies themselves - some power supplies are damaged,
with typically the capacitors all split on the tops, and yellow foam leaking out the tops. The diodes
on the board itself are usually 100% ok. The glass diodes are used for the green ATX grounded
POWER ON wire, and I usually put the bigger, black diodes with the silver band, across the
12 volt RELAY contacts, since the black diodes are usually higher capacity.




As you can see in above photos, there are LOTS of diodes on a power supply, often in PAIRS,
which is what you need ! They can all be tested with an LED and 2032 Battery in a few seconds...
   WHILE YOU HAVE THE CASE OPEN, you can clean up the wiring a bit...

Above, I have cut off the orange 110/220 switch wires - I think they are actually dangerous, since
if accidentally switched, they can do tremendous damage. Unless you fly with a huge tower computer
from North America to the Far East every day, it is just more sensible to properly wire them for
your own continent...


NOTE that adding AT power supplies to an OLD "AT" power supply, for example, on a wonderful
old win98 machine, running thousands of old Win98 games that will NOT run at all on new computers,
is EXACTLY the same as the diagrams above. The first AT supply just gives +12 volts to a relay,
that turns on all the other AT supplies...
The first step in adding an old AT supply to an ATX, is to add the 110 Volt cord which will go to the second AT

This 110 Volt cord goes to the relay on the second AT supply used.

The relay on the second AT supply is fixed somewhere convenient - I often hot melt glue it to the
fan plastic. NOTE in photo below, that you can get a DIODE from an old power supply !


In the photo below, we see the first ATX power supply sitting on top, with JUST the cable going to the
motherboard , except for the yellow ( +12 volt ) and black ground going to a connector to the relay
on the second power supply, the AT, by the fan.

I often cut off the case sides and TOP of the SECOND supply, to make it fit better, and use the BOTTOM
case section of the power supply to BOLT it firmly to the tower case, in this case, the TOP of the tower,
upside down.

On the top of the tower case, you can see where I drilled 3 holes and bolted the second supply
underneath. I hot melt the bolts to keep them from rattling loose.
AGAIN, as I did on the last case example, while I have the case open I check to see if there are
any hot chips on the motherboard, using the baby finger test- if it is too hot to hold your baby finger on the
chip, then I heatsink it with chunks of old aluminum heatsinks, and affix with a dab of silicon, heat-paste,
and hot melt in place with high temperature hot melt glue.


The nice thing about hot melt glue is that it will just peel off if you need to access something later...
In the mean time, it expands a bit so it does not damage anything with hot/cold cycles, and it is not
conductive.. great stuff. I had one technicial comment that hot melt glue will just melt when the
chips heat up the aluminum heatsink -- my reply is, of course, if the aluminum heatsink gets THAT HOT,
(HI TEMP liquid hot melt glue will BURN your skin !), then the heatsink you cut to size is way too small in the
first place - the whole point of putting on a heasink is to cool the offending chip down the point that
that your baby finger test shows "warm" at the most, and the chip is running cool. If the heastsink
that you add is burning hot after 1/2 hour running, then cut out a much bigger piece of aluminum
and try again. Don't quit until the heatsink / chip are nice and cool - it will pay off later.
As on the example case at the beginning, I remove all the metal from the back of the fans, and
turn them all around so that they blow IN cold air at high speed.

I drill holes at the FRONT, BOTTOM, and install a fan to bring cold air from the front,

and I leave the TOP FRONT of the case wide open to exhaust all the air from the entire tower.
Since hot air RISES, this is the best way to get rid of the hot air, and blow it AWAY from the
computer at high speed, so that it does not re-circulate, and get drwan back into the inlet fans!

LASTLY -- WHAT IS a Switch Mode Power Supply, ? ?
In the old days, a power supply to change 110 Volts to lower voltages, just used huge transformers
and pounds of copper coils. The first coil of wire was 110 Volts. The second winding of copper was
the low voltage, in this example, 12 VOLTS. The tranformers were BIG, and HEAVY ! This is because
the " 60 cyle " Alternating electricity used is OFF about half the time!

Look a a diagram of the
WAVE of electricity... called a SINE ( pronounced " SIGN" ) wave...

4 DIODES are used to make this wave into a POSITIVE ONLY or Direct Current ( DC ) wave.
The 4 diodes are called a FULL WAVE BRIDGE RECITFIER.
Like all electronics, this is really simple.

