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AMDReview Site News!
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Company(s): N/A
User Contributed
Product: Power Supplies
Availability: Now
Author: L.Vogt
Price: N/A
Supplier: N/A
Date: 7-3-02
What's What and Why
Power supplies are the most important part of your computer system. Problem
is, when you say the words "Power Supply" all people think of is the little
grey box with the wires coming out. The correct power supply is meant to last
the life of your machine. These days, with cases becoming cheaper and being
imported from all over the world, people have been putting together Ultra Gaming
Machines and not thinking of what's backing up all that super uber hardware
you dropped big bucks for. Maybe you got a good deal on a case/power supply
combo on Pricewatch,
but what did you get and does it matter?
Characteristics of a Power Supply
Various voltages have to be supplied to your motherboard and components without
ripple or sag I cannot count the times we have seen good motherboards get driven
to an early grave as the power supply couldn't keep up with the demands of the
system.The Voltages +3.3, +5, +12, +5 , -5, and -12 have to be solid and unwavering
in their support of your components or you will have trouble. Problems can range
from simple hangups for no apparent reason to full on burnups of expensive equipment.
Your power supply is the interface between your wall and PC. Depending on how
well that power supply does its job will effect how long your machine lives,
how well it performs and if all of that gear you bought will go up in a puff
of smoke.
There have been thousands of write-ups on video cards, RAM, motherboards and
heatsinks, but very little on power supplies. Perhaps this is because they're
not quite as sexy as the rest of the hardware that can come in various colors
or packaging. But it is the single most important component of the machine,
for both the life of it and how stable it will run. Below there are two power
supplies rippedjust for you. Both are rated for 300 watts. One came out
of a case on Pricewatch
for $25, the second one was purchased for $35 (and that does mean just the power
supply was $35).
Looking at both closely, which do you think is putting out 300 watts?
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Most of the Joe Generic El
Cheapo Power Supplies that come with standard computer cases are often rated 300
watt Peak. This means it's designed to supply that much power for a few seconds
(usually at start up). It's actual running capacity is closer to a 160 watts.
Team B is the power supply on the right which is rated 300 watts continuous and
is probably peaked at a raw 450 watts.
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On close examination of El
Cheapo you will notice that some components are missing. One example may be filter
coils, where your AC comes into the power supply, that haven't been installed
to save a few pennies.
The coils are supposed to be there to smooth out the AC current coming into the
PS. As you can also see by the good power supply that has the filter coils,
filtering the AC current coming
inside is really important to remove the noise before it hits full wave bridge
rectifier. This extends the life of all the hardware. You may also notice the
two large black round things (Capacitors). They take the converted AC to DC voltage
and smooths it, the larger being the better of the two. In this case the difference
between 500uF and 1500uF. Further examination shows the transistors and the heatsink,
obviously the one on the left is lacking in both these areas, which really shows
the difference in quality between the two units. Whereas the one on the right
has so much heat dissipation capacity that we had problems taking pictures of
the rather large transistors it supports.
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Let's take a look at the internal connection from the socket to the mainboard
of the power supply. What a difference a gauge makes! Not to mention soldering
and insulation. Again, this shows exactly how many cheap power supply manufacturers
try to save a penny or two per unit to the detriment of your whole system.
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Now let's take a look at the external connectors.
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With El Cheapo you get a pathetic
show. Trying to use this with multiple hard drives would mean you would probably
need additional Y-Connectors. However, the P4 ready, which has all the connectors
most people will ever need, is a reflection of what the power supply is made to
handle.
Voltages during testing
El Cheapo(Under Load)
12V=11.35V-11.9V
5V=4.4-5.0V
+3.3=2.4-3.7V
P4 Rated(Under Load)
12V=11.96-12.0V
5V=4.98-5.0
+3.3=3.28-3.31
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In the final test, which
we performed by running a regulated AC control to see how well a power supply
would handle undervoltage situations instead of the 110/115V, we took it as
low as 80V. El Cheapo's voltages sagged and dropped out. On the 80V test it
went up in smoke, while the P4 ready kept chugging along and maintained all
of the voltages at the proper level. So to bring it all into perspective, that
Uber Machine you just built, what PS are you using? And how much do you think
that $5 you saved will cost you in the end?
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Noise: The input filtering that he discussed can indeed play an important
role in avoiding mains noise, spikes etc interfering with your system. But
it's primary role is in fact different. The common mode filters used are there
to stop noise getting onto the mains FROM the power supply. This is important
because, at these power levels even the best designed switching power supply
will put a lot of noise onto the mains without them. This can interfere with
the operation of other items in the house. Even worse, there are numerous
standards around the world dictating just how much noise your product can
put onto the mains network. As a system builder, importing and selling cheap
power supplies which are not approved to these standards can
get you into hot water. I am not sure about the US, but in the UK and the rest
of europe the responsibility for testing and ensuring that products are complient
is the manufacturer of the end product. In short, if you use cheap non-CE approved
power supplies in systems you sell in europe, and they are found to be too noisy,
you as the system builder can go to prison for a while. 3 - 6 months I think?
Safety: Not all 'countries of origin' are as safety conscious as perhaps
the more developed nations are or should be. I don't trust anything sold in
europe without a CE mark on it. Yes, the CE directive covers safety too! Not
that a sticker is not just a sign of an unscrupulous manufacturer just putting
on a sticker. After all, have you ever tried to sue a chinese company?? What
do they care! Even though some of the big power supply companies may have
their product made in the same factories, they
still have names to protect, so they will ensure that the products are suitable
for whatever market they are going into.
Power delivery: Here is a little pitfall for those who are running
their systems close to the limits of the power supply. Which you should never
do anyway! A lot of the power supplies save cost by using the same transformer
winding for both the 3.3 and 5V rails. No problem normally, but you have to
realise that the available power from these two rails is dependent upon the
power rating of common transformer winding, rectifier diode, capacitor ripple
current and so on. If you dig into the specs you will often see a combined
maximum power rating for the 3.3 and 5V rails. Usually this is not much more
than for the 5V rail on it's own. Take a look at http://www.enermax.com.tw/eg365ax-ve-fca.htm.
115W on the 3.3V rail and 175W on the 5V rail, right? Wrong. That would be
290W combined. The max available is actually 200W combined. Draw any more
than that and BOTH rails will drop, causing you problems. At least Ennermax
are up front about it! There are one or two companies that use separate output
windings and release a bit more combined power, but it is still something
to be weary of.
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XP:nForce2,VIA KT600
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64: nForce3, AMD8000, K8T
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Intel Motherboards
Latest Chipset: 875P
w/Graphics: 865G
VIA: P4X
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