UPS Eaton Nova AVR 625 - Not so fast...

[hgg]

Below are some of the EATON UPS power transitions without any load connected:












I did the same test to the Cyberpower by unplugging and plugging from mains
very fast and many times and it was rock steady.  So, there must be something
wrong with the EATON UPS.  Maybe I will replace all the capacitors and the
comparator & opamp.

Below is the transition of the Cyberpower CP900EPFCLCD I've just bought
but with a 200Watt load connected.  It's output is better than mains...
Highly recommended!   

[Jeroen3]

Maybe you should buy an atx power supply with a higher nominal load so there are larger smoothing caps.

[mij59]

Below are some of the EATON UPS power transitions without any load connected:

Interesting data, seems the ups switches to battery power in less than 20 msec, wondering if several  bounces, like  in the second output pulse after the triggering could affect the power supply of the computer

[hgg]

Maybe you should buy an atx power supply with a higher nominal load so there are larger smoothing caps.

My current PSU is a 500W ATX. 
The Cyberpower waveform is with a 200W load (PC & LCD) connected on the 500W PSU.

There is nothing wrong with my PSU.
The problem is in the crappy EATON UPS.

Interesting data, seems the ups switches to battery power in less than 20 msec, wondering if several  bounces, like  in the second output pulse after the triggering could affect the power supply of the computer

And this is from what I managed to do manually by playing with the mains plug to the UPS.
From what I've observed during brownouts, it gets much worse than that with faster and continuous
transitions.  Our mains power is not the best...

[wraper]

My current PSU is a 500W ATX. 
The Cyberpower waveform is with a 200W load (PC & LCD) connected on the 500W PSU.

There is nothing wrong with my PSU.
The problem is in the crappy EATON UPS.

There is nothing wrong with EATON waveforms, especially something that could cause computer PSU to shut down. Also why are you capturing waveforms without any load? Unless you show that something wrong with waveforms under load, I say your ATX PSU is faulty crap.

[hgg]

I've just connected the EATON UPS to a different PC (250watt load) with a different PSU and tried again to
recreate the problem and captured some transitions.

First a very well behaved transition : (blackout)



...and below the real problem of the EATON UPS captured:  (brownout)



Power was lost for 240ms !!!
The UPS is definitely faulty.
(Looking at the graph can you think what can create this type of behavior? )

But the initial problem of my PC rebooting had two causes.  One was the actual hardware
fault above and the second problem was with my PSU.  But not because it was of low quality. 
On the contrary.  It is the Corsair CX500.  (I have been using it for just over a year.)

http://www.corsair.com/en-us/builder-series-cx500

The "problem" is, that is has active PFC for increased efficiency. 
This type of power supply does not like square wave approximations
and the output from the EATON is not even close to an approximation...

[bktemp]

It looks like the battery in the UPS is dead or the output is heavily overloaded. The voltage is regulated by chaging the duty cylce of the generated square wave (actually the phase shift between both half bridge drivers). The peak amplitude is determined by the battery voltage and the tranformer ratio.
Initially the UPS starts with a typical duty cycle, but the voltage is way too low. Therefore duty cycle increases, but the battery can not supply enough current and the voltage falls further. At the end the PC shuts down and the the voltage recovers without the load.

[hgg]

It looks like that but its not.
The battery is in mint condition and fully charged.
The PC does not have an APFC PSU and did not shutdown or reboot.

[FlyingHacker]

Maybe measure the current flowing from the battery (keeping in mind it may be a lot more than your meter can handle) and see if that is in line?