Power Supplies (UPS)
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Line Interactive UPS
Which one is right for you?
When you are running on your UPS
To protect your equipment from power failure, slowdowns and brownouts, you
need more than a simple surge suppressor. Blackouts and brownouts make up as
much as 90% of all power disturbances affecting electrical equipment. You will
need a dependable Uninterruptible Power Supply, or UPS to keep your switches
and PBXs up for an extended period of time.
UPSs all come with a nickel-cadmium or lead-acid battery backup, to get you
through anywhere from a few minutes to several hours of time without power.
Battery power supplies direct current, and since your equipment will only run
on alternating current, there's also a conversion that takes place, facilitated
by an inverter. The conformity of the inverter's output wave to a true 60-cycle
sine wave is an important measure of the inverter's quality. Most UPSs have
microprocessors that regulate some of the functions and communicate over a LAN.
Although there is only so much variation you can produce with UPSs, telecom
equipment fares best with purer output waveforms, extended battery time and
the ability to manage the devices remotely.
energy spike occurs when there is a rapid load reduction on the power grid.
This can cause voltage levels to jump as much as 100%, causing electrical components
to become unstable and forcing a system crash. Surges, which are basically the
same as a spike, but of longer duration, will physically damage equipment. Surges
are caused by lightning, a storm blowing power lines together, or sometimes
by the electric company. Line noise or electrical static is caused by low-level
The per-hour loss for a 900-number service without power is over $50,000, illustrating
vividly the point that downed equipment is more than just a nuisance. UPSs protect
you from all types of power variations, but most important is protection from
a power outage, which results in lost revenue and wasted employee time.
brownout results when there is a uniformly lower voltage that doesn't distort
the power signal. Brownouts sometimes occur when internal office equipment,
especially air conditioners and laser printers switch on; or during peak demand
for power by a local heavy use industry. New equipment may continue to operate
fine under these circumstances for some time, but it will cause damage in the
When a power failure occurs and the UPS switches power to the battery, the
signal generated by the inverter and supplied to the equipment may not be a
true sine wave (it may be called a "modified" or "simulated" sine wave). The
modified or simulated sine wave can range from a square wave to a trapezoidal
wave. These pseudo-sine waves are the product of less expensive components than
those used to make true sine wave generators. Computers using the power supplies
found in most desktop PCs and servers will work fine with square waves, better
with trapezoidal waves, and best with true sine waves. Generally speaking, only
continuous on-line UPSs require the true sine wave to be effective.
UPSs also have a third component; the rectifier module. The rectifier keeps
the batteries charged by changing AC current to DC. UPSs are classified by the
way its 3 components, the inverters, rectifiers, and batteries are connected.
Here are some of the more common configurations:
Standby UPSs feed AC power from the utility line through the bus, to the equipment.
It will only switch to battery during a blackout or brownout. Surge protectors
and filters are also utilized to smooth out high frequency spikes and line noise.
Standbys commonly work best on single-use computer equipment.
Like the standby, the online interactive passes the AC directly through, but
will ride out fluctuations to preserve battery life. To accomplish this, a regulator
filters the voltage, raising or lowering it to the proper range. When the voltage
is too far out of range, the CPU will utilize the battery. As with the standby,
filters are used to even out high frequency spikes and eliminate line noise.
With an online UPS, the inverter is always on, converting DC to AC so there
is no delay in switch-over in the event of a failure. These work by converting
the power from the wall outlet from AC to DC, continually charging the batteries,
through the inverter where it is converted back to AC and sent out to the equipment
that is relying on it for backup, a process called "double conversion". This
design facilitates voltage regulation and pure sine wave output with limited
distortion. Some also have isolation transformers which block out surges and
spikes by separating the input and output lines.
Which one is right for your business?
Standby UPSs are generally not used for telecom equipment because the square
wave output is not tolerated by even the best equipment. These UPSs are best
for PCs because they usually supply just enough time to shutdown. Telecom equipment
needs a much longer back-up period.
With line interactive and online UPSs, the battery is always on the "power
bus", hence there is no switchover time and no power interruption. There is
also a pure sine wave output. Built in to the design is superior voltage regulation,
surge protection and noise/spike filtering. Both can be outfitted with extra
battery packs for extended periods of outage.
Line interactives can deliver the perfect sine-wave, but the option to provide
that will cost extra. They usually have a fair switchover time, usually less
than four milliseconds. Their surge protection meets industry standard specs,
although they cannot absorb the many joules of energy that the onlines can,
due to the interactive's lack of isolation transformers. Line interactives are
less error prone than the Online UPSs, partly because aside from some filtering,
they are at rest most of the time. If you have only infrequent outages, you
may find this the best choice, however the Line interactive UPS may not completely
compensate for voltage shifts.
get the clean AC signal from an Online UPS, you will pay more in up-front cost
due to expensive special circuitry and in maintenance, with the double conversion
process resulting in extra power usage. The special circuitry that makes the
Online's signal so clean is also more prone to failure than that used by the
interactive. Some reports suggest that the onlines run half as long between
failures as do the interactives.
When you're running on your UPS
When telecom equipment stability is your prime concern, you'll want to ride
through the power-outage waiting for the power to return. In this case preventive
maintenance is key.
Before an outage occurs, you will want to know:
1. The current charge on the battery
2. The battery temperature
If your battery is too warm, it will lose its effectiveness and it may be a
sign of another problem. Sometimes the batteries are installed backwards, or
an overloaded UPS transformer may be heating up a battery pack nearby.
Load on the system, measured in KVA's is key in determining the necessary capacity.
UPSs are rated by how much load they can support. If the devices supported by
the UPS are drawing too much current, the UPS will be unstable. Some UPSs will
support an adapter card with sensors that measure such external surrounding
conditions as the current temperature and humidity and the presence of smoke
and fire. They can even tell you whether the door to the room has been opened.
Some UPSs offer a Graphical User Interface (like Windows, which uses graphics
instead of characters and works with a mouse or trackball) displaying all of
the above information on simulated, dials, meters, and LEDs.
Most UPSs now allow you to interface with network managing software
to monitor your UPS. Besides passive monitoring, you will be able to send commands
to the UPS to run diagnostic tests and to turn on and off devices that are plugged
into them. This would be useful during an outage. If you see your battery runtime
meter drop, you may decide to run off some non-critical equipment to preserve
power for the PBX. You can do this right from your remote console.
There is no question that with the potential loss or damage to costly equipment,
the investment in an Uninterruptible Power Supply is a sound one.
Shop on-line for the right UPS for
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