I posted yesterday about a PSU which was only operating the fans and LEDs but not mobo or processor. The general concensus of opinion was that it was no longer powerful enough to run my hardware. However, I've disconnected everything except the HDD and still nothing. Could this still mean the same thing or should I be looking at another area? Cheers, Grezza.
Hi grezza. From your earlier thread I understand that your computer worked OK with a borrowed power supply. If that is the case then you have proved that everything in the computer is working properly except your own power supply. You haven't told us what you have in your computer, and the key components are the processor and graphics cards. I would guess that you need at least 400Watts, and possibly more than that if you are getting a cheap power supply.
Power supplies are rated according to how much power they can deliver total on the various voltage rails. There are +12V, +5V, +3V, -5V, -12V and 5V standby. The total power for all these is what is quoted. There are 2 problems in this. The first is that although the total may be adequate, one individual rail may not be able to supply enough power for a particular application. For example it is possible (but unlikely) that a computer may have so many fans running on the +12 supply that the power capability is exceeded even though the 3.5V that is used for most motherboard and processor functions is well within the limit.
The other problem is that manufacturers rarely say if the power rating is peak or average. The peak capability is limited primarily by the capability of the transformers and output transistors to deliver the current, while the average is limited by the ability of the power supply to dissipate the heat generated. Making a power supply with a good short term capability is quite simple and cheap with modern components. Managing the heat generated by a longer term high current demand takes more material and so costs more. Adding protection circuits to look after both the power supply and computer in case of a fault, voltage spike or overload also adds to the cost.