How to Calculate UPS Battery Backup Time

When I first asked this question myself, a friend of mine kindly sent me to the manual (a joke, obviously). In the meantime, I found out that calculating ups batter back up is not such a big deal as I might have thought in the first place. In order to make everything as clear as I can, I will use a small example. Let us assume the following ideas:

Inverter efficiency of UPS battery is 90% (the norm is somewhere between 90% and 98%)
Battery end point voltage 1.67 (usually specified on the UPS itself, or in its manual)
Environmental temperature 77F

Assuming that we know the following things about our UPS : one string of batteries, 30 each, UPS rating 40kW and 6 cells per unit, we can break down the calculations in three steps:

1.) Actual battery load for 40kW

40kW … 90% efficiency means an actual 44.4kW load (you can calculate this by dividing the rating of the UPS by inverter efficiency – 40/0.9 = 44.4kW)

2.) Watts per Battery

44.4kw (previously calculated) will be divided by the number of batteries we have available, and the result will lead to 1481 watts per battery. (you can calculate this using the equation: 44.4Kw/30 = 1481W)

3.) Watts per each Cell

Giving the necessary data we will deduct that each cell needs 247W. (calculate this using the equation: 1481W / 6 (the number of cells per unit) = 247 watts per each cell)

Now we can easily estimate the run-time of your UPS battery back up system. Giving the fact that we know that each batter has about 247W per each cell, and we have a battery end point voltage of 1.67V your run time should be somewhere between 45 minutes and 60 minutes.

Various Other Formulas to calculate backup time

• Battery current at full load / Battery Ah. This gives approximate backup time.
• Battery AH/Battery current at full load. Ex:160/40 amp we get three hours back up
• Battery Ah*dc cut off voltage of ups/load(VA)
• Battery Ah*nominal dc voltage of system/load in VA
• Battery capacity X No of battery X Ah X battery(0.8)/ o/p wattage. This is will give backup time for your setup

How to Calculate Your UPS Requirement

The majority of UPS systems sold today utilize a VA (Volt-Amperes) rating. The difference between watts (W) and volt-amperes (VA) is that Watts accounts for an inefficiency called the Power Factor (PF) and VA does not. The Watts rating is going to be more accurate, unfortunately, UPS companies like to advertise the VA rating because it makes their products look better, the VA number is always higher.

• The most basic formula for determining the necessary UPS protection may be expressed by the following:
• Amps * (120 Volts) = Watts / Power Factor "PF" = VA
• Amps or "A" is the current pull of the system Voltage is a constant of 120 in North America Watts or Wattage for AC current = Volts x Amps x Power Factor "PF" Power Factor or "PF" is a number between 0 and 1, the watts after reactance loss Volt-Amperes or "VA" is Watts / PF or Watts without PF loss taken into account
• Older PC systems had less efficient power supplies with PF rating around 0.8, while newer PC power supplies are much more efficient with PF ratings often at or above .95. Incidentally, an ordinary incandescent light bulb has a perfect PF of 1.

Backup Time: How Long UPS Power Lasts

• The backup time is the time your equipment will run off of UPS power during an electrical outage. This backup time is proportional to the total load connected to the UPS. Although not a direct linear proportion, the total backup time will decrease with the more devices you connect to your UPS.
• As an example a quality UPS rated 1500VA will offer 5 minutes of battery runtime at full load, while offering 14 minutes of runtime at a half load of 750VA. The Tripp Lite OMNIVS1500XL, a line-interactive UPS, was referenced for these figures. Most UPS manufactures consider a full load VA rating with a safe PF of .8 even though modern power supplies are much more efficient. This is beneficial to the consumer since no one is going to have a power supply less efficient than a PF of .8.
• When the VA rating or Watts power rating is exceeded then a UPS is effectively overloaded. Keep in mind it is technically necessary to be aware of both the Watts and VA load when selecting an UPS. Once the power factor of the UPS is known, a quick calculation using the Watts rating of the UPS output can be done for comparison with other UPS products and to assure that sufficient "real power" is available from the UPS to power a connected load.

Convert watts to amps

Actually, watts is the fundamental unit of power and watt-hours is the energy stored. The key is to use the watts you know to calculate the amps at the battery voltage.

• For example, say you want to run a 250 watt 110VAC light bulb from an inverter for 5 hours.
• Watt-hours = watts * hours = 250 watts * 5 hours = 1250 watt hours
• Account for the efficiency of the inverter, say 85%
• Watt-hours = watts * hours / efficiency = 1250 / 0.85 = 1470 watt-hours
• Since watts = amps * volts divide the watt hours by the voltage of the battery to get amp-hours of battery storage
• Amp-hours (at 12 volts) = watt-hours / 12 volts = 1470 / 12 = 122.5 amp-hours.
• If you are using a different voltage battery the amp-hours will change by dividing it by the battery voltage you are using.

