Do my PSUs like The Button?

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Hi,

I have a strange question: A long time ago, my monitor failed (big CRT). The guys in the shop took it and said that this is the first failure of that type. When they gave me the repaired one they said it had burned relay contacts.

Inside was I guess a switched PSU with a big scary cap right on the 230V part.

I have my monitor (and my whole PC set) plugged into one extension cord with a Switch (the Button). Now, in the CRT it was understandable, that it had frequently opened and closed the contacts and therefore failed (I did ofcourse first switch it off using its normal button, only then using the main switch on the extension cord).

Q: Does this kind of turning on and off have any negative effects on the PSU in question?

Thanks,

David

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Daqq wrote:

Quote:
I have a strange question

Yes, it's a strange question .... as I asked myself the same question too :lol:

Never got an answer to it, so I sorted it out myself. The crux lies in the PSU-design. Proper designs have a current-limiter in the BigCap-circuit. Usually two NTC's. Cheapy stuff (f.i. PC-PS's, 450 Watt, € 25) lack such current-limiters. So each time you power them up .... KlaBammm (in Dutch) .... and it depends on the quality of the components used how often they can handle that.
In CRT-monitors, there is a de-magnetizing circuit that gets activated at power-up, to de-magnetize the mask in the CRT. Often a relay is used to turn it off, but it's a considerable amount of current (and also here, an NTC takes in seies with the relay-contacts)

Nard

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Strangely enough - most devices fail when you power them up. So there was this idea that many people adhere to that you keep your PC/monitor etc always powered up. In switchmode supplies this has the effect of shortening the life of the electrolytic capacitors. So next time you powerup, the unit will fail! Nard is correct with the NTCs used to limit the start current. In many cases the fuses get work hardened and brittle with each powerup cycle and the high inrush current and eventually fail. You can see the difference in a fuse that has failed this way- there is no plating on the glass of the fuse whereas a fuse that has failed due to a big short circuit has metal plated on the glass - when you see this you know something bad has gone wrong and it is worthless to try replacing the fuse. The silica filled ceramic fuses are much better in this regard.

I would have to conclude each time you power up a switchmode supply, you may be shortening its life but by the same token, keeping it powered will also shorten its life. Choose you poison!