Hi Guys
I thought it might be of some value to noobs and other peeps to have a guide on buying a UPS (Uninterruptable power supply). A UPS is often not thought about until the unimaginable happens, a lightning strike occurs whilst you are in the midst of finishing that all important work document. And in turn takes your system and all your unsaved data with it.
What is a UPS
A UPS is a backup power unit that provides continuous power when the normal power supply is interrupted. UPS systems can be stand-by, only supplying power when the regular supply is interrupted, or fulltime, relying on regular power and/or batteries to supply it while it supplies power to the protected device. A UPS is not always necessary on most computer systems, but can be important on systems that need to be up 24 hours a day, such as servers. Bearing this in mind, UPS's are a necessity if you live in an area prone to electrical storms, brownouts, surges or outages. There are three levels of power protection available to the home computer user. The levels are:
1.Surge Suppressor (These are basically a fancy fuse between the source and your hardware; they clamp down spikes, but can't fill in a low voltage level or dropout. This is a bare minimum level of protection that any piece of expensive electronics should have);
2.Line Conditioners (These devices filter noise out of AC lines. Noise can degrade your power supply and cause it to fail prematurely. They also protect against short voltage dropouts and include surge suppression.), and
3.Uninterruptible Power Supplies ( Firstly it filters the power your machine sees, smoothing out spikes and voltage fluctuations that can stress or even damage your electronics. Secondly, it provides a certain amount of dwell time in the event your power goes out entirely — this can often get you through brownouts and short blackouts. Third, when the UPS is about to run out of power it can arrange a graceful shutdown of your computer so that no unpleasant things happen to your disk filesystems).
How to select a UPS
UPSes are nowadays very inexpensive and prices are heading down. In fact prices are so low now that I'm not going to walk you through the elaborate optimisation step that would have been important even two or three years ago, of estiming the watt dissipation of your computer and matching it to a UPS rating. Instead I'll explain why this would be a waste of effort and how to buy in a simpler and more effective way.
UPS's are rated by the watts a full battery can put out before it drains. However, they are marketed using a VA (voltage-amps) figure; often, consumer-grade UPS's don't even specify a wattage on the box where you can see it. This is because the VA figure is larger and looks sexier. As a rule of thumb. assume the wattage is half of the VA rating; for an explanation of the complexities involved (if you care) see the white paper Understanding Power Factor, Crest Factor and Surge Factor on the APC website.
But even if you know the watt rating of the UPS, it is the ratio of that figure with the wattage dissipation of your computer that controls the dwell time. Your dissipation is hard to predict; it can even be effected by things like the size of monitor you use (big ones can be quite power-hungry).
Manufacturers try to get around this technical thicket by putting an expected dwell time on the box. But they exaggerate and even lie about their dwell times a lot ( "marketing"). What they'll do is quote you the dwell time you would get driving a bare minimum system with the disk drives shut off and a tiny monitor, in much the same way laptop manufacturers lie about their battery dwell times. The more honest UPS manufacturers give you a little table showing expected dwell times for different system configurations ("desktop", "tower", etc.). As a rule of thumb, assume you will get about 50% of the dwell time listed on the box for your configuration type.
My advice is to forget the numbers game. Just go online or to your local computer store and buy one of the higher-end consumer or home-office models from APC, Best, Tripp-Lite, Belkin, Opti, Powerware or some other reputable manufacturer. Go ahead and grab the model with the longest dwell time, highest watt rating, or biggest VA number you can find. I guarantee you will feel very good about your decision not to pinch pennies come your first extended power outage.
Perhaps a more compelling reason it is better to over-buy capacity rather than ending up with a UPS that is too weak for your power drain is that overstrained UPS's can fail in ugly ways, including catching fire and exploding.
Be sure you get a line interactive UPS rather than the older standby or SPS type. The older technology doesn't actually filter your power through the battery, so you're not assured of good voltage conditioning. The main advantage of an SPS (low cost) has been eroded now that line-interactive UPS's are so inexpensive.
Another important consideration is how your UPS will communicate with your computer. Do not buy a serial line UPS (one that communicates via an RS-232C cable). These are passing out of use in favor of UPS designs that use USB or Ethernet, for the very excellent reason that RS-232C interfaces are flaky, difficult to configure, and difficult to debug. Ethernet is overkill for this application; UPS's simply don't need that kind of bandwidth. We recommend sticking with USB, which is well-matched in price/performance to this job and relatively easy to troubleshoot.
Personally, I like APC UPS's (I have no connection with the company). But this is not the kind of widget for which manufacturer makes a whole lot of difference as long as you stick with one of the reputable brands. You can estimate your UPS requirements here. #Be sure to include your country of residence into the equation, when working out an estimate.
