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- To much power?
August 15, 2006, 2:59 am
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Re: To much power?
The only time you get into trouble, is if the minimum load for
a supply rail is not met.
If you look at the label on the side of the supply, some of
the supplies list a max amps (say 16 amps) and they might also
list a minimum amps (like say 2 amps). If your motherboard
does not draw at least 2 amps, then the voltage might not
be accurate to the 5% value shown on the supply. (It means
the rail voltage won't be within the +/- 5% tolerance listed
on the side of the supply.)
Basically, what it means is, if you buy a monster supply, simply
check the specifications, to see if the minimum load is 0 amps
or if it is a small number of amps. You can always meet a 0 amp
requirement, so if a supply lists all rails as 0 amps min load, then
it would be safe to use under any circumstances. If the minimum
load is larger, then it can be difficult to determine (without
instruments), whether your computer meets the minimum load. Now,
on rails like +5V and +12V, you know that a disk drive draws
around 1 amp from +5V and 0.6A or so from +12V, so that is
a little bit of load. But on 3.3V, it can be hard to guess at
an appropriate value. The load on 3.3V could be 5 amps or it
could be less (it would be a motherboard load, if it was
present, or maybe the video card uses a bit as well).
There is no minimum load shown here:
The datasheet doesn't show a minimum load here either, so I
would have to assume all rails are minimum loading of 0 amps
and safe to use.
And looking at a few other Enermax supplies, they don't show
any minimum loading data.
This picture is the label on an Antec Truepower. The first three
outputs listed, look to have 0.5A, 0.4A, 0.4A minimum currents.
Those current loads are easily met by any motherboard.
I have seen one supply with a 10 amp minimum load, and that is
the kind of product I would avoid. Many modern supplies have
excellent characteristics, so the chances of running into a problem
are probably remote.
Sometimes, people use an ATX supply to power a disk enclosure
or other kind of custom project. This is an example of a load
resistor which might be used to help meet a minimum load
Sorry I couldn't dig up more good examples.
Re: To much power?
The only consideration like that for otherwise similar power supplies is
that the stated efficiency is for a "peak" output range centered widely
around 1/3 to half the rated output or so. If you are consistently drawing
around 30-60% of rated output, you'll be close to peak efficiency. If the
PS is "too big" (5-10 times what you need) you'll simply draw a bit more
power from the electric company because the efficiency will drop.
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