Frequently Asked Questions - Inverter/UPS FAQs
- What is the difference between an inverter and a UPS?
An inverter is a device that converts DC (Direct Current) power into AC (Alternating Current) power. For example, a 12V inverter will convert battery power available at 12V DC into AC power at 230V in India.
UPS (Uninterrupted Power Supply) is a device that normally provides back-up power supply for any electrical gadget. To do this, the UPS typically includes the inverter, battery and battery charger in one standalone unit. UPS units also provide protection against many electrical problems like over-voltages, brownouts, power surges etc. and in certain cases also communicate with the equipments they are powering.
We often use the terms interchangeably in India, as given our need for back-up power, a standalone inverter (that converts only DC power to AC power) is often not very useful and we invariably need a device that is also equipped with a battery charger and hence, a UPS.
- What are the different types of Inverters available?
Inverters are classified into different types based on the waveform of the output AC power they generate. The dominant waveforms generated by commercially available inverters are – square wave, modified sine wave (also known as quasi-sine wave) and sine wave (also known as pure sine wave). A comparison of the three waveforms is shown below:
Sine wave is the most superior waveform (as it matches the waveform of the AC power that we get from the utility grid) and inverters that generate this waveform are typically more expensive while square wave inverters require minimum circuitry and hence are the cheapest. With the prices of sine wave and modified sine wave inverters coming down and the increasing need of providing back-up power and protection to sophisticated electronic devices square wave inverters are gradually being phased out.
- What are the different kind of appliances that should be used with square wave, modified sine wave and sine wave inverters?
The suitability of a particular waveform in an inverter depends upon the type of load the inverter is being connected to and the nature of usage (whether it is for continuous use or emergency use). A general comparison of the inverters based on the different waveforms is offered below:
Modified sine wave
Loads suitable for
Lights and fans only
Lights, fans, Personal Computers, TVs (there might be electrical noise in case of some models, check the specification of inverter model), other household appliances
All kinds of loads including sensitive electronics
Sine wave inverters: The major advantage of a sine wave inverter is that it ensures trouble-free and efficient operation of all electrical and electronic equipments. Please note:
- Certain appliances like sensitive medical equipment, audio/video electronics, household appliances such as variable speed drills, bread makers, light dimmers and battery chargers require waveforms with low harmonic distortion and should be connected to only sine wave inverters.
- Many inductive loads, such as appliances containing motors also produce full output only when operated with true sine wave power.
- Sine wave inverters also have a higher surge power tolerance and are able to cater to the higher surge current drawn by inductive loads during start-up.
Modified sine wave inverters: These inverters provide a good value proposition as while not as expensive as sine wave inverters, they still are compatible with a broad range of electrical gadgets used at home or office such as TV, computers, printers etc. Please note:
- When modified sine wave inverters are used to power inductive loads, such as appliances having motors, solenoids, compressors, pumps or relays, the loads tend to consume about 10-20% more power than when powered with true sine wave power.
- Appliances with electronic timers and/or digital clocks will often not operate accurately due to the noise in a modified sine wave compared to a pure sine wave.
Square wave inverters: These inverters are the cheapest and are typically suitable for running lights, fans and other devices that are not impacted by the harmonics present in this waveform. It is important to not connect square wave inverters to sensitive electronic appliances as they might cause irreparable damage to them.
- What criteria should I use for selecting an inverter?
In order to maximize the output power (AC power) that an inverter can generate from a given amount of input power (DC power), it is important to select an inverter with the following characteristics:
- High efficiency - For details on this see question below
- Low standby losses – These losses are due to the power consumed by the inverter when it is on but no loads are running. This is the case in most residential situations, so it is important to select an inverter where these losses are a minimum.
- High surge capacity – Many household and office appliances, especially those with motors consume high power when they are switched on. If the inverter does not have sufficient surge capacity to support these loads then the inverter will shut down and could potentially get damaged as well.
- Low harmonic distortion – Harmonics can lead to performance problems in motors and sensitive electronics and also impact the useful lives of these equipments, hence it is always advisable to minimize the harmonic distortion caused by the output power produced by inverters. As mentioned in the table above, sine wave inverters have low harmonic distortion while square wave inverters have the highest harmonic distortion.
