Author Topic: UPS Eaton Nova AVR 625 - Not so fast...  (Read 18447 times)

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Offline oldway

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #25 on: October 02, 2015, 08:04:12 am »
In an a line interactive UPS, inverter works in // with line, with only an inductance between inverter and line.
Inverter works as battery charger by controling phase angle between mains and inverter.
Inverter waveform MUST be sinus in a line interactive UPS.
That's definitively not an interactive UPS.
 

Offline bktemp

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #26 on: October 02, 2015, 08:06:20 am »
In an a line interactive UPS, inverter works in // with line, with only an inductance between inverter and line.
Inverter works as battery charger by controling phase angle between mains and inverter.
Inverter waveform MUST be sinus in a line interactive UPS.
That's definitively not an interactive UPS.
No, that is wrong.

Line interactive means the ups can adjust the output voltage by using multiple taps on the primary winding working as an autotransformer. As long as a voltage is present, the ups tries to switch the tap to keep the output voltage regulated. Only when the voltage fails completely or there are not enough taps too keep the voltage regulated it switches over to the battery powered inverter.

See here:
https://en.wikipedia.org/wiki/Uninterruptible_power_supply#Line-interactive
« Last Edit: October 02, 2015, 08:08:20 am by bktemp »
 

Offline oldway

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #27 on: October 02, 2015, 08:34:59 am »
If your only information you have is Wikipedia, you will not go anywhere  :-DD
http://www.baservices.nl/downloads/APC%20whitepaper%20soorten%20ups.pdf
There may have a taps changer added to regulate AC output voltage because output voltage of an on line interactive UPS without taps changer is the same as the line voltage.
This does not change nothing of what I wrote.

Wikipedia is wrong: there is no battery charger (rectification is made by the free wheeling diodes of the inverter) and current control is make by varying phase between inverter and mains.
There must be an inductance between mains and inverter as both have low impedance, battery has also low internal resistance and a very little phase difference would give a very large charging current.
Furthermore, there is no output switching between mains and inverter in an interactive UPS, only a way to switch the mains off if there is a line failure.
And you can't let work in // an inverter with non sinus wave with sinus line voltage.
« Last Edit: October 02, 2015, 09:12:42 am by oldway »
 

Offline bktemp

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #28 on: October 02, 2015, 08:57:30 am »
http://www.baservices.nl/downloads/APC%20whitepaper%20soorten%20ups.pdf
There may have a taps changer added to regulate AC output voltage because output voltage of an on line interactive UPS without taps changer is the same as the line voltage.
This does not change nothing of what I wrote.
Can you show me any line interactive ups without the tap changer? I have never seen one.

Quote
Wikipedia is wrong: there is no battery charger (rectification is made by the free wheeling diodes of the inverter) and current control is make by varying phase between inverter and mains.
Wikipedia just shows a very simplified block diagram.
APC uses the main transformer for charging to reduce the size and cost, but it is not mandatory for a line interactive ups!

Quote
There must be an inductance between mains and inverter as both have low impedance, battery has also low internal resistance and a very little phase difference would give a very large charging current.
I have several line interactive ups from APC and none of them has a visible magnet shunt.
To be able to generate a high enough output voltage even under full load, the transformer produces a much lower voltage than the battery voltage. So there is no current flowing into the batteries even if the transformer is connected to mains.
To charge the batteries they use the stray inductance in the transformer as a boost converter to increase the voltage to the batteries.

Quote
And you can't let work in // an inverter with non sinus wave with sinus line voltage.
You are wrong again, here is only one example:
http://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=BR550GI&total_watts=600
Quote
Topology: Line Interactive
Waveform Type: Stepped approximation to a sinewave
 

Offline oldway

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #29 on: October 02, 2015, 09:52:12 am »
Quote
Can you show me any line interactive ups without the tap changer? I have never seen one.
The firm SAB NIFE where I worked as a development engineer was making interactive ups from 5 to 20kVA's with no taps changer.

