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I have a lab computer I built to run VM's and that can cater for old and new hardware devices to help me with my job. It contains a fair amount of hardware, some of which doesn't need to be on all of the time. I wanted to place this hardware on a separate ATX PSU to preserve it's life and perhaps reduce UPS load (it runs 24/7). By doing this I could power down the secondary PSU while the computer is running. I have a simple ATX on/off switch on the secondary PSU and it's working ok. However it has an issue where if I place a 3.5 hard disk in one of my caddies (connected to the secondary PSU), the SCSI optical devices/bus will reset over and over again. Interestingly this doesn't happen with a 2.5 drive in the caddy. So I'm wondering if this is an in rush current issue? All devices on the secondary PSU are on the same chain which I didn't think would be an issue as there isn't anything very power hungry on it. Only the SCSI bus is affected by this. Everything else on the secondary PSU operates fine with a 3.5 disk in one of the caddies.

The secondary PSU has the following devices connected:

2 x SCSI optical drives (CD and CDRW) 2 x SATA bluray burners 3 x SATA disk caddies 1 x SAS HP Ultrium LTO tape drive 1 x LS-120 floppy 1 x 120mm fan for cooling the caddies

What are peoples thoughts?

Thanks, James.

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  • Doesn't seem like a great idea to me. A modern, efficient, switching power supply should waste little when providing low power. As for wearing out, the only component that deteriorates with use is the fan, which has a mechanical bearing. All other parts have indefinite life, though a mains power spike can destroy a PSU.
    – DrMoishe Pippik
    Commented Oct 7, 2021 at 18:49
  • Points taken, although I've had plenty of equipment die in the past simply from being on standby so I would like to be able to turn these devices off without them burning away all day long. Maybe someone will have an answer for the actual fault I'm having soon but thanks for the input.
    – James Mason
    Commented Oct 7, 2021 at 20:45
  • @DrMoishe Pippik: You said: "...As for wearing out, the only component that deteriorates with use is the fan, which has a mechanical bearing..." That is wrong. Electrolytic capacitors which are part of every modern computer power supply wear down. Their capacity decreases and their ESR rises until the point where the power supply fails.
    – r2d3
    Commented Oct 9, 2021 at 9:24
  • @r2d3, Ancient electrolytics did have a short lifetime. On modern devices, they fail only rarely, though there have been occasions when a manufacturer buys a bad lot, e.g. between 1999 and 2007: see hackaday.com/2019/04/12/… . Thankfully, electrolytics' reliability is now much better.
    – DrMoishe Pippik
    Commented Oct 10, 2021 at 0:52
  • Regardless how "good" capacitors have become "the only component that deteriorates with use" is still wrong. And even though high quality capacitors exist, they degrade. Quality products come with a data sheet that specifies life time taken into account environment conditions: products.nichicon.co.jp/en/pdf/XJA043/e-uwx.pdf
    – r2d3
    Commented Oct 10, 2021 at 9:26

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