q : why dual power supply?
a : generic power supplies are those that came bundled with the casing and as such are
made of cheap parts and or construction quality is of the so so variety.
as such they seem to fail to deliver power stated on their labels. this is specially
obvious when used in amd athlons and geforce4 video card combinations. i have seen
a 300 watt psu with a filter choke on the 3.3volt rail burned out and another not only
burned out but also desoldered itself out of the circuit board, while in another the
5 volts rectifiers shorted out. the power supply simply can not hack it. this is not to
say that generic power supplies are bad, it is just a matter of derating the psu to be
able to use them safely and thus avoid psu failures. having said those, to answer the
question, dual psu is intended as a cheaper alternative to buying an enermax or a hec
psu which costs 5 to 8 times that of a generic psu.
q : i used two 300 watts atx psu, so now i have 600watt psu?
a : no, this is not about simple addition, we must remember that we don't know the
true capability of the psu in the first place, but the saying "two heads are better
than one", is applicable here.
q : i used a 300 watt psu for my mobo and 200 watts for my peripherals, why is my system
still unstable?
a : if you are using athlons and geforce4ti video cards and plenty of pci cards, then a generic
psu even at 300 watts rated is not enough. i have seen many 300watt psu wherein construction
is very simmilar to a 145watt psu made by astech. 300watt psu such as "lanlon" is a good
example of a capable 300watt psu. so if you are now using a 300 watt psu and can use your pc
but with minor stability issues or if you have many add-ons like fans, two or more harddisks,
then a 2nd psu can help your pc system.
q : is it safe to use dual power supply, will my mobo burn is case something goes wrong?
a : dual psu when implented correctly is not less safe than using a single power supply.
the atx design specs has enough safeguards and is supposed to shut down your psu in case of
overvoltage/overcurrent conditions occuring at the output and undervoltge in the input, some
psu's even went to the extent of incorporting an overtempterature cut off sensor to shut down
your system in the event of overheating of the psu. so which psu have these features? it is hard
tell unless we can open up the psu and look, or test them...more often than not, it is the psu,
not the motherboard that gets fried.
q : how do i implement dual psu for my pc?
a : there are many ways to implement a dual power supply arrangement for your pc.
you can 'google' for dual psu and the web offers many choises. i have enumerted some which i
have tried on my own:
1. two atx psu's with one acting as master and the second one slave, both psu's
are not altered in any way. to power on the two units simultaneously, an extender
device is used, the master's 20 pin header connects to the mobo in the ussual manner
while a 4pin molex to 20pin female header is used to connect to the slave psu, the idea
is to short the pin14,(PS_ON) to ground, a relay can be used for this purpose, but a
simpler way is to use an npn transistor switch in leiu of the relay.
2. an atx/at psu combo with the atx supplying the mobo and the at psu supplying the
peripherals like hardisks, optical drives, flopies, fans, etc...
q : what is a cd-rom psu?
a : an atx or an at psu is modified to fit inside a cd rom casing, the object is to be able to
fix the 2nd psu inside the pc casing, on the 5.25 drive bay, or even the 3.5 inch drive bay.
q : what type of power supply to use for a cd rom psu?
a : although an atx psu is possible to use for a cd rom psu, i preffer the at type since we only
need the 5 and 12 volts rail for peripherals, and a 200watt at psu is sufficient in most cases.
q : how does your cd-rom psu operate?
a : since the cd rom psu is tapped into the main atx psu, power is applied to the cd rom psu once
you plug in your pc to the wall, immdiately a standby 5 or 12 volt is available regardless of
your pc being up or not, this is usefull if you want your fans running even after you power
down your pc, a relay is used to turn on the 5 and 12 volt rails to sychronize them with the
coresponding rails on the main atx psu.
q : how do you attach the cd rom psu to your main atx psu?
a : there are two connections, one is a 220volt power tapped into the atx 220volt receptacle inside
the main atx psu, and the other is a 4pin molex to turn on the 5/12volts rails thru a relay.
q : how about heat, does this cd rom psu add heat inside the casing:
a : to get an idea of the heat that can be produced by the cd rom psu, let us consider the following
loads, cd rom at 25watts, cd writer at 25 watts, two hardisks at 22 watts, ten case fans at 2 watts
each for a total 104 watts, assuming an efficiency of 70%, then 44 watts is lost to the cd rom psu
and this is in the form of heat. considering that an average cdrom casing has a surface area
of about 120 square inches, then assuming perfect heat transfer from psu to cd rom casing,
then we are talking 0.37 watts per square inch, not very significant? consider further that
with the exception of the fans, the rating for the harddisks and cdrom/cdrw are peak values,
they will be lower at idle so expect the 0.37 figure to be lower most of the time.
