UPS Calculator

[Whiteninja]

Hi,

A client of us has a R36000 UPS.
The current load is 6KW.

i've found a calculator for the runtime on battery. But is is only 45min with this load.

I expected much more.

Can someone explain me how this is calculated?

Second question:
When (percentage) will the UPS say the battery is low? what is the treshold for that?

Kind regards Pieter

[Matti_Kurkela]

R36000/3 is a modular UPS: extra batteries and expansion modules can be added to the base unit.

Here are the the specifications:
http://h18000.www1.hp.com/products/servers/proliantstorage/power-protection/rackups/parallel3phase/specifications.html

With the load of only 6 kW, I assume just the base unit is used.

Note that the battery runtime is listed in the specifications only as ">5 minutes at 100% load". The maximum power rating of the base unit is 36 kW.

36 kW / 6 kW = 6, so this UPS is currently running at 1/6 of its full capacity, and the simple estimate would be that it therefore could run roughly 6x the time.

6 * 5 min = 30 min, so this simple estimate would actually predict *worse* performance than the run-time calculator you found.

The battery runtime calculator can probably take into account the electrochemical properties of the batteries, and/or the UPS's power efficiency at various power levels.

Of course the documented performance ratings will be somewhat on the pessimistic side, so that the UPS can perform to the specifications even when it has an old battery that's about due for replacement.

To your second question:
The "battery low" alert level might be adjustable according to site requirements.

If the UPS is connected to a system that controls a chemical or mechanical process that takes at least 10 minutes to stop without nasty consequences, you'd want to set the alert level higher than when the UPS is powering documentation Web servers which can easily be shutdown in less than 3 minutes.

MK

[Whiteninja]

The R36000UPS consists of 3 R12000 that are coupled together.

What I do not understand is how they calculate this.

I would expect 36000W UPS and a load of 6000W that should give me 6hours of battery power.
Then how comes it only lasts 30 to 45min?

Even if the capacity was 12000(3 phases 12000 per phase) i would expect 2h should be possible.

[Matti_Kurkela · Accepted solution]

36000 W is the UPS's power rating, but it does not tell anything about the size of the UPS's energy reserve.

The two most important electrical parameters for any storage battery are:
- battery voltage, measured in volts (V)
- storage capacity, typically measured in ampere-hours (Ah)

When multiplied together, you get watt-hours (Wh) which is an useful parameter for characterizing the total amount of energy stored in the battery.

In theory, if you have a 100 Wh battery, it means you could use it to power a 100 Watt load for 1 hour... or a 50 Watt load for 2 hours... or a 1000 Watt load for 0.1 hours.

In practice, the batteries also have a maximum power limit: if you try to use a battery to power a load that needs too much power, the battery's internal connections may overheat and melt, causing short circuits, ruining the battery and possibly causing it to explode.

Although the R36000 UPS has a power rating of 36000 Watts, the specifications do *not* say that the battery capacity is 36000 Watt-hours (aka 36 kiloWatt-hours); in fact, by the stated running time estimate at full power, I suppose the battery capacity in the basic configuration is considerably less than that.

MK

[Whiteninja]

thx

so i guess the UPS has a capacity of 3000Wh.

Thanks for the explanation. It's been most helpfull.

kind regards

[Dennis Handly]

>I guess the UPS has a capacity of 3000Wh.

Or using MKS, 10.8 Mega Joules, the SI unit for energy.