Can sudden PSU plugging cause tempo power surge?

[JoeyLemor]

Hi,

My ATX PSU doesn't have a power switch at the back so I have to unplug the power cable when I have to work on the motherboard. I have noticed that whenever I plug in the power cable back to the electric outlet, the CPU fan whirls for a few seconds, then stops (even though I haven't triggered the motherboard PWR switch yet).

Is this a temporary "power surge" or "power jump"? Can this cause electrical component failure?

 

[HalComps]

have you tried just turning it off at the wall? then switching it back on and see if you get the same. also you could get a surge protector, you can get them at most hardware stores.

 

[kmcferrin]

I think that it's fairly common to not have a power switch on the PSU. Plugging/unplugging the PSU from the wall shouldn't have a different effect that flipping the switch on the PSU. Either way, it's cutting the power to the components.

The reason that the fan would spin up is that ATX power supplies are providing power to components even if the system is turned off. Most likely the fan spinning is the standard behaviour for when power first is applied to the mainboard.

 

[JoeyLemor]

--- have you tried just turning it off at the wall? then switching it back on and see if you get the same. also you could get a surge protector, you can get them at most hardware stores. ---

The PSU power cable is plugged into a UPS, and probably the UPS already has a power surge protector built-in.


--- The reason that the fan would spin up is that ATX power supplies are providing power to components even if the system is turned off. Most likely the fan spinning is the standard behaviour for when power first is applied to the mainboard. ---

Actually, I got concerned over this issue because I have another motherboard whose fan doesn't stop spinning once the PSU has been plugged in. This motherboard cannot perform POST/boot, so I guess that that might be the cause of the problem. But if you also notice the sudden whirling of the fan on your motherboard, I guess this is something normal

 

[HalComps]

some PSU's require a load on the output in order to discharge the capacitors fully. Even when the PC is turned off, a PSU will draw some power from the wall, most of it going to power the 5Vsb (standby) rail.

this might explain why your still getting a power surge when plugging back in..

 

[JoeyLemor]

Thanks. I think that might explain it. The capacitors discharge once a load is connected. I just wonder if these sudden discharges can cause the DC level to spike-up for a split second? I used to have a motherboard that had leaky capacitors. Could PSU unloading have been a contributing factor or was it just normal for cheap mobos to have leaky capacitors?

 

[edfair]

The power supply brings up the fan power circuits on initialization. It takes a second or two for the power control circuits to sequence things to their normal power off state.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[acewarlock]

leaking capacitors was a world wide problem for a few years when someone was selling bad capacitors, If you want to read the whole story goto

http://www.badcaps.net