Choosing and Managing the Right UPS

 In Blog, Technology

Have you ever spent time working on a document or software project and became so engrossed that you forgot to hit “Save” for a while?  Then the power went out and all was lost since the last save.  Fortunately, that is not as common as it used to be since a lot of us use laptops and they have their own onboard power, but you get the idea.  Computers need to have power and an unexpected power loss can be disastrous.

What about this?  You have your workstation plugged into a UPS, so you are safe.  The power goes out, but you are still up and running because of your UPS.  You are VPN’ed into your office machine and that is when it hits you.  Your workstation and monitor are plugged into a UPS but your wireless router is not so you cannot finish your job right now unless the power comes back online before your UPS runs out of juice.  When was the last time you hit “Save?”

Or this scenario?  You have everything critical plugged into a UPS.  Now you are set, right?  Then the power goes out and guess what?  Your UPS fails because unbeknownst to you, the batteries are dead.  How long have you had that UPS?

UPSs are an important part of any office computer system whether at home or in an actual office.  VVMS refers to those as the OO and HO.  OO is the Office Office and HO is the Home Office.  Enough said about that.

For the sake of this blog post, I am going to divide UPSs into two (2) major categories: Workstation UPSs and Server/Rackmount UPSs.

Workstation UPS

This is simpler than dealing with UPSs for servers but there are still some things to consider beyond just purchasing the UPS and plugging in your computer.  Here are my suggestions:

What Equipment Needs a UPS

Know what needs to have a UPS backup and what does not. Know all the components that you use.  Have a plan for what you will do if the power fails.  Typically, you will want to work for a few minutes hoping that the power will come back on.  If it does not, you will need to make sure your work is saved, and the equipment is properly shut down.

If you are using a laptop with good batteries, then that will not be as much of a concern.  Even if you use an external monitor, you can always switch back to the laptop’s internal monitor if required to do so.  If your laptop is plugged into a docking station or a port extender, that should be powered off the UPS.

If you are using a workstation then the workstation and monitor(s) will need to be powered through a UPS.

If you are on a home network of some kind, the router (wireless or otherwise) will need to be connected to a UPS if you intend for the home network to stay functioning.  Many cable modems have their own internal batteries but not always.  If your’s does not and you need to stay connected to the outside world then your cable modem needs to be plugged into a UPS.

Don’t forget that the more items you plug into a single UPS, the shorter the time it can stay up after the power fails.  Consider multiple UPSs.  That may not be necessary but that should be considered.  It will be necessary if the cable modem and router are not collocated with your workstation.

Battery Replacement

Some UPS systems will include a battery sensor of some kind that will give you an idea of the health of your batteries. Consider this feature when purchasing a UPS.  Alternatively, set up a schedule of when to replace your batteries.  They should last at least a year.  But I don’t trust them past the second year.  They should comfortably last two years, but the goal is to replace them before you depend on a battery that is starting to fail.


The UPS manufacturer will want you to use their replacements, but likely the UPS manufacturer is not making their own batteries.  They just put their name on someone else’s battery.  You can purchase batteries from a battery supplier with the same or better specifications than your original batteries at a lower cost.  Some of these suppliers will have a chart that will tell you which of their batteries will fit which UPS manufacturer by model number.

If you are not purchasing a battery as an exact replacement, then there are a few things you will need to match up for them to work properly.  The replacement battery should be the same physical size so that it fits into the case properly.  The voltage and the amp-hour (AH) should match the original.  Lastly, the terminals should be in the same place and should be the same type and size.  The most common terminals for UPSs are the FASTON connectors.  These are flat metal blade connectors that are generally either .250-inches wide or .187-inches wide.  There are other terminal types in use, but the FASTON terminals are very common.

Many companies sell replacement UPS batteries.  They generally have sufficient information for you to identify what terminal types you are using.  If all else fails, you can go back to the manufacturer for the exact replacement.  Just be prepared to spend a little more.  I have found as much as a 300% difference in pricing between the original UPS manufacturer’s price and the price charged by a battery supplier.


The last thing I want to mention is the outlets. UPS’s generally have at least two banks of outlets.  Only one bank is connected to the battery backup system.  If you plug something critical into the bank that is not protected by the battery, then you haven’t accomplished what you want to accomplish.


Be prepared to add a power strip to the battery-protected side if you do not otherwise have enough outlets.  I put the items with the highest power needs on the outlets on the UPS itself.  Lower power equipment such as routers should have no problem being plugged into a power strip that is, in turn, plugged into the battery backup side.  Hypothetically if I had a UPS with four (4) battery backup outlets, I would plug in my workstation, and my monitor(s), directly into the outlets on the UPS.  I would plug in a power strip into the remaining outlet and use that to power up lower power peripherals that needed battery backup.

You probably do not need to plug your printer into a battery-protected outlet.  That is only necessary if you will need to print something while on battery backup.  That is often not the case.  When it is not the case, then move it to the side that is not backed up by the battery or plug them into a separate outlet altogether.  Printers are large power users so don’t waste valuable UPS power on the printer.

