Power Supplys and System performance

By snakebuster ·
I have a customers machine doing funny things, not a stranger to us. Power supply is 300w and devices connected pretty much max it out while at idle. Will the start-up draw of a cd/dvd recorder or another device cause other parts of the motherboard to get flaky? If I install 400W I have laying around, could it make the start-up problem go away? I'm pretty sure it only happens when the customer pushes the system to the max.

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Voltage Drops

by TheChas In reply to Power Supplys and System ...

If you draw too much current (power) from a power supply, the first thing that happens is the output voltage drops.

So yes, if the system has too small of a power supply, using a high power device can cause the voltage to drop and result in other parts of the system not working properly.

If they are indeed maxing out the 300 watt supply, I would go to 500 watts rather than the 400 watt you have lying around.

If you do use the 400 watt supply, look closely at the current ratings. Some power supply manufactures have been playing the power game and rating the wattage at the combined maximum for each output and not the real world maximum for normal loads in a system. You will see a disclaimer that the combined current draw for the 5 and 3.3 volt outputs is some maximum level lower than each is rated for. The difference between rated and real power can exceed 50 watts.


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by balge In reply to Power Supplys and System ...

300W is pretty weak, especially if its a generic - try this to spec up PSU -


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You can get really screwy things happen

by OH Smeg Moderator In reply to Power Supplys and System ...

When the Current/Voltage drops below the threshold of the devices that are connected to it. The most common thing is that the CPU is underpowered and causes the system to literally tie itself up in knots.

As for the 400 W that you have laying around you can use this to test with but unless it is one of the better ones like an Antec I wouldn't recommend using it for full time use if the 300 W is maxed out at idle a 400W will not have sufficient power either and will be overworked so it will fail sooner and quite likely take the rest of the insides of the computer along for the ride.


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Yes, but...

by Charles Bundy In reply to Power Supplys and System ...

Your question lacks enough info to formulate a good reply. What makes up the system (e.g. parts break down.) Where are devices plugged in?

I will offer this, no self respecting engineer would spec a PS that is maxed out at idle, meaning minimum current draw. SOP is to calculate MAXIMUM current draw (FULL LOAD) then add a 20% factor on top of that.

Get a PS that meets that design criteria.

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the best I can suggest you do

by jck In reply to Power Supplys and System ...

Is go at least 500W. You can get generic 500W supplies from Newegg and the like for easily under $40 with free shipping.

Considering a lot of CPUs now have 95 watts plus TDP, and many videocards draw 10 amps plus (@12vDC = 120W) you're looking at 215 watts there. a 300 watt supply is gonna fall short almost always unless it's a bare PC.

Good luck with that though.

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