Uninterruptible Power Supplies
by Deryck Webb
One of the most enigmatic and under-appreciated pieces of equipment needed
with any spectrometer system is the uninterruptible power supply (UPS). To many users
it is simply a box of batteries that is supposed to power the system during electrical
outages, and few know any other specifications about the system i.e. what is the runtime
of your UPS, what is the kVa? , or what is the wattage? This article will describe our
recent experiences here at NANUC; what UPS systems we have and why, and what our
testing and monitoring procedures are for our UPS systems.
I will admit for many years I took our UPS's for granted assuming they would do
their job when needed. But then those questions kept coming, posed by myself and
others. What runtime do I have? What is the correct backup power for my application
(kVA)? What is kVA? Will my UPS perform when the chips are down and the power is
out? I decided it was time to learn more about UPS systems and I am very lucky to have
a great supplier who came in and helped me test all the systems here at NANUC.
Like the name indicates a UPS provides power when outside power has been lost,
but that function, although very important, is a small part of the service provided by a
UPS. UPS systems provide a constant source of clean or conditioned power to sensitive
electronic devices whether the power is out or not. Dirty or unconditioned power
contains various fluctuations in voltage and/or current, which can disrupt the operation of
What can power fluctuations do? They can cause processing errors, soft failures,
resets and lockouts on computer systems, and they can cause hard failure of electronic
components. Power fluctuations can also cause nuisance tripping in process control
equipment. Voltage and current fluctuations occur in a building for a number of reasons.
Fluctuations may occur at the electrical power source. Your electrical provider may have
troubles with transformers, power lines or generators. Lightning strikes cause
fluctuations in line voltage as well. Your facility may not be hit directly, but any local
lightning strike can have far reaching effects on remote electrical systems. Finally, you
and your co-workers are also introducing power fluctuations to your sensitive electronic
equipment, by turning off and on different lights, appliances, and other systems
throughout the day.
A UPS system filters out these power fluctuations by passing power through a
series of enclosed batteries. The potentially 'dirty' AC power is used to charge a series of
batteries within the UPS. The batteries then funnel DC power through an inverter to
provide constant AC power to your NMR system or application. Therefore the power
derived from a UPS is provided by the batteries which will either be draining or charging
depending if power is being supplied or not.
In order to properly size a UPS system it is necessary to determine the demands of
your applications. Some UPS suppliers rate UPS systems by volt-ampere (VA) and other
small UPS systems use Watts. An example of how to determine each will be shown
below. The arithmetic product of the voltage and the amperage, i.e., V x A, gives a result
in Volt-Amperes often stated simply, VA. The volt-ampere is a universally accepted
measure of electrical capacity for the UPS industry. VA capacity simply states that a
given device may draw so many amps (A) at a particular voltage (V). Consult the
supplier's specification literature to determine electrical demands of the application. For
example the Varian Installation Planning literature (Pub. No. 01-999038-00, Rev. E0504).
3.3 Electrical Outlets
Table 15 lists the electrical outlet requirements of system
components. The sections below details the requirements of each
The third cabinet for 750- or 800MHz systems requires:
220V x 30A = 6600 VA or 6.60 kVA
|Table 15. Electrical Outlets/Circuits Requirements
||Required Number of Outlets / Circuits
(single phase at 50-60 Hz)
|Host workstation and
||120/220 Vac, 15A minimum
or 220 +10/-7% Vac, 15 A
|Performa XYZ PFG module
||220 Vac, 20 A
||120 or 220 Vac, 15 A
|SMS autosampler accessory
||120 or 220 Vac, 15 A
||120 or 220 Vac, 15 A
|VAST autosampler accessory
||120 or 220 Vac, 15 A
||0 or 1
|Accessories and test
||120 Vac, 20 A or 230 Vac, 10 A
|UNITYINOVA two-cabinet console
||220 Vac, 20 A
|Solid-state Power cabinet
||208/220/240 Vac, 30 A
|Solid-state Power cabinet
||208/220/240 Vac, 30 A
|Solid-state Accessory cabinet
||90-132 Vac, 15 A or 190-
240 Vac 15 A
|Third cabinet for 750- or
||220 Vac, 30 A
|UNITYINOVA VT CP/MAS
||110-125 Vac, 15 A (USA)
220-240 Vac, 15 A (Europe)
A 750-800 MHz system would require at least a 6.6 kVA UPS system. Most likely a UPS
supplier would recommend a capacity about 10%-15% higher in order to accommodate
peripherals and allow for an extended run time.
