Author Topic: UPS Eaton Nova AVR 625 - Not so fast...  (Read 18439 times)

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Offline hgg

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UPS Eaton Nova AVR 625 - Not so fast...
« on: September 30, 2015, 12:43:17 pm »
Hi everybody,

I have a problem with my computer UPS.  Its the Eaton Nova AVR 625.
https://powerquality.eaton.com/SEA/Products-services/Backup-Power-UPS/Nova-AVR-UPS/Nova-AVR-specs.asp?CX=35

It was working alright for the last couple of years but now has the following problem.
It works fine in a blackout when mains power is completely off but it cannot keep up
during very fast brownouts.  If power goes out for a fraction of a second, then the PC
switches off and reboots.  I have replaced the battery but the same thing happens.

It is sold as an online line interactive UPS but I am not sure about that. 
Can you guess that from the pictures?

The mainboard:


The main transformer:


A couple of fuses under the heatsink:


One of the CEP83A3 N-Channel Mosfets:


One of the two LM324 opamps:


The main MC68HC908 8bit Microcontroller:


The USB control board:


...and finally some musical relays...:


Do you think that this problem is caused by the relays?  (..being Chinese quality parts..)
There are no big capacitors on the board. I have two of these UPSs and they both have
started doing the same thing.   

Any ideas?

Thank you for you help.
George.
« Last Edit: October 01, 2015, 07:29:49 am by hgg »
 

Offline mij59

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #1 on: September 30, 2015, 12:49:46 pm »
May there is a problem with the power supply of your computer, have you tried the ups with an other computer ?
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #2 on: September 30, 2015, 12:52:26 pm »
Both the PC and the connected LCD display switch off together.
I have two of these UPSs connected to different computers and they both have started doing the same thing.
 

Offline firewalker

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #3 on: September 30, 2015, 12:55:31 pm »
Check all the electrolytic caps.

Alexander.
Become a realist, stay a dreamer.

 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #4 on: September 30, 2015, 12:59:01 pm »
I will measure them later when I have some time, but at least visually they all looked fine.
 

Offline mij59

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #5 on: September 30, 2015, 01:08:38 pm »
Please post a picture of the copper side of the mainboard, first check for bad solder joints, connectors etc.
On the usb control board is a bad solder joint, but don't think that is the fault.
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #6 on: September 30, 2015, 01:11:58 pm »
I suppose you mean the one above the label C16.
 

Offline mij59

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #7 on: September 30, 2015, 01:17:34 pm »
I suppose you mean the one above the label C16.
Yes looks like the pins of a voltage regulator.
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #8 on: October 01, 2015, 05:25:25 am »
I've just checked all the electrolytics. 
The capacitance values are close (lower values) and they have the following ESR values:

a) 1000uF   16V   0.034 Ohm
b)     47uF   50V   0.714 Ohm
c)   120uF   16V   0.572 Ohm
d)     47uF   50V   0.651 Ohm
e)     47uF   50V   0.600 Ohm
f)      22uF   50V   0.602 Ohm
g)    10uF    50V   2.020 Ohm
h)     47uF   50V   0.946 Ohm

Do you think they need replacement ?

I have also checked all the solder joints and they seem fine.  Even the one on the USB board.
It just has less solder.

Why does the UPS works during a blackout but not during a brownout?

Below is a photo of the underside of the board:


 

Offline krish2487

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #9 on: October 01, 2015, 09:20:55 am »
From the ppics of the transformer, If the farther side has more than 3 wires of the same gauge ( cant see clearly in the pics, it almost certainly is a line interactive UPS. The multiple wires are to indicate different taps to switch between to regulate output voltage.


caps (g) and (h) look suspiciously bad. All the more of they were not a single cap and multiple in parallel. I d replace them for a good measure.


The brownout can happen due to several reasons.


1. The line brownout transitions are extremely fast and narrow in duration (high slew rate) - confusing the processor to take a decision.


2. The brownout voltage itself in on the cusp inbetween two voltage taps and varying by a small amount, leading the processor to go nuts trying to decide between which taps.


3. The processor has gone nuts. (unlikely because as you reported the UPS works fine in black outs)


4. Most often the stepdown and sense analog circuitry will have a couple of op amps, it is also possible that one of the op amps and /or associated circuitry is the cause (This seems more likely, since I dont see a sense tap on the transformer, meaning non isolated voltage sensing.) It is possible that during one of the brownout or spikes one or more of the components in the circuit path were affected.


I d start by checking and replacing the op amps.