- What is inverter efficiency and why does it matter?
The efficiency of an inverter determines the amount of AC output power it generates for a given input of DC power. This usually ranges from 85% to 95%, with 90% being about average.
When running such things as motors, the efficiency actually has two parts to it - the efficiency of the inverter, and the efficiency of the waveform. Waveform efficiency means that most motors and many electronic appliances run better and use less power with a sine wave. Typically, an electric motor (such as a pump or refrigerator) will use from 15% to 20% more power with a modified sine wave than with a true sine wave. Thus when choosing an inverter based on efficiency, you should also consider the type of loads being powered to determine true system efficiency.
- What is the difference between the “VA rating” and “W rating” of an Inverter/UPS?
The capacity of an Inverter/UPS is specified in terms of its VA rating and W (Watt) rating. The Watt rating relates to the amount of power it can deliver, and the VA rating relates to the amount of current it can deliver. Neither the VA nor the W rating of an Inverter/UPS can be exceeded.
The Watt rating of a load represents the “actual power” consumed by it while the VA rating is the “apparent power” consumed by it and is larger than the actual power due to some currents called reactive or harmonic currents that flow in and out of loads without actually delivering any power to it. The ratio of the actual power to the VA rating is also called the “Power Factor” (PF). For many types of electrical equipment the difference between apparent power and actual power is very slight and can actually be ignored, but for some computers the difference is very large and important. In a study done by PC magazine, it was found that typical personal computer systems exhibit a power factor of 0.65 which means that the apparent power (VA) was 50% larger than the actual power (Watts). Normally most Inverter/UPS can handle loads with power factor ranging from 0.7 to 1.
The best approach to size an Inverter/UPS is to use the Watt rating of the load and ensure that the Watt rating of the Inverter/UPS is greater than the VA rating of all the loads put together. This ensures that even if you don’t know the power factor of the individual loads, the Inverter/UPS capacity has the requisite safety margin built into it.
- How should I select the right inverter capacity?
You can use the Glowship inverter wizard to calculate the inverter capacity required for running your loads.
The Glowship wizard allows you to pick your appliances along with their wattages and calculates the suitable inverter capacity taking into account an additional buffer you would like to provide for additional loads you might want to connect to the Inverter/UPS in future.
- What is an UPS and where is it normally used?
UPS stands for Uninterrupted Power Supply and is used for two primary purposes – Protecting computers and other sensitive loads from damage or loss of data caused by Line (Mains) power disturbances, and secondly to provide back-up power to critical loads when the primary power goes down. The different types of UPS differ in the extent and the manner in which they serve the above two purposes and these details are provided below.
- What is an Offline UPS, how does it work, and what are its advantages and disadvantages?
The Offline UPS, or, Standby UPS as it is popularly known is the most common type of UPS used primarily for Personal Computers.
In normal use, the UPS connects the power line directly through to your computer and its battery charger draws only a slight current to keep the UPS battery topped off. When the power fails, the UPS switches into action – and switch is the key word. A relay inside the Offline UPS switches the wires that go to your computer from the wall outlet (passing through the UPS) to an inverter connected to the battery pack inside, or, outside the UPS. The inverter then supplies power to your computer with the batteries as the energy source. The inverter only starts when the power fails, hence the name “standby”.
The topology of the Offline UPS is shown below:
The switching process requires a small but measurable amount of time. All available off-line UPSs switch quickly enough that your computer never notices the lapse. Most off-line UPSs switch in 3 to 10 milliseconds (one cycle in a 50Hz environment is 20 milliseconds). Even the slowest off-line UPS has a safety margin when it comes to switching time.
The main drawback of the off-line UPS is that it offers very limited protection against power problems. Only a few UPS manufacturers add filters and surge circuitry that provides adequate noise filtration and surge suppression to electrical disturbances from the grid power, but the offline topology in general cannot cope with sustained over-voltages or prolonged sags. The protection against under-voltage problems is limited to switching to battery back-up power – which means that the battery capacity limits the protection period.
The advantages of the offline UPS are its low cost and high efficiency (typically 95% - 98%). It is not a complete power protection solution but given its cost and efficiency, serves the purpose of protecting your computer against a single power problem – the outage.
