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1. Why the need for Uninterruptible Power?
The quality of power is not perfect. In an increasingly hi-tech, automated world, a growing number of loads are sensitive to momentary power interruptions, voltage sags & blackouts. They are also affected by over-voltage conditions such as swells and surges. The losses & costly down-time associated with such disturbances are the drivers behind the need for power protection.
2. How long do power interruptions normally last?
• Sags & Brownouts: Cycles to seconds
• Momentary Interruptions: Cycles to seconds
• Minor Under- & Over-Voltages: Indefinitely
• Blackouts & Failures: Minutes to hours
3. What are the Benefits of a UPS?
• Equipment back-up or ride-through during short power disturbances.
• Temporary backup during the startup or testing of a motor generator.
• Time to facilitate an orderly shutdown of programs and systems during an extended outage.
• General immunity to power disturbances.
• Device lock-up
• Costly downtime
• Equipment resets
• Inconsistent or lost data
• Delays in patient care/treatment
• Premature circuit board and component failure
4. Who uses a UPS?
• Lighting Companies
• Motion Picture Production
• Office Complexes & Commercial Buildings
• Original Equipment Manufacturers (OEMs)
• Postal Services
• Recording Studios
• Retail Stores
• Security Systems Companies
• Sports Stadiums & Arenas
• Telecom & Phone Companies
• Theme Parks
• Transit & Traffic Control Systems
• TV Stations
5. What are the Applications?
• Computers, Servers & Networks
• Automation & Control
• Medical & Emergency Services
• Laboratory & Diagnostic Equipment
• Test & Measurement
• Security & Monitoring
• Industrial Fabrication Equipment
• Emergency Lighting
• POS Equipment, ATM’s & Banking
6. What are the basic UPS Topologies?
Off-line: This type transfers to battery power only when a low voltage level is breached. Under normal conditions, utility power supplies the load.
• For less critical loads with a wide input voltage tolerance
• Lowest cost
Line Interactive: Similar to off-line, it includes automatic voltage regulation (AVR) which allows a much wider input voltage swings before transferring to battery, thus extending battery life.
• For sensitive loads where voltage fluctuations are common
• Medium cost
On-line: This type is always connected to the load, so there is zero transfer time. It is used in very sensitive and critical applications and usually corrects most power quality problems.
• Higher cost
• Lower efficiency
7. What is “Line-Interactive” (AVR)?
This is the term used to describe automatic voltage regulation (AVR) which corrects minor sags & swells in the incoming AC voltage without the need to transfer to battery.
In the case of applicable Marathon Power models:
• If the line voltage drops to between 75-90%, AVR ‘boosts’ it back to 120V (+/-10%)
• Should it drop below 75%, the UPS transfers to battery power.
• If the line voltage rises to between 110-125%, AVR ‘bucks’ it back to 120V (+/-10%)
• Should it rise above 125%, the UPS transfers to battery power.
8. What is Transfer Time?
This is the time it takes an off-line or line-interactive UPS to transfer from utility to battery power at the onset of a power disturbance.
Most off-line & line-interactive designs use the ‘zero-crossing’ point to detect and transfer. It typically takes 2-8 milliseconds to transfer, depending on where in the cycle the line voltage disappears.
9. What is a Simulated Sine-Wave?
This ‘on-battery’ output wave shape (red trace) has become a common alternative to a pure sine-wave (green trace) since it is compatible with most loads.
10. What are the Pros & Cons of this Wave Shape?
• A stepped square-wave is superior to simple square-wave since it has a PEAK & an RMS voltage similar to that of a sine-wave
• Is simpler & less expensive to generate than pure sine-wave
• Most equipment uses a linear or switch-mode power supply to convert 120VAC input to one or more lower voltages to power the circuitry within. Both types are compatible with a simulated sine-wave.
• For applications requiring extended run-times, a pure sine-wave is preferable. A simulated sine-wave often contains noise and transients that cause heat rise in loads that are fed by it.
• Some devices requiring backup contain timing or synchronization circuitry that tracks the sine-wave curve. Using a stepped square-ware to backup these device may cause them to malfunction.
11. How is a UPS sized?
The VA (Volts x Amps) rating is used for this. It’s a measure of the supply voltage multiplied by the current and indicates total power requirement.
To determine required size, either:
• Add the VA ratings for each piece of equipment to be backed-up or,
• Note the continuous current under full load and multiply by the corresponding voltage.
Always ensure that the UPS VA capacity is higher than the total equipment VA rating. The above applies ONLY to relatively constant loads. If the load is variable or contains high inrush or startup current, this will need to be factored into any sizing calculations. This will avoid possible overload conditions or premature failures.
12. What is the difference between VA & Watts?
The VA rating is the apparent power of the load.
The watt rating is the real power of the load. It is the apparent power x the power factor.
The power factor can range from 0.1 to 0.99 depending on the type of equipment:
• It is typically 0.6 to 0.8 for electronic loads (computers, microprocessor controlled devices, etc.),
• Less than 0.4 for inductive loads (relays, contactors etc.),
• Greater than 0.9 for resistive loads (lights, heaters, etc.)
13. What if the load is rated in Watts?
In this case, the following should be done:
Divide the watt rating by the power factor. If that is unknown, use a number from the ranges given on the previous page.
• Be conservative and use the lower number. For Example:
• A 750W computer load would yield a VA rating of 1250VA by way of the following: 750W / 0.6 = 1250VA
• Select a 1500VA unit to allow for some margin
14. Why is this important?
For two main reasons:
a. If a load is rated in watts, then its VA rating will most likely be higher. This must be considered so that the UPS is sized correctly
b. Back-up time depends on the real power (W), not the apparent power (VA), of the load. Two loads that use the same voltage and draw the same amount of current may have a different power factor. Therefore, their real power consumption will differ and this affects battery discharge rate. The higher the power factor, the shorter the back-up time. Backup times quoted for UPS’s are based on their use with computer type loads.
15. What are the communication options?
There are various choices including:
1. UPSMON Power Monitoring and UPS Control Software via:
A. Serial (RS-232 Port)
B. USB Port
2. Dry Contacts – an AS-400 Relay I/O Card for the:
A. Vault Series
B. Track Series
C. External for all Series
A. Net Power SNMP/Web Card
B. Net Agent SNMP/Web Card
16. What are the Energy Storage options?
A. Sealed, lead-acid, battery
• Either 6V or 12V DC *
• Rechargeable to 90% within 4-8 hrs *
• User replaceable / Hot swappable *
• Typical lifetime of 3-5 years
• Overload & Discharge protected
• UL Recognized
• Lower temperature = longer life
• Provide ˜ 300 charge/discharge cycles
• Available from MP under warranty and MP or manufacturer out of warranty
• Recycle due to hazardous content
B. Maintenance-free, Supercapacitor
• Various module sizes and voltages *
• Rechargeable to 100% within a few minutes *
• High temperature tolerant
• Lighter weight
• Expected lifetime of 12-15 years
• Provide > 500,000 charge/discharge cycles
• Cell Balancing
• UL Recognized
• RoHs Compliant
• No recycling required
* Model Dependent
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