Note that most off-line and on-line UPS does not have a voltage stabilizer in the mains.
I worked also by AEG, one of the greatest industrial UPS manufacturer in Europe, and I have NEVER see an installed on line UPS with voltage stabilisator in the main circuit.

Quote
Wikipedia just shows a very simplified block diagram.
APC uses the main transformer for charging to reduce the size and cost, but it is not mandatory for a line interactive ups!
You simply did not understood the principles of a line interactive UPS.
There is a good reason for this: those informations are not available on Internet.
Customers does not give schematics and diagrams of their UPS on Internet....You have to work in these firms to have such informations.

Quote
I have several line interactive ups from APC and none of them has a visible magnet shunt.
Transformer with separate windings side by side give an short circuit voltage of about 20%
Magnetic shunts are used to increase this value above 20%.
It's possible that the design is such that 20% was enough.

Quote
To be able to generate a high enough output voltage even under full load, the transformer produces a much lower voltage than the battery voltage. So there is no current flowing into the batteries even if the transformer is connected to mains.
That's right, charging current is controlled by changing phase difference between mains voltage and inverter.

Quote
To charge the batteries they use the stray inductance in the transformer as a boost converter to increase the voltage to the batteries.
Wrong: what you say is impossible....energy from stray inductance of transformer is absorbed by RC suppressor of the semiconductors and by the load.
The PWM inverter is bidirectionnal and can supply energy to the battery from the main if not perfectly in phase with the main. That's what is used to charge the battery without the need of a battery charger.

Quote
You are wrong again, here is only one example:
http://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=BR550GI&total_watts=600
Without schematics and diagrams to see what really has be done, it is not possible to answer this.
One of the principles of a line interactive UPS is just to be able to correct a distorted mains sine waveform, this why this name interactive, as it can to be interactive with mains voltage and correct it before feeding the load...Your statement is almost against this principle of working of a line interactive UPS...




« Last Edit: October 02, 2015, 09:55:17 am by oldway »
 

Offline bktemp

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #30 on: October 02, 2015, 10:20:46 am »
Note that most off-line and on-line UPS does not have a voltage stabilizer in the mains.
I worked also by AEG, one of the greatest industrial UPS manufacturer in Europe, and I have NEVER see an installed on line UPS with voltage stabilisator in the main circuit.
Of course not. An online ups works completely different and therefore does not need an additional stabiliser, because it creates a completely new sine wave.

Quote
Quote
To charge the batteries they use the stray inductance in the transformer as a boost converter to increase the voltage to the batteries.
Wrong: what you say is impossible....energy from stray inductance of transformer is absorbed by RC suppressor of the semiconductors and by the load.
The PWM inverter is bidirectionnal and can supply energy to the battery from the main if not perfectly in phase with the main. That's what is used to charge the battery without the need of a battery charger.
Someone achieved the impossible:
http://www.google.com/patents/US5302858
« Last Edit: October 02, 2015, 10:22:25 am by bktemp »
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #31 on: October 02, 2015, 10:23:56 am »
Two of the relays had a NC 0.25 Ohm resistance instead of the 0.01 Ohm of the other ones,
so I've replaced them.  I have also resoldered most of the through hole components.
I did not replace any capacitors because they were fine.

The result:  190VAC without any load instead of the 240VAC...   :palm:
Luckily, no explosions.   :)
UPS is going exactly where it was supposed to be.  The trash bin.

I am going to buy a new one.
Anyway, thank you very much for your help!
George.
 

Offline mij59

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #32 on: October 02, 2015, 10:54:01 am »
Two of the relays had a NC 0.25 Ohm resistance instead of the 0.01 Ohm of the other ones,
so I've replaced them.  I have also resoldered most of the through hole components.
I did not replace any capacitors because they were fine.

The result:  190VAC without any load instead of the 240VAC...   :palm:
Luckily, no explosions.   :)
UPS is going exactly where it was supposed to be.  The trash bin.

I am going to buy a new one.
Anyway, thank you very much for your help!
George.

Most computer power supplies can handle even lower input voltages, so it should not be a problem, may be the multimeter reading is off due to the square wave form.
Well some you win, some you lose.
 