UPS power expressed in Watts is usually seen in smaller applications such as
computers. The computer used as a web-server here at NANUC utilizes a small
Energizer UPS (Figure 1). When determining the wattage of a given system one must
utilize the power factor (pf). The power factor is defined as the fraction of power actually
used by an electrical appliance compared to the total apparent power supplied. The value
is usually expressed as a percentage. A power factor indicates how far an electrical
appliance causes the electric current delivered to be out of phase with the voltage.
Current out of phase with voltage lowers
the overall power being used for the
application. Often this power loss is
transformed into heat.
In a study done by PC
Magazine, it was found that typical
personal computer systems exhibit a
power factor of 0.65.
The computer specifications can be
Notice that the wattage is not known nor
is the power factor, but the VA can be
Dell MMP 115 V x 6 A = 690VA
If we assume a power factor of 0.65, then
690 VA x 0.65 = 552 Watts (W)
This number seemed excessive, because the Energizer UPS for this computer was only
rated for 400W. There is a problem somewhere.
After some internet research and discussing the numbers with my UPS supplier it
was determined that the amperage numbers supplied by Dell and Sun (which also had
high amp values) were heavily padded. Nominally most computers would only draw 1.2
to 2.0 Amps. Using this value we get a more reasonable number:
115V x 1.5A = 172.5 VA
172.5 VA x 0.65 = 112.13 W
NMR suppliers are rigorous in suppling accurate information on voltage, amperage
and power factor so it is possible to consult manufacturer literature and determine UPS
needs. For other applications i.e. computers, pumps, and compressors it is recommended
to consult a qualified UPS supplier.
NANUC has two NMR systems, which require four separate UPS systems for
backup. One system provides conditioned power and UPS support for the 500MHz Unity
Inova two-cabinet console. Another system provides conditioned power and UPS support
for the 800MHz Unity Inova two-cabinet console and the third amplifier cabinet. The
third system provides conditioned power and UPS support for the RV12 Edwards high
vacuum pumps, which provide the required refrigeration for the 2.2 Kelvin He bath. See
Table 1 for more specific listings of the Nanuc UPS systems.
The 800MHz UPS #1 is made up of the UPS unit containing 1 row of 4 PbCa
batteries 48V, 150 Amps and a battery pack which contains two strings of 4 PbCa
batteries 48V, 75 Amps (Figures 2 and 3). The 800MHz UPS #1 supplies UPS power to
the Inova two cabinet console and the third amplifier cabinet.
The 800MHz UPS #2 is made up of the UPS unit containing 1 row of 4 PbCa
batteries 48V, 60 Amps and a battery pack which contains one string of 4 PbCa batteries
48V, 75 Amps (Figure 4). The 800MHz UPS #2 supplies UPS power to the RV12
Edwards hi vacuum pump.
The 800MHz UPS #3 is made up of the UPS unit containing 1 row of 4 PbCa
batteries 48V, 45 Amps there is no battery pack (Figure 5). The 800MHz UPS #3
supplies conditioned power from a gasoline generator (Figure 6) to the RV12 Edwards hi
vacuum pumps in extended power outages.
The 500MHz UPS #1 is made up of the
UPS unit containing 1 row of 4 PbCa batteries
48V, 75 Amps and a battery pack which contains
two strings of 4 PbCa batteries 48V, 75 Amps
(Figure 7). The 500MHz UPS #1 supplies UPS
power to the Inova two cabinet console.
You will notice that the run time of each UPS was not mentioned. Could it not
simply be calculated given the UPS kVA and the system requirements of the load? There
are many inconsistencies that make such a calculation difficult. Is the NMR system
operating or idle and is there temperature control (high temperature or low temperature?)
