In this month’s newsletter, I answer one
of the more frequently asked questions we get at Power Solutions.
“How do I properly evaluate
battery specifications for the run time of my UPS?” Along with that I’ll explain another popular query, “What impact does a
UPS’s Inverter Efficiency, ambient room temperature and the batteries’
watts per cell have on a UPS’s run time?”We are dedicated to providing you reliable power
quality solutions and superior service. This includes sharing information
that is relevant to your business.
Please feel free to call or email me to discuss
how Power Solutions can help you properly size your UPS and
establish a reliable power protection strategy.
Newton Black, Power Specialist
Power Solutions LLC
a Battery Upgrade or Replacement for Your UPS?
Power Solutions provides upgrade
options, installation and battery replacement solutions for ALL
Whether you need a new battery
for your APC, Powerware, Best, Tripplite, Liebert or Belkin UPS System we
have the solution for you – usually in stock
and available for same day shipment.
If you prefer, our technicians
are available to install your new batteries and properly dispose of your
explains how to calculate the battery run time you should expect for
a specific brand and model of UPS Battery.
For the purpose of this exercise
there are some items that we need to know including the UPS inverter
efficiency, allowing us to calculate the kWb, the DC endpoint or cut-off
voltage and finally the average room ambient temperature therefore we
will make certain assumptions.You
can easily change these assumptions to suit your application.
Let’s make the following
-Inverter efficiency 90%.(Industry norm is 90%-98%)
-End point voltage 1.67.(Typical reference used
in battery specifications)
-Ambient Room Temp 77F.(Typical reference used in battery
A UPS system has one string of
batteries, consisting of a quantity of 30 each, Northstar Model NSB12-475and
the rating of the UPS is 40kW.The
battery has 6 cells per unit.
Calculate the Actual Battery Load for a 40kW UPS Load
40kw load assuming a 90% inverter efficiency is
actually 44.44kw battery load
ups load) DIVIDED BY .90 (90% inverter efficiency) = 44.44kw (actual
load on the batteries)
Calculate Watts Per Battery
Each battery will see 1481 watts
load on the batteries) DIVIDED
BY 30 batteries = 1481 watts per battery.
Calculate watts per Cell
Each cell of each battery will see 247 watts
1481 watts per battery DIVIDED BY 6 (cells per unit)
= 247 watts
247 watts per cell
Step 4:Estimate Your Expected Run-Time
The specifications for this battery show that at 247
Watts per cell and 1.67V your run time is between 45 and 60 minutes.