advanced battery management--A three-stage charging system designed to prolong the service life of UPS batteries. By charging the batteries only when necessary, battery life is significantly improved. Charging stage one: quickly recharges battery to approximately 90% of capacity. Charging stage two: fully charges the battery to 100%. Charging stage three: rest mode prevents overcharging. Charging stage one is initiated after a power outage or periodic UPS self-test.

ampere (A) or amp--The unit for the electric current; the flow of electrons. One amp is 1 coulomb passing in one second. One amp is produced by an electric force of 1 volt acting across a resistance of 1 ohm.

ampere-hour (AH)--Quantity of electricity or measure of charge. How many amps flow or can be provided over a one hour period. Most batteries are rated in AH.

array--Any number of photovoltaic modules connected together to provide a single electrical output. Arrays are often designed to produce significant amounts of electricity.

absorption charge - The second stage of three-stage battery charging. Voltage remains constant and current tapers as internal battery resistance increases during charging. (Ensures complete charging.)
alternating current (AC) - The type of electrical power supplied by utilities or made when a generator is run. The unique characteristic of this form of electricity is that it reverses direction at regular intervals. For example, 120 Vac 60 Hz. power reverses flow 60 times a second, hence the rating 60 Hz. (cycles).

B

bulk charge - The first stage of three-stage battery charging. Current is sent to batteries at the maximum rate they will accept while voltage rises to full charge level.
battery backup--A battery or a set of batteries in a UPS system. Its purpose is to provide an alternate source of power if the main source is interrupted.
battery capacity--The battery ampere-hour capacity at full charge, standard temperature, and at a specified (usually C10) discharge rate.
battery charger--A device or a system which provides the electrical power needed to keep the battery backup fully charged.
battery current limit--System voltage control that limits the battery charge current to a preset value.
bi-directional converter--A device which changes (or converts) alternating-current power to direct-current power and vice versa.
blackout--A total loss of the AC utility (commercial power).
brownout--A reduction in the voltage of the AC utility without complete loss of power.
buck and boost--A proprietary voltage regulation process used when an overvoltage or undervoltage situation occurs in the UPS. Undervoltage is boosted to make the voltage greater, and overvoltage is bucked to reduce it. The result is less reliance on the UPS battery, extending overall battery life.
bus voltage--The actual voltage supplied to the load as measured at the bus bars.
bypass--A circuit used to change the path of the electrical power so that it goes around (or bypasses) its normal path. In the UPS, the bypass circuit is used to route the power around the major electronics in the UPS so they can be serviced without power interruption.

C

cell--The basic unit of a photovoltaic panel or battery

charge controller--An electronic device which regulates the voltage applied to the battery system from the PV array. Essential for ensuring that batteries obtain maximum state of charge and longest life.

current - The rate of flow of electrical charge. The flow of amps is often expressed as current.
clean power--Electrical power which has been conditioned and/or regulated to remove electrical noise from the output power.

D

deep discharge--Discharging a battery to 20-percent or less of its full charge.

direct current (DC)--A type of current which never reverses its direction. Since the current flows in only one direct on, the average value of the current cannot be zero unless the current has stopped flowing.
double-conversion--A UPS design in which the primary power path consists of a rectifier and inverter. Double-conversion isolates the output power from all input anomalies such as low voltage, surges and frequency variations by converting AC to DC to AC. See Online UPS.

discharge rate--The rate, usually expressed in amperes or time, at which electrical current is taken from the battery.

