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AX1500i UPS overlaod


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I have been running an AX1500i with an APC ups model sua2200rmi2u for many years. Recently they decided to get a divorce and stop working together. 

The UPS works with anything else on (new) battery. The AX1500i works, when plugged directly into the wall.

When I turn the AX1500i off! with the switch on the back, plug it into my UPS and send the UPS to battery, the UPS reports an overload and shuts down immediately. The overload seems to be real. I can measure no short on the power cable when plugged into the psu (reads 600kOhms or so)

Trying to find the cause I have some questions:

- I have read somewhere, that the power switch does not really disconnect the line voltage - is that so?

- might the OVP (over voltage protection) cause a short even in the switched off state due to some voltage spike from the ups?

- any further ideas, tests to perform?

Many thanks

Ozo

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does it overload when you switch the PSU button ON? or when the computer is already running and you go to battery ?

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12 minutes ago, LeDoyen said:

does it overload when you switch the PSU button ON

Yes

 

12 minutes ago, LeDoyen said:

or when the computer is already running and you go to battery ?

Yes

 

I am reading about possible compatibility issues of stepped sinewave UPSes with APFC PSU now - maybe I was living on the edge all those years.

Thank you

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when the PSU gets switched on from the button on the back, it will load the caps on the primary side and that should definitely overload your UPS since it will pull as much current as possible for a short time.

Now for when it's already on and switching to battery, no idea yea.

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Puhh glad I can post again - that 3 messages per day limit is a bit odd.

I measured the power draw between PSU and UPS with several current sensing resistors and found that the PSU draws a 5A spike and then quickly tapers off, if the resistor is above 0,6 Ohm. If the resistor is below 0,6 Ohms, the UPS and PSU get into some kind of oscillation with currents as high as 16A, when switched to battery. My solution for now is a 20 watt 0,9 Ohms resistor in series with the AC output sockets. This dampens the oscillation very well and I have no more overload warnings.
 
As the power switch does not break the line - does it still provide 5 Volts to the motherboard? I´m asking because I measured around 36 Watts draw with the power switch turned off. ( My measuring equipment is a Keithley 2750 and some 10 watt resistors placed in series and i performed several sanity checks ). I did not disconnect all USB and or power connections to see, if the current draw gets less. I also did not measure the phase angle - maybe the current is just imaginary. *wink*
 
Many thanks
Ozo
 
 
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ohh no - also no editing function. Now I have to waste one of my precious posts per day.

"36 Watts draw" is not entirely correct I measured 160 mA and calculated the power draw as if they were in phase.

 

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when the switch is off, there's no power to the PSU at all. the 5VSB rail is off too, no 5V to the motherboard.

Maybe you're measuring some input protection ? 36W must indeed be a bogus reading or an error of some sort, given how strict power usage regulations are for power supplies. Even with the PSU switched ON  and the PC OFF it shouldn't use that much unless you leave USB power delivery ON in bios and are charging your phone on the PC or something 😛

If you activate ErP options in BIOS, the total system draw has to be be under 1W.

Switched off, you'll get 0, but you'll kill the PSU input protection in short term by switching on and off constantly.

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Unfortunately the days of service manuals are long gone - then I would know, what that switch does.

Yeah Im pretty convinced the 160 mA are from the filtering circuit and out of phase ("wattless power" from the filter-caps across the line). The switch is after the filter circuit so that it is always conencted and draws 36 VA. 

Propbably that is the reason why some "cheap power meters" also report power usage in other cases and proper ones factoring in the phase of the current do not. If I want to find out badly, I´ll go ahed and measure the phase.

Many thanks again - case closed

 

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