To choose an uninterruptible power system (UPS), first work out the load (watts and volt-amperes, VA, running at around 80% of rated capacity), then choose the type (offline, line-interactive or double-conversion online), then decide the battery by “how long it must hold”, and then schedule battery life and ambient temperature into maintenance. If the load is worked out wrongly, the other three choices are wasted. This article divides selection into 4 stages:
Stage ① | Load and capacity: which equipment to protect, how much power it draws in total, converted to VA.
Stage ② | Type and output: how long the switchover takes at a power cut, whether the output voltage is stable, and the waveform.
Stage ③ | Backup time: how long it must hold after a power cut — to save files and shut down, or to hold until a generator takes over.
Stage ④ | Battery life and environment: how often the battery is replaced and how hot the place is.
For where to put the UPS and how to manage the temperature there, see How Much Should Factory Temperature and Humidity Be Controlled? Which Condition to Watch for Solder Paste, Moisture-Sensitive Parts and Static, in 5 Stages from Setting the Window to Audit; this article starts from “which equipment to protect and how long it must hold at a power cut”. Each stage below covers what to do, what public sources say, and what Jiahon can help with; sources, exceptions and this article’s own summary are in the Notes at the end.
Figure 1: The four stages of choosing a UPS — load and capacity, type and output, backup time, battery life and environment (schematic, not to scale).
Stage ①: Load and capacity — first work out how much power the things to protect draw
What to do:
First list the equipment to be connected to the UPS (for example a control computer, measuring instruments, network equipment), and copy the power draw from each nameplate: watts (W) or volt-amperes (VA).
Watts and VA are not the same: VA is voltage times current, and watts are VA times the power factor. If a device lists just watts, convert to VA with the power factor (if the power factor is not written, confirm with the equipment maker first); if the device already lists VA, use it directly.
Add up the VA of all the equipment, then leave margin: a UPS runs at around 80% of its rated VA, which also leaves room to add equipment later.
Example: equipment drawing 400 W in total with a power factor of 0.9 is about 444 VA; to run at around 80% of rated, the UPS’s rated capacity should be at least about 556 VA (this article’s summary).
Do not connect loads that suddenly draw large currents (for example motors and laser printers) to the same unit; such loads have to be worked out separately, or please inquire (this article’s summary).
What public sources say: A public page from a machine-room equipment supplier says that VA is current times supply voltage, and watts are VA times the power factor; the power factor of modern electronic equipment is mostly 1.0 or 0.9, and older computers are often 0.6 to 0.7; a UPS is recommended to run at around 80% of its rated VA or a little lower, with room left for expansion; for models of 10 kVA and below, choose by VA or kVA (Notes table 1).
What Jiahon can help with:
UPS Uninterruptible Power System: the body text of the product page says a capacity of 800 VA. The wattage and power factor are not written in the body text; please inquire; for the number and type of output sockets, please inquire. The keyword tags of the product page also list 650, 1,000, 1,500 and 2,000 VA and dual 110 V / 220 V voltage, with no matching specification in the body text; whether other capacities exist, please inquire.
A search of the site’s products (October 13, 2026) found just this one UPS; for other capacities and types, please inquire.
Stage ②: Type and output — how long the switchover takes at a power cut, and whether the voltage is stable
What to do:
First look at whether a brief switchover at a power cut is acceptable: for office equipment it usually is; for loads that cannot stand interruption, such as production line control, servers and measuring instruments, first consider the types that need no switchover (this article’s summary).
Then match the three common types:
| Type | How it works | Used for |
|---|---|---|
| Offline | In normal times the mains supplies the load directly; at a power cut it switches to the battery inverter | Individual equipment such as a single computer |
| Line-interactive | In normal times the mains is regulated through a transformer tap before supplying the load; at a power cut it switches to the inverter | A small number of important servers and network equipment |
| Double-conversion online | The mains is first rectified to DC and then inverted to AC, with the battery in the middle; no switchover at a power cut | Important loads that cannot be interrupted |
- Also ask about the output waveform: if the power of the connected equipment is sensitive to waveform, confirm the output is a sine wave (this article’s summary).
Figure 2: The power paths of the three kinds of UPS (schematic, not to scale).