So at this point we have a DIRECT CURRENT, wave of power. But lets look at the wave
in more detail.... If you take 110 VOLTS typical North American power, and use a BRIDGE
RECTIFIER, you get a DIRECT CURRENT, or D.C. WAVE, with just positive pulses...

At the top of the wave, like a peak of a mountain, the voltage is NOT 110 Volts, but more like
170 VOLTS ! Notice that in the "valley, between the two mountains, the voltage DROPS to
NOTHING ! This is Zero volts. The typical 60 Hertz ( a Cycle per one second) drops to ZERO
between each PEAK, so that about half the time, the power is OFF, -- doing NOTHING !
The terminology of 110 VOLTS comes from the AVERAGE of the power from the PEAK, at
about 170 Volts, averaged into the "valley" at zero volts, across the entire wave. If you choose
5 different places to take an average over the entire "mountain", you might get:

And if you take the AVERAGE, or , in Statistical Mathematics language, the "MEAN" of all the
points, you get 110 Volts, instead of the PEAK voltage of 170 volts! The RATING of a
SINE WAVE of electricity changes constantly, so to get an AVERAGE or MEAN, the rating
is called RMS, or, ROOT, MEAN, SQUARE, which, like all electronics, is really, really simple!
The Square ROOT of +9 is 3. The Square root of NEGATIVE 9 is also... +3. This is the
mathematical way of using 4 DIODES to make a Full Wave Bridge Recitfier, where all the
values are going to END UP as positive... So if you take the PLUS wave AVERAGE, and
the NEGATIVE wave average, and take the SQUARE ROOT, you end up with the SQUARE
ROOT as ALL POSITIVE... Now, you have the Square root, so you just SQUARE the
positive value BACK to the full value - that is, 3 x 3 = 9, which was the original value. Except,
where you were trying to AVERAGE PLUS 9 and NEGATIVE 9 ( the answer is always ZERO )
now the +9 became +3, the -9 became + 3, and when you AVERAGE, and then SQUARE, you
end up with +9 and +9 that now you can AVERAGE properly...! It is just a quick trick to get
all positive numbers, and then allow you to take an average... OK, now that we understand why
Positive "peak" 170 Volts is called " 110 Volts " lets look at the 60 CYCLE WAVE of 110 volts
more closely...

Look at the areas were the SIN WAVE is almost ZERO volts. It is, in terms of POWER, doing
NOTHING ! Whatever device like a Radio, or TV, or computer, if it was to get just the
Direct Current Wave after the DIODES changed it to ALL POSITIVE, would be OFF about
half the time! This is awful. By using big CAPACITORS, which are like BATTERIES, the
WAVE can be changed to make it less severe on the "OFF" areas, but you can NEVER have
COMPLETE, FULL, USEFUL, POWER! This is not so bad on a kettle, or a
toaster, but when it comes to a COMPUTER, that works on the principle of ON / OFF electricity,
the idea that the power itself is turning on and off all the time is terrible.



A switch mode power supply, commonly used on a computer, is, again, really simple.
The +/- ( Plus / minus ) A.C. ( Alternating Current ) power comes in, goes through 4 diodes
to become a PLUS /PLUS wave, which then goes into two very large capacitors, that act like
batteries ( for 1/10th of a second or less ). Then the +170 Peak to Zero Volt bouncing wave
is evened out to a smaller wave, centering near 110 Volts. Then that power is put through
3 transistors, that turn OFF and ON, about 400 times a second, chopping the D.C. voltage
into pulses, that are fed into a TRANSFORMER, that lowers the 110 Volts, to +12, +5 and
+3.3 Volts etc. that are the correct voltages for a computer. These pulsing voltages have to be
rectified or made just POSITIVE waves again, so they are fed through a second set of DIODES
and changed into POSITIVE ONLY, and then put through capacitors to smooth out the peaks
and values of the waves. There are CHOKES ( a coil of wire wraped around a metal core ) that
remove tiny spikes at the top and bottom of the waves. Then, finally, the +12, +5 and +3.3 Volts
are OUTPUT to the MOTHERBOARD of the computer, and the Devices, such as Harddrives and
The difference between the SWITCH MODE supply and the OLD, traditional huge coil of COPPER
supply is in the EFFICIENCY.

