What is an Uninterruptible Power Supply (UPS)?

 

An uninterruptible power supply (UPS) uses batteries and an inverter to supply AC power when main power is not available. When main power is restored, a rectifier is used to supply DC power to recharge the batteries.

 

What equipment can be connected to a UPS?

 

All Computer Equipment such as Servers, Modems, Hubs, Patch Panels etc.

Emergency Lightning, Theater Lights, Intensive Care Units

Security, Closed Circuit TV, Fire and Alarm Systems.

Switch Boards, Fax Machines, Dot Matrix and Bubble Jet Printers.

Radar Equipment, Hospital Scanners, MR's and any Plant Processors.

 

What equipment must NOT be connected to a UPS?

 

Laser Printers, Photo Copy Machines and Laser/Fax/Photo Copiers.

Kettle’s, Urn's, Heaters, Refrigerators and Fluorescent Lights, or any type of Light with a starter Coil.

Another UPS. Accept where the 2nd UPS is less than 10% of the main UPS.

 

What to consider when buying a new UPS

 

Must be a “TRUE ON-LINE” or “DOUBLE CONVERSION UPS” AC to DC – DC to AC

Line-Interactive & Off-Line UPS. Inverter only Work during a Mains Fail.

Must have “NO SINGLE POINT OF FAILURE”!

Can the UPS be Paralleled when upgrading?

UPS must have a Battery Management System. Adjustable Float with Temperature.

UPS must have an “AUTOMATIC BATTERY TEST” to calculate Autonomy.

Must Monitor: Fan, Fuse Fail, Battery, Transformer Temp, etc.

UPS Must be Short Circuit Protected.

UPS must have a full Diagnostic Of Failure or Fault.

UPS Must Protect Load. Inverter must not switch off during Mains Fail.

UPS must have software to monitor Status over long distances / Internet. “Intelligent Energy Management” Adjust Fan speed with load & temp.

SNMP Card allows you to monitor UPS status continuously.

Will the UPS go in a “Sleep Mode” when the Power is removed?

 

UPS Categories

 

The general categories of modern UPS systems are on-line, line-interactive, and standby. An on-line UPS uses a "double conversion" method of accepting AC input, rectifying to DC for passing through the battery (or battery strings), then inverting back to 120v AC for powering the protected equipment. A line-interactive UPS maintains the inverter in line and redirects the battery's DC current path from the normal charging mode to supplying current when power is lost. In a standby ("off-line") system the load is powered directly by the input power and the backup power circuitry is only invoked when the utility power fails. Most UPS below 1 kVA are of the line-interactive or standby variety, which is usually less expensive.

 

What UPS technologies can be used on large power units?

 

For large power units, Dynamic Uninterruptible Power Supply is sometimes used. A synchronous motor/alternator is connected on the mains via a choke. Energy is stored in a flywheel. When the mains power fails, an Eddy-current regulation maintains the power on the load. DUPS are sometimes combined or integrated with a diesel-generator forming a diesel rotary uninterruptible power supply, or DRUPS.

 

Basic UPS units for personal/SOHO use

 

Offline / standby UPS. Typical protection time: 0 - 20 minutes.

Capacity expansion: Usually not available

 

The Offline / Standby UPS (SPS) offers only the most basic features, providing surge protection and battery backup. With this type of UPS, a user's equipment is normally connected directly to incoming utility power with the same voltage transient clamping devices used in a common surge protected plug strip connected across the power line. When the incoming utility voltage falls below a predetermined level the SPS turns on its internal DC-AC inverter circuitry, which is powered from an internal storage battery. The SPS then mechanically switches the connected equipment on to its DC-AC inverter output. The switchover time can be as long as 25 milliseconds depending on the amount of time it takes the Standby UPS to detect the lost utility voltage. Generally speaking, dependent on the size of UPS connected load and the sensitivity of the connected equipment to voltage variation; the UPS will be designed and/or offered (specification wise) to cover certain ranges of equipment, i.e. Personal Computer, without any obvious dip or brownout to that device.