What public sources say: A public technical page from an electrical machinery maker divides UPSs into three classes by IEC 62040-3: offline (output voltage and frequency follow the input, and at a power cut the inverter takes over in a few milliseconds), line-interactive, and double-conversion online (the mains is rectified and then inverted, the output is independent of the mains, and no switchover is needed at a power cut; the page calls it the architecture commonly used to protect important loads). A public white paper from a power equipment maker (version 10) adds: the offline type’s output is not a sine wave, it has no voltage regulation circuit, switches in about 10 milliseconds, and is not practical above 2 kVA; the line-interactive type is common from 0.5 to 5 kVA, has a sine wave output and corrects the input voltage by transformer taps, but cannot regulate the frequency; the double-conversion online type is common from 10 kVA up, and models of 5 kVA and below are not cost-effective; it also recommends choosing by “actual output performance and operating mode”, not by advertising wording (Notes tables 2 and 3).
What Jiahon can help with:
UPS Uninterruptible Power System: the product page says it is the offline type (Offline Standby), switching at once when the mains is cut; the application scenes the product page lists are office workstations, small servers and NAS, surveillance recorders, and computers in factory offices (the facilities room and the quality office). The switchover time figure, output waveform and output voltage accuracy are not written on the product page; please inquire. The product page also writes “voltage stabilizing and filtering”, while the white paper says the offline type has no voltage regulation circuit; how the two statements fit together, please inquire.
A search of the site’s products found no line-interactive or double-conversion online UPS; to protect production line control equipment that cannot stand interruption, please inquire first.
Stage ③: Backup time — how long it must hold after a power cut
What to do:
First decide what “holding” is for: to let the equipment save files and shut down normally, a few minutes are enough; to let a production line finish a batch, or to hold until a generator takes over, much longer is needed (this article’s summary).
Backup time depends on two things: battery capacity, and the load at the moment of the power cut. The more the UPS’s capacity exceeds the load, the less hard the battery works and the longer it holds.
There are two ways to lengthen it: change to a model of larger rated capacity, or add an external battery (whether the model supports this, please inquire) (this article’s summary).
Read backup time from the maker’s “load versus time” curve or table; do not work it out yourself by dividing battery capacity by load; it becomes shorter as the battery ages (this article’s summary).
What public sources say: A public page from a machine-room equipment supplier says that the more a UPS’s capacity exceeds the load, the longer the battery bank’s backup time, because the battery is not running at full load. A public guide from EUROBAT (the European association of automotive and industrial battery manufacturers) says that for a stationary lead-acid battery to meet the full discharge requirement over its whole life, the capacity at the first calculation is multiplied by an ageing factor of 125%; the battery’s rated capacity is based on the 10-hour rate at 20 °C (Notes tables 1 and 4).
What Jiahon can help with:
- UPS Uninterruptible Power System: the tag on the product page says a built-in battery; the battery capacity and specification, backup time under different loads, and whether an external battery can be added are not written on the product page; please inquire.
Stage ④: Battery life and environment — how often to replace the battery, and where to put it
What to do:
First ask for the battery’s design life, then schedule the replacement. Public data says a float ambient temperature above 20 °C shortens life, so if your site is hotter than that, life has to be discounted.
Put the unit away from heat sources, and avoid a stuffy cabinet; do not put the UPS by a wall the sun reaches or next to a machine’s exhaust vent (this article’s summary). For how to manage the temperature of the place, see How Much Should Factory Temperature and Humidity Be Controlled?.
Whether the model has a battery status display and a self-test function is also part of selection (this article’s summary).
When the planned replacement time comes, replace even if there has been no power cut; finding at a power cut that the battery cannot hold is usually too late (this article’s summary).
What public sources say: The EUROBAT public guide divides the design life of valve-regulated lead-acid batteries into 4 classes: standard commercial 3 to 5 years, general purpose 6 to 9 years, long life 10 to 12 years, and very long life over 12 years; it also says that a float ambient temperature above 20 °C shortens life, that every sustained 10 °C rise cuts life by about half, and that above 40 °C there may be thermal runaway as the float current keeps increasing. The guide gives no replacement age (Notes table 4).
What Jiahon can help with:
- UPS Uninterruptible Power System: the product page says an LED panel shows voltage, charge and running status in real time. The battery’s design life, the way of replacement and the battery model, the working temperature range, and whether there is a self-test function are not written on the product page; please inquire.
Further Reading
To see the related process steps through, you can go on to these articles:
- How Much Should Factory Temperature and Humidity Be Controlled?: how to manage the temperature and humidity of the place where the unit sits.
