Overloading Rails - How safe is it?


Jul 31, 2004
How safe would it be if I potentially overloaded the +5 rail? This is assuming that I would have a good quality PS like a Fortron or Sparkle and my theoretical +5V max power draw was ~10A past the PSU's max rating.

I'm planning on replacing the PSU on an older Athlon XP system with modest power consumption, so I'm looking at relatively inexpensive 300-350W power supplies. The problem is that the motherboard doesn't have the 4-pin power connector. If I understand correctly, the CPU in this configuration will draw power from the +5 rail. This along with my Radeon 9500 Pro will probably draw a lot of power from +5.

A lot of 300-350W power supplies, particularly the Fortrons/Sparkles that I am leaning toward, have a max of 30A on +5. I figure that my theoretical +5 max would be around 10A over that.

Should I worry about this potential overload? After all, if I'm playing a game I would expect to have full utilization of the CPU, videocard, and memory. Or perhaps I am just thinking about this too hard?

Note that I'm making a lot of estimates based on takaman's calculator. Since the 9500 Pro wasn't listed I'm assuming that it's similar to the 9700 Pro but with somewhat lower power consumption.

Ice Czar

Jul 8, 2001
SockMan! said:
Should I worry about this potential overload?

yes, and more to the point its not just the +5V rail but in most supplys the combined total wattage of +3.3V and +5V rails

and then there is the total capacity of all three of the rails


while your typical draw will be much lower,
its the worse case senerio you calculate for,
the FSPs in particular are conservatively rated, but 10A is asking alot

you sure your not looking at ATX12V v1.3 hybrids?
where some of the capacity has been pulled off the +3.3V & +5V rails and shifted to the +12V?
( refer to my post > http://hardforum.com/showthread.php?t=880989 )
older supplies would thus be more powerful on the rails you need within the wattage class
the safe alternative is to bump up a wattage class to say a 400W