 

Line-Interactive UPS

 

Typical protection time: 5 - 30 minutes.

Capacity expansion: Several hours

 

The Line-Interactive UPS is similar in operation to a Standby UPS, but with the addition of a multi-tap variable-voltage autotransformer. This is a special type of electrical transformer that can add or subtract powered coils of wire, thereby increasing or decreasing the magnetic field and the output voltage of the transformer.

 

This type of UPS is able to tolerate continuous under-voltage brownouts and over-voltage surges without consuming the limited reserve battery power. It instead compensates by auto-selecting different power taps on the autotransformer. Changing the autotransformer tap can cause a very brief output power disruption, so the UPS may chirp for a moment, as it briefly switches to battery before changing the selected power tap.

Autotransformers can be engineered to cover a wide range of varying input voltages, but this also increases the number of taps and the size, weight, complexity, and expense of the UPS. It is common for the autotransformer to only cover a range from about 90V to 140V for 120V power, and then switch to battery if the voltage goes much higher or lower than that range.

 

In low-voltage conditions the UPS will use more current than normal so it may need a higher current circuit than a normal device. For example to power a 1000 watt device at 120 volts, the UPS will draw 8.32 amps. If a brownout occurs and the voltage drops to 100 volts, the UPS will draw 10 amps to compensate. This also works in reverse, so that in an overvoltage condition, the UPS will need fewer amps of current.

 

Double conversion / Online UPS

 

Typical protection time: 5 – 30 minutes

Capacity expansion: Several hours

 

The Online UPS is ideal for environments where electrical isolation is necessary or for equipment that is very sensitive to power fluctuations. Although once previously reserved for very large installations of 10kW or more, advances in technology have permitted it to now be available as a common consumer device, supplying 500 watts or less. The Online UPS is generally more expensive but may be necessary when the power environment is "noisy" such as in industrial settings, for larger equipment loads like data centers, or when operation from an extended-run backup generator is necessary.

 

The basic technology of the online UPS is the same as in a Standby or Line-Interactive UPS. However it typically costs much more, due to it having a much greater current AC-to-DC battery-charger/rectifier, and with the rectifier and inverter designed to run continuously with improved cooling systems. It is called a Double-Conversion UPS due to the rectifier directly driving the inverter, even when powered from normal AC current.

 

In an Online UPS, the batteries are always connected to the inverter, so that no power transfer switches are necessary. When power loss occurs, the rectifier simply drops out of the circuit and the batteries keep the power steady and unchanged. When power is restored, the rectifier resumes carrying most of the load and begins charging the batteries, though the charging current may be limited to prevent the high-power rectifier from overheating the batteries and boiling off the electrolyte.

 

The main advantage to the on-line UPS is its ability to provide an electrical firewall between the incoming utility power and sensitive electronic equipment. While the Standby and Line-Interactive UPS merely filter the input utility power, the Double-Conversion UPS provides a layer of insulation from power quality problems. It allows control of output voltage and frequency regardless of input voltage and frequency.

 

Hybrid Topology / Double conversion on demand UPS

 

Recently there have been hybrid topology UPS’s available in the market. These hybrid designs do not have an official designation, although one name used by HP and Eaton is Double Conversion on Demand. This style of UPS is targeted towards high efficiency applications while still maintaining the features and protection level offered by double conversion.

 

A hybrid (double conversion on demand) UPS operates as an offline/standby UPS when power conditions are within a certain preset window. This allows the UPS to achieve very high efficiency ratings. When the power conditions fluctuate outside of the predefined windows, the UPS switches to online/double conversion operation. In double conversion mode the UPS can adjust for voltage variations without having to use battery power and can filter out line noise and control frequency. Examples of this hybrid/double conversion on demand UPS design are the HP R8000, HP R12000, HP RP12000/3 and the Eaton BladeUPS.