Is there a laser printer hooked up to the UPS? How old are the UPS batteries? The only
way to truly find out is by unplugging the power and allowing the UPS to supply the load
independently. During our tests spectrometers were idle with no temperature control, and
the UPS's were allowed to deplete down to a 5 minute runtime level. Here are the results
To safely increase the load on the spectrometer UPS, in order to simulate amplifier
pulsing or VT power, a high vacuum pump was added to the load. The pump would not
usually be a load on the spectrometer UPS. The VT and amplifiers were not operating
during this test as it was not known how long the UPS would last and sudden power
losses were not desired. From the graph we can see how the runtime and voltage quickly
climbs to an initial maximum and then slowly goes down. The runtime and the actual
time the UPS powers the system were inconsistent. The maximum runtime displayed
was about 30 minutes, but the test lasted almost 90 minutes. Your UPS supplier will
attempt to calibrate the system so the displayed runtime and actual runtime are similar,
but the runtime is dependent on the load which could be different depending on pulse
sequence and VT demands. The voltage had a maximum of just under 49 Volts and
decayed at a constant rate. The test lasted 87 minutes in total and the final displayed
runtime was 5 minutes. The final voltage was 45.57 Volts.
To test the UPS operating the high vacuum pumps the backup pump was used.
The UPS ran the pump until it could no longer provide adequate power. This UPS simply
ran one high vacuum pump. The maximum runtime displayed was over 80 minutes, but
the test lasted only 73 minutes. At 73 minutes the pump ceased operation. The voltage
had a maximum of just over 46 Volts and decayed at a constant rate. The final voltage
when failure occurred was 41 Volts (Graph 2).
The 500 UPS operates the host computer and console system. The maximum
runtime displayed was about 33 minutes, but the test lasted almost 43 minutes. The
voltage had a maximum of just under 48 Volts and decayed at a constant rate. The test
lasted 43 minutes in total and the final displayed runtime was 5 minutes. The final
voltage was 44.05 Volts (Graph 3).
To test UPS #3, which would run the pumps in case of an extended power outage,
the gas generator had to be set up outside. The generator has an area outside NANUC
where it can be secured to the wall. A short cord from the generator to the outlet on the
wall supplies power to a series of outlets within Nanuc (Figure 8,9).
A long cord then extends from the outlets in Figure 9 to the console room and to UPS #3.
Before the generator could be hooked up to the UPS, the voltage and frequency coming
from the generator had to be determined. If the frequency, voltage or amperage provided
from the generator are outside the input specifications of the UPS, the UPS would not
charge properly and the batteries would deteriorate in an extended power outage. We
watched the UPS as it toggled between charging and battery mode. The input power was
outside specifications. When the generator was first started up the frequency was only
40Hz and the voltage was 105 volts, which is well below the input specifications of the
UPS. In Movie 1, one can see the adjustment of the frequency as seen on an
oscilloscope. The frequency was modified by adjusting the idling speed of the generator.
The generator will need to be monitored if additional loads are applied over and above
the UPS because the frequency fluctuates significantly when new loads are applied.
Also, during an extended power outage normal operations at NANUC would be
suspended. NMR systems would be shutdown and unused UPS battery packs would be
'daisy-chained' together to provide up to 14 hours of UPS time to the hi-vacuum pumps
which must maintain the 2.2 K He bath on the 800MHz system. The electrical generator
could supply UPS #3 and the hi vacuum pump as long it is able to run.
In conclusion, UPS systems should be an integral part of any NMR system,
however questions concerning system sizing and run time are not easily answered and
can vary depending on overall load and the age of the UPS system involved. The only
way to truly determine your runtime is by unplugging the input power. This should be
done in a controlled fashion, limiting any risk of damage caused by sudden power loss.
UPS systems should be tested at least semi-annually. We highly recommend contacting a
qualified UPS supplier or technician when buying and/or maintaining a UPS system.
(Click to view movie)