PC Power Supply Failures After Running on a UPS
Posted: Sat Jun 11, 2022 11:08 am
Had an interesting set of coincidences happen today.
I run 4 PCs in the Office and Shop. Three are on one UPS and the workbench PC has its own UPS.
Both UPS are older APCs and the ATX power supplies in these machines are around 10 years old. One may be older.
Around 2:45 AM we had a large area power failure due to a nearby car wreck and the PCs were on UPS power.
As you might expect the beeping woke me up and I proceeded to shutdown the machines orderly while they ran on UPS.
I then shut down the UPS units to conserve battery and more importantly stop the beeping.
I was already awake when power came back on and I began to restart the network and machines.
Two PCs, on different UPS units, would not power up.
Hmm...
Being prepared I already had one new ATX supply and a used one so I installed them.
Both machines booted.
So why would two power supplies fail after simply being shut down?
Here's my theory:
The power supplies are old and the caps aged. Maybe 75,000+ hours of operation.
When they transferred to UPS power the caps saw increased ripple current.
These UPS run at a slightly higher frequency than line (clocks run super fast) and they have high harmonic content.
The high harmonic content and frequency "finished off," and maybe boiled off, the remaining electrolyte in the standby or primary side HV caps.
Other than that theory I don't have much to go on.
I'm thinking this power outage may have, in an odd way, done me a favor.
I run 4 PCs in the Office and Shop. Three are on one UPS and the workbench PC has its own UPS.
Both UPS are older APCs and the ATX power supplies in these machines are around 10 years old. One may be older.
Around 2:45 AM we had a large area power failure due to a nearby car wreck and the PCs were on UPS power.
As you might expect the beeping woke me up and I proceeded to shutdown the machines orderly while they ran on UPS.
I then shut down the UPS units to conserve battery and more importantly stop the beeping.
I was already awake when power came back on and I began to restart the network and machines.
Two PCs, on different UPS units, would not power up.
Hmm...
Being prepared I already had one new ATX supply and a used one so I installed them.
Both machines booted.
So why would two power supplies fail after simply being shut down?
Here's my theory:
The power supplies are old and the caps aged. Maybe 75,000+ hours of operation.
When they transferred to UPS power the caps saw increased ripple current.
These UPS run at a slightly higher frequency than line (clocks run super fast) and they have high harmonic content.
The high harmonic content and frequency "finished off," and maybe boiled off, the remaining electrolyte in the standby or primary side HV caps.
Other than that theory I don't have much to go on.
I'm thinking this power outage may have, in an odd way, done me a favor.