Rackmount UPS for Servers


Purchasing rackmount UPSs for servers can be a little more complicated than purchasing a UPS for a workstation.  The time that equipment must stay up online without power is more critical.  Employing automatic shutdown logic can help but if the goal is to keep everything running as long as possible before shutdown must take place then more power will be necessary.  Is the wait for power to be restored dependent on the power company or is there some sort of secondary power source such as an emergency generator that must come online and stabilize?  When using an emergency generator, the total time that the UPS must keep the equipment up should be the maximum time it will take the emergency generator to come online and stabilize.  Emergency generators must be tested routinely to make sure that they will start and come online as expected.  But in practice, they don’t always start as expected.

If not using an emergency generator, then the total time that the UPS must keep equipment online is the sum of the total time it will take to properly shut down the equipment plus the time that you want the equipment to stay operational before the equipment shutdown must commence.  If hypothetically you want the equipment to stay online for 15 minutes before you start the shutdown process and the shutdown process will take 5 minutes, then you will need 20-minutes of runtime.

The total time a UPS can stay online depends on the capacity of the UPS including battery health and total load that is being placed on the UPS.  This will be discussed in greater detail below.

Eliminating a Single Point of Failure

My preferred scheme is to use servers with dual power supplies with each power supply being plugged into a separate UPS and finally each UPS going to a separate breaker.  This will help prevent a single point of failure. For example:

  1. If a server power supply fails, then the second power supply will keep everything up and running normally.
  2. If one of the two UPSs has a problem, then the other UPS will keep everything up and running normally
  3. If a circuit breaker trips, then the other circuit will stay up and everything stays up and running.

If there is a power failure, then the two UPSs will share the load and the power will stay up longer.

With that in mind, when the dual power supply scheme is followed, I size everything as if it is the only source of power.  Because if something fails, it just might be the only source of power.

Sizing a UPS

You need to determine what must be kept alive by each UPS.  Make a list of each item and its power requirements.  Each piece of equipment is likely to have its power requirements specified in Volts and Amps.  Most modern equipment can now automatically do its adjusting for voltage based on the supply being used. It is not uncommon for voltage to be expressed in a range such as 100-240 volts (or something similar).  This means that you can plug this piece into an outlet without concern if the voltage falls within that range.

For the sake of this exercise, we are going to consider the voltage to be 120-volts.  The voltage is likely to be 117 volts AC here in the US, but we will use 120 volts to keep things simple.

Next, we have to know the volt-amps of the equipment.  If it is stated on the label, then you are ahead of the game.  It is often not stated.  The current stated on the label is the peak that it will draw.  Chances are very good that it will draw less.  I have a server that says that its Amp rating (usually abbreviated as “A”) is 5 or 5-amps.  To calculate the Volt-Amps, multiply the voltage (in this case 120-volts) by the amps (in this case 5-amps) and that will yield 600 volt-amps.

Repeat these calculations for every piece of equipment that will be plugged into the UPS.  Add up the total VA.  That will be the total VA when the equipment is operating at full load.  You can take some relief in the fact that your calculations will be higher than actual values so you will be building in some margin of safety, which is good!

A commercial UPS that is rack-mountable, will contain the runtime when under full load.  They will often give you a runtime for when they are under half-load also.  You might guess that the runtime is going to be twice as long as it is under full load.  The good news is that it will be longer than that.  I randomly looked at the spec for a Tripp Lite Smart Pro rackmount UPS.  It is rated at 2200VA.  It can operate at full load for 8 minutes whereas it will operate for about 20 minutes when under half load.  That difference seems to apply to many commercial UPS units, but you will need to check the specs of any unit that you are considering.

To keep the math simple, consider the total VA as the amount of load that you need to power.  Find a UPS that will work for twice that amount, which means that if your servers and associated equipment are operating at full power, that will mean the UPS is operating at half load.  As an example, if your total VA is 1,500 VA then you will want a UPS capable of supplying 3,000 VA at full power.  That means that you will not exceed 50% of the UPS’s full power so you will have a longer run time.

Remember that the 1,500 VA was your equipment running at full power, which in most cases it will be less, so you will be loading your UPS at less than half of its capability.  The bottom line is that you should be able to stay up online longer than the half-power figure supplied by the UPS manufacturer.


Just like in the smaller UPS units, keeping your UPS working correctly requires you to keep your UPS running on healthy batteries.  What I have said about batteries in the Workstation UPS section fully applies.  Your rackmount UPS may even use the same type of batteries but just more of them.  Or it may be fewer batteries but larger in size.  I would plan to replace the batteries every two years.  The idea is to replace them before they degrade too much, not after they are failing.

Recycling Batteries

No matter if you are talking about workstation UPSs or rackmount UPSs when you replace the batteries, you will have to dispose of the batteries properly.  These batteries are a lot like your automobile batteries.  They are likely lead-acid batteries.  Unlike your car battery, they use a “gelled” electrolyte so that they can be placed at any angle and not spill the electrolyte.  You cannot just throw these away.  Locate a service that recycles automobile batteries.  They will likely accept these batteries also.  Some of these services will pay a small fee for failed automobile batteries.  Do not expect to get any such rebate for these batteries but at least you will know that they will be properly disposed of and not end up in landfills poisoning the soil for future generations.


Following these examples will provide you with a UPS system that will keep you out of trouble.  Most failures I see result from not maintaining healthy batteries or not properly plugging in all the right equipment into the designated UPSs.  Too many loads on one UPS and too little on another.  The overloaded UPS will not stay online for as long as is expected.

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