UPS Software
Your UPS communicates with your computer so it can gracefully shut the computer down when an outage has lasted too long for the battery to cope. In order for graceful shutdown to actually happen, your computer needs to be watching whatever messages come over the UPS cable for the one that says terminate. Then it needs to tell the operating system to shut down. Your UPS usually comes with a CD full of such software, software that (manufacturer dependant) may:
1. Automatic shutdown of equipment during long power outages.
2. Monitoring and logging of the status of the power supply.
3. Display the Voltage/Current draw of the equipment.
4. Restart equipment after a long power outage.
5. Display the voltage currently on the line.
6. Provide alarms on certain error conditions.
How long can equipment on a UPS keep running after the power has gone?
That depends on how big a UPS you have and what kind of equipment it protects. For most typical computer workstations, one might have a UPS that was rated to keep the machine alive through a 15 minute power loss. If it is important for a machine to survive hours without power, one should probably look at a more robust power backup solution that includes a generator and other components. Even if a UPS powers a very small load, it must still operate it's DC (battery) to AC converter (the inverter), which costs power. A rough extrapolation from APC's documentation, leads me to guess that its 2000 VA UPS can operate it's own inverter (with no extra load) for just over 8 hours. A 1250 VA UPS could run its converter for about 5. These are very rough guesses based on information provided by one vendor.
What else do I need to consider?
It would be nice to know how long your site's typical power outages are. In some places, with nice weather and a flaky power grid, the power is almost never out for more than 5 minutes, but this could happen quite frequently. In this case, you may as well use a UPS with a VA rating close to your equipment rating with no extra batteries. If your area has longer outages, in the half hour or hour range, as is often the case in thunderstorm country, you can either buy UPS's with multiples of the VA rating of the equipment, since oversizing a VA rating for a UPS has the effect of lengthening the amount of time your equipment can stay up in case of a power outage, or you can buy additional battery units for a smaller UPS. You can probably get away with doing simple math to determine how much longer a larger UPS will keep your equipment running, but I recommend running a few tests before committing to a large purchase order. Also, your UPS vendor will almost certainly be glad to help you size the equipment you need. If all else fails and you guess wrong, or move equipment to a location with different power status, you may be really, really glad if you bought a UPS that can be expanded with additional battery units.
Some major UPS manufacturers
Belkin- http://catalog.belkin.com/IWCatSectionView.process?Section_Id=201476
APC- http://www.apcc.com/
Opti- http://www.opti-ups.com/
Powerware- http://www.powerware.com/
If you're feeling keen or crazy (whatever the case may be) there is an interesting article on making your own Ghetto UPS here.
#Pictures used were gleamed from APC Australia website
#Additional information courtesy of jetcafe.org
PV
I thought it might be of some value to noobs and other peeps to have a guide on buying a UPS (Uninterruptable power supply). A UPS is often not thought about until the unimaginable happens, a lightning strike occurs whilst you are in the midst of finishing that all important work document. And in turn takes your system and all your unsaved data with it.
What is a UPS
A UPS is a backup power unit that provides continuous power when the normal power supply is interrupted. UPS systems can be stand-by, only supplying power when the regular supply is interrupted, or fulltime, relying on regular power and/or batteries to supply it while it supplies power to the protected device. A UPS is not always necessary on most computer systems, but can be important on systems that need to be up 24 hours a day, such as servers. Bearing this in mind, UPS's are a necessity if you live in an area prone to electrical storms, brownouts, surges or outages. There are three levels of power protection available to the home computer user. The levels are:
1.Surge Suppressor (These are basically a fancy fuse between the source and your hardware; they clamp down spikes, but can't fill in a low voltage level or dropout. This is a bare minimum level of protection that any piece of expensive electronics should have);
2.Line Conditioners (These devices filter noise out of AC lines. Noise can degrade your power supply and cause it to fail prematurely. They also protect against short voltage dropouts and include surge suppression.), and
3.Uninterruptible Power Supplies ( Firstly it filters the power your machine sees, smoothing out spikes and voltage fluctuations that can stress or even damage your electronics. Secondly, it provides a certain amount of dwell time in the event your power goes out entirely — this can often get you through brownouts and short blackouts. Third, when the UPS is about to run out of power it can arrange a graceful shutdown of your computer so that no unpleasant things happen to your disk filesystems).
How to select a UPS
UPSes are nowadays very inexpensive and prices are heading down. In fact prices are so low now that I'm not going to walk you through the elaborate optimisation step that would have been important even two or three years ago, of estiming the watt dissipation of your computer and matching it to a UPS rating. Instead I'll explain why this would be a waste of effort and how to buy in a simpler and more effective way.
UPS's are rated by the watts a full battery can put out before it drains. However, they are marketed using a VA (voltage-amps) figure; often, consumer-grade UPS's don't even specify a wattage on the box where you can see it. This is because the VA figure is larger and looks sexier. As a rule of thumb. assume the wattage is half of the VA rating; for an explanation of the complexities involved (if you care) see the white paper Understanding Power Factor, Crest Factor and Surge Factor on the APC website.