What if you don't have a constant load? The obvious thing to do is the thing to do. Figure out an average power drawn. Consider a repetitive cycle where each cycle is 1 hour. It consists of 20 amps for 1 second followed by 0.1 amps for the rest of the hour. The average current would be calculated as follows.

• 20*1/3600 + 0.1(3559)/3600 = 0.1044 amps average current.
• (3600 is the number of seconds in an hour).
• In other words, figure out how many amps is drawn on average and use steps 1 and 2. Step 3 is very difficult to predict in the case where you have small periods of high current. The news is good, a steady draw of 1C will lower the capacity much more than short 1C pulses followed by a rest period. So if the average current drawn is about a 20 hour rate, then you will get closer to the capacity predicted by a 20 hour rate, even though you are drawing it in high current pulses. Actual test data is hard to come by without doing the test yourself.

Popular UPS Systems

APC BR1500LCD

UPS - What is a UPS?

What is a UPS?:

An uninterruptible power supply (UPS) is primarily used to provide a backup power source to the parts in the computer case, the monitor, and any other device plugged in to the UPS.

The UPS is Also Known As:

battery backup, uninterruptible power source

Important UPS Facts:

In addition to acting as a backup when the power goes out, most UPS devices also act as power "conditioners" by ensuring that the electricity flowing to your computer and accessories is free from drops or surges. If a computer is not receiving a consistent flow of electricity, damage can and often does occur.

While a UPS system is not a required pieces of a complete computer system, including one as part of yours is always recommended. The need for a reliable supply of electricity is often overlooked.

Popular UPS Manufacturers:

APC, Belkin, CyberPower, Tripp Lite, Ultra

UPS Description:

The uninterruptible power supply sits between the utility power (power from the wall outlet) and the parts of the computer. In other words, the computer and accessories plug into the UPS and the UPS plugs into the wall.

UPS devices come in many shapes and sizes but are most commonly rectangular and free standing, intended to sit on the floor near the computer. All uninterruptible power supplies are very heavy due to the batteries located inside the device.

One or more batteries inside the UPS provide power to the devices plugged into it when power from the wall outlet is no longer available. The batteries are rechargeable and often replaceable, providing a long term solution to keeping your computer system running.

The front of the UPS will usually have a power switch to turn the device on and off and will also sometimes have one or more additional buttons that perform various functions. Higher-end battery backup units will also often feature LCD screens that show information about how charged the batteries are, how much power is being used, etc.

The rear of the UPS will feature one or more outlets that provide battery backup. In addition, many UPS devices will also feature surge protection on additional outlets and sometimes even protection for phone and cable lines.

UPS devices are manufactured with varying degrees of backup ability. To determine how powerful of a UPS you need, first use the Journey Systems Power Supply Calculator to calculate your computer's wattage requirements. Take this number and add it to the wattage requirements for other devices you would plug into the UPS. Take this totaled number and check with the UPS manufacturer to find your estimated battery runtime when you lose power from the wall.

Free Up Wasted Space

Removing unused programs is a great way to free up disk space, which will speed up your computer. Another way to find wasted disk space is to use the Disk Cleanup tool by following these steps:

1. Open My Computer, right-click Local Disk, and then click Properties.
2. On the General tab, click the Disk Cleanup button. Disk Cleanup will spend a few minutes examining your disk.
3. The Disk Cleanup dialog box opens. As you can see in Figure 2, it found almost three gigs of space on my computer that it could free up!
4. Select the desired check boxes in the Files to Delete list, and then click OK. Disk Cleanup will spend several minutes clearing space.
5. If you have more than one hard disk, repeat this process for each hard disk listed in My Computer.

Disconnect Unused Network Connections

If you've ever had a network with more than one computer, you probably found it useful to share files between the computers by mapping a network drive. Network drives allow one computer to read and write files to another computer's hard disk as if it were directly connected. I use network drives all the time, and for me, they were the most significant source of slowness.

The problem with network drives is that Windows XP will attempt to connect to the network drives when Windows starts. If the remote computers don't respond immediately, Windows will wait patiently. Additionally, some programs will attempt to connect to the network drives when you browse for files and folders. If you've ever tried to open a file and had to wait several seconds (or minutes!), it's probably because the program was trying to establish a network connection—even if the file you are opening is on your local computer.