Offline oldway

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #33 on: October 02, 2015, 11:00:04 am »
Quote
Of course not. An online ups works completely different and therefore does not need an additional stabiliser, because it creates a completely new sine wave
And what about the situation when load is feeded by mains voltage ?
If customer agree with mains voltage variations in this case, why sould he not agree with the same variations of a line interactive UPS without taps changer ?

Quote
Someone achieved the impossible:
http://www.google.com/patents/US5302858
A patent never proove it works  :-DD
There are thousands of patents who never worked...

@hgg: buy an on line UPS with sine output, that's the best technology even if it is more expensive and less efficient.
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #34 on: October 02, 2015, 11:11:37 am »
Quote
Most computer power supplies can handle even lower input voltages, so it should not be a problem, may be the multimeter reading is off due to the square wave form.

You made me think again.
Before the repair I measured the output voltage with the UT61E and showed 250VAC,
but after the repair I used the UT-136C which is not true RMS.  That's why the 190VAC.   :palm:

Now it measures 240VAC spot on. 
I think I will try it with a load.

Quote
@hgg: buy an on line UPS with sine output, that's the best technology even if it is more expensive and less efficient.
Indeed, that's exactly what I was planning to do.
I will try first to see if this one works any better and move from there.
A variac would have been handy for testing the brownout behavior but I don't have any.
 

Offline bktemp

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #35 on: October 02, 2015, 11:31:04 am »
Quote
Someone achieved the impossible:
http://www.google.com/patents/US5302858
A patent never proove it works  :-DD
There are thousands of patents who never worked...
Watch this video:
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #36 on: October 02, 2015, 11:44:49 am »
That is what I was watching yesterday...  :)

I've plugged it in again and started to play with the mains cable in order to simulate
fast mains transitions and after some tries the PC rebooted.  The problem continues.

I would have to buy a new one.
Anyway, at least I've tried and thanks again for your help.

It would be interesting to see a repair video from Dave, but shipping it to Australia...   :)
 

Offline bktemp

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #37 on: October 02, 2015, 12:02:28 pm »
I've plugged it in again and started to play with the mains cable in order to simulate
fast mains transitions and after some tries the PC rebooted.  The problem continues.
Did you try to measure both the input and the output voltage on the ups simultaneously as oldway has suggested? It should be easy to trigger on those fast transients.
I am still not fully convinced the ups is faulty.
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #38 on: October 02, 2015, 12:11:13 pm »
No, I haven't.  The less you probe mains, the better...  :)

If the UPS was ok, the PC should have stayed on.
Maybe the power supply of the PC does not like the crappy waveform which is basically a simple square wave.
Not even a staircase approximation.  The same thing started to happen with a different PC (new PSU) connected
to an identical UPS in a different workplace.

(I think that a modification to make it function like a Schmitt trigger would have solved the problem.
For example if the controller senses a drop in voltage and has to connect the inverter to the output,
it should also add a small delay like 5 seconds for example, even if the mains voltage has recovered.)
« Last Edit: October 02, 2015, 12:25:42 pm by hgg »
 

Offline bktemp

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #39 on: October 02, 2015, 12:28:14 pm »
No need to probe mains directly. You can use 2 transformers to get the voltage down. It must not be precise, but at the moment we have absolutely no information about the timing when switching to battery mode. If it takes less than 10ms, then the ups is moste likely fine and can be used for something else.
Most power supplies are rated for at least 20ms hold up time under full load, so when not fully loaded a pc should run for quite a long time (50-500ms) without power before shutting down.
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #40 on: October 02, 2015, 12:37:27 pm »
I know I have one transformer lying around.  I will have a look to see if I find another one
and measure the switching delay.  I would have to measure the time from mains going off
till the UPS output switches on.

The problem though never happens when you go ON-OFF, but when ON-OFF-ON-OFF very fast.
 