Look at the SIZE of the transformer on the top, that puts out 5 AMPS of power at 12 Volts, 60 Hertz..
Then look at the size of the transformer on the bottom, which at 400 Hertz ( times a second)
which puts out THE SAME power, 5 Amps of power at 12 volts. The Switch mode transformer is
incredibly small.
Look at the OFF time of the 60 Hertz transformer, compared to the OFF time of the switch mode

NOW lets compare the "OFF" times of the cycles:

SINCE the Switch mode, 400 Cycle power supply is "ON", producing power 99% of
the time, compared to the old 60 Cycle transformer that is only on HALF the time, the
switch mode transformer can be MUCH SMALLER, and still do the same work...
ALSO, since the wave to the 400 Cycle transformer is tiny, it does not need HUGE
capacitors to smooth out the waves. The switch mode supplies produce MUCH better
DIRECT CURRENT, which is needed by a typical computer...

So that now you understand HOW a switch mode power supply works, lets walk through
the parts of the supply...





To clarify the steps in adding a power supply, here are the typical STEP-BY-STEP INSTRUCTIONS.

NOTE: There are 4 possible combinations of typical power supplies to work with...

1/ You have an OLD computer with an AT power supply, and want to add another AT supply.
2/ You have an OLD computer with an AT power supply, and want to add a NEW ATX supply.
3/ You have a NEWER computer with an ATX power supply, and want to add an OLD style AT supply.
4/ You have a NEWER computer with an ATX power supply and want to add another ATX style supply. 

The most COMMON situation, today, is that you have an ATX style power supply, and want to add another ATX.

(I am assuming that all computers that anyone wants to upgrade are NOT the newest, most expensive,
types that have just been released, with PCI-EXPRESS, 4 Crossfire Graphic cards, and Dual or Quad
or 6 or 8 Pentium processors! These just -released computers have very powerful power supplies, custom made, and likely
do not need upgrading in the first place! Anyone with a $3000 or $4000 computer would not "ADD" another old supply! )

In the diagrams above, you can quickly see the typical ATX power connector that goes to the motherboard.
I LEAVE the original connection to the motherboard, from the FIRST, power supply.
On the FIRST power supply, I generally do NOT use the wires that go to the CD/DVDs, the Harddrives,
the Floppy, etc. ( unless you are using a video card, on the motherboard, that uses the +12, Ground, Ground and
+ 5 volt power plug. Since this device is a "motherboard"  device, I leave the power connected from the same
source as the motherboard ) You can open the case, and SNIP the wires, like I do, so that they are not flopping
around inside the case, or you can bundle them out of the way, and TAPE the ends with black electrical tape
so they do not accidentally short out, or, you can, if you think the original ATX power supply is big enough to
handle the load, leave them connected to CD/DVDs, Harddrives, etc. ( I do not - I am ADDING a second power

power supply since there is NOT enough power, so I try to lighten the load as much as possible on the FIRST,
original, Motherboard, power supply, by diss-connecting all other devices except the motherboard )

On the SECOND power supply, I DO NOT USE the wires going to the motherboard, but only use the wires
that go to the harddrives, the floppy, and the CD/DVDs.

Normally, I open the SECOND power supply, and snip OFF all the wires that go to the motherboard, since the
First power supply already HAS these connections, and the huge bundle of wire just gets in the road, and
can be dangerous loosely flopping around inside the case. If any of the ends of the connector touch a pin on the
motherboard or to ground, they will short and cause damage. Another solution would be to wrap the unused
motherboard connector with typical black electrical tape, so that the ends cannot accidently short out... The only
wires on the SECOND, ADDED power supply's MB connector that I leave, are the GREEN wire, and the
small orange or brown SENSE wire, if there is one, going to pin 13 of the MB connector. That wire is shown
clearly in
UNDER PHOTOGRAPH # 13 is a description of how to identify the ADDED, small, Orange or Brown SENSE
wire, that is present on "SOME" older ATX supplies. On some supplies, it is MISSING, and you can tell by looking
inside the power supply, as well, to see where PIN 13's wire goes to. If it goes to the SAME bundle as all the other
orange wires, then there IS NO "sense" wire, and you do not have to bother with it. If there IS a sense wire, which
goes to another location, usually clearly MARKED in Black INK on the power supply board, then this wire must be
connected inside the power supply to the bundle of orange wires, the +3.3 Volt power source"IF" you snip off all the
Motherboard connector wires. This is so that the power supply "sees" +3.3 volts that it expects to see from the
motherboard, even though it is NOT connected to the motherboard at all. ( If you just cover the motherboard
connector with black tape, the SENSE wire is already connected to the OTHER pin 13 power wire, and you do
not need to do anything.)