When you need to match a type, please prepare four items first: the list of equipment to protect and the watts of each, the switchover time you can accept, how long it must hold, and the placement and ambient temperature. You are welcome to contact Jiahon.
Further reading: Power Supply vs UPS: What Is the Difference
At a power cut, what an SMT line fears most is not the machines stopping but “boards stopped halfway”
When an SMT line loses power, the most troublesome thing is the product in the middle of the process: boards inside the reflow oven, material baked halfway in the oven, boards that have just been printed with solder paste on the printer. The use of a UPS on an SMT floor is mainly to give these machines time to stop safely and to let the control computers save and shut down normally:
Write the rules for the process after a power cut beforehand. In the engineering data, one substrate pre-bake specification says that if the oven fails or the temperature profile does not meet the requirement, stop work, leave the material in the oven and notify the foreman; after a power cut, re-bake with the same program. Another specification says that if a power cut cannot be repaired within 1 hour, the operator checks and counts the material and puts it in a nitrogen cabinet for storage. A UPS cannot carry the whole line, so “how to handle work in process after a power cut” has to be written into the specification and not left to the UPS alone.
Control computers and equipment hosts come first. The computers used by AOI, SPI, test machines and MES may have programs or data damaged by a sudden power cut; the UPS capacity first protects these (see Stage ① of this article for working out the load).
A UPS tripping can also cause equipment faults. One equipment repair record in the engineering data is a machine that showed an error code after the UPS tripped; replacing the UPS did not help, and the fault was finally cleared by replacing a module of that equipment. The UPS itself also needs to be on the regular inspection list; for battery life see Stage ④.
Notes: Sources and Exceptions
This is for readers who need to check; skipping it does not affect the practice above. Where your process specifications and the written specifications of the UPS and battery differ from this article, theirs prevail.
Where each stage comes from
| Stage | Content | Source |
|---|---|---|
| Load and capacity, backup time | VA and watts, power factor, running load, the relation of backup time to capacity, the unit for selection | A public page from a machine-room equipment supplier (source 1; no year shown on the page) |
| Type and output | The three classes, switchover time | A public technical page from an electrical machinery maker (source 2; the footer shows 2025, no publication date) |
| Type and output | How IEC 62040-3 writes its classification, the features and limits of each type | A public white paper from a power equipment maker (source 3; version 10, copyright shows 2024) |
| Backup time, battery life and environment | Design life classes, the effect of temperature, the basis of rated capacity, the ageing factor | EUROBAT public guide: guide to IEC/EN standard specifications for valve-regulated lead-acid stationary batteries and battery banks (source 4; 2022) |
| Jiahon’s own material | Names and specifications on product pages, published articles | Jiahon product pages and articles |
Table 1 | VA, watts and capacity
| Item | Content | Source |
|---|---|---|
| VA and watts | VA is current times supply voltage; watts are VA times the power factor | Source 1 |
| Power factor | Modern electronic equipment is mostly 1.0 or 0.9; older computers are often 0.6 to 0.7 | Source 1 |
| Running load | Recommended to run at around 80% of rated VA or a little lower, leaving room for expansion | Source 1 |
| Backup time | The more the UPS’s capacity exceeds the load, the longer the battery bank’s backup time | Source 1 |
| Unit for selection | Choose by VA or kVA at 10 kVA and below | Source 1 |
Table 2 | How IEC 62040-3 writes its classification
| Item | Content | Source |
|---|---|---|
| Classification | Output performance is written in three parts, “input dependence – waveform – dynamic performance”; input dependence has three levels, VFD, VI and VFI | Source 3 |
| VFD | Output voltage and frequency follow the input (offline) | Sources 2, 3 |
| VI | Output voltage is regulated, frequency follows the input (line-interactive) | Source 3 |
| VFI | Output is independent of the mains (double-conversion online) | Sources 2, 3 |
| The white paper’s advice | Select by actual output performance and operating mode, not by advertising wording | Source 3 |
Table 3 | What public sources say about the three types
| Type | Switchover time | Features and limits the public data mention |
|---|---|---|
| Offline | About 10 milliseconds (white paper); a few milliseconds (electrical machinery maker) | Low cost, small size, high efficiency; output is not a sine wave and there is no voltage regulation circuit; not practical above 2 kVA; often used to protect individual equipment such as a single computer |
| Line-interactive | Under 10 milliseconds | Sine wave output; corrects the input voltage by transformer taps without going to the battery; cannot regulate frequency; when the voltage is often low the battery is used often, which may shorten battery life; not practical above 5 kVA; common from 0.5 to 5 kVA; often used to protect a small number of important servers and network equipment |
| Double-conversion online | 0 milliseconds | Good voltage regulation, easy to parallel, usable in redundant designs; not cost-effective below 5 kVA; common from 10 kVA up; called the industry standard architecture for important loads |
Source: 2, 3 (for the line-interactive row, just 3).
