need suggestion to select right wattage psu

currently i got 400watts psu .
my sys specs are amd 7750
gigabyte ga 78mh mb
igp 3200
hd 500+240+160 sata and one ide 40gb hd
dvd rw
2 80mm fan

but recently my sys switches off automatically and guessd psu maynot able to deliver required power. and one power connector to mb is melted(plastic case)
now i want suggestion in selecting new psu

shall i go for some branded 400watts itself or
should i opt for higher wattage psu say 450 or 500watts (sorry for bad english as i posted from mobile)

eXtreme PSU Calculator

HERE

A Guy

And a calculator from Antec:
Antec Power Supply Calculator

My philosophy is that if I'm replacing a component I might as well upgrade. So I would look at the cost of a larger supply and if it is reasonably close to the price of a straight-across replacement I would go for the improvement.

Your symptoms can also be caused by overheating.

And a power connector that has melted at the motherboard? You need to address why that has happened right away.

I agree with both responders above (note the Antec calculator is really the eXtreme calculator). But if you follow the instructions, you only get the minimum recommended for your current hardware. Therefore I recommend a few settings so you can get a PSU that will support you through several upgrades for years to come. Here's my canned text on sizing using the eXtreme calculator:

Use the eXtreme PSU Calculator Lite to determine your minimum power supply unit (PSU) requirements. Plug in all the hardware you think you might have in 2 or 3 years (extra drives, bigger or 2nd video card, more RAM, etc.). Be sure to read and heed the notes at the bottom of the page. I recommend setting Capacitor Aging to 30%, and if you participate in distributive computing projects (e.g. BOINC or Folding@Home) or extreme 3D animated gaming, I recommend setting both TDP and system load to 100%. These steps ensure the supply has adequate head room for stress free (and perhaps quieter) operation, and future hardware demands. Research your video card and pay particular attention to the power supply requirements for your card listed on your video card maker's website. If not listed, check a comparable card (same graphics engine and RAM) from a different maker. The key specifications, in order of importance are:

1. Current (amperage or amps) on the +12V rail,
2. Efficiency,
3. Total wattage.

Don’t try to save a few dollars by getting a cheap supply! Digital electronics, including CPUs, RAM, and today's advanced graphics cards, need clean, stable power. A good, well chosen supply will provide years of service and upgrade wiggle room. Look for power supply brands listed under the "Good" column of PC Mechanic's PSU Reference List. Note that some case retailers “toss in” a generic or inadequate PSU just to make the case sale. Be prepared to “toss out” that supply for a good one with sufficient power.

Most PSUs have an efficiency rating of around 70%. This means for every 100 watts of power a PSU draws from the wall, only 70 watts is delivered to the motherboard, with the rest wasted in the form of heat. The best supplies are 85 to 90% efficient, and as expected, cost more. I strongly recommend you pick a quality supply with an efficiency rating equal to or greater than 80%. Look for 80 Plus - EnergyStar Compliant labels.

Too big of a PSU hurts nothing but your budget. Your computer will draw from the PSU only what it needs, not what the PSU is capable of delivering. If a computer needs 300 watts it will draw 300 watts regardless if the PSU is a 350W, 650W, or 1000W PSU. In turn, the PSU, regardless its size will draw from the wall only what it needs to support the computer. In this example, it will draw 300 watts, plus another 45 – 90 watts, depending on the PSU’s inefficiency.

As noted, the eXtreme Calculator determines the minimum requirements. If the calculator (with the changes I suggested) recommends a 400 watt minimum, a quality 400W supply will serve you just fine. But a quality 550W – 600W supply will have, among other things, larger heat sinks to dissipate potentially more heat. It might have a larger fan too. The 400W supply will run most of the time closer to capacity, while the larger supply will be loafing along, rarely breaking a sweat. To help the smaller heat sinks get rid of the wasted 80 watts (20% of 400) of heat, the fan in the 400W supply may need to run full speed, while the fan in the larger supply, with bigger sinks just loafs along too – but in near silence.

Don't forget to budget for a good UPS with AVR (automatic voltage regulation). Surge and spike protectors are inadequate.

thanks for the suggestions it helped me a lot
i used 30% capacitor ageing and got around 550Watts which is clearly way short of my current psu 400watts

add on increased after i assembled the config .found corsair 600 watts will be ok!!!

i just want to know few things

why the power connector from psu to mother board is melted(plastic case) 4pin!!! is it because of psu?
now my systems works but all of sudden it switches off(it doesnt even give any warning)!!!

if i get a high wattage psu (600watts) will both the prob solved!!!