PS: R182 and R67 SMD resistors in the previous pic , towards the top seem burnt. Is that the voltage divider section for AC??.
If god made us in his image,
and we are this stupid
then....
 

Offline mij59

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #10 on: October 01, 2015, 09:36:20 am »
A lot of the solder joints on the main board are not that good, there's a small darker band on the solder indicating the connection is bad, e.g. below C49.
Resolder the pins of connectors, power transistor etc.
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #11 on: October 01, 2015, 11:22:47 am »
krish2487 hi,
Yes, the transformer has 3 wires, so its a line interactive UPS.
It seemed strange to me the fact that there are no big smoothing capacitors in the circuit,
but then I looked at the output of the UPS...

With no load:


With a 15" LCD monitor connected:


Output Ripple with light loading...:


I am not sure if this output is any good for any of your PC components, even for 5 minutes...
I am starting to think that a pure sinewave UPS is a better idea.

Quote
4. Most often the stepdown and sense analog circuitry will have a couple of op amps, it is also possible that one of the op amps and /or associated circuitry is the cause (This seems more likely, since I dont see a sense tap on the transformer, meaning non isolated voltage sensing.) It is possible that during one of the brownout or spikes one or more of the components in the circuit path were affected.

In the first picture immediately right of the heatsink you can see a Cosmo 1010 optocoupler.
Two more are on the other side of USB control board.  (The unit has RJ45 protection as well.)
So maybe its protected from such spikes.

I don't like the thought of replacing the opamps.  They are heavily populated with tiny SMD devils
in a very small space....



What can I check on them without removing them?
I will replace the caps just to be sure and I have just removed a relay to check its switching speed.

Quote
PS: R182 and R67 SMD resistors in the previous pic , towards the top seem burnt. Is that the voltage divider section for AC??.
Sorry, this was not a good photo. 
The red stuff is the glue that they put to hold in place the SMD parts.

Quote
A lot of the solder joints on the main board are not that good, there's a small darker band on the solder indicating the connection is bad, e.g. below C49.
Same here.  Its the flux residue.


 

Offline mij59

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #12 on: October 01, 2015, 12:40:50 pm »

Quote
A lot of the solder joints on the main board are not that good, there's a small darker band on the solder indicating the connection is bad, e.g. below C49.
Same here.  Its the flux residue.



Its no the flux residue thats creating the darker ring, the ring is caused by missing solder.
Take a look at the 3 pins to right of the flux residue, the solder should have flown up on the pin, the solder doesn't stick very well to the pin. 
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #13 on: October 01, 2015, 12:54:23 pm »
Although the soldering is not the best, I've tested the connections and they are ok.
I will reflow all the pins that are in a similar condition, just to be on the safe side...

I have also tested two of the relays and they have a switching time of 4.8ms which is
inside the maximum 10ms specified in the datasheet.  Maybe they should be faster (?)



I am going to buy some new capacitors and relays and test them.
 

Offline mij59

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #14 on: October 01, 2015, 01:05:37 pm »

I have also tested two of the relays and they have a switching time of 4.8ms which is
inside the maximum 10ms specified in the datasheet.  Maybe they should be faster (?)



I am going to buy some new capacitors and relays and test them.

Test the NO and NC contacts of the relay with an Ohm meter.
Please test how long it takes for the ups to supply the computer when mains fails.
 

Offline krish2487

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #15 on: October 01, 2015, 05:07:40 pm »
Meh, the MSW UPS are just fine for computer load.
High harmonic content and all but should not affect the performance.


The ringing too is just fine, should not be a problem. Its more likely the scope probe introducing a ringing, more than the circuit and load.


Neither is the relay switching time. 4.8 ms is ~ 1/2 of 10 ms which itself is a half cycle duration for 50 Hz.
It is pretty conservative switching time. I wouldnt worry about the relay switching time.


Which leads me to another question, is the brownout behavior consistent whenever it happens??  or is it more of a random appearance??
If it is random then I would not worry about it.
Freescale should have an application note about the UPS. It wont give you exact circuit (This is roughly a 2 decade + old circuit ) but it should provide you with a more informed idea of where exactly you should start board level debugging.


I seriously doubt you will get any kind of schematics/manuals for that.
If god made us in his image,
and we are this stupid
then....
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #16 on: October 01, 2015, 06:54:55 pm »
Quote
Test the NO and NC contacts of the relay with an Ohm meter.
I measured two of the relays and the NO & NC resistance is 0.01 Ohms, so I guess they are fine.
I will measure the other 3 as well, but it looks like that the problem is not from the relays.

