PowerPlant vs. Double Conversion UPS


#1

Hi,

I’m curious what’s the difference between a power plant and a double conversion UPS?
Double conversion UPS do the same thing as the power plant, converting AC to DC and back to AC, for quite a bit cheaper than the power plant.

Double conversion UPS such as these:

Tripp Lite SmartOnline 120V 1kVA 900W Double-Conversion UPS

Tripp Lite 1000VA Smart Online UPS

They can be loud, but I have one here modified to use a large low speed fan that doesn’t make any noticeable noise at listening position.

Thanks ahead for the insight


#2

(Speaking for myself, not for PS Audio)

Most UPSs don’t make anything near a sine wave, the cheapest make square waves, the slightly better make few steps to approximate a sine and most of the ones that claim something like “True Sine”, etc. are just a better approximation, but still with many small but sharp edges, those edges are a lot of noise, if you filter the edges out you loose the ability to respond quickly to changes in current draw. Most audiophile power supplies take huge gulps near the peaks of the input power so they are very sensitive to the instantaneous current available.

(See https://forum.psaudio.com/t/power-cord-for-dsd-sr/5445/21 or https://forum.psaudio.com/t/power-cord-for-dsd-sr/5445/30 )

There are some audiophile online USBs, I have one and it isn’t bad for low current devices and I never hear it’s fan, but for amps the efficiency of double conversion is too low and the lack of instantaneous current delivery would be a real problem.

Note that the Tripp Lite 1000VA Smart Online UPS has different outputs: “Pure Sine Wave” in “Battery Mode” and “Sine Wave” in “AC Mode” And it’s output regulation is +/-2% in “Line Mode” or “Battery mode” and +/-10% (!) in “Economy Line Mode”. What they mean by Pure Sine Wave and Sine Wave isn’t clear, but 2% distortion leaves a lot of room for high frequency edges.


#3

I have both … a P20 regenerator as well a 3Kva double conversion “pure sine” UPS.
The UPS can be set in “bypass mode” (or where it basically feeds from the grid; with a 10 or 20ms changeover should the mains fail); OR in double conversion (online) mode, thus feeding my P20 via batteries 24/7.
So here’s the thing: P20’s own “power improvement meter” reports less of an improvement when fed in double conversion (battery) mode.
So there is no doubt in my mind that a decent double conversion UPS improves the power quality to some extent but nowhere near the level of control and improvement of the P20.


#4

Ted’s right. Moreover they use a class D output stage and cannot handle power factors of less than 1 without even more distortion. If you try and power anything with a PF of 0.7 (common for amps and preamps) you’ll get a nasty divot out of the peak of the sine wave under any heavy current use. These are fine as intended, as battery backups, but not to replace a real regenerator like a Power Plant.


#5

Thanks for the insights Ted, and Paul.

I was afraid of this… my wallet ran away, let me chase it down, once I catch it I’ll order probably a P12.