E

electric current--A flow of electrons; electricity, amps.

electrical grid--An integrated system of electricity distribution, usually covering a large area. As in "off the grid".

electrolyte--A liquid conductor of electricity. In batteries, usually H2SO4, sulfuric acid, but may be any number of things. Seawater is the most common electrolyte in the world - and by suspending a zinc and a steel sheet in it, you can get a little electricity.

energy--The ability to do work. Stored energy becomes working energy when we use it.

energy density--The ratio of energy available from a battery to its volume (Wh/1) or mass (Wh/kg). "watts to weight" ratio.
efficiency--The ratio of the output power from the UPS to the input power from the utility. This shows the percentage of the input power that is available as useful output power. For example, a UPS that is 95% efficient delivers 95% of the utility power it receives to the load. The remaining power takes the form of dissipated heat.
emergency shutdown--Used to instantly or quickly shutdown all of the electrical power available to the UPS and the load. An emergency shutdown device is usually used during a crisis to prevent damage to the UPS and the load. Some computer-room installations require a Remote Emergency Power Off (REPO) capability as part of their security/safety system.

F

float charge--Float charge is the voltage required to counteract the self-discharge of the battery at a certain temperature.
float voltage--The set output voltage of the DC power system (not including temperature compensation or other adjustments).
frequency--The number of cycles (oscillation positive and negative) completed in one second. Defined as Hertz (Hz).
full load--The greatest load that a circuit is designed to carry under specific conditions; any additional load is considered an overload.

fuel cell--A device that converts the energy of a fuel directly to electricity and heat, without combustion. Because there is no combustion, fuel cells give off few emissions; because there are no moving parts, fuel cells are quiet.

G

grid - When used in reference to utility power, it refers to a system of electrical transmission and distribution lines.

gel-type battery--Lead-acid battery in which the electrolyte is composed of a silica gel matrix.

grid-connected (PV system)--A PV system in which the PV array acts like a central generating plant, supplying power to the grid.

H

hertz (Hz.) - The frequency, or number of times per second, that the flow of AC electricity reverses itself. Also referred to as cycles (see alternating current).
high battery protection - A control circuit that disconnects charge current flowing to battery(s) when voltage reaches a dangerously high threshold. Prevents damage created by excess gassing (or boiling) of electrolyte.
hydrometer - A simple device that measures the specific gravity of battery electrolyte. Specific gravity readings express state of charge/discharge of battery.
harmonic distortion--The presence of harmonics that change the AC voltage waveform from a simple sinusoidal to complex waveform. Harmonic distortion can be generated by a load and fed back to the AC utility line, causing power problems to other equipment on the same circuit.

I

inverters--Devices that convert DC electricity into AC electricity (single or multiphase), either for stand-alone systems (not connected to the grid) or for utility-interactive systems.

idle current - The amount of electrical power required to keep an inverter ready to produce electricity on demand.
isolation--The separation (often through the use of an isolation transformer) of one section of a system from undesired electrical influences of other sections.

UP

J

K

kilowatt (kW)--One thousand watts of electricity. Ten 100-watt light bulbs use one Kilowatt of electrical power.

kilowatt-hour (kWh)--One kW of electrical power used for one hour. The most common measurement of electrical consumption, most grid connected electrical meters measure kW/h for billing purposes. 1 kWh=3600 kJ.

L

LCD--Liquid Crystal Display
line-interactive--A UPS containing an off-line inverter that must transfer on during a blackout, but provides faster transfer times than an off-line UPS. Power conditioning and surge suppression are provided to protect the connected load.
light emitting diode (LED) - A device used to display various status functions.
line loss - A voltage drop caused by resistance in wire during transmission of electrical power over distance.
line-tie - An electrical system that is connected to a utility distribution grid. For example, Trace SW line-tie inverters are designed to connect to and interact with utility power.
load - Any device that consumes electricity in order to operate. Appliances, tools, and lights are examples of electrical loads.
low battery protection - A control circuit that stops the flow of electricity from batteries to loads when battery voltage drops to dangerously low levels.

M

modified sine wave - An AC wave form (generated by many inverters) that is a pulse width modified square wave. It consists of a number of very small on/off steps rather than a fully smooth wave.
manual bypass switch (MBS)--A manually operated transfer switch used to bypass the major electronics in the UPS, so the UPS can be serviced without power interruption.