Offline oldway

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #41 on: October 02, 2015, 01:32:59 pm »
There a lot of differents schematics of power stage of UPS but the correct one of the true line interactive UPS is this one.
There is no switching of the output, inverter and mains works in // with an inductor between them and inverter interact on line voltage to correct distortion of waveform.
There is one output transformer (T1) with magnetic shunts for coupling inverter and mains.
Greatest problem with this technology is that the inverter is highly overloaded when mains fails because it has to feed the load and the short circuit of the mains (current limited by inductance).
Line must be opened as fast as possible (by thyristors) to limit this current.

I have made a lot of experiences and tests of such a line interactive UPS using a 10KVA inverter with modifications for varying phase between inverter and mains and measuring resulting charging current.

I don't need to look at videos of Dave, I have 30 years of experience in power electronics....
With all the respect I have for Dave that I appreciate very much, Dave is not God ! (nor I... :-DD )

NB: one of the avantages of line interactive UPS is that there is no switching, nor transfer of the load.
When mains fails, there should nothing occurre to the load as inverter is already working in // with the mains.

@hgg: you have a storage  DSO, why not measure the transfer time of your UPS instead of looking if you computer is rebooting or not ?
Your approach of the problem is absolutely not profissional.
When you have such a problem, you have to know exactly what happen...What is the transfer time ? Is this always the same or not
« Last Edit: October 02, 2015, 01:39:54 pm by oldway »
 

Offline bktemp

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #42 on: October 02, 2015, 01:57:27 pm »
There a lot of differents schematics of power stage of UPS but the correct one of the true line interactive UPS is this one.
That matches the schematics for all APC UPS I have seen. But I can not see anything in there that confirms what you are saying. I see an autotransformer for line interactive with the full bridge on the secondary and a relais to disconnect mains for battery mode. It also matches the pictures of the ups on this thread.

Quote
There is no switching of the output, inverter and mains works in // with an inductor between them and inverter interact on line voltage to correct distortion of waveform.
There is one output transformer (T1) with magnetic shunts for coupling inverter and mains.
Greatest problem with this technology is that the inverter is highly overloaded when mains fails because it has to feed the load and the short circuit of the mains (current limited by inductance).
Line must be opened as fast as possible (by thyristors) to limit this current.
That may be the case for a large 10kVA UPS, but not for the common home or office use ones. I have several APC one here from a few 100VA upto a few kVA, they all are line interactive ones and use the battery charging as described in the patent. Look at Dave's video, they have no magnetic shunt (at least not visible, but since primary and secondary are wound on top of each other it is almost impossible to add a shunt somewhere inbetween). And they do not have a thyristor. They have large relais to disconnect the transformer when mains fails.

Quote
NB: one of the avantages of line interactive UPS is that there is no switching, nor transfer of the load.
When mains fails, there should nothing occurre to the load as inverter is already working in // with the mains.
Can you give me any reference for that? All sources I have found for line interactive describe it the other way: Line interactive is an offline/standy ups + voltage adjustment via the autotransformer. No waveform correction (except for emc filtering at the input/output).
« Last Edit: October 02, 2015, 02:04:32 pm by bktemp »
 

Offline oldway

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #43 on: October 02, 2015, 03:34:04 pm »
Try only to explain to me how an UPS as you describe can "interact" actively with mains ?  :-DD
To add a voltage regulator in the line is not actively interact...its only stabilizing the mains voltage with a voltage regulator.
I never heard an AC voltage regulator named "line interactive" device...
Only in the power stage as I described, the inverter interact with mains because it is coupled through an inductor with main.
They use the name interactive for a non interactive schematic...That is wrong.

Quote
Can you give me any reference for that? All sources I have found for line interactive describe it the other way: Line interactive is an offline/standy ups + voltage adjustment via the autotransformer. No waveform correction (except for emc filtering at the input/output).
Try to do the same for your statements...As I said, you will not find schematics (only a very few, if any) on Internet...Manufacturers of UPS don't give any schematics, nor diagrams of their products.

Even I worked with great UPS manufacturers and I still have a lot of schematics, I can't publish them on Internet.