- What is a Line-interactive UPS, how does it work and what are its advantages and disadvantages?
The next step up the UPS ladder is the line-interactive UPS and it is the most common topology used for small business, web and departmental servers.
In the line-interactive topology, the inverter is always connected to the output of the UPS. Operating the inverter in reverse during times when the AC power is normal provides battery charging. When the input power fails, the transfer switch opens and power flows from the battery to the UPS output. With the inverter always on and connected to the output, this design provides additional filtering for incoming power compared to the standby topology.
In addition, the line-interactive topology also incorporates a multi-tap transformer to buck (reduce) or boost (increase) the voltage, thereby providing some degree of voltage regulation (also known as “Automatic Voltage Regulation”) as the input voltage varies. Voltage regulation is an important feature when low voltage conditions exist, otherwise the UPS would transfer to battery power and frequent battery usage can cause premature battery failure. The buck or boost range is typically limited to 10% and while some models will provide both buck and boost other less expensive models will just provide boost capability.
The topology of the line-interactive UPS is shown below:
The inverter in this topology can also be designed such that its failure will still permit power flow from the AC input to the output, thereby eliminating the potential of single point failure by providing two independent power paths.
High efficiency (typically 90%- 96%), small size, economic price point coupled with the ability to correct low or high line voltage conditions make this the dominant type of UPS in the 0.5-5 kVA power range.
- What is an On-line UPS, how does it work and what are its advantages and disadvantages?
This is the most common UPS topology above 10kVA and is designed to provide continuous power protection against all power problems to mission critical equipment in data centers and server rooms. This topology ensures a consistent quality of power supply regardless of disturbances in the incoming mains. There are actually 2 sub-categories of On-line UPS known as – Double Conversion On-line and Delta Conversion On-line, with the former being the more popular technology.
In the Double Conversion On-line topology, the primary power path to the loads is the inverter instead of the AC mains, thus the inverter is ON 100% of the time and hence the term on-line. The name double-conversion arises from the operation of the device. It first converts line voltage (AC) into battery-compatible low-voltage DC using a rectifier. The rectifier supplies power to the inverter in addition to charging the batteries. The DC from the batteries is then converted by an inverter back to the highly controlled and regulated AC. This process thus effectively removes any electrical disturbance on the utility (input) side of the UPS.
The topology of the line-interactive UPS is shown below:
The Double Conversion UPS is the only truly uninterruptible system because the inverter is always connected to the load and is always drawing power from the battery source irrespective of whether the mains power is present or not. Therefore, during an input AC power failure, on-line operation results in no transfer time. This topology also provides protection against all forms of power irregularity including surges, spikes, over-voltages, sags, brownouts and blackouts. This topology also maintains a significantly closer output voltage tolerance compared to the line-interactive topology as it uses solid-state voltage regulators instead of transformer taps to cope with under and over voltages.
While the Double Conversion On-line topology provides nearly ideal electrical output, the constant wear on the power components reduces its reliability and the reduced efficiency (typically 80 – 90%) results in higher life cycle costs for the UPS.
- Can you provide a comparison of the advantages and disadvantages of Off-line, Line-interactive and On-line UPS?
Sure, please find below a quick summary. For more detailed explanations, please refer to the questions above.
Low cost, high efficiency (typically 95 – 98%), compact
Uses battery during brownouts, limited or no protection against power irregularities, impractical over 2KVA
Best value for Personal Computers
High reliability, high efficiency (typically 90-96%), reasonable voltage conditioning
Impractical over 5KVA, does not protect against all forms of power irregularities
Most popular UPS – ideal for for small office, web and departmental servers and/or harsh power environments
On-line (Double Conversion)
Near ideal electrical output, highest protection against all power irregularities, ease of paralleling
Lower efficiency (typically 80 – 90%), relatively more expensive under 5kVA
Default choice for providing back-up power and protection to mission critical equipment and servers at data centers
- Can you provide a comparison of the extent of protection against power irregularities provided by Off-line, Line-interactive and On-line UPS?
Sure, please find below the summary based on the typical features available in each topology:
X / △
X / △
X / △
○: Highest Protection △: Limited Protection X: No Protection
- How fast will my UPS respond to a power outage or blackout?