Quote
Please test how long it takes for the ups to supply the computer when mains fails.
I will try that as well, but the UPS works fine with blackouts.

Quote
Which leads me to another question, is the brownout behavior consistent whenever it happens??  or is it more of a random appearance??
No, its more like a random appearance.  I guess it depends on how fast the brownout is.

Quote
If it is random then I would not worry about it.
What do you mean you wouldn't worry?  :)  The PC reboots off while working...
 

Offline oldway

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #17 on: October 01, 2015, 08:47:34 pm »
I really wonder how it would be possible it should be a line interactive UPS. :scared:
When mains fails, it is like a short circuit because all the loads are still on.
You need to limit the short circuit current feeded by inverter by a big inductance in serie with the mains.
This inductance is generaly produced by a magnetic shunt in the transformer.
I did not see such a magnetic shunt in the transformer.
Output waveform of inverter must also be sinus in an interactive UPS.

For me, that's not an interactive UPS, but probably an off line UPS with inverter running all the time.
Switching between mains and inverter is done by relais.
Load is normaly feeded by mains and switched on inverter in case of mains failure.

Check this, because you can't make a diagnose without be sure first of the principle of working of your UPS.
 

Offline krish2487

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #18 on: October 02, 2015, 05:51:17 am »
@oldway
you are right. I have been blind.
It is not a Line interactive UPS.
It is a push pushpull output stage. Hence the square wave output.
If god made us in his image,
and we are this stupid
then....
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #19 on: October 02, 2015, 06:00:48 am »
So, my suspicions were correct.

Do you think that it deserves some more debugging time, or shall I throw it in the bin and keep the parts...?

Quote
I did not see such a magnetic shunt in the transformer.
Can you find an internet photo of a similar configuration so that I understand better what you mean?
Thanks.
 

Offline mij59

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #20 on: October 02, 2015, 06:45:17 am »
Do you think that it deserves some more debugging time, or shall I throw it in the bin and keep the parts...?

First resolder the main board, may be this solves the problem.
Just wondering how do your check there's a brownout ? may be the computer is shut down by a virus.
 

Offline oldway

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #21 on: October 02, 2015, 06:45:50 am »
So, my suspicions were correct.

Do you think that it deserves some more debugging time, or shall I throw it in the bin and keep the parts...?

Quote
I did not see such a magnetic shunt in the transformer.
Can you find an internet photo of a similar configuration so that I understand better what you mean?
Thanks.
@krish2487: Do not forgot that the transfer time is not only the switching time of the relay but you have to add the time of detection of mains failure.
The first thing I would do is to check if the inverter is sincronized with mains or not.

Quote
It was working alright for the last couple of years but now has the following problem.
It works fine in a blackout when mains power is completely off but it cannot keep up
during very fast brownouts.  If power goes out for a fraction of a second, then the PC
switches off and reboots.  I have replaced the battery but the same thing happens.
You are not sure that what happens with mains voltage is the same than what was happening in the past.
You can't be sure of that something has changed in your UPS.
What is clear for me is that it is a low cost, low technology UPS and you can't wait for good protection with such an UPS.
The only secure technology is on line UPS.
« Last Edit: October 02, 2015, 07:36:46 am by oldway »
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #22 on: October 02, 2015, 07:35:52 am »
Quote
Just wondering how do your check there's a brownout ?
From an incandescent light bulb.

oldway thank you for the pictures. 
From what I can see there is no magnetic shunt on this transformer.

Quote
The first thing I would do is to check if the inverter is sincronized with mains or not.
Any hint on how to do that?... :-[
 

Offline oldway

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #23 on: October 02, 2015, 07:45:27 am »
Quote
From what I can see there is no magnetic shunt on this transformer.
You must have two separate windings side by side with magnetics shunts between them as on the picture.

 
Quote
Any hint on how to do that?... :-[
Use a low voltage transformer to pickup mains voltage waveform for one channel of your scope and measure the inverter waveform on the second one as you did...or even more easy, sincronise your scope  on line and see if inverter waveform is stable on the screen.
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #24 on: October 02, 2015, 07:54:41 am »
Quote
You must have two separate windings side by side with magnetics shunts between them as on the picture.
I meant there is no shunt in my transformer.

Quote
Use a low voltage transformer to pickup mains voltage waveform for one channel of your scope and measure the inverter waveform on the second one as you did...or even more easy, sincronise your scope  on line and see if inverter waveform is stable on the screen.
Hmmm, nice.  I might do that.  Thanks!

So, do you think that this definitely is not a line interactive ups?
Its sold as one.  I guess it interacts with the mains to a degree...   :)

 


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