UPS power factor & non linear load

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cppoly

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New York
How is a UPS considered a non linear load and have a power factor?

If the input to the UPS is normal utility power, then the equipment that is fed from the UPS is still being fed from the utility power. When power fails, the UPS's load switches over to battery supply. But at this point, the utility is no longer feeding the load, so shouldn't there be no non linear loads upstream of the UPS?
 
iwire

iwire

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Even a cheap off line UPS is going to have a switched-mode power supply to charge the battery and if it is a 'full conversion' UPS it is actually online 24/7 converting the full load from AC to DC to the batteries then DC back to AC.
 
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Phil Corso

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Boca Raton, Fl, USA
Cppoly...

Depends on the characterstics of the loads connected to the UPS! Easy enough to confirm with a Clamp-On Ammeter... definitely easier with a an oscillisope!

Regards, Phi Corso
 
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cppoly

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New York
iwire said:
Even a cheap off line UPS is going to have a switched-mode power supply to charge the battery and if it is a 'full conversion' UPS it is actually online 24/7 converting the full load from AC to DC to the batteries then DC back to AC.
Click to expand...

Good point. Constantly charging the batteries. But this can't be the full load of the UPS I assume. For instance, a 40 kVA UPS can't be feeding 40 kVA of harmonics back into the building power if it's just for battery charging.
 
ron

ron

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Location
New York, 40.7514,-73.9925
cppoly said:
How is a UPS considered a non linear load and have a power factor?

If the input to the UPS is normal utility power, then the equipment that is fed from the UPS is still being fed from the utility power. When power fails, the UPS's load switches over to battery supply. But at this point, the utility is no longer feeding the load, so shouldn't there be no non linear loads upstream of the UPS?
Click to expand...

Is it double conversion (AC to DC to AC all the time) or offline, where it only goes to battery during a power quality problem?

Double conversion means that the rectifier is always on carrying significant load and is the load that the utility source "sees".
 
iwire

iwire

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Location
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ron said:
Is it double conversion (AC to DC to AC all the time) or offline, where it only goes to battery during a power quality problem?

Double conversion means that the rectifier is always on carrying significant load and is the load that the utility source "sees".
Click to expand...

That was what I was trying to say as well. :)
 
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