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Why pure sine wave in IT?

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TheMG:

--- Quote from: Pawelr98 on August 17, 2020, 05:55:32 pm ---Active PFC circuit may not like the square wave.

--- End quote ---

BINGO!

That's exactly it. The square wave, modified sinewave, whatever you want to call it, creates problems with the active power factor correction circuitry in some power supplies. With a sine wave output, you avoid the issue altogether.

I don't know if that is still an issue with the more modern PFC controller ICs, but it certainly was a significant factor when active PFC power supplies first started being introduced into the market.

perieanuo:

--- Quote from: thobo on August 17, 2020, 12:55:58 pm ---I just stumbled over this question myself as I was searching for a new UPS for my IT Rack. There is big difference in costs for the modified sine wave and the pure sine wave online UPS's.
What technical reason makes a pure sine wave UPS necessary? Most IT tech uses switching power supplies, in my rack 100%. My assumption is, that switching power supplies does'nt benefit of a pure sine wave UPS, because after their filtering the first thing is a rectifier and ripple cap(s). It shouldn't matter if the input is pure sine wave or modified sine wave, isn't it ?

regards
  Thomas

--- End quote ---
hi!
well, it's kinda complicated.all the chain powered after the ups works ok with pure sine, which is difficult (costly) to obtain on big powers.with other sine wave, all chopper input stages are exposed to the big chalenges: any harmonic can have a distructive effect on chopper stage.not only as others say, some capacitors suffering.of course they are right, but the risk on the power supply powered by non-pure-sine is multiplied.also the harmonics (high frequency of course) transcend the power supply powered by the ups and get into small final voltages.
So it's more complex then some big fat input capas that dye from non-respected operating conditions.
the answer is worth by a exposeum  like 40 pages with lots of math inside.
regards,pierre

coromonadalix:
A pure sinewave  will prevent you from having problems with ac/dc adapters and or other stuff

With modified sinewave i had problems with laptop adapters and other appliances, they simply refused to power on and / or start, and some of them need to sense a 50/60hz sinewave in some cases ??

David Hess:
If a switching power supply has a problem with a modified sine input, then it is defective, whether it has active power factor correction or not.  Still, it does happen.

Some loads, but hopefully not any switching power supply, will perform poorly with a modified sine source.

Pure sine wave inverters like those found in double conversion or online uninterruptible power supplies allow the output to be phase locked to the AC line so switching between the inverter and AC line can occur at any time without any discontinuity.

coppice:

--- Quote from: Pawelr98 on August 17, 2020, 05:55:32 pm ---Active PFC circuit may not like the square wave.

--- End quote ---
Its not just active PFC. Most server supplies have filter caps directly across the mains input. Put a square wave into those and huge currents can flow, overheating the caps.

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