N

noise--Random, sporadic, or multi-frequency electrical signals that become part of a transmission making the signal or information more difficult to identify.
nominal system voltage--The DC output voltage generally used to describe a type of system, usually 24 V or 48 V.

O

ohm--The unit of resistance to the flow of an electric current.

open-circuit voltage (Voc)--The maximum possible voltage across a photovoltaic cell or module; the voltage across the cell in sunlight when no current is flowing.
oscilloscope - A device that displays the wave form created by an electrical generating device such as a generator, inverter, or utility.
overload/overcurrent protection - A control circuit designed to protect an inverter or similar device from loads exceeding its output capacity. (A fuse, for example, is an overcurrent protection device.) All Trace inverters have internal circuitry to protect themselves from overload/overcurrent conditions.
off-line UPS--A UPS type which feeds power to the load directly from the utility and then transfers to battery power via an inverter after utility drops below a specified voltage. The delay between utility power loss and inverter startup can be long enough to disrupt the operation of some sensitive loads. Also called a standby UPS.
online UPS--A UPS in which the inverter is on during normal operating conditions supplying conditioned power to the load through an inverter or converter that constantly controls the AC output of the UPS regardless of the utility line input. In the event of a utility power failure, there is no delay or transfer time to backup power.
outlet--Any point on a wiring system where current is taken to supply electrical power for a load.
overvoltage shutdown (OVSD)--A protection method that will shutdown any rectifier module with an output voltage over a preset maximum value.

P

parallel connection--A way of joining two or more electricity-producing devices (i.e., PV cells or modules) by connecting positive leads together and negative leads together; such a configuration increases the current.
parallel wiring - A group of electrical devices, such as batteries or PV modules, wired together to increase ampacity, while voltage remains constant. (Two 100 amp hour 12 Vdc batteries wired in parallel will form a 200 amp-hour 12 Vdc battery bank.).
parallel online UPS--Online UPS technology that provides redundant sources of conditioned backup power so that the critical load is protected even in the event of UPS component failure.

photovoltaic (PV)--Pertaining to the direct conversion of light into electricity.

photovoltaic (PV) array--An interconnected system of PV modules that function as a single electricity-producing unit. The modules are assembled as a discrete structure, with common support or mounting. In smaller systems, an array can consist of a single module.

photovoltaic (PV) cell--The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy (dc voltage and current).

photovoltaic (PV) panel--often used interchangeably with PV module (especially in one-module systems), but more accurately used to refer to a physically connected collection of modules (i.e., a laminate string of modules used to achieve a required voltage and current).
photovoltaic system - The components that form a solar electric generating system, usually consisting of PV modules, charge controller, circuit protectors (fuses or breakers) and batteries.

power factor--The ratio of the average power and the apparent volt-amperes. Affected by the inductance and capacitance of the load. A pure resistance, such as an electric heater would have a power factor of 1.00.

pulse-width-modulated (PWM) - A function of many of the newer charge controllers and battery chargers which instead of applying a steady DC voltage to the battery, sends out short pulses. The width of the pulses varies with the battery state of charge.

Q

R

resistive voltage drop--The voltage developed across a cell by the current flow through the resistance of the cell.
RS-232--Also called serial ports; a method of communicating digital information in which the data bits are transmitted sequentially over one line.

S

self discharge--The rate at which a battery, without a load, will lose its charge. This can vary considerably depending on the type of battery and age. It can be as low as 3% a month for a new AGM battery, and as high as 10% a week for an older Lead-Antimony (industrial).

solar energy--Energy from the sun. The heat that builds up in your car when it is parked in the sun is an example of solar energy.
scalable UPS--A UPS that allows for expandability; for example, enables a UPS to accommodate a larger load by purchasing additional power modules.
single-phase power (1Ø)--Power that is provided by a single source which normally includes one hot lead and a grounded return line (neutral).
square wave--Output waveform generated by very basic, low-cost UPSs. Functions adequately for less sensitive loads, but may not provide acceptable quality input for some types of electronic equipment.
start-on-battery--Enables user to power up UPS in the absence of utility power.
surge--A transient (or momentary) wave of current, potential, or power in an electric circuit.