The transfer time from mains to battery power differs for different UPS topologies. In case of Off-line UPS, the transfer time is typically less than 10 milliseconds, in case of line-interactive UPS, this is typically less than 4 milliseconds and in case of On-line UPS, it is zero. Thus the switchover time for all UPS topologies are quick enough (one cycle in a 50Hz environment is 20 milliseconds) so that computer workstations will mostly never notices the lapse.
- When should we use a single or 3 phase UPS?
The choice of either a single phase or three phase UPS depends on the load that needs to be protected. UPS with single phase inputs are typically used when the protected load is less than 10kVA. When the total load to be protected is more than 10kVA, typically a UPS with three phase input is chosen, even where the inverter output is single phase. Larger UPS units with three phase input and three phase output are used when the load is more than 20kVA and the loads can be either single phase or three phase in nature. Three phase UPS are more compatible with a three phase DG set and these UPS systems can also be used to feed single phase loads, and with good load balancing, the DG does not need to be oversized.
- How much UPS capacity do I need?
Determine the total load (in watts) of the equipment you want to protect. Add 10-20 per cent to allow for future growth and then select the appropriate UPS capacity based on the minimum amount of runtime you need.
- What kind of equipments should I connect to the UPS?
UPS is used to typically provide back-up power and protection against power faults to computers, sensitive electronics, medical equipments etc. They should not be connected to resistive and inductive loads running motors as the surge current requirement of these loads could either damage the UPS or end up rapidly discharging the battery thereby impacting the duration for which back-up power/protection is available for the critical loads.
- Can I connect a laser printer or office multi-function fax/printer to my UPS?
It is not recommended to use these appliances on a UPS. Laser printers have a large heating and sealing component that can draw up to 1000 watts and multi-function fax/printers draw a huge amount of surge current during start-up. Therefore you must have a greater VA rated UPS to do the same job which makes the UPS backup very uneconomical. Hence these equipments have not been included in the Product selector
- We have a generator – do we still need a UPS?
An auxiliary generator provides back-up power just as a UPS does but requires much more time to kick in and stabilize before it can start supporting your critical loads. Hence, a UPS is required to ensure that the equipment stays running until the generator kicks in. In addition, the UPS also improves the quality of the power produced by the generators.
- What is the overload capacity of the UPS?
A UPS is normally designed to handle overloads for a short period of time. For example, some UPS can handle 110% overload for 10 minutes and 150% for 60 seconds. In the overload condition, the UPS transfers the load to bypass (for a few minutes) until the overload condition is reversed. If the overload condition continues, the UPS automatically shuts down.
- How much UPS battery runtime do I need?
During an outage, you need enough battery runtime to gracefully shut down systems or switch to backup generators. You may add optional external batteries (please check if the UPS model is compatible with external batteries) to increase runtime.
- Does the Inverter/UPS come with internal batteries, or, do I need to connect batteries externally?
The battery configuration for different Inverter/UPS models can be classified as below:
- Internal batteries only – In this case the batteries are provided internally and the UPS provides different runtimes depending upon the load connected to it.
- Internal batteries with extendable runtime option – In certain models, additional batteries can be connected externally that together with the internal battery increases the UPS runtime. The option to connect additional batteries externally is not available with all models and you need to check the specifications of the specific model to ascertain this.
- External batteries only – In these models, the batteries can only be connected externally.
- What type of batteries should I connect to my Inverter/UPS?
The choice of the appropriate battery depends on the following factors:
- Desired back-up duration
- Average operating temperature range
- Space availability
- Environmental factors
- Topping up requirements
UPS that come with internal batteries typically use VRLA (Valve Regulated lead Acid) batteries which are also known as Sealed Maintenance Free (SMF) batteries.
While connecting external batteries to Inverters any of the different lead acid batteries can be connected with the popular ones being – Flooded batteries (Flat plate, Tubular, Tall Tubular) and SMF VRLA batteries (AGM and Gel). Please refer to the questions below for a comparison between these battery types.
- Can I connect any capacity/any number of batteries to an Inverter/UPS to increase its runtime?
