UPS and Battery Backup Glossary

A

Active PFC: Active power factor correction: circuitry in a power supply that shapes input current into a near-sine wave, giving a power factor around 0.95 to 0.99. Some active-PFC supplies misbehave on simulated sine wave UPS output. Learn more
Amp-hour (Ah): A battery's charge capacity: the current it can deliver for a stated time, normally specified at the 20-hour rate for VRLA batteries. Multiply by voltage to get watt-hours. Learn more
apcupsd: An open-source daemon for monitoring APC UPS units and shutting down computers on low battery. Learn more
Apparent power: Volts multiplied by amps (VA). It can exceed real power when current is out of phase with voltage or distorted. Learn more
AVR (automatic voltage regulation): A line-interactive feature that boosts low voltage or trims high voltage with transformer taps, without using the battery. Learn more

B

Battery-backed outlet: A UPS outlet that receives power from the inverter during an outage, as opposed to a surge-only outlet. Learn more
Blackout: A complete loss of utility power, from a fraction of a second to days. Learn more
Boost and trim: The two AVR actions: boost raises low input voltage, trim lowers high input voltage. Learn more
Brownout: A sustained period of low voltage, sometimes deliberate when a utility reduces voltage under heavy demand. Learn more
Bypass: A path that feeds the load directly from utility power, skipping the UPS electronics, used during faults or maintenance. Learn more

C

C13 / C14: IEC 60320 connectors common on computers, servers and rack UPS outlets. C13 is the cord end, C14 the equipment inlet. Learn more
C19 / C20: Larger IEC 60320 connectors for high-current servers and PDUs. Learn more
Clamping voltage: The voltage at which a surge protector begins diverting surge energy. Lower is generally better; see VPR for the standardized rating. Learn more
Cold start: Starting a UPS on battery power when no utility power is present. Learn more
Connected equipment guarantee: A manufacturer's promise to cover damage to equipment plugged into its UPS or surge protector under stated conditions. Learn more
Crest factor: The ratio of peak current to RMS current. Non-PFC power supplies have high crest factors that stress UPS inverters. Learn more

D

DC mini UPS: A small battery unit that outputs DC (often 5, 9, 12 or 24 V) directly to devices like routers, avoiding inverter losses. Learn more
Design life: The battery maker's expected life under ideal conditions, usually at 25 °C. Real service life is shorter. Learn more
Double conversion: The online UPS method: AC is rectified to DC and inverted back to clean AC continuously. Learn more

E

Eco mode: A high-efficiency mode on some online UPS units that passes utility power through and switches to the inverter only when needed. Learn more
Extended battery module (EBM): An external battery pack that connects to a compatible UPS to extend runtime. Learn more

F

F1 / F2 terminal: Flat quick-connect battery terminals, 0.187 in and 0.250 in wide respectively. Learn more
Float charge: The low, constant voltage that keeps a fully charged lead-acid battery topped up. Learn more
Frequency variation: Departure from the nominal 60 Hz or 50 Hz, common with generators. Only online UPS units correct it. Learn more

G

Graceful shutdown: An orderly, automatic shutdown of computers triggered by UPS software before the battery runs out. Learn more

H

Harmonics: Currents or voltages at multiples of the fundamental frequency, created by nonlinear loads. Learn more
HID (USB): Human Interface Device class: the standard USB protocol most UPS units use to report status to operating systems. Learn more
High-rate battery: A VRLA block designed for short, heavy discharges, often rated in watts per cell over 15 minutes. Learn more
Hold-up time: How long a power supply keeps its output in regulation after input power disappears, typically around 16 ms or more for computer PSUs. Learn more

I

Inverter: The UPS circuit that converts battery DC into AC output. Learn more

J

Joule rating: A surge protector's energy absorption figure. Useful as a rough durability indicator, not a measure of protection quality. Learn more

L

LiFePO4: Lithium iron phosphate, a lithium battery chemistry with long cycle and calendar life used in newer UPS units and power stations. Learn more
Line-interactive UPS: A UPS that passes utility power through an autotransformer with AVR, switching to battery only when the input is out of range. Learn more
Load percentage: The share of a UPS's watt rating your equipment uses. Learn more

M

MCOV: Maximum continuous operating voltage: the highest voltage a surge protector can withstand continuously. Learn more

N

NEMA 5-15: The standard North American 125 V, 15 A plug and receptacle. Learn more
Network management card: An add-in card that gives a UPS its own network interface for web, SNMP and shutdown signaling. Learn more
NUT (Network UPS Tools): Open-source software that monitors many UPS brands and coordinates shutdown across multiple machines. Learn more

O

Online UPS: A UPS whose inverter supplies the load at all times (double conversion), giving zero transfer time. Learn more
Overload: A load above the UPS rating. The UPS alarms and may shut off its output on battery. Learn more

P

PDU: Power distribution unit: a rack power strip, optionally metered or switched. Learn more
Peukert effect: The reduction in a battery's usable capacity at high discharge rates, pronounced in lead-acid batteries. Learn more
Power conditioner: A device that filters noise and may regulate voltage, without battery backup. Learn more
Power factor: Real power divided by apparent power (W / VA). Learn more
Power station (portable): A portable battery with inverter and outlets, typically lithium, designed for long runtime rather than seamless switchover. Learn more
Pure sine wave: Inverter output that closely matches a utility sine wave. Learn more

R

Real power: Power actually consumed, in watts. Learn more
Runtime: How long a UPS can support a given load on battery. Learn more

S

Sag: A short drop in voltage lasting from a fraction of a cycle to about a minute, often caused by large loads starting. Learn more
Self-test: A brief automatic or manual transfer to battery used to check battery health. Learn more
Sensitivity setting: A UPS option that sets how strictly it judges input power before switching to battery. Learn more
Simulated sine wave: A stepped approximation of a sine wave (also called modified or stepped sine) used by lower-cost inverters. Learn more
Site wiring fault: A UPS indication of missing ground or reversed hot and neutral at the outlet. Learn more
SNMP: Simple Network Management Protocol, used by network management cards to report UPS status to monitoring systems. Learn more
SPD (surge protective device): The code term for surge protectors. Type 1 and 2 install at the service or panel; Type 3 at the point of use. Learn more
Spike (transient): A very short, high-voltage event lasting microseconds to milliseconds, from switching or lightning. Learn more
Standby UPS: Also called offline: passes utility power through and switches to battery on failure. Simplest and cheapest design. Learn more
Surge-only outlet: A UPS outlet with surge protection but no battery backup. Learn more
Swell: A short rise in voltage above normal. Learn more

T

THD (total harmonic distortion): A measure of how far a waveform departs from a pure sine wave, expressed in percent. Learn more
Transfer time: The gap between utility failure and battery power reaching the load in standby and line-interactive UPS units. Learn more

U

UL 1449: The UL safety standard for surge protective devices, which defines the VPR rating. Learn more
UL 1778: The UL safety standard for uninterruptible power supply equipment. Learn more

V

VA (volt-ampere): The unit of apparent power. Learn more
VPR (voltage protection rating): A standardized UL 1449 rating of the voltage let through by a surge protector during a test surge. Lower is better. Learn more
VRLA battery: Valve-regulated lead-acid: the sealed AGM or gel batteries used in most UPS units. Learn more

W

Watt-hour (Wh): A unit of energy: one watt for one hour. Battery Wh = volts x amp-hours. Learn more