Uninterruptible devices allow you to minimize the dependence of household and computer equipment on the presence of electric current in sockets. During power outages, they will come in handy for backup power to electrical appliances. But before proceeding with the calculations of the required battery capacity in the UPS for certain needs and for a specific time, it is necessary to choose the right uninterruptible power supply by type.

Common types of uninterruptible power supplies

The simplest kind of "uninterruptible" is standby UPS, intended solely for safety net. With sudden surges in voltage and current in the mains, they switch the load to the battery, the charge of which lasts for several minutes. Redundant UPSs will serve as a suitable solution for saving data and safely shutting down a computer, nothing more.

Specially for routers and laptops, low- voltage UPSs with low-voltage outputs for 9/12/15/18 V are produced. They are also actively introduced into alarm, video surveillance and access control systems.

Safety nets in networks with unstable voltage are provided by interactive "uninterruptibles". Such devices are designed for low-term power supply of a computer and related peripherals within one workplace (for 10-30 minutes). In parallel, they smooth out voltage fluctuations in the mains (within a couple of tens of volts). Those. the second role of interactive UPS is work as voltage stabilizers. When the voltage goes beyond the operating range, the load automatically switches to the battery of the uninterruptible power supply.

Interactive UPSs perform both the role of a connection reserve and a voltage stabilizer.

Inverter UPSs (online) are considered to be the most advanced. Their work is established in a wide range of voltages with voltage equalization without jumps and subsidence when switching to a battery load. UPS online with the same power can be connected in parallel, understaffed with external batteries. Advanced inverter "uninterruptible" models can be used to back up entire buildings.

For autonomous power systems based on solar panels, hybrid UPSs with an MPPT controller and a pure sine wave output are produced. However, they are also compatible with traditional electrical networks. Such UPS models guarantee the most accurate control of the parameters of operation and distribution of the generated energy. Models of "uninterruptible" with the correct sine wave are used for backup power to the most sensitive electronics.

Hybrid UPS with an MPPT controller is well suited for use in autonomous power systems based on solar panels.

Mobile charging stations offer the best autonomy in the class. They are described in detail in a separate article “Autonomous power supply: what are portable charging stations?”.


Batteries

The following types of batteries are used in uninterruptible power supplies:

  • lead-acid AGM - reliable batteries with stable voltage characteristics, designed for approximately 400-500 charge / discharge cycles;
  • multi -gel - an improved version of AGM batteries with a more viscous electrolyte; withstands 700-800 charge/discharge cycles;
  • gel GEL - gel batteries with a thick electrolyte in a jelly-like state have a long service life, high capacity, a wide operating temperature range and excellent reliability, however, such batteries are more expensive and do not tolerate deep discharge; their resource often exceeds 1000 charge / discharge cycles;
  • lithium-iron-phosphate LiFePo4 - the most advanced type of rechargeable batteries, characterized by high energy capacity with compact dimensions, the complete absence of the "memory effect", low self-discharge, resistance to large temperature fluctuations; withstand LiFePo4 batteries over 7000 charge/discharge cycles;
  • nickel-cadmium NiCd - infrequent guests on board "uninterruptible"; despite the high reliability, low self-discharge rate and good service life (about 1500 charge / discharge cycles), such batteries are made using toxic substances as a filler and have the notorious "memory effect"; their use is expedient in severe environmental conditions with strong temperature fluctuations.
Uninterruptible power supplies use different types of batteries - each with its own advantages and disadvantages.

Power supplies for "uninterruptibles" last about 5 years (under ideal conditions, up to 10 years). The decrease in the declared service life is due to frequent and long-term backup power to the equipment until the batteries are completely discharged, as well as the impact on the battery of temperature fluctuations and strong overloads.

Principles for calculating the required connection power

Calculating the approximate battery life of connected equipment from a UPS is not so difficult. To do this, you need to know the total capacity of the batteries on board the "uninterruptible device", their voltage and the power of consumers. Also, the efficiency of the UPS inverter is taken into account(from the device passport or an average value of 0.85).

All these indicators are added to the formula of the following form:

C (Ah) * V (V) * η / P (W) = T (hours)

For a better understanding of the essence, let's consider the calculation of the estimated operating time of the equipment connected to the UPS using a real example. Let's assume that there is an "uninterruptible power supply" with three 12-volt batteries with a total capacity of 27 Ah (three batteries of 9 Ah). The UPS powers a home PC, which consumes approximately 200 Wh of power:

27 Ah * 12 V * 0.85 / 200 W = 1.377 hours (1 hour 23 minutes)

Most often, UPSs are used in conjunction with personal computers and peripherals.

You can count a little differently. In particular, there is a formula for determining the required battery capacity for a specific time of equipment operation from a UPS. It looks like this:

T (hours) * P (W) / η / V (V) = C (Ah)

We check it in practice with the same conditions from the example above (the operation of the equipment must be ensured for 1 hour. 23 minutes (1.377 hours)):

1.377 hours * 200 W / 0.85 / 12 V = 27 Ah

Things are a little more complicated if the equipment is switched on periodically (for example, a refrigerator). The 200W food storage compressor runs for approximately 2 minutes at 10 minute intervals. Its average power consumption is 200W*2min. / 10 min. = 40 W. This indicator must be substituted into the calculations of the expected battery life from the UPS:

27 Ah * 12 V * 0.85 / 40 W = 6.885 hours (6 hours 53 min.)

The “uninterruptible power supply” with a trio of 12-volt batteries of 9 Ah each is enough to ensure the operation of a home PC for 1 hour 23 minutes. or the refrigerator for almost 7 hours. Similar calculations can be made for other household appliances, knowing the level of power consumption of the equipment and the characteristics of the "uninterruptible".

A well-chosen UPS will help to establish autonomous operation of the refrigerator for several hours in a row.

To simplify the task, calculators are designed to calculate the operating time of the UPS from batteries. You can find them on Google and other search engines.


Laptop and router powered by Powerbank

In the material "How to organize remote work during power outages" we covered in detail the possibility of powering a router and a laptop from a Powerbank battery. And how long, in this case, will a conditional wireless router with the parameters of the consumed voltage and current 9 V / 1 A stay afloat? Let's guess.

To calculate the battery life of the router, we use the following formula:

W (Wh) * η / (V (V) * I (A) = T (hours)

The capacity of the batteries of the power bank in W * h is usually indicated on the nameplate, and for the efficiency we take an average figure of 0.8. The popular model Xiaomi Mi Power Bank 3 20000 has a battery capacity of 74 Wh. On his example, we perform the calculations:

74 Wh * 0.8 / (9 V * 1 A) = 6.578 hours (6 hours 35 minutes)

In order not to be left without the Internet during power outages, the router can be powered from a Powerbank battery.

Note that in order to properly power the router from the power bank, you may need special cables with built-in voltage boosters or Quick Charge / Power Delivery triggers. Also, these devices are available as separate solutions with USB connection ports. We talked about them in more detail in the aforementioned article "How to organize remote work during power outages".


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Remember that there are no hopeless situations. You can mitigate the consequences of rolling and emergency blackouts if you have ingenuity and sober calculations for the selection of suitable equipment for backup power supply for home and computer equipment.