TWO things have to be done on the ATX supplies - the GREEN small wire on the motherboard plugs has to
be connected together, through two diodes, so that when the MOTHERBOARD "turns on" the power supplies,
by shorting the Green, small wires to GROUND ( Zero volts ), both power supplies turn on together.
ABOVE, in the
PHOTOGRAPHS # 10 and # 11, under the heading "ATX POWER SUPPLY..." you see a photograph of
the FIRST power supply, the ORIGINAL, motherboard CONNECTOR, with a green, small wire.
   THAT wire, is grounded by the motherboard, when the motherboard wants to TURN ON the power supply.
Since we want to turn on a SECOND ATX supply as well, we have to CONNECT that green wire, on the
ATX motherboard plug, to the SECOND  ATX power supply's green wire.
SOME instructions on the web indicate that you just connect the two green wires together. This would "WORK"
but it has the problem that any electrical spikes or "noise" from one power supply can travel through the green
wires, to the other power supply, and cause strange outputs. By installing DIODES, the two power supplies
are isolated from each other, but BOTH can be grounded by the motherboard, which is what we want...
Two typical diodes are shown in the pictures above, and hundreds of "typical" diodes will work, since the
tiny voltage and power needed to GROUND the green wires is easily handled by almost ANY diode.
You should be able to find the typical small signal, general purpose diodes at ANY electronic store, typically
like Radio Shack ( in the U.S. ) or The SOURCE ( In Canada). If you have pile of old power supplies, you
can use almost all or any of the diodes from the circuitboard. They can be easily tested, as shown in the

PHOTOGRAPH # 22 above, using a typical BIOS, computer battery, available everywhere. If the diode will light up
a typical LED light, then it should work just fine on the green wires, since the voltages are about the same...
Power supplies do have special diodes called "ZENER" diodes, that will not work, but these will also not
light up an LED using the test battery, so you can quickly eliminate them. Using two identical DIODES is
recommended, and they often appear as sets of two in power supplies.
PHOTOGRAPH # 20, you see how BOTH DIODES, point down with the black stripe DOWN, to the
motherboard plug.

FINALLY, if you have connected the DIODES on the green wires of both ATX power supplies, made sure that
the SENSE wire on pin 13 of the ADDED power supply is connected to +3.3 Volts ( IF the wire is there at all),

you have to connect the 110Volt WHITE ( Neutral ) , the BLACK ( live 110 Volt power) and the GREEN (Ground)
from the first ATX power supply, over to the SECOND ATX power supply. If there is a switch on the 110volt of
the first power supply, I wire in the BLACK, live, 110 Volt wire going to the second power supply on the OUTPUT
side of the switch, just like the black wire on the switch going to the first ATX supply, so that turning OFF the
switch will turn off BOTH supplies at the same time. If there is no switch on the first supply, just connect BLACK to
Black, White to White, and Green to Green, and the only way to turn off the power is to pull out the 110 Volt wall
plug. NOTE: Never open an ATX computer case unless you turn OFF the 110 Volt supply, since ATX power supplies
NEVER turn off inside the case, as long as there is power !!! !  !! !!  - The +5 Volt supply to a wire called VSB is
ALWAYS live, which allows the computer to turn on with a MODEM call, with a LAN connection, with a TIMER
in the BIOS clock, or with movement of the MOUSE or taping a key on the keyboard.... People forget that +5 volts
is always LIVE, and start ripping out cards and changing harddrives on an ATX case, because the computer is "OFF",
and they often do severe damage! Just because the Power button is "off" and the LED lights on the front of the computer
are "OFF", and the monitor is "OFF", means nothing, the computer is still "ON" unless you turn "OFF" or diss-connect the
power from the 110 Volt wall plug!



If you do NOT cut off the extra wire bundles on both the ATX POWER SUPPLIES, then the process is easier, but
you have useless wire bundles dangling all over.

ON the FIRST, original ATX supply, you have to cut the green, wire to the motherboard PLUG, and on the PLUG side
wire in TWO DIODES, pointing black strip down to the plug. One diode then connects to the original ATX supply green,
and other diode connects to the SECOND, added ATX supply's green wire.


ABOVE, you can look at BOTH the old 20 PIN ATX connector, and the NEWER 24 Pin ATX connector, and see the
GREEN WIRE, Labelled PS_ON, This is the wire you need to cut, and put in two diodes, both pointing with black stripe
pointing to the connector. PHOTOGRAPH # 10, above, shows the two diodes clearly. Note that ALL the pins on the
20 pin MB connector, and the 24 pin MB connector are IDENTICAL on the top - the 24 pin just has 4 added pins on
the bottom.