Regards
RAj1402

raj1402 said:

why the power connector from psu to mother board is melted(plastic case) 4pin!!! is it because of psu?
now my systems works but all of sudden it switches off(it doesnt even give any warning)!!!

The melted plastic is a problem that goes far beyond the usual power supply issues. The only way the plastic could melt is if there is either resistance so great that the metal contacts become red hot - like a toaster, or there is arcing (sparks jumping a gap). Neither are good and both are a fire hazard. This could be caused because the connector was not fully seated into the socket and not making good contacts, or the socket or connector were/are deformed.

If the plastic that is melted is on the male connector from the power supply, and the female socket on the motherboard is un-melted and clean, then replacing the power supply will also replace the connector and if the new connector fits correctly into the socket then it would solve this issue (melted parts).

If the socket on the motherboard is melted then unfortunately you may need a new motherboard. (If you are handy with a solder gun you could attempt to replace the socket, but in most cases - not an option).

if i get a high wattage psu (600watts) will both the prob solved!!!

Both problems could be caused by the faulty connection. That is why I said that you need to address that issue first. Not only could it be all that is wrong, but it is hazardous and should be fixed straight away.

Once the faulty connection is addressed then you will retest the system to see if any issues persist.

Good Luck.

The only way the plastic could melt is if there is either resistance so great that the metal contacts become red hot

Ummm, no, actually, that is "bass ackwards". If the resistance is great, you, in effect, have an "open" circuit and like turning off a switch, you stop all current flow. If current is not flowing, you have no friction, thus no heat.

But as Ohm's Law tells us, when resistance goes down, current goes up. So if there is a "short" (0 or near 0 ohms or no resistance) in the circuit somewhere, too much current will be drawn through the circuit and the connector. When current goes up, many more electrons are zipping along banging into each other and the conductor, creating lots of heat, and in this case, extreme heat for that connector.

If the plastic that is melted is on the male connector from the power supply, and the female socket on the motherboard is un-melted and clean, then replacing the power supply will also replace the connector and if the new connector fits correctly into the socket then it would solve this issue (melted parts).

If the socket on the motherboard is melted then unfortunately you may need a new motherboard. (If you are handy with a solder gun you could attempt to replace the socket, but in most cases - not an option).

The problem is, replacing the melted parts does not fix the "short". Working power supplies only deliver what is demanded of them. That is, a 1000W supply does not pump out 1000W because it can, it pumps out what the "load" is demanding. So if a connector on the motherboard saw so much current it melted the connector, that is a clear indication something on the motherboard has shorted out, and is drawing excessive current. In other words, while your PSU may be bad, I suspect the motherboard is too.

It takes more than being handy with a solder iron (a soldering gun would be WAY to hot, and the tip way to big for any precision work, BTW). Motherboards are multi-layered PCBs (printed circuit boards), typically with 3 or 4 layers (strata) of signal traces and circuitry.

I must apologize for not picking up on the "melted" connector comment in your opening post. That gives me concern there is still something wrong with the motherboard, or a device that is powered through the motherboard, such as a card, or the CPU.

now my systems works but all of sudden it switches off(it doesnt even give any warning)!!!

How long does it work before switching off?

I too missed the reference to the melted connector! As Digerati says, that is likely caused by at least an intermittant short, causing too much current draw. A Guy

I also have this info from our resident guru Paul on another newsgroup I frequent:

"Are you careful to mate the latches on the power connector(s)?

The connectors can "thermal walk-out" from the motherboard. As the
connector gets warm, it expands a bit. Over hundreds of power cycles,
power connectors can gradually work themselves out of the socket.
The latch on the 2x2 and main power connectors, is intended to snap
together, to keep the contacts fully engaged, and prevent walkout.
Once the connector walks out, the badly made connection arcs and
heats up, damaging the pins.

It could also be a problem with the Vcore circuit itself, or even
a partial short on the CPU side of the circuit. That could cause
an abnormal level of current flow on the 12V.

Even extreme overclocking, could burn the pins. An example would be
a D 805 overclocked to 4GHz, which draws well over 200 watts.

Paul "

*********

For the OP:
You have 2 issues that need to be worked out:
1) The damaged connector(s) must be corrected.
2) The reason the connector became damaged must be determined.

As Digarati says, you may be dealing with a defective motherboard. But there is a small possibility that you may be lucky and the problem is only a poor connection.

The hope is that you can replace just one component to make the repair. This is, of course, providing the connector and socket are not both damaged. If they are both melted and damaged beyond repair then you are looking at a new power supply and a new motherboard.

Pictures of the connector and the socket would go a long way towards someone being able to tell you if they are beyond repair.