Look at the topology of an interactive UPS: no battery charger, no transfer switch of the output.
« Last Edit: October 02, 2015, 04:09:13 pm by oldway »
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #44 on: October 02, 2015, 04:10:04 pm »
oldway can you suggest a quality line interactive UPS with a sine wave output.

I will buy the Cyberpower CP900EPFCLCD
http://www.cyberpower-eu.com/products/ups_systems/pfc-sinewave/cp900epfclcd.htm

...except if you know of a better solution.
I don't want to spend more than 200 euros.
 

Offline oldway

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #45 on: October 02, 2015, 04:25:15 pm »
I know I have one transformer lying around.  I will have a look to see if I find another one
and measure the switching delay.  I would have to measure the time from mains going off
till the UPS output switches on.

The problem though never happens when you go ON-OFF, but when ON-OFF-ON-OFF very fast.
Why is your computer rebooting when there is a mains failure and a transfer to the inverter ?
A SMPS has an hold up time, this the time the power supply of your computer can still provide a viable output without an input supply.
With a high quality SMPS, you should have specifications of this hold up time.
This old up time can be reduced if the electrolytics capacitors have loose their capacitance.
The UPS has a transfer time, that's the time taken by the UPS to switch from mains to the inverter.

If your computer is rebooting, that means that the transfer time is greater than the old up time.

In such a situation, this UPS is worse than nothing as it increases the short mains failures.
For this reason, it is far better to choose a TRUE line interactive UPS (without any transfer time, as there is no transfer), or an on line UPS who has only a transfer in case of inverter failure or battery low voltage protection.

I had bad experience with true interactive UPS and I don't like this solution. I often had to replace exploded power blocs of such UPS...Reliability is not that good. (can't work with gen set)

I recomend to go for on line UPS, that's the best technology and the most reliable.
« Last Edit: October 02, 2015, 04:31:40 pm by oldway »
 

Offline oldway

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #46 on: October 02, 2015, 04:44:33 pm »
oldway can you suggest a quality line interactive UPS with a sine wave output.

I will buy the Cyberpower CP900EPFCLCD
http://www.cyberpower-eu.com/products/ups_systems/pfc-sinewave/cp900epfclcd.htm

...except if you know of a better solution.
I don't want to spend more than 200 euros.
If I understood right, load is feeded by utility voltage (mains) and transfered on inverter in case of mains failure.
Transfer Time (Typical)    4ms
That's short but again you have to be sure that the old up time of the SMPS of your computer is greater than 4ms.
Far better to choose an on line UPS where there is no transfer at all.
 

Offline hgg

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #47 on: October 02, 2015, 04:59:23 pm »

I think that the switching lower time limit depends on how fast is the switching time of the relays
they are using.  If you "upgrade" the UPS with solid state relays maybe it will become much better.

Online is indeed better, but it gets very hot and it has fans making noise all the time.
My system is completely silent and I don't want any noise from the UPS.  Besides that,
they are very expensive...   I don't want to pay more than 200 euros for a UPS.

I am curious about the transfer time of my UPS and tomorrow I will buy a transformer
just to test it.
 

Offline oldway

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #48 on: October 02, 2015, 05:14:31 pm »
Quote
I think that the switching lower time limit depends on how fast is the switching time of the relays
they are using.  If you "upgrade" the UPS with solid state relays maybe it will become much better.
I don't think so...4ms is allready very good, you need a time to detect the mains failure and another to switch...1/4 of cycle, that's what we succeed with SCR's.
About price and noise, I think that if you want to buy an UPS, it is because you really need one...Than price and noise are not the most important factors : you have to look for highest effective protection and security.

And don't forget to replace the batteries when needed... :-DD
 

Offline oldway

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Re: UPS Eaton Nova AVR 625 - Not so fast...
« Reply #49 on: October 02, 2015, 05:59:11 pm »
If you want a low cost solution, you could use your actual UPS only as an inverter , without the transfer relays (inverter diretly connected to the output), no mains connection and add a battery charger able to furnish the full DC curent of the inverter, more recharging current for the batteries. :-+
 


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