CONNECT the 110 Volt BLACK, WHITE and GREEN wires to the SECOND ATX SUPPLY Black, White, Green.
This is shown in photographs 15 and 20 above, along with detailed instructions.

TUCK AWAY the UN_USED wire bundles and cover the live ends with black electrical tape to prevent shorts.


Cut the GREEN, Power ON wire from the first ATX power supply to the ATX motherboard plug,
and connect TWO Diodes, both pointing black stripes down, to the plug on the green wire. The top of one diode
connects back to the green wire to the first ATX supply, the other diode connects to the GREEN, "POWER
ON" wire going from the SECOND ATX's motherboard plug to the ATX supply. The diagram # 59, above
shows the green wires on the two most common ATX MB connectors. Photgraph # 10, above, shows the
actual diodes being soldered on the MB connector's green wire.

On the SECOND ATX supply, look at pin #13 on the corner of the motherboard power connector ( or Pin # 11 on the
older stylem, ATX revision # 1 style, as shown in PHOTOGRAPH # 59, above ), and see if there
are two wires in the single connector or just one. If there are two, one may be the "OLD Style" of brown. This would
be the Power SENSE wire, and inside the ATX box, it should be connected to any ORANGE, +3.3 Volt wire in the
bundle of ORANGE wires, all connected together. If there are TWO wires in connector #13 on the Motherboard
connector, and BOTH are Orange, follow them back to the power supply. One wire is usually thick diameter, and
goes to the BUNDLE of all +3.3 Volt power wires. The other wire, usually thinner, goes to a separate spot on the power
supply, and this would be the SENSE wire. Connect it inside the power supply to any wire in the bundle of +3.3 Volt
ORANGE wires. If there is JUST ONE orange wire in the corner of the Motherboard connector, pin #13, then you
don't have to do anything. Just follow it back to the ATX supply and verify that it is connected to the large bundle of
+3.3 volt Orange wires all clumped together.

CONNECT the 110 Volt BLACK, WHITE and GREEN wires from the first ATX supply to the second ATX supply.
This is shown in photographs 15 and 20 above, along with detailed instructions

On the FIRST ATX SUPPLY, you can snip OFF any unused wires - I cut off "ALL" the +5,G,G,+12 wires normally going
to CD's, Harddrives etc. It is your choice whether to leave them connected to devices, or cut them. Sometimes, if I

calculate the POWER requirements of the Motherboard, and the existing, first ATX Power supply has lots of excess
power, I will wire ONE, single, +5v,G,G,+12v cable to the main "C:" drive. Then I cut all the remaining 5GG12 cables, and
all other hardrives, and CD/DVD etc. devices are powered by the new, Second, added, Power Supply.

On the SECOND ATX power supply, you now can cut off all the wires going to the MOTHERBOARD plug, which is
not used at all. This just cleans up the inside of your computer case, increases air flow, and prevents accidental shorts.

There are lots of diagrams and Photographs above to second check everything before you finish.
IT would be adviseable to read through all the little bits of information above, and look at all the diagrams,
so that you are familiar with the entire power supplies.

NOTE: January 2012: I was talking to a friend who has the latest, greatest computers available, with the
newest software, and the biggest storage drives imaginable. When I mentioned this page on how to add
a power supply, he mentioned "HIS" way of adding power supplies.... probably the fastest, lowest
maintenance, easiest way ever done...
Buy the biggest new power supply you can get your hands on, and set it on TOP of your existing computer
case. Make a hole or use any hole you can find in the case and run the Yellow, Black, Black, Red cables in
to the case to power DVD's, CD's, Harddrives, Fans, and other equipment. He particularly uses these
outside- the- case Power supplies to power massive TERA-byte hard disks. If you have an ATX power supply,
just connect the Power ON green wire to ground, so that it is always ON, and connect any POWER SENSE
wires to the 3.3 VOLT rails inside. DONE. If you have the AT type, just connect the POWER GOOD to
+5 Volt RED wires = done. He does not even turn the EXTERNAL, Power Supplies OFF, at all, since, as he
points out, continuous "Room Temperature" cooling of all the components Drastically lessens the thermal
cycling, which is the #1 problem in computers.... He always installs a CONTINUOUS POWER CONDITIONING
high end, expensive, battery back up, and he has ZERO problems with any new computers ! Fast, simple,
reliable, easy to maintain....
Hey, If it works, why not? Just a thought...

Good luck in adding a power supply. For more electrical information, particularly about
electrical devices used on computers, see




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