Table 4 | Batteries
| Item | Content | Source |
|---|---|---|
| Design life classes | Standard commercial 3 to 5 years; general purpose 6 to 9 years; long life 10 to 12 years; very long life over 12 years | Source 4 |
| Effect of temperature | Float above 20 °C shortens life; every sustained 10 °C rise cuts life by about half; above 40 °C there may be thermal runaway | Source 4 |
| Basis of rated capacity | 10-hour rate, 20 °C, end-of-discharge voltage 1.80 V per cell (unless the maker declares otherwise) | Source 4 |
| Ageing factor | If the full discharge requirement must be met over the whole life, multiply the capacity at the first calculation by 125% | Source 4 |
| Replacement age | The guide does not give one | Source 4 |
Standards referenced
The standards cited in this article should be taken in the current edition of each issuing body.
- IEC 62040-3 Uninterruptible power systems (UPS) — Part 3: Method of specifying the performance and test requirements. Issuing body: IEC (International Electrotechnical Commission).
This is the general case and still depends on the individual case.
Exceptions and limits
What was seen and not seen: this article looked at a public page from a machine-room equipment supplier, a public technical page from an electrical machinery maker, a public white paper from a power equipment maker, and the 2022 public guide of EUROBAT; the full text of IEC 62040-3 was not read, and the way the classification is written is taken from the account of the two public sources above. The EUROBAT guide gives no battery replacement age or replacement threshold, and does not specify a float temperature, so this article does not write “replace every so many years”; schedule by the written specifications of the battery maker and the product page.
Inconsistency in the electrical machinery maker’s page: its classification list marks line-interactive as VI, but the text writes it as VFI; this article follows the white paper’s VI.
Sources with a standpoint: the power equipment maker’s white paper and the machine-room equipment supplier’s page have a sales or promotion standpoint; the capacity ranges in which offline, line-interactive and double-conversion online are each “common” (2 kVA, 5 kVA, 10 kVA) come from that white paper and are not set by a standard.
Years: the machine-room equipment supplier’s page shows no year; the electrical machinery maker’s page shows 2025 in the footer and no publication date; the white paper’s copyright shows 2024; the EUROBAT guide is 2022.
This article’s own summary: the following are this article’s arrangement of the sources and are not written that way in the sources: “400 W, power factor 0.9, about 444 VA, rated at least about 556 VA” is this article’s worked example; “loads that suddenly draw large currents are worked out separately” is this article’s suggestion; “loads that cannot stand interruption first consider the types that need no switchover” and “confirm the output is a sine wave” are this article’s suggestions; the “Used for” column of the type table comes from the use scenes in the white paper and the electrical machinery maker’s page, and the “How it works” column from the two public pages; the classification of “what holding is for” in Stage ③, “add an external battery”, and “read the maker’s curve, do not work it out yourself” are this article’s summary; the placement, battery status display, self-test and “replace on schedule” in Stage ④ are this article’s suggestions.
Scope: this article does not discuss UPS installation, earthing and power distribution, the work of replacing batteries, or generators, price and lead time.
Equipment and products: the figures and wording in “What Jiahon Can Help With” were read from the text of the product page on October 13, 2026; the product images were not looked at, and they were not verified by this article; the specification is as on the product page, and for what the product page does not write, please inquire. The body text of the product page writes just 800 VA and offline, while the keyword tags of the page have several capacities and the wording “online”, which is not consistent with the body text, and this article follows the body text. Whether the site has other UPSs was found with the site’s product search, which found just this one; a product search is not a stock inquiry, and for stock please inquire.
This article is a summary for the general case, not a restatement of standard clauses, and not an endorsement of any maker, equipment supplier or service provider, nor an assurance for your product and process. Please take your process specifications, the written specifications of the UPS and battery, and your own validation as the reference; this is the general case and still depends on the individual case.