But even if you know the watt rating of the UPS, it is the ratio of that figure with the wattage dissipation of your computer that controls the dwell time. Your dissipation is hard to predict; it can even be effected by things like the size of monitor you use (big ones can be quite power-hungry).
Manufacturers try to get around this technical thicket by putting an expected dwell time on the box. But they exaggerate and even lie about their dwell times a lot ( "marketing"). What they'll do is quote you the dwell time you would get driving a bare minimum system with the disk drives shut off and a tiny monitor, in much the same way laptop manufacturers lie about their battery dwell times. The more honest UPS manufacturers give you a little table showing expected dwell times for different system configurations ("desktop", "tower", etc.). As a rule of thumb, assume you will get about 50% of the dwell time listed on the box for your configuration type.
My advice is to forget the numbers game. Just go online or to your local computer store and buy one of the higher-end consumer or home-office models from APC, Best, Tripp-Lite, Belkin, Opti, Powerware or some other reputable manufacturer. Go ahead and grab the model with the longest dwell time, highest watt rating, or biggest VA number you can find. I guarantee you will feel very good about your decision not to pinch pennies come your first extended power outage.
Perhaps a more compelling reason it is better to over-buy capacity rather than ending up with a UPS that is too weak for your power drain is that overstrained UPS's can fail in ugly ways, including catching fire and exploding.
Be sure you get a line interactive UPS rather than the older standby or SPS type. The older technology doesn't actually filter your power through the battery, so you're not assured of good voltage conditioning. The main advantage of an SPS (low cost) has been eroded now that line-interactive UPS's are so inexpensive.
Another important consideration is how your UPS will communicate with your computer. Do not buy a serial line UPS (one that communicates via an RS-232C cable). These are passing out of use in favor of UPS designs that use USB or Ethernet, for the very excellent reason that RS-232C interfaces are flaky, difficult to configure, and difficult to debug. Ethernet is overkill for this application; UPS's simply don't need that kind of bandwidth. We recommend sticking with USB, which is well-matched in price/performance to this job and relatively easy to troubleshoot.
Personally, I like APC UPS's (I have no connection with the company). But this is not the kind of widget for which manufacturer makes a whole lot of difference as long as you stick with one of the reputable brands. You can estimate your UPS requirements here. #Be sure to include your country of residence into the equation, when working out an estimate.
UPS Software
Your UPS communicates with your computer so it can gracefully shut the computer down when an outage has lasted too long for the battery to cope. In order for graceful shutdown to actually happen, your computer needs to be watching whatever messages come over the UPS cable for the one that says terminate. Then it needs to tell the operating system to shut down. Your UPS usually comes with a CD full of such software, software that (manufacturer dependant) may:
1. Automatic shutdown of equipment during long power outages.
2. Monitoring and logging of the status of the power supply.
3. Display the Voltage/Current draw of the equipment.
4. Restart equipment after a long power outage.
5. Display the voltage currently on the line.
6. Provide alarms on certain error conditions.
How long can equipment on a UPS keep running after the power has gone?
That depends on how big a UPS you have and what kind of equipment it protects. For most typical computer workstations, one might have a UPS that was rated to keep the machine alive through a 15 minute power loss. If it is important for a machine to survive hours without power, one should probably look at a more robust power backup solution that includes a generator and other components. Even if a UPS powers a very small load, it must still operate it's DC (battery) to AC converter (the inverter), which costs power. A rough extrapolation from APC's documentation, leads me to guess that its 2000 VA UPS can operate it's own inverter (with no extra load) for just over 8 hours. A 1250 VA UPS could run its converter for about 5. These are very rough guesses based on information provided by one vendor.
What else do I need to consider?
It would be nice to know how long your site's typical power outages are. In some places, with nice weather and a flaky power grid, the power is almost never out for more than 5 minutes, but this could happen quite frequently. In this case, you may as well use a UPS with a VA rating close to your equipment rating with no extra batteries. If your area has longer outages, in the half hour or hour range, as is often the case in thunderstorm country, you can either buy UPS's with multiples of the VA rating of the equipment, since oversizing a VA rating for a UPS has the effect of lengthening the amount of time your equipment can stay up in case of a power outage, or you can buy additional battery units for a smaller UPS. You can probably get away with doing simple math to determine how much longer a larger UPS will keep your equipment running, but I recommend running a few tests before committing to a large purchase order. Also, your UPS vendor will almost certainly be glad to help you size the equipment you need. If all else fails and you guess wrong, or move equipment to a location with different power status, you may be really, really glad if you bought a UPS that can be expanded with additional battery units.
Some major UPS manufacturers
Belkin- http://catalog.belkin.com/IWCatSectionView.process?Section_Id=201476
APC- http://www.apcc.com/
Opti- http://www.opti-ups.com/
Powerware- http://www.powerware.com/
If you're feeling keen or crazy (whatever the case may be) there is an interesting article on making your own Ghetto UPS here.
#Pictures used were gleamed from APC Australia website
#Additional information courtesy of jetcafe.org
PV