The capacity of the battery that should be connected to an Inverter depends on the charging current the Inverter can provide as this determines whether the battery gets charged fully in a reasonable amount of time without getting damaged. Usually the battery capacity should be no more than 12 times the charging current that can be provided by the Inverter (e.g. a 5A charger can accommodate only 60AH (5*12=60)). In case the battery discharge is less frequent (say once in 10 days), then in such extreme cases the battery capacity can be increased to 20 times the maximum charging current of the inverter. In addition, the charging current provided by the inverter should be below the limiting current of the battery to ensure the battery does not get damaged during charging.
When connecting batteries multiple batteries in parallel, please note that the inverter’s battery charger should be able to provide the charging current required by each individual battery (e.g. if the limit current of one battery is “A” amps, for “N” batteries in parallel, the limit current for charging of inverter should be “A*N” amps). This is not a factor when connecting batteries in series as all batteries in series use the same charging current from the inverter.
- Why are batteries connected in both series & parallel? How does the battery bank capacity change as result?
Batteries are connected in both series and parallel configuration to increase the capacity of the battery bank thereby increasing the duration for which back-up power can be provided to the loads by the bank. However, while doing so, it is important to ensure that the DC voltage of the Inverter matches the voltage of the battery bank being connected to it to avoid any damage to the battery bank and to ensure appropriate charging of the battery bank by the Inverter.
When batteries are connected in series, the voltage of the battery bank goes up and is equal to sum of the voltages of the individual batteries. For e.g. if 2 nos. of 12V (150Ah) batteries are connected in series, the voltage of the battery bank will be 24V (= 12V+12V) and this battery bank can be charged by an inverter having a DC voltage rating of 24V. By connecting the individual batteries in series, the energy that can be stored in the battery bank increases to 3600Wh (=24V*150Ah).
When batteries are connected in parallel, the voltage of the battery bank is the same as the voltage of the individual batteries, while the capacity of the battery bank doubles. Please note that only batteries having the same voltage rating should be connected in parallel to ensure uniform charging/discharging of the batteries and to prevent damage to/maximize life of the individual batteries. For e.g. if 2 nos. of 12V (150Ah) batteries are connected in parallel, the voltage of the battery bank will be 12V and this battery bank can be charged by an inverter having a DC voltage rating of 12V. By connecting the individual batteries in parallel, the energy that can be stored in the battery bank increases to 3600Wh (=12V*(2*150)Ah).
- How do you compare flooded batteries (flat plate, tubular type) with sealed maintenance free VRLA batteries, what are the advantages and disadvantages of each type?
For Inverter/UPS applications, a general comparison of the different battery types is provided below:
Low power applications
Heavy duty applications, frequent power cuts
UPS applications, back-up time less than 1hr
Around 3 yrs
4 to 5 years
3 to 5 years
Tolerance to depth of discharge
Suitable for discharges upto 80% of battery capacity
Suitable for discharges upto 80% of battery capacity
Suitable for discharges upto 50% of battery capacity
Cyclic operation life (Charge cycles at 80% Depth-of-Discharge)
500 - 800 cycles
1200 – 1500 cycles
400 – 450 cycles
Charges slowly compared to tubular batteries
Inferior operation compared to tubular batteries
Satisfactory operation at extreme temperatures (both high and low)
Capacity reduces significantly at higher temperatures
Electrolyte top-up frequency
Frequent water top up required
Less frequent top up
No top up required
Can be placed in any orientation
High, proper ventilation required
Lower emissions compared to flat plate, proper ventilation required
No battery emissions
- How is the capacity of a battery defined? What does the Ah capacity of a battery mean?
Battery capacity is normally defined in Ah (Ampere-hour) and represents the maximum amount of energy that can be extracted from the battery under certain specified conditions. However, the actual battery capacity during operation can vary significantly from the nominal “rated” capacity as actual capacity depends on the age, rate at which energy is being drawn from the battery, historical usage pattern (charging, discharging cycles followed) and temperature.
Lead acid battery capacity for Inverter/UPS applications is normally rated at a 20hr draw and is specified as C20 capacity of the battery. For e.g. C20 capacity of 100Ah means that the battery is capable of providing 5Amps of current when discharged by a load over 20hrs (5A*20h = 100Ah) under standard temperature conditions. This battery can be discharged at a faster rate (i.e. the load could draw a higher current from the battery, say 10A) but this ends up reducing the total energy (Ah) that can be extracted from the battery.
