Somewhat OT - can underpowered power supplies damage a system?

Thomas Cameron thomas.cameron at
Wed Aug 18 14:20:12 UTC 2010

On 08/18/2010 02:34 AM, Robert G. (Doc) Savage wrote:
> On Wed, 2010-08-18 at 00:27 -0500, Thomas Cameron wrote:
>> Say, hypothetically, I have 8 identical Intel DG45ID motherboard-based
>> system with 8GB memory and a single drive with a cheap-o generic 300w
>> power supply.  All running Linux, so sorta on-topic.
>> Say those systems have been running for over a year, but lately they've
>> been really flaky.  Random lockups, sometimes they boot with garbage
>> characters on the screen instead of the normal OS boot, sometimes they
>> hang at various parts of the boot sequence, spontaneous reboots when
>> kickstarting.
>> Say the Antec web site says I need more like a 350w power supply, and I
>> read somewhere that PSUs tend to age and get less efficient over time,
>> so I am guessing that I've been starving these things for juice for
>> weeks or maybe months.
>> Hypothetically, could I have actually damaged these systems if the PSU
>> was under-powered?  Or would a new, higher powered PSU fix the problems
>> I've seen?
>> I would guess that too much juice might hurt the systems, but would too
>> little actually damage anything?
>> I know it's not thermal, they're in a very cold room with dedicated HVAC
>> and the airflow is great.
>> Hoping someone who knows more about electronics can chime in.
> Thomas,
> Your suspicions about cheap-o PSUs may be well-founded. A power supply's
> Achilles heel is often the electrolytic capacitors used to absorb and
> filter out high frequency components on its main power output lines.
> There are a lot of square-wave-to-sine-wave conversion operations that
> take place in modern power supplies.
> When electrolytic capacitors (the big ones that look like beer cans) age
> the paste-like electrolyte inside begins to dry out. The heat inside a
> PSU accelerates this aging process. The telltale sign is AC ripple on
> the +5V and +12V outputs. You can see this on an oscilloscope and
> measure it with an inexpensive voltmeter set to read AC volts.
> When 120VAC at 60Hz leaks onto DC power rails, the instantaneous voltage
> (the sum of AC and DC voltages) applied to delicate logic may be many
> times higher than the nominal low DC voltage that should be there. This
> can easily confuse circuitry trying to measure the electrical charge
> stored in a memory cell that represents a 0 or 1 bit.
> I've seen this cause spontaneous reboots, system freezes, and all sorts
> of seemingly random behavior. It's quite common in home PCs whose PSUs
> have been inhaling dust and pet fur for 4-5 years. It's less common in
> data centers, but equipment close to the floor can still accumulate a
> lot of dirt. Lower temps in a data center may slow heat-related
> deterioration, but cheap PSUs will still age faster than well designed
> units with quality parts.
> BTW, this problem is not confined to PSUs. You've probably read about
> motherboards with bad capacitors. A few years ago there was a major
> scandal involving defective capacitors sold to many top tier motherboard
> manufacturers. Tens of thousands of motherboards made with those bad
> parts are causing headaches for sysadmins today.
> If you have any doubts about a particular machine, go ahead and replace
> its power suppply with a known good one. If you can afford it and can
> find one that fits, you might try replacing a cheap-o PSU with one from
> a vendor like PC Power&  Cooling.
> Good luck.
> --Doc Savage
>    Fairview Heights, IL

Thanks Doc.  We've already replaced all of them with Ensoniq units.  I 
was really more worried about whether I had damaged the boards.

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