I am not as patient as Windows, and I'd rather not wait for unused network connections to respond. To reduce this problem, disconnect any unused drives by following these steps:

1. Open My Computer.
2. On the Tools menu, click Disconnect Network Drive.
3. Select the network drives that you no longer need, and then click OK.

After I disconnected the network drives on my computer, my computer was able to restart in 1 minute, 45 seconds—about 40% faster!

Remove Autostartup Programs in Systemtray

The next step in restoring your computer's performance is to identify any unnecessary programs that start automatically. Often, programs configure themselves to run in the background so that they appear to start quickly when needed. Some of these programs show an icon on your taskbar to let you know that they're running, while others are completely hidden. These autostart programs probably won't noticeably slow down your computer as it starts up, but they will steal away trace amounts of memory and processing time as your computer runs.

Windows XP comes with the System Configurationtool (Msconfig.exe), an excellent way to manage the startup process. To start it:

1.	Click Start, click Run, type Msconfig, and then press Enter.
2.	On the Startup tab, you'll see a list of all the programs and processes that are set to run when Windows XP loads.
3.	Speed up your overall start time by clearing the check box next to any item you think you don't need.
4.	Click Apply, and then restart your computer for the changes to take effect.

My favorite way to examine autostart programs is to use the Autoruns freeware tool from Sysinternals. Autoruns lists every program that will automatically start and allows you to quickly delete the link to the program. Many autostart entries are important parts of Windows XP, including Userinit.exe and Explorer.exe. So you should not simply delete everything that you don't recognize. Instead, you should look up each entry at Paul Collins' Startup Applications List to determine whether you want it to start automatically.

For example, Figure 5 shows Autoruns revealing a file called nwiz.exe that is set to start automatically. I visited The Startup Applications List, typed in nwiz and discovered that it's used to set my desktop layout preferences. I'd like to keep this functionality, so I won't delete it.

Figure 5: The Autoruns freeware tool.

I also found a file named Wzqkpick.exe. After reading the description at The Startup Applications List, I decided I don't need to load that file automatically. I deleted the link using Autoruns by right-clicking it and then clicking Delete. This procedure works best for advanced users of Windows XP. If you aren't sure a program is unneeded—leave it!

The Startup Applications List may provide instructions for removing the startup program. If available, you should follow those instructions instead of deleting the link by using Autoruns.

How to Fix Bigger Problems

Many of the Windows XP Performance and Maintenance newsgroup users are experiencing serious, sudden performance problems. One day, their computer was fine and the next it was painfully slow. This type of problem is often caused by a computer virus or failing computer hardware. The suggestions in this article probably won't fix those types of problems. Instead, perform a virus scan on your computer. If that's not the issue, you should contact your computer vendor's technical support team for additional assistance. The troubleshooting process for this type of problem requires the knowledge to examine the computer's performance on a process-by-process basis, and usually includes a "process of elimination" phase where drivers, services, and hardware are removed/replaced one-by-one until the problem disappears. There's a very good chance that the computer won't start at all at some point in this process, so it's best to have support during the process.

Searching for "Windows XP Performance" on the Internet turns up a large number of performance tweaks. Some of these are useful, but most should not be attempted unless you understand exactly what you are doing. In particular, many of the tweaks that claim to improve your performance may only help under very specific circumstances. For example, in our own Windows XP Performance and Maintenance newsgroup, one user recommended disabling Internet Connection Firewall to solve a performance problem. Even if this did improve performance, it would leave the computer vulnerable to attacks from the Internet. I'd rather have a slightly slower computer than a hacked computer!

How do I turn off visual effects in Windows XP?

This is what I call "the demo problem" because I feel like some of the whiz-bang features that we find in modern operating systems are there purely to look cool, to make the system look good when someone's watching what you're doing. I mean, really, do we need three different kind of window-open-zoom features?

What's nice with Windows XP is that it's relatively straightforward to turn this feature off, though WinXP has the problem of whether you use "classic" or "new" mode with your Start Menu. I'll show both.

First, off, click on Start ; Control Panels and if you're using the newer view, you'll see this:

You want to click on "Performance and Maintenance" and now you'll see:

Click on "Adjust visual effects" and ...

Oh, wait, I want to show you the classic path there first: Now click on the "System" icon then on the "Advanced" tab and:

Jeez, it's still complex, but don't panic, you want to simply choose "Settings" under "Performance" (as shown) and you'll end up in the same place:

However you've gotten here, you can see that you just need to choose "best performance" and just about all the visual effects should be disabled and, hopefully, your computer will go a bit faster.