square wave inverter--The inverter consists of a dc source, four switches, and the load. The switches are power semiconductors that can carry a large current and withstand a high voltage rating. The switches are turned on and off at a correct sequence, at a certain frequency. The square wave inverter is the simplest and the least expensive to purchase, but it produces the lowest quality of power.

sulfation--A condition that afflicts unused and discharged batteries; large crystals of lead sulfate grow on the plate, instead of the usual tiny crystals, making the battery extremely difficult to recharge.
series wiring - A group of electrical devices, such as batteries or PV modules, wired together to increase voltage, while ampacity remains constant. (Two 100 amp hour 12 Vdc batteries wired in series form a 100 amp hour 24 Vdc battery bank.)
sine wave - The output wave form of an electric generator or utility. A smooth wave going above and below zero is created.
surge capacity - The amount of current an inverter can deliver for short periods of time. Most electric motors draw up to three times their rated current when starting. An inverter will "surge" to meet these motor-starting requirements. Most Trace inverters have surge capacities at least three times their continuous ratings.

T

transformer--Steps AC voltage up or down, depending on the application.

trickle charge--A charge at a low rate, balancing through self-discharge losses, to maintain a cell or battery in a fully charged condition.
transfer switch - A switch designed to transfer electricity being supplied to loads (appliances etc.) from one source of power to another. (A transfer switch may be used to designate whether power to a distribution panel will come from a generator or inverter.)
temperature compensation--Adjustment of the rectifier output voltage to provide the optimum charging voltage for the battery. One of the components in system voltage control, calculated by the Supervisory Module calculation based on battery temperature.
terminal block--An insulating base equipped with terminals for connecting secondary and control wiring. Used on hardwired equipment, such as a UPS, when input plugs and output receptacles are either impractical or unavailable.
three-phase power (3Ø)--Power that is provided by a single source with three outputs with a phase difference of 120 ° between any two of the three voltages and currents.
transfer switch--A switch which will transfer current from one circuit path to another without interrupting the flow of the current.
transient--The fast radical change in a smooth sine wave that occurs in both voltage and current waveforms during the transition from one steady-state operating condition to another.
trickle charge--With the trickle charging process, the battery receives a constant voltage feeding a low current. Constant use of this method dries the electrolyte and corrodes the plate, reducing potential battery service life by up to 50 percent.
two-phase power--Power which is provided by a single source with two outputs which may be 180 degrees out of phase or 120 degrees out of phase.

U

uninterruptible power system (UPS)--A system designed to automatically provide power, without delay or transients, when the normal power supply is incapable of supplying acceptable power. Some UPSs also filter and/or regulate utility power.
UPS topology--Overall term describing the internal circuitry of a UPS. There are three basic UPS topologies: standby (off-line), line-interactive, and online.

V

VAC--Volts ac

VDC--Volts dc Vmp--Voltage at maximum power

Voc--Open-circuit voltage

Volt (V)--A unit of measure of the force, or 'push,' given the electrons in an electric circuit. One volt produces one ampere of current when acting a resistance of one ohm.
Volt-ampere (VA)--Voltage (V) multiplied by the current (ampere); apparent power. For instance, a device rated at 10 amps and 120 V has a VA rating of 1200 or 1.2 kVA.

W

Wafer--A thin sheet of semiconductor material made by mechanically sawing it from a single-crystal or multicrystal ingot or casting.

Watt (W)--The unit of electric power, or amount of work (J), done in a unit of time. One ampere of current flowing at a potential of one volt produces one watt of power.

Waveform--The shape of the curve graphically representing the change in the ac signal voltage and current amplitude, with respect to time.
Watt hour (Wh) - Electrical power measured in terms of time. One watt hour of electricity is equal to one watt of power being consumed for one hour. (A one-watt light operated for one hour would consume one watt hour of electricity.)