Designing mains power feed for maximum equipment lifetime

Question

I want to establish how or if mains power feed to mains powered equipment can be designed to optimise equipment lifetimes. In my case I have a specific item of equipment that I am concerned about but my question is a general one about what design rules or lessons may be applied to even such a simple system to ensure optimum lifetime.

Of interest is how to supply power to or remove power from equipment - whether it is best to leave power supplied and rely on internal switching or to use intermediate switching points, and whether aspects such as mains power surges and spikes or power outages make a significant difference to what is done.

As a specific example - in my case I have a notebook PC (Dell Inspiron 15R) that I use as a desktop PC. I use it in a fixed location and do not have a battery installed (the battery is disconnected and stored away). So this laptop is similar to a desktop PC as regards power supply. This would also presumable apply to batteryless routers, switches, printers etc. There seem to be two options regarding how to supply power.

1) Keep the equipment plugged into a power strip with on/off button and switch on at the power strip when I have to use it and off when use is finished. In this way, however, the power supply of the equipment gets a voltage spike when I switch on the power strip, and absorbs energy to ground (absorbing the remaining currents) when I switch it off.

2) Always keep the equipment plugged into the power socket at the wall, leaving it connected even when not in use. In this way, instead, the equipment (in my example the power supply and motherboard) is always under voltage and never completely "at rest".

So, from an electronic point of view, in which of the two ways is equipment likely to get less damage and live longer?

Answer 1

When designing a system aimed at ensuring long equipment life even simple issues can have wider benefits when viewed as something which can be optimised.

The best solution will vary with equipment design.
Both Methods have good and bad points.

Always on

Has a SMALL chance of major mains spike (lightning, transformer issues etc) causing damage. How serious this is depends on your supply company, quality of circuits and local environments.

• Some geographic areas are far more prone to lightning strike.

• Distribution systems that sag at periods of high load and/or lose power often (daily in some situations) have higher risk.

• Power networks which service factories and industrial loads are liable to be "noisier" and have more spikes or surges.

I live in an area with a high quality power system and few outages and no significant load sag, and low lightning risk - I have had two equipment losses due to surges caused by lighting in 30 years. (Lightning strikes were local in both cases - strike and sound almost coincident).

Always on

Maintains some warmth (small in modern equipment) which may help with condensation.

Components in a standby circuit MAY have somewhat lower lives BUT are designed for long life in this mode.

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When turning on via power strip; Spikes from a power strip and voltage rise on turn on are NOT the same. Any decent power strip DOES NOT spike.

Some have surge suppressors built in and even a low cost MOV suppressor plugged into the power supply connection point to the strip will reduce small spikes.
MOVs wear out with surges but in a relatively environment will last a along time.

For REALLY long life I'd aim at

• Well designed equipment intended to last - in your case you have existing target equipment.

• Good environment

  • Temperature sensible - comfortable human occupation temperature range,

  • Non condensing atmosphere - neither very high or very low atmosphere.

  • Good ventilation, any air vents/fan ports clear of dust and air passages blown out occasionally to keep them clear internally.

  • Low contamination - minimise dust. Keep insects away.
    (I have seen equipment installed in high dust locations with inevitable results, and ants nests inside equipment. )

• Low-surge, high-stability mains power supply.

  • If power fails very often a simple UPS may be in order to allow a more gradual and controlled shutdown.

  • If spikes and surges are common then extra effort with suppressors. Operation from a 1:1 isolating transformer may help alleviate spikes.

Answer 2

Both will work ok and will not damage anything. I have several notebooks and some are always plugged in, some are regularly disconnected, everything just works fine for many years already. Modern devices are designed to work under both conditions.

Answer 3

The standby choices can be done in many ways, which is not a problem per se.

Power supplies which have been known to run for decades use only the highest quality parts , use conservative currents relative to rated DC or ripple current and have conservative voltage stress relative to max ratings, and designs with conservative junction temperature rise. Interfaces are all protected with adequate filters, fan fail detection , OVP, OCP, OTP, and UVP.

When intelligent design, diligent stress verification with a high quality control system for materials, design and processes will result in power supplies built to last a lifetime.

On going reliability life testing is part of verifying your quality.

The leaders in this arena often come from Japanese suppliers with OEM's like Hitachi & Sony or PSU suppliers like Lambda, TDK, OKI, MURATA, Shindengen , some whom I have worked indirectly with on Supplier qualifications. The culture for design quality is quite different from other countries I have worked with, and I learned a lot from their engineers and design methods with strict controls and specifications.

I have also worked indirectly with Hammond in Canada and Keith Billings, a guru in Power Supply design with several books, started when he was at Hammond.