Mundy

Power consumption calculation is simple. Take a sum of numbers signed on  every power supplay in your servers. And calculate VA as reverse Callandor (thanks) formula.

I.e.

    (400+500+450+...)/0.7

It will guarantee that maximum computer consumption does not affect your UPS. UPS will not crush, not burn out if power consumption larger than maximum allowed. Simply power quality will lower. It is really bad for your servers too.

Why VA is used for UPS instead of W for power supplay. UPS must hold power until servers becomes down. It is easyer to calulate time using VA. Example: UPS 2200 VA with 2 AH (amper-hour) capacity. 220 V out.

2200 VA / 220 V = 10 A

60 minutes * 2 AH / 10 A = 12 minutes  UPS will hold 10A power at 220 V

If power consumptions is less then 10 A for example 5 A time will be not 24 minutes but slightly more about 26-27 min.

Taking total servers power and down time as target you can calculate parameters of new UPS. Usually manufacturers are publish power in VA and offline work time. The parameters you really need is UPS VA and battary AH. Serious manufacturers are always publish them. The only thing you need is check if UPS maximum allowed current is less then possible consumption it is

  UPSmac A > (400+500+450+...)/0.7/220 A

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