Power supplys

Hi first time on this site and i hope someone can help . my PSU died and looking around for a replacement, i am getting confused by watt’s and amps , a Zalman 750 watt is 30 amp on the +5 rail and is expensive , yet a £35 PSU 750 watt is 45 on the same rail . i thought you had to have at least 36 amp min ,
so what am i missing? cheap or expensive ? thanks for any reply , brian5451

Hi and Welcome![QUOTE=brianr5451;2288874]Hi first time on this site and i hope someone can help . my PSU died and looking around for a replacement, i am getting confused by watt’s and amps , a Zalman 750 watt is 30 amp on the +5 rail and is expensive , yet a £35 PSU 750 watt is 45 on the same rail .[/quote]Quality PSUs give their rated power, el-cheapo-models only at the moment of their self destruction.

i thought you had to have at least 36 amp min ,
What for? Modern systems have the highest power demand on +12V. Depending on the system configuration, a quality PSU with 400~500 W is often more than enough.

cheap or expensive ?
Look for quality (Enermax, Fortron, just to name a few). Find out, what power is really demanded by your system and get a PSU that meets these demands. A heavily oversized PSU will just increase your electricity bill without further benefit.

Michael

Older systems, pre Pentium 4 days, almost exclusively used the 5v and 3.3v rails to supply power to the entire system. Little power was required on the 12v rail.

Nowadays the reverse is true, almost all of the components use the 12v rail(s), with little power needed for the 5v and 3.3v rails.

If you see a PSU with a higher amperage rating on the 5v rail, it is a very old design.

Don’t buy cheap ever, your PSU is the single most critical component of your computer.

[QUOTE=brokenbuga;2289004]
If you see a PSU with a higher amperage rating on the 5v rail, it is a very old design.[/QUOTE]Or an oversized monster :eek:
The bad thing: If you need to replace the PSU for an older system with high demand on 5V, then you are lost (or forced to buy an extraordinary oversized PSU) :frowning:

Michael

Ok a little Electrical engineering here.

Watts = Volts * amps

so a 750 watt supply draws 6.25 amps if connected to a 120v outlet (US) or 3.125 amps from 220v.

if your 5v rail is rated at 30 amps your supply can use 150 of it’s 750 watts for the +5 rail

You could check the specs on all your components and see what they use. Or you could just wing it.

If you using a fast quad processor that draws a lot of power. So does a high end video card. Everything else in a system doesn’t draw that much.

So if you have a decent processor and a fast video card 750W is plenty of power. If you have 2 smoking fast video cards, an overclocked processor, and 4 hard drives. Get the 1KW power supply.

As for cheap VS expensive. An expensive supply can supply power to meet a load faster then a cheap one so if your gaming on-line and go into a room with 100 other people your processor and video card go from idle to full power in a few nano seconds. If you have a cheap supply your machine can hang because it can’t get the power fast enough.

Also look at the efficiency rating. A 70% efficient power supply will waste 25% of it’s power as heat. More heat inside your case and more money spent to run your machine.

Hi thanks for your answers , i think now i will go for a higher watt PSU possibly 850 watt . many thanks for all your replys , brianr5451