I have the following setup at home:

  • one PC (300 W PSU)
  • two 22 " TFT monitors
  • a speaker system
  • one external hard disk with separate PSU -

all of the devices are plugged into a multiple socket with a foot-operated switch (sorry for the poor wording. What's the real name for this ?).

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Nomally (and during operations) I am well below the maximum ratings of both the safety fuse and the multiple socket (both rate at 230VDC, 16 A ==> 3680 W).

However, I just yesterday replaced the multiple socket for the second time, because the switch is no longer operational (it is always 'ON'). When I moved into a new home a year ago, I noticed that the safety fuse often triggered when I switched on the multiple socket. I then replaced the fuse with a more lazy one (meaning it does not trigger as fast on power surges)

I suspect that the issue at hand is, that the moment I switch on the TFTs and the computer PSU immediately begin loading their capacitors and I get a really hefty spike.

How could I go about this? Would it be enough to to attach a ferrit bead to the TFT cables?

  • I have a hard time seeing how this question falls into the scope of the site. But I guess its not up to me to argue since I am a new user here. – Kellenjb Feb 9 '12 at 0:26

It's more likely that the problem you're experiencing is high inrush current. All the gear you have connected is going to use switchmode power supplies, which have characteristic high inrush current when first connected to power as large capacitors inside charge. The inrush current for a switchmode supply can be many times higher than its normal consumption, though only for a very short period (less than a second). See the inrush current row of this table.

It is possible that the combined inrush is enough to damage your board/pop fuses. The only way around this would be a board that can handle more current (may not be practical/easy to find one), or to stagger-start the devices - that, is don't have them all energise at once. Neither of these solutions is ideal, you may need to look at spreading the devices over two boards.

  • 1
    @ Terry - Correct, it is an inrush current. This is due to an incorrect Power Factor which can be greatly reduced with a "Green" ATX power supply. – SteveR Feb 8 '12 at 15:17
  • that's what I meant with "loading their capacitors" and "hefty spike". Good to know that the correct (English) term is 'inrush current'. My idea was that you could reduce the current by increasing the inductance of the cable either by applying a ferrit bead - which is quite possibly not enough - or by using longer cables. Are there any devices that would allow me to stagger-start the components - like something I can put in between the multiple socket and the component? – yas4891 Feb 8 '12 at 19:03

The problem could be your computer power supply, especially if it is a few years old. The PC supply is a "switching" type power supply. The older supplies have a poor efficiency rating of like 80%. This is due to an inherited problem in their design called "power factor correction", PFC. Newer "Green" type power supplies have a much better PFC and an efficiency rating of 90%+. That means they waste less power.

I would also suspect the design of the power strip. Maybe you should buy a different brand.

It will also help if you turn off the PC (from the switch on the PS) before powering the strip up and down.

Adding a ferrite bead will do nothing for this problem. Basically that will only eliminate noise in your TFT displays.

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