The capacity to which the lead acid battery is discharged before it is charged again (known as depth of discharge) also influences battery capacity and its life (number of charge/discharge cycles it can provide). The recommended depth of discharge for lead acid batteries should be less than 80%.
- What kind of Inverter/UPS and battery should I buy for my requirements?
Please use the Glowship Inverter/UPS wizard, it helps you:
- Enter details of the loads you wish to provide back-up power to
- Select the Inverter/number UPS - Capacity, waveform and topology best suited to your requirements
- Select the suitable Battery – Capacity and technology depending upon the number of hours of back-up you require
- How do I purchase an Inverter/UPS and battery on Glowship?
It’s simple! Please follow the steps below:
- Open the Glowship Inverter/UPS Product Selector
- Select the loads you wish to provide back-up power to and the extra capacity you would like to budget for addition of any other loads in future
- Click on “View Recommended Products” to see the Inverter/UPS models that match your requirement
- Select the Inverter/UPS model and click on “Buy Now”
- If you would like to select batteries as well, click on “Select batteries” icon
- On the battery wizard
- The “Your Load” and “System Voltage (DC)” are already pre-filled
- Select the back-up time you require
- Click on “View Recommended Products” to select the battery models that match your requirement
- Select the battery model and click on “Buy Now”
- Your shopping cart now contains both the Inverter/UPS model and the battery model you have selected
- Make the payment online
The Inverter/UPS along with the battery will be delivered and installed at your residence/office
- Why is it important to use the Glowship product selector before making a purchase?
The product selector will help you select the specific models Inverters/UPS and batteries that are best suited to your requirement. Choosing the suitable capacity of Inverter/UPS and the right technology (waveform and topology) will ensure reliable operation of Inverter/UPS and provide suitable protection to you electrical equipments. Choosing suitable battery capacity and battery technology ensures you are able to provide the requisite back-up to your electrical loads.
- How does the Glowship product selector determine the right Inverter/UPS capacity?
The Glowship product selector takes into account the type of load, power factor to determine the Inverter/UPS capacity. All the loads selected are assumed to be running at the same time and hence are used to determine the capacity of the Inverter/UPS.
The product selector also takes into account the higher surge power consumed during start-up by a few loads (e.g. Air Conditioners, Refrigerators etc.) to recommend the capacity that is suitable for running of these loads. Multiple such loads should not be switched on the same time (e.g. if both the Air Conditioner and Refrigerator are connected to the Inverter they are normally started one after the other) so for the purpose of calculating the suitable inverter capacity the product selector takes into account the load that has a higher surge power consumption.
- How does the Glowship product selector determine the right Inverter/UPS technology to be used?
The Glowship product selector takes into account the type of load for which back-up power is required to recommend the suitable waveform/topology of the Inveter/UPS. For more details on understanding waveform & topology refer to the section above
- What are the benefits of buying Inverter/UPS & batteries on Glowship?/ What is the Glowship PentaVantage?
PentaVantageTM is the biggest reason to buy from Glowship! The advantages are described below:
- We help you select the Right Product: Glowship Wizard & Glowship Knowledge Central combines to help you choose the Inverter/UPS & battery model that best fits your requirements.
- We carry only Genuine, Reliable products: Glowship brings to you genuine and high quality products at the best prices from leading manufacturers
- Make a Trusted purchase from Verified Dealers: Glowship carries listings from only verified dealers and is the first marketplace to provide comprehensive ratings on service & delivery for each dealer thereby offering you the flexibility to make a purchase from the dealer of your choice
- We offer you a One-stop Solution: All dealers selling on Glowship offer you free installation & AC-side wiring at a nominal cost thus offering you the convenience of a high quality, one-stop solution, so, you don’t need to look anywhere else!
- Glowship Asset Management: Purchasing from Glowship offers a free subscription to the soon to be launched Glowship Asset ManagementTM that will allow you to monitor the health of your products, provide warranty claims management and other services to ensure you maximize the return on your investment.