ae and ae and ae......: getting know about Power Supply Unit (PSU) for beginner

olaaaa... :D

it's a hot day ! even in a hill.. :(

today, i would like to share my limited experiences (I'M NOT AN EXPERT IN THIS TOPIC) about PSU. PSU is one of PC parts usually forgotten. Most of people buy a good PC without paying attention in PSU. Whereas, PSU plays an important jobs in PC system. Yes, PSU is a device that giving ur PC a life ! If there is no PSU, then ur good-powerful-cool PC will be nothing because it cant be used.

Stupidy, a good PC deserves a good PSU. If u can buy an expensive PC u should be able to buy a good (expensive) PSU. As for me, the budget for PSU is about 10% of PC total budget.

What is a good PSU? Must a good PSU has an expensive Price? What makes the PSU worth to buy?

okay, before i answer these questions lets talk about PSU it self. I hope from what i explains below, these questions will be able to answers :)

PSU SPECs

if we have a PSU, usually we'll see many words in the body explaining PSU's capabilities.

# POWER

power in electricity can be shown as watt (real) or VA (apparent) ; VA stands for Volt Amperes.

so, what is power?? let me describe it in my way.. :)

- Volt Ampere (VA)

VA is the result of volt (V) * current ( A )

or in mathematical VA = V * A

why VA is an apparent? because actually the devices don't use as much as the values from the formula above.

- Watt

watt is the real power that devices used. This information is the main point of a PSU. If u need a 400W power u need buy at least a 400W PSU.

so, what makes the VA and Watt different?

there are a coefficient called power factor ( pf ). VA values always bigger than Watt values. so, in mathematical i can say that pf = watt/VA ; 0< pf <1

pf = 1 means the PSU system is a good system because there are no "power loss". pf will be useful in the countries that use VA to make the bill !

- PFC

PFC stands for power factor correction. this is a circuit in a PSU. A PSU with PFC has better pf than PSU without PFC. there are two kinds of PFC

a) pasif PFC or PPFC. this is an earlier PFC circuit formed by capacitor. pf values of PFC is about 0.7 - 0.8 while non PFC PSU gives 0.5 - 0.6.

b) active PFC or APFC is a newer PFC circuit that gives up to 0.99 values of pf

for example : if there is a PPFC PSU (pf=0.8) then to serve a 400Watt, it actually need 500VA to fulfill it.

- RAIL

rails are the lane of PSU. in PC PSU there are (the important ones) 3,3 v rail, 5 v rail, and 12 v rail. a new model PSU usually consists of two or more 12 v rail. Nowadays 12 v plays important parts of PSU because this rail deliver the most power of PSU.

- RIPPLE

ripple is fluctuation of PSU rail. the a perfect PSU will give a constant value of its rail. of course there are no perfect one :D. 5 % or below of ripple may indicates a good PSU.

- over X protection (OxP)

OCP (current) and OVP (voltage) is a protection for PSU. PSU will be shutted down if there are any over values in current or voltage.

- peak and continuous power

peak power is a short time power that PSU can deliver. Continous power is the the power that PSU can give all the time. if PSU's peak power is used, the PSU will be dead soon enough.

- efficiency

efficiency is a ratio between output power and input power. As an example, if ur PC consumes 400W and the input needs 500W then the efficiency is 400/500 = 80%

# CONCLUSION

so, from what i explain above? what is a good PSU???

first of all, u need to know how much power ur PC need... u can use PSU calculator to predict it.. one of the best PSU calculator can be found here : http://www.extreme.outervision.com/psucalculator.jsp

just for a safety, please choose a slight bigger values from what u get from the PSU calculator.. for example, if the PSU calculator say that u need a 350W PSU, i recommend that u better buy a 400W PSU.

the second one, choose a PURE POWER PSU !!! why? because i'm sure it will be good if u get from what u paid. so, if u need a 400W PSU, please buy a real 400W PSU. dont be fooled by its label !

the next step is u need to pay attention in PFC. as i explain above, PFC is very useful if ur country uses VA values for ur electrical bill. but, if the electrical bill still based on WATT values, i can say that PFC is not worth enough.. in additional, PFC helps u to protect from a bad electric wave. Please note that, some countries have rules about PFC. A PSU in those countries must use APFC.

then, u need to concern in efficiency. the bigger efficiency values the better PSU u will get. for now, a 80% efficiency is a must and be a trend :) in some countries, a electrical bill is based on WATT consumption. So, i can say that the more efficient ur PSU the less money u will spend to pay ur electrical bill :)

Today's PC parts uses 12 V rail as their power source. Graphic card, HDD, Motherboard, and others. so, 12V rail is something special. you may need at least 30A currents in 12V rail. it will gives u 360 VA just in 12V rail. then 5v rail can serve 25 A so there is 125 VA. And the 3,3v rail can serve 20A so there is 66 VA. so from examples above the total power of the PSU is 360+125+66 = 551 VA.

please note that, in the PSU label there should be (usually) printed a PURE POWER of PSU in WATT. so, if the PSU label says 400W and there are informations about pf = 0.8 and efficiency = 85%, these mean :

a) PSU can deliver (DC output) 400W continous power

b) PSU actually deliver 500VA continous power --> from pf

c) PSU actually consumes 470,588 Watt (ac input) or 588.235 VA --> these values will be used to create ur electrical bill

so, in short :D good PSU are :

1) pure power. u will get what u paid !

2) small ripple. 12v rail is true 12v , 5v rail is true 5v and 3,3v rail is true 3,3v rail. there are no ripple :) --> 5% is threshold for each rail

3) high efficiency (80 % or above) and APFC

additional :

4) protection --> OVP, OCP

5) modular cable for cable management and air flows

6) must have all connectors u need

7) warranty ;)